nanostructured materials

c 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim10.1002/14356007.c17 c01

Nanostructured Materials 1

Nanostructured MaterialsBernardH. Kear, Department of Ceramic and Materials Engineering Rutgers The State University of NewJersey, Piscataway, NJ 08855, United StatesGanesh Skandan, Nanopowder Enterprises Inc., Piscataway, NJ 08854-3908, United States

1. Introduction . . . . . . . . . . . . . . . . . 12. Characteristics of Nanostructured

Materials . . . . . . . . . . . . . . . . . . . 13. Production of Nanostructured Pow-

ders . . . . . . . . . . . . . . . . . . . . . . 23.1. Spray Conversion Processing . . . . . . 33.2. Sol Gel Processing . . . . . . . . . . . . 33.3. Aqueous Solution Processing . . . . . . 33.4. Physical Vapor Synthesis . . . . . . . . 43.5. Chemical Vapor Condensation . . . . . 53.6. Chemical Vapor Reaction . . . . . . . . 63.7. Liquid Flame Spray . . . . . . . . . . . . 64. Processing of Nanostructured Bulk

Structures and Coatings . . . . . . . . . 7

4.1. Equal Channel Angular Pressing . . . 74.2. Liquid Phase Sintering of n-WC/Co . 74.3. Thermal Spraying of n-WC/Co . . . . 84.4. High-Pressure Consolidation . . . . . . 85. Processing of Novel Nanostructured

Materials . . . . . . . . . . . . . . . . . . . 85.1. Composite Nanoparticles . . . . . . . . 85.2. Films with Nanoscale Porosity . . . . . 85.3. High Green Density Compaction

Method . . . . . . . . . . . . . . . . . . . . 96. Applications of NanostructuredMate-

rials . . . . . . . . . . . . . . . . . . . . . . 97. Future Perspective . . . . . . . . . . . . . 118. References . . . . . . . . . . . . . . . . . . 11

1. Introduction

This article deals with the synthesis andprocessing of nanostructured ceramics andceramic metal composites. Optoelectronicma-terials such as porous silicon, multilayer nanos-tructured thin lms (Thin Films), biomimeticmaterials such as hydroxyapetite, and carbonfullerenes (Carbon, Chap. 7.) are not covered.

Materials with ne-scale structures have longbeen recognized to exhibit remarkable and tech-nologically attractive properties. Interest hasbeen growing in a new class of ultrane-grainedmaterials, called nanocrystalline, nanophase, ornanostructured materials (n-materials) [13],wherein the particle or grain size is 1 100 nm.This interest stems not only from the outstandingproperties that can be obtained fromsuchmateri-als, but also from the realization that early skep-ticism about the ability to produce high-qualitynanoscale powders at a competitive cost was un-founded. Today, dozens ofmethods are availablefor producing nanopowders frommetals, ceram-ics, and cermets, some of which have alreadybeen commercialized. Accordingly, the empha-sis is shifting from powder synthesis to powderprocessing, i.e., the challenge of making use-ful coatings or bulk structures from nanopow-

ders. Nanostructured bulk materials and protec-tive coatings present major opportunities for ad-vances in materials properties and performancein a broad range of engineering applications.

Figure 1.Schematic showing different classes of nanostruc-tured materials (adapted from [4]).1) Powder particles; 2) Nanostructured coatings/lms; 3)Nanostructured monolithic bulk; 4) Nanocomposite bulk1) 4) can be porous or dense

2. Characteristics of NanostructuredMaterialsAs shown in Figure 1, the general term nanos-tructured refers to powders, coatings/lms, and

2 Nanostructured Materials

bulkmaterials in which at least one of the phasesis nanoscale [4]. In some cases, the individualpowder particles are single crystals, while inothers each particle may be composed of sev-eral nanocrystals. Nanocomposite materials in-clude different combinations of metals, ceram-ics, and polymers. Furthermore, coatings andbulk structures can contain nanoscale closed oropen porosity.

Figure 2. Fraction of atoms residing at grain boundaries asa function of grain size (width of grain boundary = 1 nm)Table 1. Nanomaterial properties and corresponding grain/particlesize effects

Nanomaterial property Corresponding grain/particlesize effects

Enhanced sinterability of metaland oxide ceramic powders

An ultrane particle size(< 100 nm) gives rise to a highdriving force for densication

Improved UV scattering UV scattering is optimum at aparticle size of 30 50 nm

Enhanced gas sensitivity The gas sensitivity of a materialis proportional to the surfacearea and hence becomessignicant in nanomaterials

Very high hardness and wearresistance

Sintered nanophase metals andcermets display very highhardness and wear resistancebecause of their unique owcharacteristics

Stable colloidal suspensions Nanoparticles that are notagglomerated lead to increasedstability of colloidal dispersionsbecause of a smaller particlesize in the liquid medium

A feature of nanoscale materials is the highfraction of atoms that reside at particle surfacesor grain boundaries. Figure 2 shows a plot ofvolume fraction of atoms that reside at the grainboundaries of a nanoscalematerial with decreas-ing grain size [5]. At a grain size of less than20 nm, as much as 30% of the atoms can bepresent at the grain boundaries. Accordingly, the

interfaces play a crucial role in determining themechanical, optical, and electrical properties ofthe material.

In general, nanoscale materials exhibit dra-matic changes in properties, such as enhancedsinterability at low temperatures [6], [7], im-proved UV scattering [8], very high hardnessand wear resistance [9], [10], enhanced gas sen-sitivity, [11], smaller particle size in colloidalsuspensions, superior magnetic and dielectricstrength, and enhanced optoelectronic proper-ties [12]. Table 1 lists some of the unique charac-teristics of nanomaterials and the correspondinggrain/particle size effects.

3. Production of NanostructuredPowdersCeramic and ceramic metal nanopowder syn-thesis techniques fall into two broad categories:(1) precipitation from salt solutions, and (2) con-densation from the vapor phase. Specic meth-ods have evolved that differ only in the meansby which thermal and/or mechanical energy isprovided to the precursor species. These includelaser ablation [13], microwave plasma synthesis[14], precipitation from organometallic or aque-ous salt solution [15], spray pyrolysis [16], sprayconversion processing [17], and gas condensa-tion with an evaporative source [18] or a chemi-cal precursor [19]. At issue in each of these tech-niques are particle size, distribution, morphol-ogy, purity, and degree of agglomeration. Whilesome of these processes, such as precipitationfrom a solution, produce very small individualparticles (< 10 nm) that form larger agglomer-ates, others, such as spray conversion process-ing, produce micron-size particles consisting ofgrains in the 20 50 nm size range.

Described below are several processes ineach category of nanopowder synthesis: (1)spray conversion processing (SCP) for WC/Co[17], sol gel processing ofmulticomponent ox-ides, and aqueous solution processing (ASP) forK-doped MnO2 [20], which involve precipita-tion from salt solutions, and (2) physical vaporsynthesis (PVS) and chemical vapor condensa-tion (CVC) for Al2O3, TiO2, and Fe2O3, chem-ical vapor reaction (CVR) for nonoxide ceram-ics and liquid ame spray (LFS) for single-phaseandmulticomponent oxides, which involve con-


densation of nanoparticles from the gas phase.The PVS process involves evaporation of ele-mental species, such asAl and Fe, that are subse-quently oxidized in the gas phase,while theCVCand CVR processes involve pyrolysis of vaporsof organometallic compounds and halides, re-spectively, in a hot zone, followed by condensa-tion. The LFS process involves injection of liq-uid precursor droplets into a combustion ame.

3.1. Spray Conversion Processing

Tungsten carbide/cobalt (WC/Co) hardmetalis composed of a high volume fraction(> 60 vol%) of hard WC particles that are ce-mented together with a much softer Co-richbinder phase. Typically, such cemented carbidesare produced by mechanical mixing of the con-stituent WC and Co powders, followed by coldpressing and liquid-phase sintering. After sinter-ing, the material has a characteristic bicontinu-ous structure, in which the WC and Co phasesform interpenetrating networks in three dimen-sions. Such a composite structure displays highhardness, superior wear resistance, and goodfracture resistance. Hence, WC/Co hardmetalis the material of choice for a host of applica-tions, but particularly machine tools, drill bits,and wear-resistant parts.

The difculty of uniformly mixing ultraneWC and Co powders by mechanical means hasheretofore limited the scale of theWC grain sizeattainable in the nal sintered product to about0.3m. Rutgers University and Nanodyne Inc.have developed an alternative powder process-ing technology, called spray conversion process-ing (SCP), which produces premixed powderson the submicron scale.

The production of n-WC/Co powders by SCPtechnology involves essentially three steps: (1)mixing of aqueous solutions of tungsten andcobalt salts to x the composition of the start-ing solution, (2) spray drying of this solutionto form a homogeneous precursor powder, and(3) uid-bed thermochemical conversion (pyro-lysis, reduction, and carburization) of the pre-cursor powder to the desired n-WC/Co prod-uct powder. Using a pilot-scale production unit(Fig. 3), Nanodyne produces n-WC/Co powderswith compositions extending over the range ofcommercial interest from 3 25wt% Co.

Figure 3. Schematic of Nanodynes pilot-scale unit for theproduction of nanostructured WC/Co powder.a) Solution mix tank; b) Spray dryer; c) Cyclone; d) Feedbin; e) Fluid bed reactor; f) Filter; g) Afterburner

3.2. Sol Gel ProcessingSol gel processing is a versatile methodfor producing not only multicomponentoxide nanopowders, but also for synthesizingnanocomposite particles. Bursill et al. [21]synthesized BaTiO3 and PbTiO3 nanoparticles(ca. 25 nm grain size) by the sol gel method.Below a critical size, there is no paraelec-tric/ferroelectric phase transition in BaTiO3.Es-tournes et al. [22] found that Ni nanoparticlesdispersed in silica gel exhibit superparamag-netic behavior. Similarly, Piccaluga et al. syn-thesized Fe2O3 SiO2 nanocomposite particlesby a gelation method using tetraethoxysilaneand iron(III) nitrate as starting materials. Amor-phous iron(III) oxide particles with a diameterof 3 4 nm were observed, which displayed su-perparamagnetic behavior.

To produce powders with a very high surfacearea (e.g., 700m2/g for SiO2), Beaucage et al.[23] developed an aerosol gel method in whichthe sol gel chemistry is carried out in the gasphase.

3.3. Aqueous Solution ProcessingMany methods exist for synthesizing nanopow-ders from aqueous solution precursors. For in-stance, metal chloride solutions can be re-duced with sodium trialkylborohydride to form


Figure 4. Micrographs of solution synthesized K-doped MnO2 showing (a) initial nanoparticle agglomerated structure, (b)partially transformed structure after 4 h of reux, and (c) completely transformed nanobrous structure after 24 h of reuxing.

2 5 nm metal powders, e.g., n-Ni and n-Fe.Mixed metal chloride solutions can also be em-ployed for synthesizing alloy powders, e.g., n-Ni/Cr and n-M50 steel [24] and hydroxide andoxide powders, e.g., n-Ni(OH)x and yttrium-stabilized zirconia (n-YSZ). In addition, a pro-cedure has been developed for synthesizinglarge quantities of nanopowders by ultrasoni-cally spraying an aqueous solution of mixedsalts into a tank containing the reductive solu-tion. This method permits solution dispersal ofnanoparticles in a non-agglomerated form andcontinuous removal of reaction byproducts.

High surface area K-dopedMnO2 nanoberscanbe synthesizedby reacting aqueous solutionsof KMnO4 and MnSO4 in the presence of ni-tric acid, by using a reuxing technique in com-bination with controlled solution mixing [20].The initial nanoparticle agglomerates are grad-ually transformed into a nanobrous structure(Fig. 4). Depending critically on the synthesisconditions, the ber diameters range from 5 to50 nm, with lengths up to a fewmicrometers andspacings in the range 20 200 nm. The K-dopedMnO2 nanobers are c-axis oriented monocrys-tals, and have the cryptomelane-type hollan-dite structure with the approximate compositionKMn8O16. In this structure, about half of theavailable K+ sites are occupied and the rest areempty. For this reason, this type of manganeseoxide is a molecular sieve that is particularlyattractive for catalytic and ion-exchange pur-poses. In general, such intrinsically nanoporous

materials make excellent cation-exchange ma-terials. Moreover, with surface areas of > 250m2/g, they are promising catalysts for oxida-tion reactions and ionic/electronic conductorsfor rechargeable batteries.

3.4. Physical Vapor SynthesisThe synthesis of nanoparticles by the physi-cal vapor synthesis (PVS) method, rst intro-duced byGranqvist and Buhrmann [25], andGleiter et al. [3], [26] (Fig. 5), involves evap-oration of metal species under a reduced pres-sure of inert gas in a ultrahigh-vacuum chamber.Nanoparticles develop in a thermalizing zonejust above the evaporative source due to interac-tions between the hot vapor species and themuchcolder inert gas atoms in the chamber. These par-ticles are convectively transported and collectedon a liquid-nitrogen-cooled stainless steel drum.Oxide ceramic powders are synthesized by oxi-dizing themetal nanoparticles in the gas phase orafter deposition on the cold nger. Subsequently,Nanophase Technologies [18] developed a con-tinuous process that eliminates the dependenceon natural convection. In this process (Fig. 6),precursor material is introduced at a controlledrate into a chamber. In the chamber, a plasma arcis formed between a nonconsumable electrodeand the precursor. The precursor, typically ahigh-puritymetal rod, passes through the plasmaarc and is melted and vaporized. A reactive gas,typically oxygen, is introduced into the chamber


and reacts with the evaporated precursor, caus-ing nanoparticles of oxides to be formed uponcondensation. Additional gas is turbulently in-troduced to accelerate cooling of the particles.The gas propels the nanoparticles into a collec-tor housing which contains a lter that allowsthe gas to exit but traps the aky agglomeratednanocrystalline particles. The nanoparticles thatcollect on the lter media are periodically har-vested. Nanopowders of Fe2O3, Al2O3, TiO2,and CeO2 are routinely produced in tonnagequantities by the PVS method under the tradename Nanotek.

Figure 5. The original gas condensation process for pro-ducing nanoparticles, introduced by Gleiter et al. [3]

A less economical method of generatingmetal vapors is by laser evaporation of metal tar-gets. Alternatively, oxide targets can also be ab-lated to form oxide nanoparticles directly. Sev-eral researchers have used Nd:YAG, Excimer, ora CO2 laser to generate plumes of metal vapors,which are subsequently oxidized downstream toform nanoparticles [2729].

3.5. Chemical Vapor Condensation

The synthesis of nanoparticles by the chemi-cal vapor condensation (CVC) method, rst in-troduced by Chang et al. [19], involves con-trolled thermal decomposition of organometal-lic precursors in a reduced-pressure environ-ment. By using a hot-wall reactor and an in-ert carrier gas for the precursor, nonoxide ce-ramic nanopowders can be synthesized. Using a

combustion ame reactor allows oxide ceram-ics to be produced (Fig. 7). A unique feature ofthe combustion ame/CVC process is the spe-cially designed burner which gives a completelyuniform at combustion zone with a uniformtemperature prole and gas-phase residencetime over its entire surface. Thus, nanoparti-cles are produced that are essentially monodis-persed. Furthermore, by rapidly quenching theclusters/nanoparticles as they emerge from theame, non-agglomerated powders can be gener-ated.

Low-pressure at ames had not previouslybeen investigated for purposes of nanopowderproduction.One studyperformedat lowpressure[30] yielded some important information butfocused on very low precursor concentrationsthat minimally affect the chemical ame struc-ture. In addition, this work was performed in anopen ame without a substrate. Such ames arecharacterized by a signicantly different thermalame structure without a quench zone after thepeak ame temperature.

In contrast, atmospheric ames have beenstudied at great length and are routinely used forpowder synthesis. The low-pressure stagnation-point ames being scaled by Nanopowder En-terprises Inc. offer some signicant advantagesover atmospheric-pressure synthesis [31]. First,high concentrations of ame radicals can bemaintained at lower temperatures. This impliesthat precursor decomposition temperatures canbe lower, resulting in less sintering of collid-ing particles. This in turn, leads to reduced ag-glomeration. Second, the residence times of thesynthesized particles in the low-pressure envi-ronment are shorter. Both volumetric ow ratesper unit burner area and distance to the stag-nation plane are similar in atmospheric amesynthesis reactors, but the pressure in the com-bustion ame/CVC process is about 35 timeslower, leading to a reduction in residence timeof nearly an order of magnitude. This impliesthat (1) the synthesized nanoparticles in com-bustion ame/CVC spend substantially less timein the hot zone of the ame, and (2) the nanopar-ticles suffer fewer potentially agglomeratingparticle particle collisions, since the overalltemperatures are lower. Third, the inherent uni-formity of the stagnation ow environment, cou-pled with the increasing strength of the ther-mophoretic force relative to the drag force at


Figure 6. Schematic of the Nanophase Technologies Physical Vapor Synthesis (PVS) technique [18]

low pressures, suggests that particles which con-dense at different radial locations will experi-ence similar trajectories and hence time/temper-ature histories.

Figure 7. Schematic of the combustion ame/CVC process

3.6. Chemical Vapor Reaction

Konig et al. [32] developed a chemical vaporreaction process at H. C. Starck and Co. for pro-ducing nanoparticles of metals and nonoxide ce-ramics. Precursor compounds, which are typi-cally halides, are evaporated upstream in evapo-rators that are incorporated in the gas preheater.The precursor metal compounds and the reac-tants, which are typically H2, CH4, or NH3, are

introduced into the reactor through two coaxialnozzles in the form of coaxial laminar compo-nent streams. The laminar ow leads to a nar-row distribution of residence times of the nucleior particles. Thorough mixing between the owstreams is achieved by incorporating an obsta-cle in the otherwise strictly laminar ow, so asto generate a Karman vortex path. To preventthe reactants from being deposited on the reac-tor wall, to which there is a strong energetic bias,the reactionmedium is screened from the reactorwall by introducing an inert gas layer. The re-action occurs at temperatures between 500 and2000 C, in accordance with the following ex-amples:

2 TiCl4 + 2NH3 +H2 2 TiN+ 8HCl

TiCl4 +CH4 TiC+ 4HCl

2 TaCl5 + 5H2 2 Ta + 10HCl

3.7. Liquid Flame Spray

Recognizing the need to deliver precursorsat high rates into a hot zone for pyrolysis,Karthikeyan et al. [33] have developed a pro-cess, called liquid ame spray (LFS), in whicha liquid precursor chemical is atomized, and theatomized liquid droplets are used as the spray


feedstock for producing nanoparticles. Twouidatomizers were incorporated along the axis ofan oxy-hydrogen ame spray gun. The atom-izer produces micrometer-sized droplets of theliquid jet and injects them into the hot zone ofthe combustion ame. Nitrates, acetates, and or-ganometallics can be dissolved in an appropriatesolvent, such as isopropyl alcohol, and injectedinto the combustion ame. As the liquid dropletsare accelerated by the ame, heat transfer fromthe ame to the droplets leads to evaporationof the solvent, condensation of the precursor,chemical reaction, and formation of particles inthe gas phase. While the process allows the for-mation of a high-surface oxide material, con-trol of particle size is an issue, as the atomizerproduces a range of droplet sizes, and differentdroplets have different thermal histories in thespray ame, depending on their size and injec-tion velocities.

4. Processing of NanostructuredBulk Structures and Coatings

4.1. Equal Channel Angular Pressing

Efforts at producing dense materials from dis-crete metal nanopowders have met with limitedsuccess, primarily due to the inability to con-trol oxygen contamination. Metallic nanoparti-cles have been produced in an ultrahigh-vacuumchamber and compacted in situ to prevent oxy-gen contamination [3436]. While it has beenpossible to reduce theoxygen content to less than0.5 atom% in materials such as copper, such acomplicated process is less likely to be viable onan industrial scale.

Valiev et al. [37], [38] have developed an al-ternative approach to forming dense nanocrys-talline metallic materials. Instead of consolidat-ing powders by traditional powder metallurgytechniques, the new process, called equal chan-nel angular (ECA) pressing, relies on severeplastic deformation to rene the microstructure.One can either start with an ingot or ball-milledpowders. By extruding the material through in-tersecting channels of identical cross section,full consolidation and grain-size renement areachieved simultaneously. Nanocrystalline mate-rials of Pb Sn, Zn Al, andAl Cuwith a grain

size of less than 100 nm, have been achieved bythis process. Such materials are superplastic anddisplay exceptional mechanical properties [39].

4.2. Liquid Phase Sintering of n-WC/Co

n-WC/Co powders synthesized by the SCPmethod are densied by liquid-phase sinteringwith the addition of a grain-growth inhibitor,such as VC or Cr3C2. In VC-doped n-WC/Comaterials, the hardness increases with increas-ing VC concentration up to a maximum of 2190VHN at 0.8wt% VC (Fig. 8). These data corre-late with a reduced mean free path for the cobaltbinder phase, i.e., reduced WC grain size. Mea-surements also show that nanograined materialspossess superior hardness at all compositions.The relatively high hardness (> 1850 VHN) athigh Co content (> 10wt%) is not accompaniedby a decrease in fracture toughness [40].

Figure 8.Hardness versus VC (grain growth inhibitor) con-tent in WC/7wt% Co alloys

Another interesting observation is the strik-ing difference in response of micrograined andnanograined materials to a scratch test. The mi-crograined material shows evidence of com-bined plastic deformation and fracture of theWC grains, whereas the nanograined materialyields by pure plastic deformation, despite itshigh hardness. Evidence for superior abrasivewear resistance of n-WC/Co, as well as for im-proved cutting performance of n-WC/Co drillbits has been obtained [21].


4.3. Thermal Spraying of n-WC/Co

Thermal spraying is awidely used industrial pro-cess for applying protective coatings tomaterialssurfaces. The coating process involves feedingprealloyed powders into a ame or plasma gun(Fig. 9). The particles are rapidly heated to forma sprayof partially or completedmelteddroplets.The large impact forces created as these particlesarrive at the substrate surface promotes strongparticle to substrate adhesion and the formationof a dense coating. An attractive feature of theprocess is its ability to produce coatings of al-most any desired material, ranging in thicknessfrom 25m to several millimeters, at relativelyhigh rates.

Nanostructured coatings of hardmetals suchas WC/Co offer signicant potential improve-ments in abrasive wear resistance and hardnesscompared with conventional WC/Co coatings.Preliminarywork on thermal spray deposition ofNanocarb WC/12Co and WC/15Co has yieldedpromising results.

4.4. High-Pressure Consolidation

Using a high-pressure/high-temperature(HPHT) hot pressing unit of advanced design,developed by Voronov et al. [41], a new classof WC/Co/diamond nanocomposites are be-ing produced [42]. The HPHT unit consists ofshaped anvils of tungsten carbide and supportingprestressed steel rings. The anvils compress ashaped insert made of lithographic stone, whichtransmits a near-isostatic pressure to the reactioncell. The reaction cell consists of a resistivelyheated graphite crucible, which is capable ofreaching 2000 C in a few minutes.

During high pressure/low temperature(HPLT) sintering, the nucleation rate of thestable phase is increased, thereby accomplish-ing metastable/stable phase transformation atrelatively low temperature [43], [44]. For ex-ample, at 5GPa and 600 C, nanoparticles of-Al2O3 transform completely into -Al2O3.This transformation-assisted consolidation ap-proach is being used to fabricate fully densematerials from oxide nanoparticles.

5. Processing of NovelNanostructured Materials

Apart from the four major powder productiontechnologies of commercial importance (seeChap. 3), several processing methods have de-veloped for specic materials.

5.1. Composite Nanoparticles

Vollath et al. [45] have developed a two-stagemicrowave plasma technique in which nanopar-ticles formed near the inlet of the reactor arecoated downstream with a layer of a second ma-terial, e.g., an Al2O3 layer on a ZrO2 particle.The structure of these nanocoated particles de-pends strongly on the crystallization behavior ofthe phases forming the kernel and the coating.The main applications of these new nanocoatedparticles may either be seen in the formation ofdiffusion barriers to avoid grain growth or in themodication of physical properties of the coreand the chemical properties of the surface.

Che et al. [46] have developed a modi-ed spray pyrolysis method for the synthesisof SiO2-encapsulated Pd nanoparticles. Thesecomposite nanoparticles were formed from apalladium nitrate solution containing ultraneSiO2 particles by ultrasonic spray pyrolysis.A precursor particle formed below 700 C inthe drying stage was composed of a homoge-neous mixture of n-SiO2 and PdO H2O. WhenPdO was decomposed above 700 C, metallicPd nanoparticles were formed in the SiO2 ma-trix. Because of the high surface free energy, themetallic Pd particles coagulate and condense inthe interior of the composite particle. As a re-sult of the relocation within the composite parti-cle, SiO2 is forced out of the particle toward thesurface, and an SiO2-encapsulated Pd particleis formed. Similar structures of Ag SiO2 andCu SiO2 were prepared by Crane et al [47].

5.2. Films with Nanoscale Porosity

SiO2 lms with nanoscale porosity have attrac-tive properties such as low dielectric constant


Figure 9. Schematic of the thermal spray coating process along with the various processing parameters.

(< 2) and low density. Such lms nd appli-cations as the interlayer dielectricmaterial in de-vices. Jin et al. [48] have developed a sol gelmethod to form such nanoporous thin lms, inwhich processing parameters, such as processow for deposition and post-deposition curing,relative rates of reaction, gelation, aging, anddrying, are controlled to improve mechanicalproperties and dielectric constant.

Skandan et al. [49] have developed alow-pressure ame deposition (LPFD) process,which utilizes the at-ame burner described inSection 3.4. LPFD is a one-step deposition pro-cess that completely avoids the use of powdersas starting material. This is benecial in termsof signicant cost reduction, as well as the abil-ity to easily access the critical thickness rangeof 1 10m. The LPFD process is capable ofdepositing lms at rates greater than 1m/min,up to any thickness that one desires. The ex-perimental arrangement for operating the atame in lm-forming mode is similar to thepowder-formingmode, except that the cold plateis replaced with a heated substrate. The super-heated clusters or nanoparticles emerging fromthe hot zone of the ame are allowed to impingeupon a heated substrate. The nanoparticles sinteras they arrive at the substrate and form a lm orcoating. The desired extent of nanoscale poros-ity is obtained by controlling the number densityof nanoparticles in the gas phase and the temper-ature of the substrate.

5.3. High Green Density CompactionMethod

High green density is a prerequisite for achiev-ing a high sintered density. Due to the increasedsurface area in nanopowders, it is not possibleto achieve high green densities when the pow-der is pressed at conventional pressures. Ivanovet al. [50] have developed a pulsed densicationmethod for oxides such as Al2O3 and ZrO2, inwhich compression waves of 100 500s in du-ration and up to 2.5GPa in amplitude are gen-erated by a pulsed magnetic press. Green com-pacts with densities of up to 0.8 of the theoret-ical density have been reported. Similar resultshave been obtained by cold compaction under apressure in excess of 5GPa [51]. Higher pack-ing densities may be attributed to interparticlesliding and plastic deformation.

6. Applications of NanostructuredMaterials

Nanopowders are used (1) as dispersed phasesin uid media, (2) on supporting substrates, (3)for consolidation into dense structures, and (4)as feedstock for the formation of lms and de-position of coatings.

Some of the notable areas where nanopar-ticles, nanostructured sintered materials, and


nanostructured lms/coatings are being used orunder development are as follows.

Chemicalmechanical polishing slurries, con-taining nanoparticle dispersions of SiO2, Al2O3,and CeO2: The eld of chemical mechanicalpolishing (CMP) of semiconductor materials isexperiencing dramatic growth. While CMP wasoriginally a process for expensive microproces-sor production by major IC manufacturers thatcould support its cost, it is now used for an everwidening array of products, from modem chipsto DRAMs. Manufacturers are beginning to useCMP in special niches, such as silicon on insu-lator wafer fabrication andmultichip module as-sembly.While the equipment,materials and pro-cess technology form the different componentsof the CMP process, the slurry itself is a criti-cal element. The particle composition, size anddistribution, dispersability, morphology, shape,and hardness contribute to the polishing perfor-mance. According to the National TechnologyRoadmap Interconnect requirements projecteduntil 2005, there is a need for reduction in parti-cle size extending well into the nanoscale range(< 100 nm). This is because smaller size allowsner surface nish, while non-agglomerationandnarrowsize distribution assure that the slurrydoes not scratch the surface.

Ultraviolet scatterers such as TiO2 and ZnOhave maximum UV scattering efciency in theparticle size range 30 50 nm. Therefore, sun-screens containing nanoparticles have a corre-spondingly higher sun protection factors. Fur-thermore, provided they are non-agglomerating,the stability of the suspension is also improved.

Cosmetic pigments such as Fe2O3 in the formof nanoparticles can be used in cosmetic appli-cations because of their ner texture and abilityto spread easily on a surface.

Conducting inks containing nanoparticles ofCu and Ag enable a lower sintering temper-ature: Cu and Ag are among the few metal-lic nanoparticles that are not pyrophoric andcan be handled in air. Such conducting ultraneparticles are dispersed in a liquid medium andused to form ne conducting lines on plasticsand ceramic substrates. The low sintering tem-perature (about one-third of the melting point)allows low-temperature processing, especiallywhen dealing with polymers.

Sintered nanostructured WC/Co: As-synthesized nanophase WC/Co is milled, com-

pacted, and liquid-phase sintered to produce avariety of tools for mining and drilling oper-ations. The high hardness and wear resistanceincreases the efciency of the drilling operation.

IR windows: Sapphire (single-crystal Al2O3)is presently the material of choice for IR win-dow applications because of its superior opticaland mechanical properties compared to Y2O3,MgO, and AlON. However, processing single-crystal components is expensive. PolycrystallineAl2O3, AlON, and AlN with a nanocrystallinegrain size of less than one-tenth of the wave-length of radiation is being considered as a po-tential replacement for sapphire. The nanoma-terial is expected to have superior mechanicalproperties and comparable optical properties,compared to sapphire.

Sputtering targets: Sputtering is a widelyaccepted industrial process for depositing thinlms. The quality of the sputtered lm dependsgreatly on the properties of the target, includ-ing density, composition, and grain size. Usingnanoparticles as starting materials is likely toyield very high density targets that have an ultra-ne microstructure and a uniform composition.

Dielectric materials: For the past severalyears, much emphasis has been placed on low-temperature processing of thick-lm ferroelec-tric materials for applications in multilayer ce-ramic capacitors (MLCCs), transducers, sen-sors and actuators for the following reasons: (1)ne-grained (0.7 1.0m) ferroelectric materi-als that have high permittivity and very goodpiezoelectric properties (e.g., = 4000 6000 atroom temperature in BaTiO3, and d = 500 pC/Nin Pb(ZrTi)O3) can only be synthesized by low-temperature processing, (2) when the fabrica-tion temperature is less than 900 C, reactionsbetween the electrodes and the dielectric can besignicantly reduced, and (3) low-temperatureprocessing allows replacement of the expensiveAgPd electrodeswith cheaperNi and/orCu elec-trodes.

Gas sensors: Thin lms of oxides such asSnO2 and TiO2 containing nanoscale porosityhave applications as gas sensors. Thin lm sen-sors for monitoring CO, CO2, NOx, SOx, andother gases are usually fabricated by deposit-ing dense materials that have a columnar struc-ture. The current trend is to fabricate integratedmicroelectronics-based gas sensors as (1) it ismore economical in the long run, (2) has a faster


response time, and (3) higher sensitivity. It hasalready been demonstrated that a dense lmwitha nanoscale grain size has a faster response time.It is expected that a porous lm with the grainsand pores in the nanoscale regime will have aneven faster response time.

Low-voltage displays: One of the areas ofdevelopment for the next generation of atpanel displays is phosphor powders that havehigh efciency at a low operating voltage.Doped nanoparticles of oxidic materials such asY2O3:Eu andY2O2S:Eu have higher cathodolu-minescence efciency at operating voltages (ca.200V) than their coarse-grained counterparts.It is expected that further enhancements in theperformance by way of surface passivation willlead to higher photoluminescence and electrolu-minescence efciencies.

Engine components: Si3N4 reinforced withne particles of SiC has evolved as a high-tem-perature structural material. Reducing the scaleof Si3N4 and SiC has led to improved strengthand toughness. In addition, the material displayssuperplastic behavior.

7. Future PerspectiveMajor advances have been made in the scienceof nanophase materials, and signicant progresshas been made on the technological front. Inparticular, impressive improvements have beenmade in the high rate processing of nanopow-ders at a competitive cost. Looking ahead, ma-jor innovations can be expected in the prepa-ration of high-performance nanophase coatingsand consolidated parts. The most immediatepay-off should be in the processing of ther-mally sprayedWC/Co-base coatings and liquid-phase sintered parts. On the other hand, in viewof recent advances in high-pressure consolida-tion of nanoceramic powders, it is evident thatwithin a few years, commercialization of sin-tered nanophase ceramics will be realized.

The use of nanopowder in dispersed form isan established technology in the catalysis in-dustry. Further improvements in catalytic per-formance can be expected as a consequence ofthe ability now to produce nanoparticles thatare tailored with respect to composition, struc-ture, and morphology. In addition, dispersingnanoparticles in uidmedia presents new oppor-

tunities that are being intensely pursued. A goodexample is the use of aqueous suspensions ofmonodispersed ceramic nanoparticles as abra-sive medium for planarization of semiconductorand optical devices.

8. References

Specic References1. R. Birringer, U. Herr, H. Gleiter, Trans. of Jpn.

Inst. Met. 27 (1986) 43.2. H. Hahn, J. Eastman, R. Siegel, Suppl. Ceram.

Trans. 1 B, (1988) 1115.3. H. Gleiter, Progress in Mat. Sci. 33 (1990) 4.4. R.W. Seigel, Nanostruct. Mater. 3 (1993) no.

1, 1.5. J. R. Weertman, Scripta Metallurgica et

Materialia 24 (1990) 1351.6. G. Skandan, H. Hahn, M. Roddy, W.R.

Cannon, J. Am. Ceram. Soc. 77 7, (1994)1706.

7. H. Gleiter, Nanostruct. Mater. 1 (1992) no. 1,1.

8. J. Robb, L. Simpson, Drug Cosmet. Ind. 3(1994) 32.

9. L. E. McCandlish, B. H. Kear, B. K. Kim,Nanostruct. Mater. 1 (1992) no. 2, 119.

10. K. Jia, T. E. Fischer, Wear 200 (1996) 206.11. N. Yamazoe, Sensors and Actuators B5

(1991) 7.12. G. S. Tompa et al., MRS Symp. Proc. 358

(1995) 701.13. G. F. Gaertner, H. Lydtin, Nanostruct. Mater.

4 (1994) no. 5, 559.14. D. Vollath, K. Sickafus, Nanostruct. Mater. 1

(1992) 427.15. D. Gallaghar, W. Heady, J. Racy, R. Bhargava,

J. Mater. Res. 10 (1994) 4, 870.16. G. Messing, S. Zhang, V. Jayanthi, J. Am.

Ceram. Soc. 76 (1993) 11, 2707.17. B. H. Kear, L. E. McCandlish, Nanostruct.

Mater. 3 (1993) 19.18. Q. Ford, Ceram. Ind. 31 (1993).19. W. Chang, G. Skandan, H. Hahn, S. C.

Danforth, B. H. Kear, Nanostruct. Mater. 4(1994) 345.

20. D. Reisner, T. D. Xiao, P. R. Strutt, Proc. of13th Annual Battery Conference onApplications and Advances, Long Beach CA,Jan. 13 16, 369 (1998).

21. L. A. Bursill, B. Jiang, J. L. Peng, W. L. Zhong,P. L. Zhang, Technical Report, DE97-626946.


22. C. Estournes, T. Lutz, J. Happich, T. Quaranta,P. Wissler, J. L. Guille, J. Magn. Magn. Mater.173 (1997) nos. 1 2, 83 92.

23. J. Hyeon-Lee, G. Beaucage, S. E. Pratsinis,Chem. Mater. 9 (1997) 2400.

24. K. E. Gonsalves, T. D. Xiao, G.M. Chow, C. C.Law, Nanostruct. Mater. 4 (1994) 130.

25. C. Granquist, P. Buhrmann, J. Appl. Phys. 47(1976) 2200.

26. R. Birringer, H. Gleiter, H. P. Klein, P.Marquardt, Physics Letters 102A (1984) No.8, 365.

27. G. F. Gaertner, H. Lydtin, Nanostruct. Mater.4 (1994) no. 5, 559.

28. R. Uyeda, M. Kato, Technical Report of Toyota26 (1973) 66.

29. H. Lee, W. Riehmann, B. Mordike, Z.Metallkunde 84 (1993) 79.

30. D. Lindackers, M.G.D. Strecker, P. Roth,Nanostruct. Mater. 4 (1994) 545.

31. N. Glumac, Y-J. Chen, G. Skandan, J. Mater.Res. (in press).

32. US 5 356 120, (T. Konig, K. Bachle, H. Ewel,V. Rose, G. Zippenfenig, R. Klafki).

33. J. Karthikeyan, C. C. Berndt, J. Tikkanen, J. Y.Wang, A.H. King, H. Herman, Nanostruct.Mater. 8 (1997) no. 1, 61 74.

34. R. Birringer, U. Herr, H. Gleiter, Transactionsof the Japanese Institute of Metals 27 (1986)Suppl. 43.

35. A. Tschope, R. Birringer, PhilosophicalMagazine B 68 (1993) 223.

36. P. Sanders, G. E. Fougere, L. J. Thompson, J.Eastman, J. R. Weertman, Nanostruct. Mater.8 (1997) no. 3, 243 252.

37. A.V. Korznkov, I.M. Safarov, D.V.Laptionok, R. Z. Valiev, Acta Metall. Mater.39 (1991) 3193.

38. R. Z. Valiev, R. S. Mishra, J. Groza, A.Mukherjee, Scripta Mater. 34 (1996) 1443.

39. R. S. Mishra, R. Z. Valiev, A.K. Mukherjee,Nanostruct. Mater. 9 (1997) 473 376.

40. K. Jia, T. E. Fischer, Wear 203 204 (1997)310.

41. O. Voronov, A. Rahmanina, Proc. of IV Int.Symposium on Diamond Materials, Nevada,1995.

42. R. Sadangi, O. Voronov, B. H. Kear, CIMTEC98, 9th International Conference on ModernMaterials & Technologies, Florence, Italy,June 98, in press.

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Ullmann's Encyclopedia of Industrial Chemistry Naphthalene and HydronaphthalenesStandard Article

Gerd Collin1, Hartmut Hke2, Helmut Greim31DECHEMA e.V., Frankfurt/Main, Federal Republic of Germany 2Weinheim, Federal Republic of Germany 3Institut fr Toxikologie und Umwelthygiene, TU Mnchen, Freising-

Weihenstephan, Federal Republic of Germany

Copyright 2003 by Wiley-VCH Verlag GmbH & Co. KGaA. All rights reserved. DOI: 10.1002/14356007.a17_001.pub2 Article Online Posting Date: March 15, 2003

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Naphthalene was discovered in coal tar by A. GARDEN in 1819.

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1. Physical and Chemical Properties Gerd Collin

Naphthalene [91-20-3], C10H8, Mr 128.18, mp 80.29 C, bp 217.95 C (101.3 kPa), forms colorless flakes or monoclinic crystals with a characteristic odor. It is readily soluble in benzene, diethyl ether, chloroform and carbon disulfide, soluble in ethanol, and insoluble in water. Naphthalene is volatile in steam and readily sublimable. It forms azeotropic mixtures with, for example, ethylene glycol, acetamide, m-cresol, and benzyl alcohol. Some important physical properties are as follows:

1. Physical and Chemical Properties2. Production3. Uses4. Alkylnaphthalenes5. Hydronaphthalenes6. Economic Aspects7. Toxicology

Density (20 C) 1.1789 g/cm3

Refractive index (99.5 C) 1.5829 Heat capacity (25 C) 1.294 kJ/kgHeat of fusion 148 kJ/kgHeat of vaporization 352 kJ/kgVapor pressure at 70 C 0.525 kPa at 88 C 1.33 kPa

at 181 C 40 kPa

at 270 C 295 kPa

at 349 C 1.01 MPa

at 479 C 4.13 MPa

Critical temperature 475 CFlash point (closed cup) 80 C

Naphthalene and Hydronaphthalenes : Ullmann's Encyclopedia of Industrial Chemistry : Wiley InterScience

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Naphthalene can be catalytically hydrogenated in the liquid phase, preferably in the presence of nickel, with high selectivity to give tetra- and decahydronaphthalene, and in the gas phase in the presence of oxidic catalysts less selectively to give mixtures of tetra-, hexa-, octa-, and decahydronaphthalene. Liquid-phase oxidation with various oxidants or gas-phase oxidation with air in the presence of vanadium pentoxide catalysts gives (via 1,4-naphthoquinone) phthalic acid, which is readily dehydrated to phthalic anhydride ( Phthalic Acid and Derivatives). The 1-position of naphthalene is the most nucleophilic. Consequently, electrophilic substitution reactions, such as nitration, halogenation, sulfonation, and alkylation at lower temperature, preferentially give the corresponding 1-substituted products; at higher temperature, isomerization occurs to give the thermodynamically more stable 2-substituted products. Nitration with nitric acid at low temperature produces 1-nitronaphthalene, and with H2SO4 HNO3 at high temperature, 1,5- and 1,8-dinitronaphthalene ( ). Halogenation forms 1-halo- and/or 1,4- and 1,5-dihalonaphthalenes, depending on the reaction conditions. Polychloronaphthalenes are obtained by catalytic chlorination at higher temperature ( Chlorinated Hydrocarbons). Sulfonation with concentrated sulfuric acid gives 1-naphthalenesulfonic acid, and at higher temperature, 2-naphthalenesulfonic acid; oleum gives 1,5-, 1,6-, and 2,7-naphthalenedisulfonic acids and trisulfonic acids, depending on the SO3 content ( ). Naphthalene can be alkylated at higher temperature with alkyl halides, alcohols, and olefins in the presence of strong acids or Friedel-Crafts catalysts, with preferential formation of 2-alkyl derivatives ( Acylation and Alkylation). Dehydrogenating condensation of naphthalene (Scholl reaction) gives perylene [198-55-0]. Acylation of naphthalene leads to mixtures of the 1- and 2-acyl derivatives, with the ratio depending on the solvent used ( Acylation and Alkylation Acylation of Polynuclear Aromatic Compounds). 1-Chloromethylation with paraformaldehyde and hydrochloric acid affords 1-chloromethylnaphthalene.

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2. Production Gerd Collin

The main feedstock for naphthalene production is coal tar. At an average content of around 10 %, naphthalene represents the most important compound in high-temperature coal tar (coke-oven tar) in terms of quantity. It can already be concentrated to over 90 % in primary tar distillation, in the naphthalene fraction boiling between 210 and 220 C, with a yield in excess of 90 %. Further refining requires separation of the co-boiling compounds ( phenols, nitrogen bases, benzo[b]thiophene, and other aromatic hydrocarbons). For production of technical naphthalene (e.g., mp 78.5 C), redistillation of the naphthalene fraction is sufficient. Generally, phenols are extracted with sodium hydroxide solution before distillation (Fig. 1). Pure naphthalene (mp 79.6 C) is produced by, e.g., crystallization or hydrorefining.

Crystallization especially separates benzo[b]-thiophene, which boils at only 2 C above naphthalene. Benzo[b]thiophene forms a eutectic mixture with naphthalene at a benzo[b]thiophene content of 93 %, and mixed crystals elsewhere in the phase diagram. Whereas until recently, naphthalene was predominantly recovered by crystallization from the melt, with formation of suspensions, newer processes of crystallization from the melt result in the formation of layers or blocks. Benzo[b]thiophene and other impurities can be separated from naphthalene by multistage countercurrent crystallization from the melt without adding selective solvents. Four to six crystallization stages are needed to produce pure naphthalene with a melting point of 80 C from a coal tar primary fraction containing 90 % naphthalene.

Hydrorefining of naphthalene is carried out at 400 C and ca. 1.4 MPa in the presence of cobalt molybdenum catalysts, whereby benzo[b]-thiophene is converted to hydrogen sulfide and ethylbenzene. Other co-boiling compounds are broken down to lower-boiling hydrocarbons and can be separated by distillation. Naphthalene produced by this method has a sulfur content of 100 ppm and contains tetralin as the main by-product (ca. 1 %).

Other possible methods for separating benzo[b]thiophene include selective sulfonation, polycondensation with formaldehyde and acid, reaction with sodium metal, and azeotropic distillation with glycols.

Naphthalene can also be recovered from pyrolysis residue oils (from the pyrolysis of hydrocarbon fractions to olefins) by distillation and crystallization, in a manner similar to the recovery from coal tar. These pyrolysis residue oils normally contain 10 16 % naphthalene [6].

In addition to recovery from coal tar, naphthalene is also produced in the United States by hydrodealkylation of aromatized petroleum-derived fractions (Fig. 2) [7], [8]. Typical feedstocks are residue oils from catalytic naphtha reforming, from naphtha pyrolysis in olefin plants, or catcracker recycle oils. These aromatized oils are distilled to give a fraction containing naphthalene and alkylnaphthalenes and, in the case of catcracker recycle oils, subjected to extraction of the aromatics. The

Ignition temperature 540 CExplosion limits in air upper 5.9 vol %

lower 0.88 vol %

Dielectric constant (20 C) 2.47Odor threshold 0.004 mg/m3

Figure 1. Naphthalene recovery from coal tar by extraction and distillation a) Dephenolated naphthalene fraction; b) Dewatering column; c) Light oil column; d) Naphthalene column; e) Cooling; f) To the vacuum unit


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bicyclic aromatic fraction, with a boiling range of, e.g., 220 270 C, is dealkylated under hydrogen pressure, either thermally above 700 C, or catalytically in the presence of a chromium oxide/aluminum oxide or cobalt oxide/molybdenum oxide catalyst at 550 650 C. Methyl- and dimethylnaphthalene fractions from coal tar can also be hydrodealkylated. The crude dealkylation product is processed to a low-sulfur pure naphthalene (mp 80 C) by distillation.

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3. Uses Gerd Collin

Worldwide, the main derivative of naphthalene is still phthalic anhydride (from catalytic gas-phase oxidation of naphthalene), an intermediate for PVC plasticizers ( Phthalic Acid and Derivatives). Other important applications for naphthalene are dyes, particularly azo dyes produced from 2-naphthol [135-19-3] and naphthalene sulfonic acids ( Azo Dyes). Naphthalene and alkylnaphthalene sulfonates are used as surfactants, and naphthalene sulfonate formaldehyde condensates as tanning agents (syntans) and dispersants, e.g., as superplasticizers for concrete ( Disperse Systems and Dispersants Formaldehyde Condensation Products). Naphthalene is used in the production of moth repellents and fumigants and the insecticide carbaryl (1-naphthyl-N-methylcarbamate). It is also used for the synthesis of tetrahydroanthraquinone from naphthoquinone and butadiene ( Anthraquinone Production) and for alkylnaphthalene solvents for carbonless copy paper (Kureha Micro Capsule Oil, KMC, a mixture of diisopropylnaphthalene isomers), the solvents tetralin and decalin, as well as chlorinated naphthalenes ( Chlorinated Hydrocarbons), of which only the monochloronaphthalenes retain commercial significance, e.g., as dye dispersants and as fungicides and insecticides for preservatives. Polychlorinated naphthalenes are rarely produced due to their toxicity and resistance to environmental degradation. 1-Methyl- and 1-chloromethylnaphthalene are used in the production of the plant growth regulators 1-naphthaleneacetamide [86-86-2] and 1-naphthaleneacetic acid [86-87-3]. The alkaline-earth salts of sulfonated dinonylnaphthalenes are important lube-oil additives. New applications are opening up for 2,6-naphthalenedicarboxylic acid and 6-hydroxy-2-naphthoic acid as intermediates for liquid crystal polymers and heat-resistant polyester fibers and films. For further details on the uses of naphthalene, see Figure 3.

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4. Alkylnaphthalenes Gerd Collin

1-Methylnaphthalene [90-12-0], C11H10, Mr 142.20, bp 244.4 C (101.3 kPa), mp 30.5 C, d 20 1.0203, is a colorless, blue-

fluorescing liquid which is readily soluble in benzene, ethanol, and diethyl ether, and insoluble in water. 1-Methylnaphthalene is present in high-temperature coal tar in a concentration of 0.5 % and is produced industrially from the methylnaphthalene fraction, which boils between 240 and 245 C, by redistillation of the 2-methylnaphthalene filtrate following crystallization and separation of 2-methylnaphthalene. 1-Methylnaphthalene can be isomerized to 2-methylnaphthalene in the presence of, e.g.,BF3, phosphoric acid, and phase-transfer catalysts [9], or on zeolite catalysts [10]. It is used for the synthesis of 1-naphthaleneacetic acid and, in mixtures with 2-methylnaphthalene, as a solvent and heattransfer oil.

2-Methylnaphthalene [91-57-6], C11H10, Mr 142.20, bp 241.1 C (101.3 kPa), mp 34.6 C, d 20 1.029, forms colorless

crystals. The compound is readily soluble in benzene, ethanol and carbon disulfide, but insoluble in water. It is recovered industrially by crystallization from the methylnaphthalene fraction of high-temperature coal tar, which contains 1.5 % 2-methylnaphthalene. 2-Methylnaphthalene can also be produced by isomerization of 1-methylnaphthalene (see above). 2-Methylnaphthalene is the feedstock for the production of 2-methyl-1,4-naphthoquinone [58-27-5] (menadione, vitamin K3), and mixtures with 1-methylnaphthalene are used as solvents and heat-transfer oils. It is used in small quantities for the production of alkylmethylnaphthalene sulfonates as textile auxiliaries, surfactants, and emulsifiers. 2-Methylnaphthalene can be used via 2-methyl-6-acetylnaphthalene [11], [12], or in an older process (also as a mixture with 1-methylnaphthalene) by oxidation with subsequent Henkel rearrangement, to give 2,6-naphthalenedicarboxylic acid [1141-38-4] ( Carboxylic Acids, Aromatic). This compound is used in the production of special heat-resistant polyester fibers and films, and of liquid crystal polymers. 2-Methylnaphthalene can be acylated in 1,2-dichlorbenzene to give 1-acyl-7-methylnaphthalene [13], which can be used as an intermediate for pharmaceuticals [14].

Figure 2. Naphthalene recovery by catalytic hydrodealkylation of alkylnaphthalene fractions ( Unidak process) a) Naphthalene column; b) Reactor; c) High-pressure gas separator; d) Low-pressure gas separator; e) Methane scrubber; f) Centrifuge; g) Melting vessel; h) Stripping column; i) Solvent recovery column

Figure 3. Uses of naphthalene


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2,6-Dimethylnaphthalene [581-42-0], C12H12, Mr 156.23, bp 261 C (101.3 kPa), mp 110 C, forms colorless crystals which are slightly soluble in ethanol and insoluble in water. It can be recovered from the dimethylnaphthalene fraction of coal tar by redistillation and crystallization; from aromatized catcracker recycle oil by aromatics extraction, redistillation, hydrogenation of the isomer mixture to dimethyltetralins, isomerization, and dehydrogenation; or by disproportionation of methylnaphthalenes to give naphthalene and dimethylnaphthalenes, from which the 2,6-isomer can be obtained analogously to the production from aromatized catcracker recycle oil. 2,6-Dimethylnaphthalene is also obtained by alkylation of 2-methylnaphthalene or naphthalene on zeolite catalysts [15], [16].

2,6-Dimethylnaphthalene can be converted to 2,6-naphthalene dicarboxylic acid by liquid-phase oxidation with oxygen in acetic acid as solvent in the presence of a cobalt acetate/manganese bromide catalyst and a co-catalyst, e.g., ruthenium chloride [17].

2-Isopropylnaphthalene [2027-17-0], C13H14, Mr 170.25, bp 268.9 C (101.3 kPa), mp 15.1 C, d 20 0.9762, is a colorless

liquid. It can be used to synthesize 1-naphthol [90-15-3] by oxidation via the hydroperoxide (Hock synthesis) ( ). Catalytic gas-phase dehydrogenation produces polymerizable 2-isopropenylnaphthalene [3710-23-4] [18].

Diisopropylnaphthalenes. Selective Friedel-Crafts alkylation of naphthalene with propene in the presence of an aluminum silicate catalyst yields as the main product a mixture of diisopropylnaphthalene isomers that is liquid over a wide temperature range. This isomer mixture is used as a solvent for carbonless copy paper [19], [20]. The solvent, trade name KMC (Kureha Micro Capsule Oil), is odorless, colorless, and environmentally harmless [21]. KMC can also be used as a solvent for scintillation measurements and as a heat transfer oil. Some physical properties of KMC are as follows:

Technically pure 2,6-diisopropylnaphthalene [24157-81-1] (mp 70 C) can be isolated from the isomer mixture by crystallization [22]. It can be converted to 2,6-naphthalene dicarboxylic acid [23-25] or to 6-hydroxy-2-naphthoic acid [16712-64-4] by liquid-phase oxidation [26]. These compounds are used as intermediates for heat-resistant liquid crystal polyesters [27].

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5. Hydronaphthalenes Gerd Collin

1,2,3,4-Tetrahydronaphthalene [119-64-2], tetralin, C10H12, Mr 132.21, bp 207.3 C (101.3 kPa), mp 35 C, d 20 0.9729,

1.5461, is a colorless liquid which is infinitely soluble in chloroform, petroleum ether (ligroin), diethyl ether, and ethanol, but insoluble in water. Tetralin is produced industrially by selective hydrogenation of low-sulfur naphthalene in the presence of nickel catalysts at 180 260 C and 1 1.5 MPa.

Tetralin is used as a solvent for fats, resins, and paints; for the production of detergents; and for the synthesis of carbaryl via 1-naphthol. It can be applied as a hydrogen-donor solvent in coal extraction ( Coal Liquefaction Solvents).

Decahydronaphthalene [91-17-8], decalin, C10H18, Mr 138.25, exists in two stereoisomeric forms: trans-decalin, bp 185.5 C (101.3 kPa), mp 32.5 C, d 20 0.8700 , 1.4696; and cis-decalin, bp 195 C, mp 45 C (101.3 kPa), d 20 0.8967,

1.4811.

The isomer mixture is a colorless liquid with a camphor-like odor. Technical decalin is infinitely soluble in butanol, soluble in chloroform, acetone, carbon disulfide and benzene, and slightly soluble in ethanol and methanol.

Decalin is produced by liquid-phase hydrogenation of naphthalene under pressure in the presence of nickel catalysts. The proportion of the two stereoisomers formed depends on the reaction conditions.

Like tetralin, decalin is used as a solvent for fats, resins, waxes, and paints. It can also be used to make cyclodecanone, an intermediate in the production of polyamide 10.

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6. Economic Aspects Gerd Collin

World production of naphthalene in 1987 was ca. 106 t. About one-fourth of this came from Western Europe, one-fifth each

Boiling range (101.3 kPa) 290 299 CPour point 130 CDensity (15 C) 0.96 g/cm3

Refractive index (25 C) 1.565Specific heat (20 C) 1.71 kJ/kg KThermal conductivity (20 C) 0.12 W/KmDielectric constant (90 C) 2.46


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from Japan and Eastern Europe, and one-eighth from the United States. In addition to coal-tar based naphthalene, petroleum-derived naphthalene has been recovered since 1961, predominantly in the United States, by dealkylation of aromatics-rich fractions from reforming and catalytic cracking. The proportion of petroleum-based naphthalene has decreased during the last decade from ca. 15 % to ca. 5 %, because coal-tar naphthalene is available in sufficient quantity. Table 1 summarizes the main uses of naphthalene as percentage of consumption in Western Europe, Japan, and the United States.

Table 1. Uses of naphthalene in % (1987)

An application for alkylnaphthalenes is the use of diisopropylnaphthalene isomer mixtures as solvents for carbonless copy paper. Production capacities for these mixtures, trade name KMC, total 10 000 t/a each in Japan and the Federal Republic of Germany. World production of 2-methylnaphthalene and 1-/2-methylnaphthalene mixtures is estimated at 1500 t/a each. For hydronaphthalenes, tetralin production is estimated to be 25 000 t/a worldwide. Naphthalenesulfonate formaldehyde condensates are produced worldwide in quantities of ca. 40 000 t/a, predominantly for concrete plasticizers. Although polyester products derived from 2,6-naphthalenedicarboxylic acid or 6-hydroxy-2-naphthoic acid have been on the market for some time, they have not yet gained major commercial importance.

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7. Toxicology Hartmut Hke and Helmut Greim

Use Western United JapanEurope States

Phthalic 40 65 70 anhydride Dyes 29 10Surfactants, tanning agents,

dispersants 15 14 5

Moth repellants, 9 5 2 fumigants Insecticides 14 Solvents and 7 2 12 other uses

Naphthalene Human Health. The health consequences of human exposure to naphthalene have been repeatedly evaluated [48-51]. Most of the information given subsequently derives from these reports.

Effects assessment. Naphthalene is readily absorbed during oral, inhalation and dermal exposure. In rodents it is metabolized by epoxidation and subsequent hydroxylation. These reactive metabolites undergo glutathione conjugation or reduction forming the 1,2-dihydrodiol. In humans, 1-naphthol, 2-naphthol, and 1,2-, and 1,4-naphthoquinone are formed. More recent data demonstrate that cytochrome P450-2F2 in cellular systems of rats and mice metabolizes naphthalene to 1R,2S-naphthaleneoxide [52] which rearranges to 1-naphthol and forms the 1,2-dihydrodiol by hydrolase activity. Oxidation of 1-naphthol forms 1,2-, and 1,4-naphthoquinone [53]. In Clara cells isolated from the lungs of naphthalene treated mice ZHENG et al. [54] reported covalent binding of 1,2-naphthoquinone to protein.

In humans, single or repeated exposures to naphthalene caused severe hemolytic anemia esp. in infants exposed to textiles (clothing/bedding), which have been stored with naphthalene mothballs. It may cause slight irritation on contact with the skin and eyes. The absence of case reports indicates that naphthalene is not a skin or respiratory sensitizer in humans.

In rodents naphthalene is of low acute toxicity and did not show sensitizing activity. Repeated oral administration of naphthalene causes cataracts in rats and rabbits at doses of 700 mg/kg bw/d and above. Despite its widespread use there are no reliable reports of cataracts in humans. Repeated inhalation exposure for 28 days produces irritation of the nasal epithelium, with mild effects at levels as low as 5 mg/m3 in rats (LOAEL). In mice, signs of chronic respiratory tract inflammation were noted at 50 mg/m3. There was no indication of hemolytic anemia in rodent studies.

Naphthalene was not mutagenic in bacterial assays and did not induce UDS in vitro. In CHO cells clastogenic effects and sister chromatid exchanges (SCE) were found in vitro in the presence and in the absence of metabolic activation. In human peripheral lymphocytes no SCEs have been induced in the presence or absence of microsomal enzymes. Other in vitro tests (micronuclei in MCL-5 cells [55], DNA fragmentation in macrophages [56], chromosomal aberrations in mice embryo cultures [57, 58]) indicated genotoxic effects. In vivo, naphthalene did not induce micronuclei in bone marrow cells of mice or UDS in rat liver cells. The metabolic formation of an epoxide, which may also be formed in the nasal cavity of rats in the


page 5 of 8

carcinogenicity studies, implies that the involvement of a genotoxic mechanism in tumor formation at this target cannot be excluded.

In a carcinogenicity study [59] by inhalation, naphthalene produced epithelial adenomas and olfactory epithelial neuroblastomas in the nasal cavity of rats from the lowest exposure concentration (50 mg/m3). This must be considered of high relevance because neuroblastomas are highly malignant and the P450 isozymes that metabolically activate naphthalene in the nasal cavity of rodents are also present in humans. In mice an increased incidence in pulmonary adenomas was seen. Since lung tumors were not seen in rats, and due to the higher capacity of the mouse lung in metabolic activation and inactivation, the pulmonary tumors seen in mice seem to be of little relevance to humans.

No studies to evaluate reproductive toxicity are available. Although no changes in the reproductive organs have been detected in repeated dose studies, appropriate studies are needed.

Exposure. Highest occupational exposures occur in mothball manufacture, from the manufacture of grinding wheels and the use of creosote.

Exposure via inhalation also occurs when organic material is incompletely combusted (e.g., in processing of coal, crude oil and natural gas, metal foundries, and power plants).

Consumer exposure to naphthalene may occur through the use of moth repellents, tar shampoos and soaps and through damp proofing operations.

Significant exposure in the mg/kg bw/d range was estimated from dermal and inhalation exposures for workers and consumers. Professional use of tar soap and shampoos exposure was considered to be low.

Indirect human exposure via the environment is low. Infants, in particular, may significantly be exposed to textiles (clothing/bedding), which have been in contact with naphthalene mothballs.

Human exposure via the environment is estimated to range from 65 ng/kg/d at the regional level to 0.25 mg/kg/d at the local level with releases from the manufacture of grinding wheels or mothballs contributing most. Environmental airborne levels are 0.14 g/m3.

Risk characterization. The available information indicates that there are no concerns regarding irritation, sensitization and mutagenicity.

The critical health effects are hemolytic anemia and carcinogenicity.

Since a NOAEL for hemolytic anemia cannot be established, there is concern due to exposure of neonates and infants to clothes that have been in contact with mothballs and following dump-proofing. The predicted exposures are high and can be close to concentrations at which local damage to the respiratory tract has occurred in rats.

In the carcinogenicity studies in rats, chronic inflammation may be a key mechanism in the development of the nasal tumors. However, it cannot be concluded whether a secondary genotoxicity due to chronic inflammation or a genotoxic effect is the relevant mechanisms of naphthalene to induce tumors. Formation of an epoxide and the clastogenic effects in vitro suggest involvement of a genotoxic mechanism.

1-Methylnaphthalene and 2-methylnaphthalene show only low toxicity; the oral LD50 values in rats were determined at 2800 and 3850 mg/kg, respectively [39]. At high oral doses in rats, acute symptoms are unspecific and indicate impairment of the nervous system and hemorrhagic edema of inner organs. After intraperitoneal injection into mice, epithelial necrosis of the lung was induced, morphologically similar to that found with naphthalene [40], [41]. Other specific phenomena that are characteristic of naphthalene exposure, i.e., hemolytic anemia and formation of cataracts, are unknown for methylnaphthalenes. In humans, no intoxications related to these aromatic compounds have been reported.

Diisopropylnaphthalenes (mixture of isomers, KMC) cause no toxic symptoms in rats up to high dosage levels: in the range from about 3.0 g/kg under acute conditions to 30 mg kg1 d1 in a long-term study for 24 months. There are generally involved unspecific, mostly reversible phenomena such as loss of body weight, digestive dysfunction, enlargement of the liver, and local disturbed circulation (hyperemia) [42]. In skin and eye irritation tests conducted on rabbits, diisopropylnapthtalenes exhibited slightly irritant, but reversible effects, which allows the product to be classified as nonirritant. Likewise, there is no evidence of sensitization [42]. No adverse effects were observed in a group of 80 workers who had had contact with diisopropylnapthalenes during production of carbonless copy paper [42]. Mutagenicity and carcinogenicity tests (24 months, oral, rat) gave no evidence of a carcinogenic potential, nor were teratogenic malformations found (mice, oral) [42]. Diisopropylnaphthalenes were rapidly released from the body, i.e., > 80 % within 15 h (mice) [42], and within 10 d (carp) [43], and they proved to be biodegradable [44].

Tetralin and decalin are irritant to the skin, eye, and to the mucous membranes on inhalation. They may cause nervous disturbances, headache, or numbness. The lowest concentration of decalin in air that exhibited an effect on humans was ca. 100 ppm; a 4 h exposure to 500 ppm was lethal to 4 from 6 rats [45]. In guinea pigs, morphological changes of the kidney, liver, and lung were observed after subacute inhalation of decalin [45]. Methemoglobinemia was induced by tetralin in cats; the same effect was found in infants after accidential exposure to tetralin [46]. The color of human urine may change to brownish green or green-gray after incorporation of decalin or tetralin [45]. Acute range finding studies revealed an oral LD50 (rat) of 4.17 g/kg for decalin and 2.68 g/kg for tetralin [45]. A TLV of 25 ppm has been suggested for decalin [47].

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ReferencesGeneral References

1. Beilstein, naphthalene 5 531, 5(1), 257, 5(3) 432, 5(3) 1549, 5(4) 1640; 1-methylnaphthalene 5 566, 5(1) 265, 5(2) 460, 5(3) 1617, 5(4) 1687; 2-methylnaphthalene 5 567, 5(1) 266, 5(2) 460, 5(3) 1627, 5(4) 1693; 2,6-dimethylnaphthalene 5 570, 5(1) 268, 5(2) 468, 5(3) 1651, 5(4) 1714; 2-isopropylnaphthalene 5 571, 5(2) 470, 5(3) 1657, 5(4) 1723; 2,6-diisopropylnaphthalene 5(4) 1768; tetralin 5 491, 5(1) 236, 5(2) 382, 5(3) 1219, 5(4) 1388; decalin 5 92, 5(1) 46, 5(2) 56, 5(3) 242, 5(4) 310.

2. H.-G. Franck, G. Collin: Steinkohlenteer, Springer Verlag, Heidelberg/Berlin/New York 1968, pp. 60 61, 180 181. 3. H.-G. Franck, J. W. Stadelhofer: Industrial Aromatic Chemistry, Springer Verlag, Berlin 1988, pp. 298 308, 328 333,

336 339. 4. G.-P. Blmer, G. Collin, Erdl, Kohle, Erdgas, Petrochem. 36 (1983) 22 27. 5. G. Collin, M. Zander, Nat. Resour. Dev. 27, 61 81 (1988).

Specific References6. Rtgerswerke AG, DE 1 815 568, 1968 (O. Wegener, R. Oberkobusch, G. Collin, M. Zander, H. Buffleb); DE 3 442 275,

1984 (J. Talbiersky, N. Drescher, H. E. Carl). 7. F. Asinger: Die petrolchemische Industrie, vol. 1, Akademie-Verlag, Berlin 1971, pp. 603 609. 8. G. F. Asselin, R. A. Erickson, Chem. Eng. Prog. 58 (1962) 47 52. Links 9. Rtgerswerke AG, DE 3 028 199, 1980 (G.-P. Blmer).

10. Rtgerswerke AG, DE 3 723 104, 1987 (J. Weitkamp, M. Neuber, W. Hltmann, G. Collin). 11. Rtgerswerke AG, DE 3 519 009, 1985 (F. Kajetanczyk, R. Steinbach, I. Ruppert, K. Schlich); DE 3 519 009, 1985 (R.

Steinbach, I. Ruppert, K. Schlich). 12. Mitsubishi Gas, JP 87 273 260, 1987 (T. Hirai, S. Kitaoka). 13. Rtgerswerke AG, DE 3 701 960, 1987 (R. Steinbach, F. Kajetanczyk). 14. Max-Planck-Gesellschaft, DE 3 120 099, 1981 (H. G. Schlossberger). 15. Hoechst, DE 3 334 084, 1983 (K. Eichler, E. I. Leupold). 16. Rtgerswerke AG, EP 280 055, 1988 (J. Weitkamp, M. Neuber, W. Hltmann, G. Collin, H. Spengler). 17. Rtgerswerke AG, DE 3 520 841, 1985 (G. Schmitt, K.-R. Kurtz). 18. K. Handrick, Proc. Neue Verfahren Kohleveredlung, Luxemburg, November 26 28, 1979, pp. 27 37.

Bergwerksverband, DE 2 644 624, 1976 (R. C. Schulz, D. Engel). 19. Kureha, GB 1 359 512, 1974 (A. Konishi, M. Takahashi, F. Kimura, T. Toguchi). 20. Rtgerswerke AG, DE 3 735 976, 1987 (R. Zellerhoff, M. Grtler). 21. J. W. Stadelhofer, R. B. Zellerhoff, Chem. Ind. (London), 1989, April 3, 208 211. 22. Rtgerswerke AG, EP 216 009, 1986 (W. Hltmann, R. Zellerhoff, R. Oberkobusch, P. Stglich, B. Charpey). 23. Teijin, JP 88 63 150, 1986 (I. Hirose). 24. Kureha, DE 3 531 982, 1986 (T. Yamauchi, S. Hayashi, A. Sasakawa). 25. Amoco, EP 329 273, 1989 (P. A. Sanchez, D. A. Young, G. E. Kuhlmann, W. Partenheimer, W. P. Schammel). 26. Kureha, DE 3 517 158, 1985 (A. Iizuka, Y. Konai, T. Yamauchi, S. Hayashi). 27. Celanese, EP 172 012, 1986 (D. E. Stuetz). 28. W. W. Zuelzer, L. Apt, J. Am. Med. Assoc. 141 (1949) 185. 29. H. W. Gerarde (ed.): Toxicology and Biochemistry of Aromatic Hydrocarbons, Elsevier, Amsterdam/London/New

York/Princeton 1960, pp. 225 232. 30. R. van Heyningen, A. Pirie, Biochem. J. 102, (1967) 842. Links 31. S. J. Fanbury, Arch. Dermatol. Syphil. 42 (1940) 53 55. 32. D. Mahvi et al., Am. J. Pathol. 86 (1977) 559. Links 33. D. L. Warren et al., Chem. Biol. Interact. 40 (1982) 287. Links 34. E. Knake, Virchows Arch. 329 (1956) 141. Links 35. B. Adkins et al., J. Toxicol. Environ. Health 17 (1986) 311. Links 36. United States Environmental Protection Agency (EPA), Rep. No. 600/887/-055 F, Washington D.C., 1987. 37. R. B. Franklin in R. Snyder (ed.): Ethel Browning's Toxicity and Metabolism of Industrial Solvents, Elsevier,

Amsterdam/New York/Oxford 1987. 38. Beratergremium fr umweltrelevante Altstoffe der Gesellschaft Deutscher Chemiker: Naphthalin, BUA-Stoffbericht 39,

VCH Verlagsgesellschaft, Weinheim, Germany 1989. 39. Huntingdon Research Centre (by order of Rtgerswerke AG), Mnster, Federal Republic of Germany, 1979

(unpublished results). 40. In [36] p. 176. 41. A. R. Buchpitt, R. B. Franklin, Pharmacol. Ther. 41 (1989) 393. Links 42. Rtgers Kureha Solvents: Toxicological and Physiochemical Studies on KMC, Duisburg 1985 (unpublished results). 43. T. Yoshida, H. Kojima, Chemosphere (1978) no. 6, 491 496. Links 44. T. Yoshida, H. Kojima, Chemosphere (1978) no. 6, 497 501. Links 45. Patty, vol. 2B, pp. 3233, 3240 3242. 46. Ullmann, 3rd ed., 12, p. 589. 47. D. J. de Renzo (ed.): Solvents Safety Handbook, Noyes Data, Park Ridge, N.J. 1986, pp. 174, 626.


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48. BUA (Beratergremium umweltrelevanter Altstoffe der Gesellschaft Deutscher Chemiker): Naphthalin, BUA Stoffbericht 39, VCH Verlagsgesellschaft, Weinheim 1989.

49. IPCS (International Programme on Chemical Safety): Environmental Health Criteria 202: Selected Non-heterocyclic Polycyclic Aromatic Hydrocarbons, World Health Organization, Geneva 1998.

50. DFG: Deutsche Forschungsgemeinschaft. Naphthalin, Gesundheitsschdliche Arbeitsstoffe, H. Greim (ed.): Toxikologisch-arbeitsmedizinische Begrndungen von MAK-Werten, Wiley-VCH, Weinheim, Germany 2001.

51. EU (European Union): Risk Assessment Report Naphthalene, October 2001 (R020_0110_env_hh). 52. MA Schulz, PV Choudary, AR Buckpitt: Role of murine cytochrome P-450 2F2 in metabolic activation of naphthalene

and metabolism of other xenobiotics, J. Pharmacol. Exp. Ther. 290 (1999) 281 290. Links 53. AS Wilson, CD Davis, DP Williams, AR Buckpitt, MM Pirmohamed, BK Park: Characterization of the toxic metabolite(s)

of naphthalene, Toxicology 114 (1996) 233 234. Links 54. J Zheng, M Cho, AD Jones, BD Hammock: Evidence of quinone metabolites of naphthalene covalently bound to sulfur

nucleophiles of proteins of murine clara cells after exposure to naphthalene, Chem. Res. Toxicol. 10 (1997) 1008 1014. Links

55. JC Sasaki, J Arey, DA Eastmond, KK Parks, AJ Grosowsky: Genotoxicity induced in human lymphoblasts by atmospheric reaction products of naphthalene and phenanthrene, Mutat. Res. 393 (1997) 23 35. Links

56. M Bagchi et al.: Naphthalene-induced oxidative stress and DNA damage in cultured macrophage J774A.1 cells, Free Radical. Biol. Med. 25 (1998) 137 143.

57. LS Gollahon, P Iyer, JE Martin, TR Irvin: Chromosomal damage to preimplantation embryos in vitro by naphthalene, Toxicologist 10 (1990) 274.

58. JE Martin, P Iyer, TR Irvin: Development of preimplantation rodent embryo culture systems for identification of developmentally-toxic chemical agents, In Vitro Cell Dev Biol 26, 20A, (1990).

59. NTP: National Toxicology Program, TR-500: Toxicology and Carcinogenesis Studies of Naphthalene (CAS No. 91-20-3) in F344/N Rats (Inhalation Studies), December 2000.


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c 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim10.1002/14356007.a17 009

Naphthalene Derivatives 1

Naphthalene DerivativesAlkylnaphthalenes Naphthalene and Hydronaphthalenes ; Chloronaphthalenes ChlorinatedHydrocarbons ; Cyanonaphthalenes Nitriles; HydronaphthalenesNaphthalene and Hydronaphthalenes ;Naphthalenedicarboxylic AcidsCarboxylic Acids, Aromatic.Gerald Booth, Booth Consultancy Services, Thorpe House, Uppermill, Oldham OL3 6DP, United Kingdom

1. Introduction . . . . . . . . . . . . . . . . . 12. Naphthalenesulfonic Acids . . . . . . . 22.1. Production and Properties . . . . . . . 22.2. Monosulfonic Acids . . . . . . . . . . . . 32.3. Disulfonic Acids . . . . . . . . . . . . . . 52.4. Tri- and Tetrasulfonic Acids . . . . . . 62.5. Alkylnaphthalenesulfonic Acids . . . . 73. Naphthols . . . . . . . . . . . . . . . . . . 73.1. 1-Naphthol . . . . . . . . . . . . . . . . . . 73.2. 2-Naphthol . . . . . . . . . . . . . . . . . . 93.3. Naphthalenediols . . . . . . . . . . . . . 113.4. Hydroxynaphthoic Acids . . . . . . . . 124. Hydroxynaphthalenesulfonic Acids . 144.1. Production and Properties . . . . . . . 154.2. 1-Hydroxynaphthalenesulfonic Acids 174.3. 2-Hydroxynaphthalenesulfonic Acids 194.4. 1-Hydroxynaphthalenedisulfonic

Acids . . . . . . . . . . . . . . . . . . . . . . 204.5. 2-Hydroxynaphthalenedisulfonic

Acids . . . . . . . . . . . . . . . . . . . . . . 214.6. Hydroxynaphthalenetrisulfonic Acids 234.7. Dihydroxynaphthalenesulfonic Acids 234.8. Dihydroxynaphthalenedisulfonic

Acids . . . . . . . . . . . . . . . . . . . . . . 24

5. Aminonaphthalenes . . . . . . . . . . . . 255.1. Naphthylamines . . . . . . . . . . . . . . 255.2. Naphthalenediamines . . . . . . . . . . . 276. Aminonaphthalenesulfonic Acids . . . 286.1. Production and Properties . . . . . . . 286.2. 1-Aminonaphthalenesulfonic Acids . . 316.3. 2-Aminonaphthalenesulfonic Acids . . 346.4. 1-Aminonaphthalenedisulfonic Acids 356.5. 2-Aminonaphthalenedisulfonic Acids 366.6. Aminonaphthalenetrisulfonic Acids . 376.7. Diaminonaphthalenesulfonic Acids . . 396.8. Diaminonaphthalenedisulfonic Acids 406.9. Toxicity . . . . . . . . . . . . . . . . . . . . 407. Aminonaphthols . . . . . . . . . . . . . . 418. Aminohydroxynaphthalenesulfonic

Acids . . . . . . . . . . . . . . . . . . . . . . 428.1. Production and Properties . . . . . . . 428.2. Aminohydroxynaphthalenemonosul-

fonic Acids . . . . . . . . . . . . . . . . . . 438.3. Aminohydroxynaphthalenedisulfonic

Acids . . . . . . . . . . . . . . . . . . . . . . 499. References . . . . . . . . . . . . . . . . . . 52

1. Introduction

Although the basis of naphthalene chemistrycan be said to have started with Erlenmeyerin 1866, conclusive chemical evidence for thestructure of naphthalene and its early deriva-tives (e.g., mono- and dinitroderivatives and-naphthylamine) was published in 1888 byReverdin and Noelting [5].

By 1900, hundreds of new naphthalenederivatives had been prepared as components forazo dyes. Not only was this early work, reportedin German patents and journals, remarkably ac-curate in view of the comparatively primitiveanalytical techniques available, but the key com-pounds that emerged at that time remain domi-nant to this day. The trivial names given to these

dye intermediates (Table 1) have also survivedand are commonly used in the industry.

Table 1. Letter acids and other code-named naphthalene intermedi-ates

A acid 3,5-dihydroxynaphthalene-2,7-disulfonicacid

Amino epsilon acid 1-aminonaphthalene-3,8-disulfonic acidAmino F acid 2-aminonaphthalene-7-sulfonic acidAmino G acid 2-aminonaphthalene-6,8-disulfonic acidAmino J acid 2-aminonaphthalene-5,7-disulfonic acidAmino R acid 2-aminonaphthalene-3,6-disulfonic acidArmstrong acid naphthalene-1,5-disulfonic acidB acid 1-aminonaphthalene-4,6,8-trisulfonic acidBadische acid 2-aminonaphthalene-8-sulfonic acidBON acid 3-hydroxy-2-naphthoic acidBoniger acid 1-amino-2-hydroxynaphthalene-4-sulfonic

acid

2 Naphthalene Derivatives

Table 1. (Continued)

Bronner acid 2-aminonaphthalene-6-sulfonic acidC (Cassella) acid 2-aminonaphthalene-4,8-disulfonic acidChicago (2 S) acid 1-amino-8-hydroxynaphthalene-2,4-disul-

fonicacid

Chromotropic acid 1,8-dihydroxynaphthalene-3,6-disulfonicacid

1,6-Cleves acid 1-aminonaphthalene-6-sulfonic acid1,7-Cleves acid 1-aminonaphthalene-7-sulfonic acidCrocein (Bayer)acid

2-hydroxynaphthalene-8-sulfonic acid

Cyanol 1-amino-7-naphtholD (Dahls) acid 2-aminonaphthalene-5-sulfonic acidDahls acid II 1-aminonaphthalene-4,6-disulfonic acidDahls acid III 1-aminonaphthalene-4,7-disulfonic acidDelta () acid 1-hydroxynaphthalene-4,8-disulfonic acidEpsilon () acid 1-hydroxynaphthalene-3,8-disulfonic acidF acid 2-hydroxynaphthalene-7-sulfonic acidFreunds acid(1,3,6)

1-aminonaphthalene-3,6-disulfonic acid

Freunds acid(1,3,7)

1-aminonaphthalene-3,7-disulfonic acid

G acid 2-hydroxynaphthalene-6,8-disulfonic acidGamma () acid 2-amino-8-hydroxynaphthalene-6-sulfonic

acidH acid 1-amino-8-hydroxynaphthalene-3,6-disul-

fonicacid

J acid 2-amino-5-hydroxynaphthalene-7-sulfonicacid

K acid 1-amino-8-hydroxynaphthalene-4,6-disul-fonicacid

Kalles acid 1-aminonaphthalene-2,7-disulfonic acidKoch acid 1-aminonaphthalene-3,6,8-trisulfonic acidLaurents (L) acid 1-aminonaphthalene-5-sulfonic acidM acid 1-amino-5-hydroxynaphthalene-7-sulfonic

acidNaphthionic acid 1-aminonaphthalene-4-sulfonic acidNW (Nevile andWinther) acid

1-hydroxynaphthalene-4-sulfonic acid

Oxy Chicago acid 1-hydroxynaphthalene-4,8-disulfonic acidOxy Koch acid 1-hydroxynaphthalene-3,6,8-trisulfonic acidOxy L acid 1-hydroxynaphthalene-5-sulfonic acidOxy Tobias acid 2-hydroxynaphthalene-1-sulfonic acidPeri acid 1-aminonaphthalene-8-sulfonic acidPurpurol 1-amino-5-naphtholR acid 2-hydroxynaphthalene-3,6-disulfonic acid2R (Columbia)acid

2-amino-8-hydroxynaphthalene-3,6-di-sul-fonicacid

RM acid 2-amino-3-hydroxynaphthalene-6-sulfonicacid

S acid 1-amino-8-hydroxynaphthalene-4-sulfonicacid

Schaeffer acid 2-hydroxynaphthalene-6-sulfonic acidT acid 1-aminonaphthalene-3,6,8-trisulfonic acidTobias acid 2-aminonaphthalene-1-sulfonic acidViolet (RG) acid 1-hydroxynaphthalene-3,6-disulfonic acid

The important Armstrong Wynne rules forpolysubstitution of naphthalene and its deriva-tives by nitration and sulfonation were also for-

mulated in this early period.Although empirical,they have stood the test of time against increas-ingly sophisticated theories and calculations.

Improved processes based on the key unitprocesses of sulfonation, nitration, reduction,hydroxylation, and amination (Bucherer reac-tion) for a wide range of naphthalene deriva-tives were developed during the next 40 years[6]. Although these were not published [7] untilafter 1945 with the end of the I.G. Farbenindus-trie era, all the important subsequent reviews [5],[810] were based largely on these comprehen-sive data.

The only signicant production developmentwork published in the last 40 years is related tothe project for the new Schelde-Chemie plant(Bayer Ciba-Geigy joint venture) designed tomanufacture 14 000 t/a of naphthalene interme-diates at Brunsbuttel [16]. The process develop-ment on important letter acids (H, J, , C, Peri,and Laurents) required a major change from thetraditional processes, optimized over 80 years,to meet present-day energy and environmentalrequirements [17].

Azo dyes and pigments continue to be majoroutlets for naphthalene intermediates (see alsoAzo Dyes). The Colour Index lists some 270different naphthalene intermediates as precur-sors to many more colorants [18]. This repre-sents about 20% of the total list of intermedi-ates. Supplementary updating volumes list onlyseven new naphthalene intermediates and rela-tively few new outlets for existing intermediates[19]. From this onemay infer that very little newcolorant research is being carried out based onnovel naphthalene derivatives. In contrast, otherareas such as agrochemicals and pharmaceuti-cals have been most active in exploiting newnaphthalene derivatives over the last 20 years[11].

2. Naphthalenesulfonic Acids

2.1. Production and Properties

Controlled sulfonation using a range of sulfuricacid and oleum strengths under a variety of re-action conditions leads to formation of mono-,di-, tri-, and tetrasulfonic acids, whose separa-tion is frequently complicated by desulfonation(i.e., reverse sulfonation) or isomerization.


Table 2. Salts of key naphthalenesulfonic acids

Salt Hydrate Solubility, g in100mL H2O

1-Sulfonic acidSodium 1/2 H2O 9.1 (10 C)Potassium 1/2 H2O 7.7 (10 C)Calcium 2 H2O 6.1 (10 C)Barium 1 H2O 1.2 (10 C)2-Sulfonic acidSodium 5.9 (25 C)Potassium 1/2 H2O 6.7 (10 C)Calcium 1 H2O 1.3 (10 C)Barium 1 H2O 0.35 (10 C)1,5-Disulfonic acidSodium 2 H2O 11.1 (18 C)Potassium 2 H2O 6.7 (18 C)Calcium 2 H2O 2.5 (18 C)Barium 1 H2O 0.21 (18 C)1,6-Disulfonic acidSodium 7 H2O 33.3 (18 C)Potassium 20.0 (18 C)Calcium 4 H2O 10.0 (18 C)Barium 31/2 H2O 6.2 (100 C)2,6-Disulfonic acidSodium 1 H2O 11.9 (18 C)Potassium 5.2 (18 C)Calcium 6.2 (18 C)Barium 1 H2O

4 Naphthalene Derivatives

Figure 1. Sulfonation of naphthalene

furic acid at 20 C and slowly raising the tem-perature to 70 C [7]. After 3 h at 70 75 C thereactionmass is poured intowater and limed out.A technical-grade product is obtained by evap-oration and a purer product by precipitating theaniline salt.

An alternative sulfonation process uses sulfurtrioxide in a solvent such as tetrachloroethane.

Uses. Naphthalene-1-sulfonic acid is furthersulfonated or nitratedwithout isolation.At lowertemperature (35 C), sulfuric acid with oleumyields the 1,5-disulfonic acid, whereas at highertemperature (100 C) the 1,6-disulfonic acid ispredominantly obtained. Nitration gives mainlythe 5-nitro and 8-nitro derivatives (see Section6.1). Production of 1-naphthol by caustic fusion(hydroxylation) has long since been supersededby alternatives for reasons of product quality(Section 3.1).

Naphthalene-2-sulfonic acid [120-18-3](2), naphthalene--sulfonic acid, C10H8O3S,Mr 208.23, crystallizes from aqueous solutionsas the hydrate (mp 124 C) or trihydrate (mp83 C). Aqueous solubilities of the free acid andits salts are somewhat lower than those of thecorresponding-isomers (Table 2). The isolatedsodium salt is known as salt.

Naphthalene-2-sulfonic acid is desulfonatedby hot aqueous mineral acids with much moredifculty than naphthalene-1-sulfonic acid; therate has been measured at 50 times slower [22].Halogenation attacks either or both the 5- and the8-positions. Bromination may be used to sep-arate a mixture of naphthalene-1-sulfonic acidfrom naphthalene-2-sulfonic acid because thelatter forms a soluble product whereas the for-mer is desulfonated.

Production. Molten naphthalene is added to96% sulfuric acid in an iron vessel and the mix-ture is agitated at 163 C for 2 h. A complex


work-up consisting of gradual dilution, heat-ing, and neutralization with caustic soda andsodium sulte ensures an 88% yield of isolated salt and desulfonation of the -isomer, whichis formed as a coproduct in 5 10% yield [7].

Uses. The major outlet for salt is the pro-duction of 2-naphthol (Section 3.2). The 2-sul-fonic acid is a stage in the production of the1,6-, 2,6-, and 2,7-disulfonic acids and the 1,3,6-trisulfonic acid. Nitration gives primarily the5- and 8-nitro derivatives as intermediates forCleves acids (Section 6.1). The 2-sulfonic acidcondenses with formaldehyde or alcohols toform surface-active agents (see Section 2.5).

The intermediate 2-thionaphthol can be ob-tained by catalytic hydrogenation of naphtha-lene-2-sulfonic acid, but is traditionallymade byzinc reduction of naphthalene-2-sulfonyl chlo-ride.

2.3. Disulfonic Acids

Naphthalene-1,3-disulfonic acid[6094-26-4] (3), C10H8O6S2, Mr 288.28, isproduced only in small proportion on disulfona-tion of nap

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