setting reaction of zinc oxide and eugenol

6
Journal of Research of the National Bureau of Standards Vol. 55, No.3, September 1955 Research Paper 2611 Setting Reaction of Zinc Oxide and Eugenol ! Henry 1. Copeland, Jr., 2 Gerhard M. Brauer, W. T. Sweeney, and A. F. Forziati Zinc oxide-eugenol mixt ures hav e been used in denti st ry for a number of years. The setting mec hani sm of these mixtures was inves tigated . X-rav diffraction da ta and electron photomi c rovaph s give that a crystll:lline compound is formed. Analysis and mol ecular-weight d ettrml.na t lons show t ha t th,s compound corres ponds t o the empirical formula (OIOH l.' O2) 2 Zn, ztnCeuge nolate. Infrared data, as well as t he nonr eactivity of met a and I?ara s ubst i tute d ph enols as compared to the ortho isomers, s uggest that the zinc eugeno- la te IS a chelate. The hard ened mass consists of zinc oxide e mbedded in a matri x of long sh eat h-like cry stals of zinc eugenolat e. The excess eugenol is so rb ed by bo th the zinc eugeno- late and the zinc oxide. 1. Introduction Zinc oxide-eugenol materials hav e b een dev eloped for utilization in a numb er of dental applicat ions. Th ey are mo st widely employed as palliative a nd a ntib acterial agents 'in the 'treatment of carious lesions [1].3 With modifiers, these mat erials are used as impress ion pastes and as surgical cement s. Gen erally, the use of zinc oxide and eugenol depends on their tend ency to form a hardened coherent mass when mix ed. Unexplained variat ions in the behavior of the mixtur es are impor tant to the clinician who uses th ese mat eri als to treat dental conditions. Of special concern are variat ions in sett ing rat e, hardn ess, and st rength of the set mass. Th e m ec hani sm of the sett ing pro cess of zinc oxide a nd eugenol is unknown . Fa cLors t hat have been re ported to produ ce variations in the physical behavior are the type of zinc oxide used, the amoun t of water present (b oth in the zinc oxide and atmo s- phere), and the ambie nt te mp era ture, Th e fol- lowing theories have becn fl,dvanced in rcgfl,J'd to the sett mg process: 1. Th e sett ing process is a purel y ph ysical one in whi ch the constitu ent s r etain tbe ir indiv iduality [2]; 2, a chemi cal reaction occ ur s and a compound resembling zinc phenol ate is formed [3J; a nd 3, the sett ing process is a combination of physical a nd chemical r eact ions [3J. Th e object of thi s inv esti gat ion was to sLudv Lhe setting of zin c oxide and eugenol mixtur es in 'Order to mor en early define ph.,·sical and chemi cal pro cesses involved. 2. Expe rimental Procedures 2.1. Mat erials . Th e zin c oxide (reage nt grade) used had a particl e SIze of around 3000 A in diamet.er and contained l ess than 2 perce nt of w ate r. It was white. An exp eri- I Th e data in this pllblicatioll were prese nted in a tbesis by H enry I. Copeland Jr., in partial fll!ril\ment of th o requirements of the Graduate School of George: town U llI ve rslty, Washlllgton , D. C ., for tbe deg ree of M as ter of Science Thi s paper was presented to the Int ernational Association for Dent al Research Chicago, March 1955; and to tho Medicinal Dh 'l' ision, American Cbcmical Society' CinCinnati, April !955. ' 2 Gues t worker at the Na tional Bu reau of Sta ndard s, and member of the Dent al Corps, U. S. Air Force . 3 F igures in brackets indicate the literature re ferences at the end of tbis pa pe r. mental type of zinc oxide (Merck Hyperfine) was also used. According to the manufactur er 's sp ecifi- cat i ons it had a parti cle si ze of 125 to 250 A in di am- eter and contain ed app roximately 5 percent of water. Thi s zinc oxide was reddish in color. Th e eugenol was US P g rad e. All other ch emi cals used were reage nt grad e. 2.2. Setting of Mixtures Mixes of zinc oxide (reagent grad e) were mad e with guaiacol , eugenol, phenol, veratrol e, safrol, an ethole, m-m ethoxy phenol, and thymol. Th e mixtur es were made with a steUi te spatula on a glass slab at r oo m tempe raLure. It was necessary to m elt the phenol and thymol prior to mixing. Th e maximum amount of oxide tha t co uld be wet t ed by the liquids was inco rporated. Setting Lime was d ete rmined by means of a pen e- trometer. A modifi cation of the ASTM Penet ration T est for Bituminou s M ater ials was ll sed with a 100-g load for 5 sec and needle. Th e tesLs were mad e at room temperaLul'e, a nd the m aterial was co nsider ed set wh en the n ee dle co uld no longer pen et rat e the ma terial or t hr ee successive pen et rations at 30-sec interv als gave id enti cal values. Sampl es of the zinc oxides were dehy drat ed by h eating at 1l0 ° C for 24 hI'. Th e dehy drat ed zinc oxides were mix ed with eugenol in the same mann er. 2.3. Temperature Change During Setting The change in temperature caused by the reaction was determin ed by m eans of a calibr ated iron- constantan th ermo couple co nn ected to a recording pot entiom eter. Zinc oxide (H yperfin e) -e ug enol mix- tures were u secl in this experiment . 2.4 . Ana lysis for Reaction Products Mixtur es of 0.5-mole zinc oxide (reagent grad e) and O, l-mol e eug enol were pr epar ed. The hard en ed mass was pulverized by grinding in a mortar to a fine powder. Th e parti cles were extracte d with chloro- form for 30 hI' in a Soxhl et ext ractor . The r esidu e left in th e filter thimble was vacuum-dried and weighed. The chloroform was di st illed off from the 133

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Page 1: Setting reaction of zinc oxide and eugenol

Journal of Research of the National Bureau of Standards Vol. 55, No.3, September 1955 Research Paper 2611

Setting Reaction of Zinc Oxide and Eugenol ! Henry 1. Copeland, Jr.,2 Gerhard M. Brauer, W. T. Sweeney, and A. F. Forziati

Zinc oxide-eugenol mixtures have been used in dentistry for a number of years. The setting mechanism of these mixtures was investigated. X-rav diffraction dat a and electron photomicrovaphs g ive ~vid~nce that a crystll:lline compound is formed. Analysis and molecular-weight dettrml.nat lons show t hat th,s compound corresponds t o the empirical formula (OIOH l.' O2) 2 Zn, ztnC eugenolate. Infrared data, as well as t he nonreactivity of meta and I?ara substituted phenols as compared to the ortho isomers, suggest that t he zinc eugeno­late IS a chelate. The hardened mass consists of zinc oxide embedded in a matrix of long sheath-like crystals of zin c eugenolate. The excess eugenol is sorbed by bot h t he zinc eugeno­late and the zinc oxide.

1. Introduction

Zinc oxide-eugenol materials have been developed for utilization in a number of dental applicat ions. Th ey are most widely employed as palliative and antibacterial agents 'in the 'treatment of carious lesions [1].3 With modifiers, these materials are used as impression pastes and as surgical cements .

Generally, the use of zinc oxide and eugenol depends on their tendency to form a hardened coherent mass when mixed . Unexplained variations in the behav ior of the mixtures are important to the clinician who uses these materials to treat dental conditions. Of spec ial concern are variations in setting ra te, hardness, and strength of the set mass.

The m echanism of the setting process of zinc oxide and eugenol is unknown. FacLors that have been reported to produce variations in t he physical behavior are t he type of zinc oxide used , the amount of water present (both in t he zinc oxide and atmos­phere), and the ambi ent tempera ture, The fol­lowing theories have becn fl,dvanced in rcgfl,J'd to the settmg process: 1. The se t ting process is a purely physical one in which the constituents retain tbeir individuality [2]; 2 , a chemical reaction occurs and a compound resembling zinc phenolate is formed [3J; and 3, t he sett ing process is a combination of physical and chemical reactions [3J.

The obj ect of this invest igation was to sLudv Lhe setting of zinc oxide and eugenol mixtures in 'Order to moren early define ph.,·sical and chemical processes involved.

2. Experimental Procedures

2 .1. Materials

. The zinc oxide (reagent grade) used had a particle SIze of a round 3000 A in diamet.er and contained less than 2 percent of w ater. It was whi te. An experi-

I The data in this pllblicatioll were presented in a tbesis by H enry I. Copeland J r., in partial fll!ril\ment of tho requirements of the Graduate School of George: town U llI verslty , Washlllgton, D. C ., for tbe degree of M aster of Science

This paper was presented to the International Association for Dental Research Chicago, M arch 1955; and to tho M edicinal Dh'l' ision, American Cbcmical Society' CinCinnati, April !955. '

2 Guest worker at the National Bureau of Standards, and member of the Dental Corps, U. S. Air Force.

3 F igures in brackets indicate th e literature references at the end of tbis pa per.

mental type of zinc oxide (Merck Hyperfine) was also used. According to the manufacturer 's specifi­cations it had a parti cle size of 125 to 250 A in d iam­eter and contained approximately 5 percent of water. This zinc oxide was reddish in color.

The eugenol was USP grade. All other chemicals used were reagent grade.

2.2. Setting of Mixtures

Mixes of zinc oxide (reagent grade) were made with guaiacol , meth~Tlguaiacol , eugenol, phenol , veratrole, safrol , anethole, m-methoxyphenol, and thymol. The mix tures were m ade with a steUi te spatula on a glass slab at room temperaLure. It was necessary to m elt the phenol and thymol prior to mixing. The maximum amount of z~nc oxide tha t could be wet ted by the liquids was incorporated.

Setting Lime was determined by means of a pene­trometer. A modification of the ASTM P enetration T est for Bituminous M aterials was ll sed with a 100-g load for 5 sec and ~{ 6-in . needle. The tesLs were made at room temperaLul'e , and the material was considered set when the n eedle could no longer penetrate the material or three successive penet rations at 30-sec intervals gave identical values.

Samples of the zinc oxides were dehydrated by heating at 1l0° C for 24 hI'. The dehydrated zinc oxides were mixed with eugenol in the same manner.

2.3. Temperature Change During Setting

The ch ange in temperature caused by the reaction was determined by means of a calibrated iron­constantan thermocouple connected to a recording potentiometer. Zinc oxide (H yperfine)-eugenol mix­tures were usecl in this experiment .

2.4. Analysis for Reaction Products

Mixtures of 0.5-mole zinc oxide (reagent grade) and O,l-mole eugenol were prepared . The hardened m ass was pulverized by grinding in a mortar to a fine powder. The particles were extracted with chloro­form for 30 hI' in a Soxhlet extractor. The r esidue left in the filt er thimble was vacuum-dried and weighed. The chloroform was distilled off from the

133

Page 2: Setting reaction of zinc oxide and eugenol

extract and the residue distilled over at 87° to 101 ° C and 2-mm Hg pressure.

Equimolar mixtures of zinc oxide (H yperfinc) and eugenol were prepared and extracted as above. The residue in th e fil ter thimble ,vas dried to constant weigh t at 1100 C and 1- to 2-mm H g pressure. The extract was filtered through a weighed Gooch cru­cible and the residue purified by washing with three 10-ml portions each of chloroform, methanol, and ether and dried to constant weight. This residue was a white crystalline material, which was examined by X-ray diffraction. The elementary analysis, molecular weight, dissociation temperature, crxstal form, refractive index, fluorescence, and density of this residue were determined.

The low-boiling solvents used for extraction and washing were distilled off from the filtra te, and the weight, refractive index, and boiling point of the remaining liquid were determined.

The experiments were repeated, using methanol, benzene, and chlorinated hydrocarbons other than chloroform as the extraction solvent.

2 .5 . Measurement of X-ray Diffraction

The X -ray diffraction m easurements were ma,de bv the Section on Constitution and Microstructure at the Bureau . Th e instrument used was a diffrac­tometer utilizing a Geiger counter and a recording potentiometer. All measurements were made through 90 deg. Patterns were obtained of zinc oxide (re­agent grade), zinc oxide (Hyperfine), eugenol , mix­tures of eugenol with each of the two zinc oxides, and a mixture of zinc oxide (Hyperfine) with guaiacol. Patterns were also obtained of the purified reaction product and a zinc oxide-water mixture.

2 .6 . Elementary Analysis 4

The purified reaction product was analyzed for carbon, hydrogen, and zinc conten t, using micro­techniques. The dry combustion method was used for th e carbon and hydrogen determinations, whereas th e zinc was determined as the sulfate by digestion in th e presence of sulfuric acid.

2 .7. Infrared Studies 5

Zinc 8-quinolinolate was prepared according to Zetzsche [4]. Zinc guaiacol ate was obtained on mixing guaiacol with zinc oxide. The unreacted guaiacol was removed by repeated washing with cold chloroform. The infrared absorption spectra of 8-quinolinol, zinc 8-quinolinolate, eugenol, zinc eugenolate, guaiacol, and zinc guaiacolate were measured. The solid samples were incorporated in potassium bromide pellets. All samples were ex­amined with a P erkins-Elmer , model 21 spectro­photometer.

, Elementary analyses were performed by R , A. P aulson, Infrared absorpt ion spectra were made by J . E . Stewart and G. Wyman.

134

L~ __ _

2 .8 . Electron Micrographs 6

Electron micrographs of t he Hyperfine zinc oxide-eugenol mixture and the purified reaction product were made at 10,000- and 4,000-diameter magnifications, respectively.

2.9. Water Sorption Study

Dried zinc eugenol ate samples were placed in a desiccator over a saturated potassium nitrate solut ion (93.3-percent relative humidi ty at 30° C). The samples were removed from the desiccators at var ious time intervals and weighed. This procedure was repeated until constant weight was obtained.

3 . Results and Discussion

The mixtures of zinc oxide (reagent grade) with eugenol (I) , guaiacol (II), or methyl guaiacol (III) set into a hardened mass.

OH OH OH I I I O,OCH, OOCH, O,OCH, I I CHz-CH=CHz CH 3

I :II III

These aromatic oils have a methoxy group ortho to a phenolic hydroxy group. Guaiacol has no substit­uent group in the para position. Methylguaiacol has a methyl group as a para substit uent. Eugenol has a para-beta allyl group.

Mixtures of zinc oxide with phenol itself (IV), veratrole (V), safrol (VI), anethole (VII), thymol (VIII), and m-methoxyphenol (IX) did not harden.

OH OCH 3 ?, I I

0 O,OCH, 0'° I CHz-CH'CH z

]][ Jz::: E

OCH 3 CH 3 OH I I I

0 O'OH O 'OCH, I I CH =CH - CH 3 C'H;-CH 3

E :lZIII II:

6 Electron m icrographs were made with F. A. H eckman .

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Page 3: Setting reaction of zinc oxide and eugenol

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These compounds do not have a methoxy group ortho to a hydroxy group.

From the above considerations, it appears thaL the par!)' groups are not involved in the setting reaction, and the ortho methoxy group is essential for setting to take place.

The dehydrated zinc oxides did not form a hard­ened mass when mixed with eugenol. The untreated reagent grade zinc oxide (less than 2 percent of water) required more than 24 hI' to set when mixed with eugenol. The Hyperfine zinc oxide-eugenol mi.;xture set in less t han 15 min. This zinc oxide had the greater water content (5 percent according to manufacturer) and also had a much larger surface area. In all experiment~ , the setting rate of eit her of the zinc oxides mixed with eugenol was more rapid in warm and humid weather than when the relative humidity was low.

The hardening process ,vas found to be exothermic in nature. Rapidly setting mixtures gave a harder product and a greatcr temperature rise.

On extraction with chloroform the reagent-grade zinc oxide-eugenol rnixture yielded approximately 80 percent of eugenol. The residue in the filter thimble showed a 10-percent increase in weight over the original weight of the zinc oxide, and analy­s is indicated that some eugenol was still in the resi­due. An insoluble film deposi ted in th e extrac tor flask suggested some chemical change had taken place.

Because the zinc oxide (H yperfine)-eugenol mi:x­tUl'e had demonstl·aLed fas ter set t ing and increased exothermic activity, the extractions were repeated, using this mixture . The following tabulation shows typical results:

BEFO R E S8'l'TI NG

Zinc oxidc (containing 1.3% of 9.60 g water).

o. 117 m o le

Weight of dry zinc oxidc ______ 9.48 g EugenoL ____________________ 19.26 g 0. 117 mole

Material in mi xt ure ______ 28.74 g

AFTER SETTING

Residue on extractioo _________ 15.5480 g Residue in extract (other than 1. 1909 g

eugenol). Eugenol recovered ____________ 11. 6676 g 65. 2 %

Material accounted fOL ___ 28. 4065 g 98. 9 %

After the chloroform was removed from the extract, t he res idue soon formed an oily paste. This paste was composed of a white crystalline material and eugenol.

X-ray diffraction measuremenLs were made to determine changes in crystal sLru cture Lhat might have occur red during setL ing. Both reagent-grade zinc oxide and Lhe Hyperfine zinc oxide gave the characteristic pattern indicating principal spacings of approxima Lely 2.9, 2.6, and 2.5 A. The small particle size of Lhe H yperfine zinc oxide caused broadening of the bases of the peaks in its pattern. There were no other diffe rences in the d iffraction pattern . Eugenol showed no peaks, being non­crystallinc.

The mi..x:Lure of reagent-grade ZlllC oxide with eugenol showed peaks indicating the presence of a new crystal form with spacings of approximately 17.0, 8.8, and 7.0 A. The zinc oxide (Hyperfine) mixed with eugenol demonstraLed Lhe presence of the same crysLal form with approximately the same spacings. The peaks were much higher in Lhe pat­tern of the latter mixture, which indicated the presence of a much greater quantity of the new crys tal form. Zinc oxide mixed with guaiacol demonstrated the presence of a new crystal form with spacings of 12.0, 9.3, and 8.7 A. A zinc oxide­water mixture gave only the characteristic zinc oxide pattern.

The diffraction pattern of the purified reaction product showed only the presence of the new crystal form, although as little as 2 percent of zinc oxide could have been detected by the diffractomeLer used.

Representative X-ray diffraction patterns are shown in figures 1 and 2. The peaks between 30 and 90 cleg have been identified as belonging to zinc oxide [5]. The peaks occurring between 6 and 26 deg are the resul t of chemical reac tion. The reaction product is identified as zinc eLl genolate in patLern 1 of figure 2.

2 .

~lt..j.l. J, .... 1 1 ~ 1

3.

8

-'

I I 16 24 32 40 48 56 64

ANGLE OF DIFFRACTION, DEGREES

FIGURE 1. X-my diffmction patterns.

72 80

I, ZnO (reagent); 2, ZnO (reagent)-Eug. mixture; 3, ZnO (Hpf.)-Eug. mixture.

35135G-55-- :! 135

Page 4: Setting reaction of zinc oxide and eugenol

I.

2 .

3.

8 16 24 32 40 48 56 64 ANGLE OF DIFFRACTION , DEGREES

FIGUR E 2 . X-ray diffraction patterns.

72 80'

1, Zinc eugenolate; 2, ZnO- Guaiacol mixtm e; 3, ZnO- W ater mixtm e.

The analysis of the compound formed by th e r eaction of zinc oxide and eugenol is given in table 1. As a compound resembling zinc phenolate had been suggested [3] as a possible reaction product, the composition of zinc eugenolate was calculated from the empirical formula and compared with the values ob tained for the new crystalline compound. The comparison indicated that the formula for the com­pound would be that of zinc eugenolate, [ (ClQH U 0 2)2Zn]n.

The molecular weigh. t was determined cryo­scopically in ace tamide (m olar freezing poin t depres­sion 1<./ equals 36 .3° C). The molecular weigh t was

T A BLE 1. Analysis of reaction product

Elemen t

Oarbon ___________________________________________ _ H ydrogen ___ _______ ______________________________ _ Zinc ____ ______________ ____________ ___ _____ ____ ___ _ Oygen (by differencel ___________________________ __

Oalculated Found

% 61. 34 5.61

16. 72 16. 33

% a 59.6

5. 7 a 17. 1 a 17.6

found to be 435. The calculated molecular weigh t when n equals 1 is 391. This indicated tha t the empirical formula for ZInc eugenolate IS

(C IOH l10 2)2Zn . Some physical properties of the ZlllC eugenolate

are given in table 2. Zinc eugenolate was found to be insoluble in all

common organic solvents, including anisole, mesityl oxide, a -chloronaphthalene, dioxanone, N, N-diethyl carb amate, ethylene carbonate, diethylphosphite, dimethylamidophospha te, tributylamine, and di­methyl formarnide.

Infrared absorption spectra were studied in an attemp t to gain more information on the molecular configura tion of zinc eugenola te . Zinc 8-quinolino­late was used for comparison because an X-ray analysis of its structure had been reported [6]. F or fur ther comparison, gu aiacol and the zinc oxide­guaiacol reaction product were used .

TABL}] 2. Some physical p1'operties of zinc eugenolate

Dissociat ion t emperature _______________ mp __ Crystal fo rm a (by petrographi c analysis) ___ __ _ Refractive index (N~) __ __________ __ _______ _ D ensity ____________________________ gjmL __ Fluorescence b (exci ted by 3650 A radia tion) ___ _ SolubilUy _______ ___ __________ ____________ _

245 0 C Monoclinic 1.69 1.6 White

( 0)

B Figure 3 and 4, respectively, show zin c eugenolate crystals and electron micrographs of a zinc oxide-eugenol m ixture.

b The presence of zinc eugenolate may be readily detected by means of the characteristic white fluorescence emitted by this compowld whell excited by ultrav iolet radiation . \\' hell Simila rly excited , zinc oxide and cugollol fl uoresce brigh t yellow and d ark brown , respectivel y. A m ixturo of zinc ox ide and eugenol fluoresces deep red.

c Very slightl y soluble hot chloroform; soluble in ammonium hydroxide. pyri­dine, hot acetamide, and !lot butyrolactonc.

FIG UR E 3. Electron micrograph of zinc eugenolate, palladium shadowed 4:1, showing the crystal habi t typical of the ex­tracted Teaction product .

• 'fbe low carbon, as well as the high zinc and oxygen percen tages, would be The small, rounded part icles seen in the background and on the surfaces of explained by tho presen ce of a small amount of zinc oxide in the purified product . the largc, crystalline for mations are probably zinc oxide.

136

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Page 5: Setting reaction of zinc oxide and eugenol

FlO URID 4. Electron miC1'o­graph of a zinc oxide-euge­nol mixture showing the small, rounded particles of zinc oxide and the thin, elongated crystals oj zinc

i1 eugenolate.

;,

7

r I

The sheaf·like aggregation is typica l of the un cx tracteci hardened mass.

Interesting changes in infrared absorpt ion oc­CUlTed, as shown in figure 5. In the 7.1- to 7.4-).i area the absorp tion due to the hydroxy aromat ic group of 8-quinolinol, eugenol, and guaiacol was not evident in t heil' zinc derivatives. Tile disappearance of this band is due to the replacement of the p henolic hydrogen by zinc. At 7.5- ).i absorption was observed in all three 7.inc compounds, whereas none was in the original hydroxy aromatics. This absorption has been attribu ted to the appearance of bond-bending strain.

An absorption band at 6.08 ).i due to the vinyl group was in both eugenol and i ts zinc derivative spectra. This was evidence that the para subst it­uent did not take part in the reaction. Absorp tion in the 8.1-).i region due to the methoxy group is present in both the original hydroxy aromatics and their zinc derivatives. However, there is a slight shift (not more than 0.1 ).i ) in the wavelength at which the absorption occurs.

The apparent inability of the set ting r eaction to take place in the absence of the o-methoxy group, the insolubili ty of the reaction product, and the infrared absorption changes suggest that zinc eugenola te is related to the metallo-pyrocatechol complexes or chelate [7].

Zinc is a bivalent elemen t with a common co­o]'clinaLion number of fOLlr. As such , zinc is a metal likely Lo form a chelate. E ugenol, guaiacol, and meL llylguaiacol Ilave a replacea ble hyd rogen and a nearby donor in the oxygen of the o-methoxy group. The cllClate formed would have a proportion of two eugenol molecules Lo one zinc. It may be repre­sented as follows:

The compound did not sorb an appreciable amount of water on storage in a high-humidity (93.3%)

137

Page 6: Setting reaction of zinc oxide and eugenol

100 r---,-----~--,----y---__,_---,__,

eo

60

40

20

A

0c:...-__ L-__ L-_--l_~___'_

4 5 6 7 9 10

100

~ 80 w u .. -, .. ---",' -, .. ~"""\"'I :.~

" , ... .......... /

'" w a.. 60

z o u; ~ 40 ~ (/)

Z <t

:: 20

8

" -• , ,

f , :0# , .... \ ,-,,,-, "

: I:

0l-. __ ....L __ ----'-___ L--

4 5 6 7 8 9 10

100 .---,-----,-----,------r-----,------,-,

80

60

40

20

0

4

,-_ ....... --\'V""-"Ir-"~r"',", . , . . ~

1','_ ,'~ ,/''''. ,.~~'

", . " ,

C

5 6

,:;1 I I : !: :. : t' ::~

7

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· · , : , 8 t

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9 WAVELENGTH, MICRONS

FIG URE 5. I nfrared absorption spectra.

10

I n each case the broken line is the hydroxy aromatic and the solid lin is the zinc derivative. A, Eugenol and zinc eugenolatej B, 8~quillolinol and zinc quinolinolate; 0, guaiacol and zinc guaiacolatc.

atmosphere for 10 days. Therefore, the formation of a hydrate at room temperature is not likely to occur.

The set massesulting from an equimolar mixture of zinc oxide and eugenol contains zinc oxide, zinc eugenolate , and eugenol. The recovery of eugenol from the extraction procedures shows the presence of excess eugenol. A comparison of data from the extraction procedures and X-ray diffraction pattern 3 of figure 1 indicates that only a portion of the zinc eugenolate formed was recovered by the extraction procedmes, and both methods show the presen ce of

138

a considerable amount of unreacted zinc oxide. The sheath-like zinc eugen olate crystals formed act as a ma trix for the zinc oxide. E xcess eugenol is sorbed by the zinc eugenola te and likely sorbed by the zinc oxide. Sorption of eugenol by zinc eugenolate is demonstrated by paste formation when zinc eugeno­late crystals are dispersed in eugenol.

4. Summary

1. The setting of mixtures of zinc oxide and eugenol involves both physical and chemical proc­esses.

2. X-ray diffraction data and electron photomi­crographs give evidence that a crystalline compound is formed by th e chemical reaction.

3. Chemical analysis and molecular weight deter­minations show that this crystalline compound corresponds to the empirical formula (CIOH l10 2)2 Zn, zinc eugenolate.

4. Infrared absorption data suggest th at zinc eugenolate is a chelate compound with the following structure:

I CHz- CH= CH z

5. The se t mass resulting from mixes of zinc oxide and eugenol consists of zinc oxide embedded in a matrix of long, sheath-like crystals of zinc eugeno­late. The excess eugenol is likely sorbed by both the zinc eugenolate and the zinc oxide.

The authors especially acknowledge the generous assistance given by H . Swanson and G. Ugrinic of the Microstructure Section, National Bureau of Standards, in performing X -ray diffraction measure­ments.

The authors thank J . B . Conn of M erck and Co., Inc., for supply ing the H yperfine zinc oxide.

5. References (1] H . J . Turkheim, Brit. D en tal J . 45, 1 (1953). (2] E. Forster , Stomatologia 27, 217 (1929). (3] W. Harvey and N. J . P etch, Brit . Dental J. 80, 1, 35

(1946) . (4] F. Zetzsche, H . Silber mann, an d G. Vieli, H elv. Chirn.

Acta 8, 596 (1925) . (5] H. E. Swanson and R. Fuyat, NBS Circular 539, vol. II

(1953) . (6] L . Merrit, Jr. , Anal. Chern. 25, 718 (1953) . (7] A. E. Martell and M . Calvin, ,ch emistry of Metal Chelates

(Prentice-Hall Inc., New Yor k, N. Y., 1952).

W ASHINGTON, April 1, 1955.

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