research article acid hydrolysis of bromazepam catalyzed ...research article acid hydrolysis of...

Research ArticleAcid Hydrolysis of Bromazepam Catalyzed byMicelles Reverse Micelles and Microemulsions

Ferdousi Begum1 M Yousuf A Mollah1

M Muhibur Rahman2 and Md Abu Bin Hasan Susan1

1Department of Chemistry University of Dhaka Dhaka 1000 Bangladesh2University Grants Commission of Bangladesh 291 Agargaon Dhaka 1207 Bangladesh

Correspondence should be addressed to Md Abu Bin Hasan Susan susanduacbd

Received 9 December 2014 Revised 25 February 2015 Accepted 9 March 2015

Academic Editor Yaorong Zheng

Copyright copy 2015 Ferdousi Begum et alThis is an open access article distributed under theCreativeCommonsAttribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Kinetics of the acid hydrolysis of bromazepam (Bz) has been investigated in micelles reverse micelles and microemulcions ofcetyltrimethylammonium bromide (CTAB) by spectrophotometric method The rate of the acid hydrolysis of Bz was found to beenhanced both below and above the critical micelle concentration (CMC) of CTAB in aqueous solution The pseudo-first-orderrate constant (1198961015840) shows an initial decrease for both low and high H+ concentrations With further increase in [CTAB] at low [H+]the 1198961015840 attains an almost constant value while at high [H+] the 1198961015840 passes through a maximum and then decreases The kineticdata for catalysis by micelles of CTAB was interpreted with the pseudophase ion exchange (PIE) model In CTABcyclohexane1-butanolwater microemulsions as the water to surfactant ratio (119908

119900) increases the physicochemical properties and droplet sizes

of microemulsions significantly change and distinct changes in reaction environment can be marked The rate of the hydrolysisreaction exhibits excellent correlation with the physicochemical properties and droplet sizes of the microemulsions and reversemicelles of CTAB At [H+] = 0001M in reverse micelles andmicroemulsions of CTAB the 1198961015840 of the acid hydrolysis of Bz decreasessharply followed by a slight increase with increasing 119908

119900

1 Introduction

Supramolecular self-assembly in other words self-organi-zation is the spontaneous and reversible association of two ormore components under equilibrium conditions into stablestructurally well-defined aggregates joined by noncovalentbonds [1] A wide variety of nanometer or micrometer scalestructures and assemblies have been generated includingmicelles [2] microemulsions [2] and vesicles [3 4] Theseorganizations from molecular self-assemblies to controllablearchitectures and materials with advanced functions maymeet the requirement of many objectives in science and tech-nology such as catalysis of chemical reactions sensors andelectronic and electromechanical devices [5ndash10] The rate ofa chemical reaction significantly changes in supramolecularself-organized media specifically in surfactant-based orga-nized media involving hydrophobic interactions such asmicelles reverse micelles and microemulsions This has

resulted in a surge of interest in the kinetics of reactionsinvolving different substrates solubilized in such organizedmedia with a view to the fundamental understanding of themechanism of reaction in different environments for theirpotential applications

Research to date includes numerous attempts to explorethe catalysis of hydrolysis reactions by supramolecular self-assembled systems such as micelles reverse micelles andmicroemulsions using a wide variety of substrates includ-ing esters [11 12] dyes [13ndash20] and drugs [11 21ndash35]Bromazepam (Bz) is used as a psychotropic drug whichundergoes acidbase hydrolysis in aqueous solution and studyof this reaction within the physiological pH range is of greatimportance because the absorption of these drugs in thegastrointestinal tract is affected by the nature of the chemicalspecies involved

Sodium decyl (SdeS) dodecyl (SDS) and tetradecyl(STS) sulfate have been reported to produce an inhibitory

Hindawi Publishing CorporationJournal of ChemistryVolume 2015 Article ID 957950 10 pageshttpdxdoiorg1011552015957950

2 Journal of Chemistry

effect in the kinetics of the acid hydrolysis of aqueous diaz-epam bromazepam and flunitrazepam drugs while negligi-ble effects were observed in the cases of polyoxyethylene-23-dodecanol and cetyltrimethylammonium bromide (CTAB)[24] The presence of N-cetyl-N-ethyl-NN-dimethylammo-nium bromide has been found to cause inhibition of the basichydrolysis of triflusal [25] The hexadecylphosphocholinemicelles inhibit the basic hydrolysis of the indomethacin andacemetacin [26] The presence of CTAB micelles enhancesthe rate of alkaline hydrolysis of penicillin [27] The rate-[surfactant] profiles for the hydrolysis of indomethacin showrate inhibition in the presence of SDS and rate enhancementin the presence of CTAB [28] At pH 13 curcumin undergoesrapid degradation by alkaline hydrolysis in the SDS micelleswhereas it is greatly suppressed in the presence of eitherCTAB or dodecyltrimethylammonium bromide micelle [29]The effect of cationic surfactants with varying hydrophobicchains and with different head groups and anionic surfactant(SDS) on the rate of alkaline hydrolysis of the carsalam and its119873-substituted derivatives have been investigated by Al-Ayedet al [30] The plots of observed rate constant (119896obs) versus[surfactants] for degradation of indomethacin under alkalinecondition were curved with negative slopes for ethoxylatedlanolin polysorbate 80 but with the cetrimonium bromidethe plots showed a marked positive change in 119896obs as the[surfactant] passed through the CMC [31] The intramolec-ular degradation of Cephaclor was catalyzed 25-fold bymicelles of CTAB [32] The rate of the hydrolysis of isatinand its derivatives of different hydrophobicities increasedon increasing the [cetyltrimethylammonium chloride] andafter reaching a maximum it started decreasing converselymicelles of SDS inhibited the rate of hydrolysis of isatin andits derivatives [33] Cationic micelles enhanced the rate ofalkaline hydrolysis of acetylsalicylic acid and trifusal at lowsurfactant concentrations although inhibited the reactionsat high surfactant concentrations while anionic micellesshow a catalytic effect and zwitterionic and nonionic micellesshow inhibitory effect at all concentrations [34] The basichydrolysis of carbofuran was catalyzed in the presence ofcolloidal aggregates with positive surface charge and largeinhibition by anionic and nonionic surfactants [35]

In spite of numerous studies there have been no reportson the investigation of the kinetics of the acid hydrolysis ofBz in reverse micelles and microemulsions To understandthe mechanism of this reaction under different reactionenvironments microemulsion may serve as a very potentialmedium and kinetic studies need to be systematically andintensively conducted for its exploration In the present workwe investigated the kinetics of the acid hydrolysis of Bzin absence and presence of micelles reverse micelles andmicroemulsions of CTAB and the kinetic results in thesedifferent media have been compared with those in aqueoussolution In addition kinetic profile for the reaction catalyzedby CTAB was treated quantitatively by pseudophase ionexchange (PIE) model We have also studied the physico-chemical properties and droplet sizes of reverse micelles andmicroemulsions of CTAB and correlated the physicochemicalproperties and119885-average diameters with kinetic results of theacid hydrolysis of Bz

2 Materials and Methods

21 Reagents Bromazepam (generously received from ACILimited) cetyltrimethylammonium bromide (CTAB) (EMerck) 1-butanol (Merck) cyclohexane (Merck) sodium hy-droxide (NaOH) and hydrochloric acid (HCl) solution wereeach reagent grade material and used as received withoutfurther purification

22 Preparation of Microemulsions and Reverse Micelles ofCTAB The CTAB1-butanolcyclohexanewater microemul-sionswere prepared at fixedCTAB (20wt) and cyclohexane(0 and 34wt) with different water and 1-butanol contentsthat ranged from high water to high alcohol content usingdeionized double distilled water following the procedurereported earlier [36]

23 Apparatus Kinetic measurements and spectral analysiswere carried out in a double beam Shimadzu UV-visiblespectrophotometer model UV1650C (equipped with a ther-moregulated cell compartment) and a rectangular quartz cellof path length 1 cm was used throughout the investigationThe reproducibility of the results in all cases has been checkedthrough replicate measurementsThe results reproducible inthe range of plusmn1 were only used for kinetic profiles Specificconductivities viscosities and refractive indices of differentCTAB microemulsions and reverse micelles were measuredwith a Jenway 4510 conductivity meter (equipped with a dip-type precalibrated cell) AntonPaar-Lovis 2000MMEmicro-viscometer (measure viscosity by rolling ball principle withan accuracy of plusmn10minus6mPa s) and Abbemat 300 refractometer(high resolution optical sensor) respectively The 119885-averagediameters of different CTAB microemulsions and reversemicelles droplets weremeasured using a ZetasizerNanoZS90(ZEN3690 Malvern Instruments Ltd UK) by dynamic lightscattering (DLS) method The particle size detection limitwas about 03 nmndash5120583m (diameter) and accuracy of the 119885-average diameter determined has been plusmn2 A He-Ne laserof 633 nm wavelength was used and the measurements weremade at a fixed scattering angle of 90∘ Samples were filteredusing VALUPREP 045120583m polytetrafluoroethylene (PTFE)filter and the 119885-average diameters were determined fromcumulants mean of the intensity average of 50 runs and thereproducibility was checked from at least 3 measurementsThe temperature of the apparatus was controlled automati-cally within plusmn001 K by a built-in Peltier device

24 Acid Hydrolysis of Bz The rate of acid hydrolysis of Bzin aqueous solution was measured spectrophotometricallyby monitoring the absorbance at the 120582max (=235 nm) of Bzwith the progress of the reaction In the cases of kinetic mea-surements absorbance at the 120582max of Bz in micelles reversemicelles and microemulsions of CTAB was monitored sincethe 120582max was found to shift slightly in the presence of thesemedia The kinetic studies were conducted at controlledtemperature The acid hydrolysis of Bz follows second-orderkinetics The hydrolysis was therefore carried out by usinga large excess of [H+] (more than 10-fold) in aqueous and

Journal of Chemistry 3k998400times103

(sminus1)

28

24

20

16

12

08

04

[CTAB] (mM)00 200 400 600 800 1000

[H+] (M) = 0001[H+] (M) = 0010

k998400times103

(sminus1)

24

20

16

12

[CTAB] (mM)00 02 04 06

Figure 1The 1198961015840 as a function of [CTAB] for acid hydrolysis of 221 times10minus5MBz Inset shows the values of the 1198961015840 at [CTAB] below theCMC

different supramolecular systems of CTAB that is underpseudo-first-order conditions of [H+] ≫ [Bz] Assumingabsorbance at 235 nm of the reaction mixture to be due to Bzonly we obtain ln[(119860

0minus 119860infin)(119860 minus 119860

infin)] = 119896

1015840119905 here 1198961015840 is

the pseudo-first-order rate constant 119860 is the absorbance atany time 119905 and 119860

0and 119860

infinare the absorbance at 119905 = 0 and

119905 = infin respectively which depend on the molar absorptivityand the initial and final concentrations of the Bz The valuesof 1198961015840 were evaluated from a least square fit of the plot ofln[(119860


infin)] versus 119905

3 Results and Discussions

31 Critical Micelle Concentration (CMC) of CTAB in AqueousSolution The variation in specific conductivity with changein concentration of CTAB in aqueous media CTAB wasmeasured to determine the CMC of CTABThe experimentalspecific conductivity values of CTAB lie on two straight linesand their point of intersection gave the CMC value for CTABin aqueous solution The CMC value at 25∘C has been foundto have a value of 087mM for CTAB in aqueous solutionwhich is in good agreement with literature data [15 36]

32 Hydrolysis in the Presence of CTAB The 1198961015840 versus [CTAB]profile for the acid hydrolysis of Bz in the presence of CTAB isshown in Figure 1 for [H+] = 0001 and 001M The standarddeviation in 1198961015840 for aqueous solution was below plusmn00014 sminus1and for micelles it was below plusmn00020 sminus1 From Figure 1 itis apparent that below the CMC the 1198961015840 increases for both

low and high [H+] For low [H+] at high [CTAB] (up to theCMC) the 1198961015840 becomes almost constant however for high[H+] the 1198961015840 decreases as the [CTAB] increases further Abovethe CMC the 1198961015840 shows an initial decrease for both low andhigh [H+] As the [CTAB] continues to increase above theCMC the 1198961015840 at low [H+] attains an almost constant valuewhile at high [H+] the 1198961015840 passes through a maximum andthen decreases This corresponds to the change in reactionmechanism during the course of the reaction dependingon [H+] In fact the mechanism of the hydrolysis of Bzchanges with change in pH At high pH that is low [H+] thebreakage of the ring occurs at the 12-amidic bonds which isconsidered to be reversible and at low pH that is high [H+]the rupture takes place in the remaining 12-amidic or 45-azomethine group and the final hydrolysis products the 2-amino-5-substituted benzophenones and glycine derivatives[24] are formed

The 1198961015840 for the acid hydrolysis of Bz in aqueous solution at[H+] = 0001 and 001M is 107 times 10minus3 sminus1 and 169 times 10minus3 sminus1respectively Under identical experimental conditions the 1198961015840has the value of 158 times 10minus3 sminus1 and 182 times 10minus3 sminus1 in thepresence of 096mM CTAB (just above the CMC) while the1198961015840 has the value of 170 times 10minus3 sminus1 and 202 times 10minus3 sminus1 for

049mM CTAB (below the CMC) and for [H+] = 0001 and001M respectively It is clear that the values of the 1198961015840 inpresence ofCTABare higher than in aqueous solution CTABthereby enhances the acid hydrolysis of Bz and serves as apositive catalyst both below and above the CMC

At very high [CTAB] the values of the 1198961015840 have beenfound to be smaller than the corresponding value in aqueoussolution for both high and low [H+] This indicates thatat concentrations far above the CMC of CTAB the rateof reaction is ultimately inhibited This may be explainedin terms of two facts Firstly with increasing [CTAB] thenumber of micelles increases and when the number ofmicelles exceeds that required to solubilize all of Bz there is adilution of the concentration of Bz per micelle as the [CTAB]is increased further This causes a reduction in the rateconstant Secondly the charged surface of CTAB in aqueoussolution may cause the repulsion of similar-charged reactantH+ or even the solubilization of the H+ into themicelle Suchrepulsion or solubilization of the H+ will result in a decreasein its activity in the solution phase An increase in the [CTAB]over that required to affect complete solubilization of the Bzmay therefore result in a decrease in the rate constant evenfor the cases where rate enhancement by micelles occurs

In the cases of our kinetic runs we have always usedthe concentration of CTAB as 20wt which correspondsto a value of ca 05M The kinetics of the acid hydrolysisof Bz has therefore been studied in aqueous solution using05M of CTAB and the result has been compared with thosein aqueous solution The 1198961015840 in 05M CTAB is lower (074 times10minus3 sminus1) than the corresponding value in aqueous solution(107 times 10minus3 sminus1) under identical experimental conditionsThis is indicative of interaction between the micellar headgroups and Bz

The enhancement and inhibition of the rate of the hydrol-ysis of Bz by CTAB micelles were treated by PIE model [37]


According to PIE model the apparent rate constant is givenby the following equation

1198961015840=119896119882[H+] + (119896

119872119870119878minus 119896119882)119898H [119872]

1 + 119870119878[119872]

(1)

Here [119872] is the concentration ofmicellized surfactant whichis given by [119872] = ([119878] minus CMC)119873 where [119878] is the con-centration of the surfactant and119873 is the aggregation number(61 for CTAB in aqueous solution at 25∘C) The 119896

119872refers to

the second-order rate constant in the micellar pseudophaseThe 119870HBr and 119870119878 are the ion exchange equilibrium constantand the binding constant of the substrate Bz to the micellesrespectivelyThe fraction of micellar head groups neutralizedby H+ ions (119898H) were obtained by solving [37]

1198982

H + 119898H [H+] + 119870HBr [Br

minus]

(119870HBr minus 1) [119872]minus 120573 minus

120573 [H+](119870HBr minus 1) [119872]

= 0

(2)

The experimental data were fitted to both (1) and (2) simul-taneously using 119896

119872 119870119878 and 119870HBr as adjustable parameters

Results of computer simulation for the data at the concen-tration of H+ = 0001 and 001M are shown in Figure 1 Thevalues of 119896

119872119870119878 and119870HBr obtained with best fitting at [H

+] =0001 and 001M are shown in Table 1

From Table 1 it is apparent that the values of 119870HBr areindependent of [H+] and the119870

119878and 119896119872depend on the [H+]

This may be due to the fact that as the concentration of Bzis constant at low and high [H+] the concentration of thereactant H+ is different in the micellar pseudophase and thebulk phase

33 Hydrolysis in CTABCyclohexane1-ButanolWater Micro-emulsions and CTAB1-ButanolWater Reverse MicellesFigure 2 represents the 1198961015840 versus water to surfactant ratio (119908

119900)

profiles for CTAB1-butanolcyclohexanewater microemul-sions and CTAB1-butanolwater reverse micelles at [H+] =0001M The standard deviations in 1198961015840 for 119908119900 and 119900119908microemulsions were maximum plusmn00056 and plusmn00029 sminus1respectively and that for reverse micelles ranged fromplusmn00032 to plusmn00050 sminus1 Figure 2 shows that the rate constantsare greatly affected by CTABcyclohexane1-butanolwatermicroemulsions and CTAB1-butanolwater reverse micelleswhich is clear indication of catalysis of the acid hydrolysis ofBz by these organized media

As the 119908119900in CTABcyclohexane1-butanolwater micro-

emulsions and CTAB1-butanolwater reverse micelles in-creases the 1198961015840 sharply decreases first and then becomesalmost constant however at higher value of the 119908

119900(gt50)

a gradual increase is apparent The rate constants attainvalue much higher than the corresponding value in aqueoussolution under identical experimental conditions

From Figure 2 in the region ldquoabrdquo of the curve (119908119900lt 20)

the rate constant decreases with increasing value of119908119900which

should correspond to the region of reverse micelles of CTABin 1-butanol where the incorporation of water into the CTABreverse micelles inhibits the reaction Part ldquocdrdquo of the curve

Table 1 The optimized values of 119896119872 119870119878 and 119870HBr for [H

+] = 0001and 001M for acid hydrolysis of 221 times 10minus5M Bz in micelles ofCTAB using PIE model

[H+] (M) 119896119872(sminus1) 119870

HBr 119870

119878(Mminus1)

0010 0016 100 2000001 0370 100 187

k998400times103

(sminus1)

120

80

40

00

Water to surfactant ratio (wo)0 20 40 60 80

a

b

c

d

MicroemulsionsReverse micelles

Figure 2 The 1198961015840 versus 119908119900profiles for the acid hydrolysis of 221 times

10minus5MBz in CTAB1-butanolcyclohexanewater microemulsionsand CTAB1-butanolwater reverse micelles at [H+] = 0001M

(119908119900gt 50) should correspond to the reaction inCTABmicelles

in water where a decrease in 1-butanol produces a slightincrease in the rate of reaction Part ldquobcrdquo of the curve (119908

119900

= 20sim50) should correspond to the cluster formation of theCTAB reverse micelles (119908119900 microemulsions) in 1-butanoland CTAB micelles (119900119908 microemulsions) in water that isbicontinuous microemulsions (BC)

34 Comparative Study for the Acid Hydrolysis of Bz in Aque-ous SolutionMicelles ReverseMicelles andMicroemulsions ofCTAB Figure 3 compares the 1198961015840 for different supramolecularself-assembled systems based onCTAB at [CTAB] = ca 05Mwith that in aqueous solution under identical experimentalconditions From Figure 1 it can be seen that at concen-trations far above the CMC of CTAB the reaction rate isultimately inhibited which may be correlated with changein binding constant between CTAB and acid dissociationconstant of Bz

The 119908119900 microemulsions (lower value of 119908119900) have been

found to bring about an increase in the reaction rate wherehigh 1-butanol content dominates CTAB1-butanol reversemicelles whereas in 119900119908 microemulsions (higher value of


(sminus1)

120

80

40

00Aqueous Micelles M(ow) M(wo)

Figure 3 The 1198961015840 for aqueous and different self-assembled systemsbased on CTAB [Bz] = 221 times 10minus5M and [H+] = 0001M Micelles([CTAB] = ca 05M) 119900119908 (119908

119900= 709) and 119908119900 (119908

119900= 364) micro-

emulsions

119908119900) the rate constant is higher as compared to aqueous

solution and the corresponding micelles but lower than thatin 119908119900 microemulsions It should correspond to the regionof direct CTAB micelles in water where the lower contentof 1-butanol was incorporated into the CTAB micelles Theschematic diagram of the acid hydrolysis of Bz in differentself-assembled systems is shown in Scheme 1

35 Physicochemical Properties ofCTABCyclohexane1-ButanolWaterMicroemulsions andCTAB1-ButanolWater Reverse Micelles

351 Viscosity Figure 4 shows the change of viscositieswith the 119908

119900for CTAB1-butanolcyclohexanewater micro-

emulsions and CTAB1-butanolwater reverse micelles Theviscosity of the microemulsions is very low less than120mPa s In CTAB1-butanolcyclohexanewater microe-mulsions (Figure 4(a)) at 119908

119900lt 20 the viscosity increases

slightly while for119908119900= 20sim50 it increases gradually whereas

at 119908119900gt 50 a sharp increase is apparent In CTAB1-

butanolwater reverse micelles (Figure 4(b)) at 119908119900lt 20 the

viscosity increases slightly while for 119908119900= 20sim50 it shows a

slight decrease and at119908119900gt 50 a sharp increase is noticeable

This increase in viscosity with the addition of water hasbeen ascribed to the increasing diameter of water filledconduits in the bicontinuous and 119900119908 microemulsions [38]The initial increase in viscosity profile should correspond tothe aggregation and attractive interaction of water dropletsin CTAB1-butanol reverse micelles (119908119900 microemulsions)With further increasing 119908

119900up to 50 the water and 1-butanol

droplets of CTAB micelles and reverse micelles coagulateto form clusters (ie the bicontinuous region) in which thegradual increase for microemulsion and decrease for reverse

in viscosity are apparent [39] Above 119908119900= 50 the sharp

rise in viscosity corresponds to the 1-butanol droplets inCTABwater micelles (119900119908 microemulsions) as the viscosityof water is higher than the 1-butanol

352 Specific Conductivity Figure 5 shows specific conduc-tivities of CTAB1-butanolcyclohexanewater microemul-sions and CTAB1-butanolwater reverse micelles against the119908119900 The conductivity of the microemulsions and reverse

micelles increases with the 119908119900 This indicates an increase

in the number of conducting species in the systems [39]At lower value of the 119908

119900 the conductivity value is low to

indicate that the hydrophilic trimethylammonium ion andcounterion Brminus of CTAB in contact with the water dropletsof CTAB1-butanol reverse micelles (119908119900 microemulsions)are not easily dissociated At higher value of the 119908

119900 CTAB

micelles (119900119908 microemulsions) are formed in water andthe orientation of the CTAB changes where the hydrophilictrimethylammonium ion and the counterion Brminus are freelydissociated in water and increase the specific conductivityIn the middle portion the conductivity increases that shouldbe corresponding to the network of the conductive channel(bicontinuous microemulsions) formed by the interaction ofwater and 1-butanol droplets of the CTAB1-butanol reversemicelles and CTABwater micelles respectively [39]

353 Refractive Index Figure 6 shows the change of refrac-tive index of CTAB1-butanolcyclohexanewater microe-mulsions and CTAB1-butanolwater reverse micelles withthe 119908

119900 The refractive index specifies the transparency of

the microemulsions With increasing119908119900 the refractive index

decreases monotonically As the refractive index is a propertysensitive to structural transitions the results suggest thatno structural modifications are involved [40] that is waterand 1-butanol remain encapsulated into the CTAB1-butanolreversemicelles (low119908

119900) andCTABwatermicelles (high119908

119900)

respectively

354 Correlations of Physicochemical Properties of CTABCyclohexane1-ButanolWater Microemulsions and CTAB1-ButanolWater Reverse Micelles with Kinetic Results of AcidHydrolysis of Bz As the 119908

119900increases the physicochemical

properties such as viscosity density specific conductivityand refractive index of CTABcyclohexane1-butanolwatermicroemulsions and CTAB1-butanolwater reverse micelleschange The viscosity density and specific conductivityincrease and refractive index decreases with the 119908

119900 The

changes in physicochemical properties with 119908119900suggest that

properties are dependent on different microstructure regionsof reverse micelles and microemulsions The viscosity versus119908119900profile shows different patterns for change in the 119908

119900

Increase in viscosity at119908119900lt 20119908

119900= 20sim50 and119908

119900gt 50 cor-

responds to the119908119900 bicontinuous and 119900119908microemulsionsrespectively (Figure 4)Thus increase in the119908

119900causes change

in reaction environment that also causes change in reactionrate of the acid hydrolysis of Bz (Figure 2)

Figures 2 and 4 show that as the 119908119900increases the

reaction rate decreases up to 119908119900lt 20 then the rate becomes


CTAB

1-Butanol

BzBr N

NNH O

+

Br

NN

NH O

Br

NN

NH O

Br

NN

NH O

Br

NN

NH O

H+H+

H+ H+

H+

+

+

+

(c)

Br

NNNH

OBr

NNNH

O

Br

NNNH

O

Br

NNNH

OH+

H+

H+

H+

H+

H+

H+

H+

+

+

++++

+

+

+

+

+

+

(a)

Br

NNNH

OBr

NNNH

O

Br

NNNH

O

Br

NNNH

O

Br

NNNH

OH+

H+

H+ H+

H+

H+

+

+

+

+

+

+

+

(b)

Scheme 1 Acid hydrolysis of Bz in (a) micelles ([CTAB] = ca 05M) (b) 119900119908 (119908119900= 709) and (c) 119908119900 (119908

119900= 364) microemulsions

Visc

osity

(MPa

s)

80

70

60

50

40


Microemulsions

wo

BC

ow

(a)

Visc

osity

(MPa

s)

80

70

60

50

40


wo BC

ow

Reverse micelles

(b)

Figure 4 Viscosities as a function of 119908119900for (a) CTAB1-butanolcyclohexanewater microemulsions and (b) CTAB1-butanolwater reverse

micelles

Journal of Chemistry 7

20

16

12

8

4

0



Spec

ific c

ondu

ctiv

ity (m

S cm

minus1)

Figure 5 Specific conductivities of CTAB1-butanolcyclohexanewater microemulsions and CTAB1-butanolwater reverse micelles

almost constant at 119908119900= 20sim50 and at 119908

119900gt 50 a gradual

increase is apparent which correlates well with viscosity andconductivity results Again the conductivity versus119908

119900profile

shows the increase in conductivity with increase in the 119908119900

which is also associated with viscosity of microemulsionsand reverse micelles of CTAB At 119908

119900gt 50 the CTABwater

micelles of sufficient numbers collide and produce a channelthat carries ions leading to increase in conductivity andviscosity increases due to the presence of micelle core [30]At 119908119900lt 20 the CTAB1-butanol reverse micelles are formed

that allow transport of ions through the water that filled coresand the viscosity slightly increases due to the interaction ofwater droplets [39] In the middle region 119908

119900= 20sim50 the

bicontinuous microemulsions are formed where water and 1-butanol droplets collide to form network structure Thus theviscosity increases due to the collision of different dropletsand the conductivity increases for the transport of ions in theconductive channel produced by water as well as 1-butanoldroplets

36 Droplet Sizes of CTABCyclohexane1-ButanolWaterMicroemulsions and CTAB1-ButanolWater Reverse MicellesFigure 7 shows the119885-average diameter versus119908

119900for CTAB1-

butanolcyclohexanewater microemulsions and CTAB1-butanolwater reverse micelles The droplet sizes of all themicroemulsions and reverse micelles are less than 100 nm[41] It can be seen from Figure 7 that the 119885-average diam-eters of CTAB1-butanolwater reverse micelles are higherthan the corresponding CTAB1-butanolcyclohexanewatermicroemulsions and decrease with increasing 119908

119900 The larger

size at 119908119900= 364 is due to the formation of CTAB reverse

Refr

activ

e ind

ex

142

141

140

139

138

137

136



Figure 6 Refractive indices of CTAB1-butanolcyclohexanewatermicroemulsions and CTAB1-butanolwater reverse micelles

micelles (119908119900 microemulsions) in 1-butanol where the elec-trostatic repulsion between the polar heads is screened by 1-butanol and facilitates the formation of aggregates as well aslarger size of the droplets [42] As the119908

119900increases the droplet

sizes decrease possibly due to the decrease in the number ofreverse micelles At 119908

119900= 709 the droplet sizes are so small

and correspond to the CTAB micelles (119900119908microemulsions)in water Additionally in the middle region the droplet sizesare almost constant that correspond to the transition fromreverse micellar phase to micellar phase via bicontinuousmicroemulsions

The polydispersity index (PDI) a width parameter hasbeen calculated from a Cumulants analysis of the DLS mea-sured intensity autocorrelation function In general valuessmaller than 01 indicate reasonably narrow distribution andvalues greater than 07 indicate that the sample has a verybroad size distributionThe PDI values in our measurementshave been evaluated for CTABcyclohexane1-butanolwatermicroemulsions and CTAB1-butanolwater reverse micellesIt has been found that the PDI values range from 0107 to0354 and 0226 to 0499 for reverse micelles and microemul-sions of CTAB respectively In all cases the PDI values arewithin the range of 01ndash07which indicates that the droplets ofreverse micelles and microemulsions are reasonably uniformin their distribution

The standard deviations in 119885-average diameters 119889of CTABcyclohexane1-butanolwater microemulsions andCTAB1-butanolwater reverse micelles have been calculatedand these depend on the119908

119900for all cases such as119908

119900= 364 (119889=

272 nm) and119908119900= 709 (119889= 030 nm) the standard deviations

in 119885-average diameters of microemulsions were plusmn0682 and


30

25

20

15

10

05

000 20 40 60 80

Microemulsions

Water to surfactant ratio (wo)

wo

BC

ow

Z-av

erag

e dia

met

erd

(nm

)

(a)

140

120

100

80

60

40

20

00


wo

BC

ow

Reverse micelles

Z-av

erag

e dia

met

erd

(nm

)

(b)

Figure 7 119885-average diameters of (a) CTAB1-butanolcyclohexanewater microemulsions and (b) CTAB1-butanolwater reverse micelles

plusmn0004 nm respectively while at 119908119900= 700 (119889 = 1246 nm)

and 119908119900= 737 (119889 = 035 nm) the standard deviations in

119885-average diameters of reverse micelles were plusmn0614 andplusmn0003 nm respectively Thus for both reverse micelles andmicroemulsions of CTAB at high value of119908

119900 the results tend

to be very close to the expected values that indicate relativelynarrow distribution of droplet sizes and at low value of 119908

119900

the results are spread out at a relatively wider range of values

37 Correlation of Droplet Sizes of CTABCyclohexane1-ButanolWater Microemulsions and CTAB1-ButanolWaterReverse Micelles with Kinetic Results of Acid Hydrolysis of BzThe droplet sizes of the CTABcyclohexane1-butanolwatermicroemulsions and CTAB1-butanolwater reverse micellesas well as the rate constants of acid hydrolysis of Bz decreasewith increasing 119908

119900as shown in Figures 2 and 7 For lower

values of 119908119900(larger droplet sizes and less viscous media) the

values of the 1198961015840 are higher due to the presence of CTAB1-butanol reverse micelles which accelerate the reactions Incontrast the formation of CTABwater micelles at higher 119908

119900

values (smaller droplet sizes andmore viscousmedia) inhibitsthe reaction and lowers the reaction rate The bicontinuousmicroemulsions are formed for intermediate values of the119908

119900

where both water and 1-butanol droplets merge to providecomplex microstructures and the values of the 1198961015840 as wellas the size of the droplets become almost constant Therate constants for bicontinuous systems are less than thecorresponding values in 119908119900 119900119908 microemulsions and theaqueous solutions

4 Conclusions

Micelles reverse micelles and microemulsions of CTABinfluence the rate of the acid hydrolysis of Bz The kineticprofiles vary depending on the change in the reaction envi-ronment due to different assembly and orientation of thesurfactants inmicelles reversemicelles andmicroemulsionsIn micellar solution the profiles also exhibit pH dependenceThe kinetic data showed good fit to the PIE model for thetitle reaction with reasonable values of the parameters The1198961015840 versus 119908

119900profiles for CTABcyclohexane1-butanolwater

microemulsions and CTAB1-butanolwater reverse micellesshow a sharp decrease in the 1198961015840 followed by a gradual increasewith increasing 119908

119900to indicate a transition from 119908119900 to

119900119908 via bicontinuous microemulsions The physicochemicalproperties and droplet sizes of these media are also greatlyaffected by change in the 119908

119900which correlates with kinetic

results with change in the microenvironment for differentorientations of CTAB

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The authors acknowledge financial support for a Subpro-ject (CP-231) from Higher Education Quality Enhancement


Project of the University Grants Commission of Bangladeshfinanced byWorld Bank and the Government of BangladeshFerdousi Begumalso acknowledges Bangabandhu Fellowshipfrom the Ministry of Science and Technology of the Govern-ment of Bangladesh

References

[1] G M Whitesides and B Grzybowski ldquoSelf-assembly at allscalesrdquo Science vol 295 no 5564 pp 2418ndash2421 2002

[2] L F Zhang K Yu and A Eisenberg ldquoIon-induced morpho-logical changes in lsquocrew-cutrsquo aggregates of amphiphilic blockcopolymersrdquo Science vol 272 no 5269 pp 1777ndash1779 1996

[3] D E Discher and A Eisenberg ldquoPolymer vesiclesrdquo Science vol297 no 5583 pp 967ndash973 2002

[4] B M Discher Y-YWon D S Ege et al ldquoPolymersomes toughvesicles made from diblock copolymersrdquo Science vol 284 no5417 pp 1143ndash1146 1999

[5] C M Drain ldquoSelf-organization of self-assembled photonicmaterials into functional devices photo-switched conductorsrdquoProceedings of the National Academy of Sciences of the UnitedStates of America vol 99 no 8 pp 5178ndash5182 2002

[6] C Du G Falini S Fermani C Abbott and J Moradian-Oldak ldquoSupramolecular assembly of amelogenin nanospheresinto birefringent microribbonsrdquo Science vol 307 no 5714 pp1450ndash1454 2005

[7] D G Kurth P Lehmann and M Schutte ldquoA route to hierar-chical materials based on complexes of metallosupramolecularpolyelectrolytes and amphiphilesrdquo Proceedings of the NationalAcademy of Sciences of the United States of America vol 97 no11 pp 5704ndash5707 2000

[8] S H Park J-H Lim S-W Chung and C A Mirkin ldquoSelf-assembly of macroscopic metal- polymer amphiphilesrdquo Sciencevol 303 no 5656 pp 348ndash351 2004

[9] E Winfree F Liu L A Wenzler and N C Seeman ldquoDesignand self-assembly of two-dimensional DNA crystalsrdquo Naturevol 394 no 6693 pp 539ndash544 1998

[10] D M Vriezema M C Aragones J A A W Elemans J J L MCornelissen A E Rowan and R J M Nolte ldquoSelf-assemblednanoreactorsrdquo Chemical Reviews vol 105 no 4 pp 1445ndash14892005

[11] G Stinga D M Mihai A Iovescu A Baran and D FAnghel ldquoEffect of organic solvents upon the basic hydrolysisof acetylsalicylic acid in aqueous-micellar solutionsrdquo RomanianJournal of Chemistry vol 50 no 9-10 pp 767ndash775 2005

[12] Y S Simanenko A F Popov T M Prokopeva E A KarpichevI A Belousova and V A Savelova ldquoMicellar effects of cationicdetergents in the decomposition of ecotoxic substrates byhydroxide ionrdquoTheoretical and Experimental Chemistry vol 38no 4 pp 242ndash249 2002

[13] L Mukherjee N Mitra P K Bhattacharya and S P MoulikldquoKinetics in microemulsion medium 4 Alkaline fading ofcrystal violet in aqueous (H

2Oaerosol OTisooctane and

H2Oaerosol OTdecane) and nonaqueous (ethylene glycol

aerosol OTisooctane) microemulsionsrdquo Langmuir vol 11 no8 pp 2866ndash2871 1995

[14] R Y Talman S Gokturk and M Tuncay ldquoKinetic cosolventeffects on the alkaline fading of crystal violet in the presenceof sodium dodecyl sulfate micellesrdquo Colloids and Surfaces APhysicochemical and Engineering Aspects vol 270-271 no 1ndash3pp 72ndash77 2005

[15] J Datta A Bhattiacharya and K K Kundu ldquoEffect of surfac-tants on the kinetics of alkaline fading of crystal violet and acid-catalyzed inversion of sucroserdquo Indian Journal of Chemistry vol27 pp 115ndash122 1988

[16] C Dolcet and E Rodenas ldquoHydroxide ion specific adsorptionon cetyltrimethylammonium bromide micelles explains kineticdatardquo Colloids and Surfaces A Physicochemical and EngineeringAspects vol 75 pp 39ndash50 1993

[17] E F J Duynstee and E Grunwald ldquoOrganic reactions occurringin or on micelles I Reaction rate studies of the alkaline fadingof triphenylmethane dyes and sulfonphthalein indicators in thepresence of detergent saltsrdquo Journal of the American ChemicalSociety vol 81 no 17 pp 4540ndash4542 1959

[18] I Molinero M L Sierra M Valiente and E Rodenas ldquoPhys-ical properties of cetylpyridinium chloride micelles and theirbehaviour as reaction mediardquo Journal of the Chemical SocietymdashFaraday Transactions vol 92 no 1 pp 59ndash63 1996

[19] Y Zhang X Li J Liu and X Zeng ldquoMicellar catalysis ofcomposite reactionsmdashthe effect of SDSmicelles and premicelleson the alkaline fading of crystal violet and malachite greenrdquoJournal of Dispersion Science and Technology vol 23 no 4 pp473ndash481 2002

[20] A M R Kabir and M A B H Susan ldquoKinetics of the alkalinehydrolysis of crystal violet in aqueous solution influenced byanionic surfactantsrdquo Journal of Saudi Chemical Society vol 12pp 543ndash554 2008

[21] C O Rangel-Yagui A Pessoa Jr and L C Tavares ldquoMicellarsolubilization of drugsrdquo Journal of Pharmacy and Pharmaceuti-cal Sciences vol 8 no 2 pp 147ndash165 2005

[22] P C Mohr A Mohr T P Vila and H-G Korth ldquoLocalizationof hydrophobic N-diazeniumdiolates in aqueous micellar solu-tionrdquo Langmuir vol 26 no 15 pp 12785ndash12793 2010

[23] MN Khan P C Gleen and Z Arifin ldquoEffects of inorganic saltsand mixed aqueous-organic solvents on the rates of alkalinehydrolysis of aspirinrdquo Indian Journal of Chemistry vol 35 no9 pp 758ndash765 1996

[24] M E Moro J Novillo-Fertrell M M Velazquez and L JRodriguez ldquoKinetics of the acid hydrolysis of diazepam bro-mazepam and flunitrazepam in aqueous andmicellar systemsrdquoJournal of Pharmaceutical Sciences vol 80 no 5 pp 459ndash4681991

[25] M Ferrit C Del Valle M Lopez R Luque and F MartınezldquoThe Stability of 2-Acetoxy-4-trifluoromethylbenzoic acid (Tri-flusal) in micellar Pseudophaserdquo Journal of PharmaceuticalSciences vol 93 no 2 pp 461ndash469 2004

[26] C Matos H Chaimovich J L Lima I M Cuccovia and SReis ldquoEffect of liposomes on the rate of alkaline hydrolysisof indomethacin and acemetacinrdquo Journal of PharmaceuticalSciences vol 90 no 3 pp 298ndash309 2001

[27] N P Gensmantel and M I Page ldquoThe micelles catalyzedhydrolysis of penicillin derivatives (Part I) and the effect ofincreasing the hydrophobicity of penicillin on its micelle-catalyzed hydrolysis (Part II)rdquo Journal of the Chemical SocietyPerkin Transactions vol 2 pp 147ndash155 1982

[28] A Cipiciani C Ebert R Germani et al ldquoMicellar effects onthe basic hydrolysis of indomethacin and related compoundsrdquoJournal of Pharmaceutical Sciences vol 74 no 11 pp 1184ndash11871985

[29] M H M Leung H Colangelo and T W Kee ldquoEncapsulationof curcumin in cationicmicelles suppresses alkaline hydrolysisrdquoLangmuir vol 24 no 11 pp 5672ndash5675 2008


[30] A S Al-Ayed M S Ali H A Al-Lohedan A M Al-Sulaimand Z A Issa ldquoEffect of alkyl chain length head group andnature of the surfactant on the hydrolysis of 13-benzoxazine-24-dione and its derivativesrdquo Journal of Colloid and InterfaceScience vol 361 no 1 pp 205ndash211 2011

[31] J E Dawson B R Hajratwala and H Taylor ldquoKinetics ofindomethacin degradation II presence of alkali plus surfactantrdquoJournal of Pharmaceutical Sciences vol 66 no 9 pp 1259ndash12631977

[32] A G Oliveira I M Cuccovia and H Chaimovich ldquoMicellarmodification of drug stability analysis of the effect of hexade-cyltrimethylammonium halides on the rate of degradation ofcephaclorrdquo Journal of Pharmaceutical Sciences vol 79 no 1 pp37ndash42 1990

[33] A S Al-Ayed M S Ali H A Al-Lohedan A M Al-Sulaimand Z A Issa ldquoMicellar effects on the alkaline hydrolysisof isatin and its derivativesrdquo Journal of Colloid and InterfaceScience vol 357 no 2 pp 393ndash399 2011

[34] M Ferrit C del Valle and F Martınez ldquoThe study of theinfluence of surfactant charge on alkaline hydrolysis reactionsof acetylsalicylic acid (ASA) and triflusal (TFL) using spec-trophotometric methodsrdquo European Journal of PharmaceuticalSciences vol 31 no 3-4 pp 211ndash220 2007

[35] M Arias L Garcıa-Rıo J C Mejuto P Rodrıguez-Dafonteand J Simal-Gandara ldquoInfluence of micelles on the basicdegradation of carbofuranrdquo Journal of Agricultural and FoodChemistry vol 53 no 18 pp 7172ndash7178 2005

[36] F Begum M Y A Mollah M M Rahman and M AB H Susan ldquoKinetics of the alkaline hydrolysis of crystalviolet in micelles reverse micelles and microemulsions ofcetyltrimethylammonium bromiderdquo Journal of the BangladeshChemical Society vol 24 pp 173ndash184 2011

[37] M N KhanMicellar Catalysis (Surfactant Science) CRC PressBoca Raton Fla USA 2006

[38] B K Paul and S P Moulik ldquoThe viscosity behaviours ofmicroemulsions an overviewrdquo Proceeding of Indian NationalScience Academy Part A vol 66 pp 499ndash519 2000

[39] A Zvonar B Rozman M B Rogac and M Gasperlin ldquoTheinfluence of microstructure on celecoxib release from a phar-maceutically applicable systemrdquoActa Chimica Slovenica vol 56no 1 pp 131ndash138 2009

[40] M Goffredi V T Liveri and G Vassallo ldquoRefractive indexof water-AOT-n-heptane microemulsionsrdquo Journal of SolutionChemistry vol 22 no 10 pp 941ndash949 1993

[41] Y-S Rhee J-G Choi E-S Park and S-C Chi ldquoTransdermaldelivery of ketoprofen using microemulsionsrdquo InternationalJournal of Pharmaceutics vol 228 no 1-2 pp 161ndash170 2001

[42] K Zielinska K A Wilk A Jezierski and T JesionowskildquoMicrostructure and structural transition in microemulsionsstabilized by aldonamide-type surfactantsrdquo Journal of Colloidand Interface Science vol 321 no 2 pp 408ndash417 2008

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy


Carbohydrate Chemistry

International Journal of


Journal of

Chemistry


Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of


Chromatography Research International


Applied ChemistryJournal of



Theoretical ChemistryJournal of


Journal of

Spectroscopy

Analytical ChemistryInternational Journal of


Journal of


Quantum Chemistry


Organic Chemistry International

ElectrochemistryInternational Journal of



CatalystsJournal of


effect in the kinetics of the acid hydrolysis of aqueous diaz-epam bromazepam and flunitrazepam drugs while negligi-ble effects were observed in the cases of polyoxyethylene-23-dodecanol and cetyltrimethylammonium bromide (CTAB)[24] The presence of N-cetyl-N-ethyl-NN-dimethylammo-nium bromide has been found to cause inhibition of the basichydrolysis of triflusal [25] The hexadecylphosphocholinemicelles inhibit the basic hydrolysis of the indomethacin andacemetacin [26] The presence of CTAB micelles enhancesthe rate of alkaline hydrolysis of penicillin [27] The rate-[surfactant] profiles for the hydrolysis of indomethacin showrate inhibition in the presence of SDS and rate enhancementin the presence of CTAB [28] At pH 13 curcumin undergoesrapid degradation by alkaline hydrolysis in the SDS micelleswhereas it is greatly suppressed in the presence of eitherCTAB or dodecyltrimethylammonium bromide micelle [29]The effect of cationic surfactants with varying hydrophobicchains and with different head groups and anionic surfactant(SDS) on the rate of alkaline hydrolysis of the carsalam and its119873-substituted derivatives have been investigated by Al-Ayedet al [30] The plots of observed rate constant (119896obs) versus[surfactants] for degradation of indomethacin under alkalinecondition were curved with negative slopes for ethoxylatedlanolin polysorbate 80 but with the cetrimonium bromidethe plots showed a marked positive change in 119896obs as the[surfactant] passed through the CMC [31] The intramolec-ular degradation of Cephaclor was catalyzed 25-fold bymicelles of CTAB [32] The rate of the hydrolysis of isatinand its derivatives of different hydrophobicities increasedon increasing the [cetyltrimethylammonium chloride] andafter reaching a maximum it started decreasing converselymicelles of SDS inhibited the rate of hydrolysis of isatin andits derivatives [33] Cationic micelles enhanced the rate ofalkaline hydrolysis of acetylsalicylic acid and trifusal at lowsurfactant concentrations although inhibited the reactionsat high surfactant concentrations while anionic micellesshow a catalytic effect and zwitterionic and nonionic micellesshow inhibitory effect at all concentrations [34] The basichydrolysis of carbofuran was catalyzed in the presence ofcolloidal aggregates with positive surface charge and largeinhibition by anionic and nonionic surfactants [35]

In spite of numerous studies there have been no reportson the investigation of the kinetics of the acid hydrolysis ofBz in reverse micelles and microemulsions To understandthe mechanism of this reaction under different reactionenvironments microemulsion may serve as a very potentialmedium and kinetic studies need to be systematically andintensively conducted for its exploration In the present workwe investigated the kinetics of the acid hydrolysis of Bzin absence and presence of micelles reverse micelles andmicroemulsions of CTAB and the kinetic results in thesedifferent media have been compared with those in aqueoussolution In addition kinetic profile for the reaction catalyzedby CTAB was treated quantitatively by pseudophase ionexchange (PIE) model We have also studied the physico-chemical properties and droplet sizes of reverse micelles andmicroemulsions of CTAB and correlated the physicochemicalproperties and119885-average diameters with kinetic results of theacid hydrolysis of Bz

2 Materials and Methods

21 Reagents Bromazepam (generously received from ACILimited) cetyltrimethylammonium bromide (CTAB) (EMerck) 1-butanol (Merck) cyclohexane (Merck) sodium hy-droxide (NaOH) and hydrochloric acid (HCl) solution wereeach reagent grade material and used as received withoutfurther purification

22 Preparation of Microemulsions and Reverse Micelles ofCTAB The CTAB1-butanolcyclohexanewater microemul-sionswere prepared at fixedCTAB (20wt) and cyclohexane(0 and 34wt) with different water and 1-butanol contentsthat ranged from high water to high alcohol content usingdeionized double distilled water following the procedurereported earlier [36]

23 Apparatus Kinetic measurements and spectral analysiswere carried out in a double beam Shimadzu UV-visiblespectrophotometer model UV1650C (equipped with a ther-moregulated cell compartment) and a rectangular quartz cellof path length 1 cm was used throughout the investigationThe reproducibility of the results in all cases has been checkedthrough replicate measurementsThe results reproducible inthe range of plusmn1 were only used for kinetic profiles Specificconductivities viscosities and refractive indices of differentCTAB microemulsions and reverse micelles were measuredwith a Jenway 4510 conductivity meter (equipped with a dip-type precalibrated cell) AntonPaar-Lovis 2000MMEmicro-viscometer (measure viscosity by rolling ball principle withan accuracy of plusmn10minus6mPa s) and Abbemat 300 refractometer(high resolution optical sensor) respectively The 119885-averagediameters of different CTAB microemulsions and reversemicelles droplets weremeasured using a ZetasizerNanoZS90(ZEN3690 Malvern Instruments Ltd UK) by dynamic lightscattering (DLS) method The particle size detection limitwas about 03 nmndash5120583m (diameter) and accuracy of the 119885-average diameter determined has been plusmn2 A He-Ne laserof 633 nm wavelength was used and the measurements weremade at a fixed scattering angle of 90∘ Samples were filteredusing VALUPREP 045120583m polytetrafluoroethylene (PTFE)filter and the 119885-average diameters were determined fromcumulants mean of the intensity average of 50 runs and thereproducibility was checked from at least 3 measurementsThe temperature of the apparatus was controlled automati-cally within plusmn001 K by a built-in Peltier device

24 Acid Hydrolysis of Bz The rate of acid hydrolysis of Bzin aqueous solution was measured spectrophotometricallyby monitoring the absorbance at the 120582max (=235 nm) of Bzwith the progress of the reaction In the cases of kinetic mea-surements absorbance at the 120582max of Bz in micelles reversemicelles and microemulsions of CTAB was monitored sincethe 120582max was found to shift slightly in the presence of thesemedia The kinetic studies were conducted at controlledtemperature The acid hydrolysis of Bz follows second-orderkinetics The hydrolysis was therefore carried out by usinga large excess of [H+] (more than 10-fold) in aqueous and


(sminus1)

28

24

20

16

12

08

04

[CTAB] (mM)00 200 400 600 800 1000

[H+] (M) = 0001[H+] (M) = 0010

k998400times103

(sminus1)

24

20

16

12

[CTAB] (mM)00 02 04 06




infin)] = 119896

1015840119905 here 1198961015840 is


0and 119860
















1198961015840=119896119882[H+] + (119896

119872119870119878minus 119896119882)119898H [119872]

1 + 119870119878[119872]

(1)


119872refers to


1198982

H + 119898H [H+] + 119870HBr [Br

minus]


120573 [H+](119870HBr minus 1) [119872]

= 0

(2)










119900)




119900(gt50)







[H+] (M) 119896119872(sminus1) 119870

HBr 119870

119878(Mminus1)

0010 0016 100 2000001 0370 100 187

k998400times103

(sminus1)

120

80

40

00


a

b

c

d






119900






(sminus1)

120

80

40



119900= 709) and 119908119900 (119908

119900= 364) micro-

emulsions























119900 CTAB







119900)

respectively




119900 The



119900


119900= 20sim50 and119908

119900gt 50 cor-


119900causes change





CTAB

1-Butanol

BzBr N

NNH O

+

Br

NN

NH O

Br

NN

NH O

Br

NN

NH O

Br

NN

NH O

H+H+

H+ H+

H+

+

+

+

(c)

Br

NNNH

OBr

NNNH

O

Br

NNNH

O

Br

NNNH

OH+

H+

H+

H+

H+

H+

H+

H+

+

+

++++

+

+

+

+

+

+

(a)

Br

NNNH

OBr

NNNH

O

Br

NNNH

O

Br

NNNH

O

Br

NNNH

OH+

H+

H+ H+

H+

H+

+

+

+

+

+

+

+

(b)



Visc

osity

(MPa

s)

80

70

60

50

40


Microemulsions

wo

BC

ow

(a)

Visc

osity

(MPa

s)

80

70

60

50

40


wo BC

ow

Reverse micelles

(b)


micelles


20

16

12

8

4

0



Spec

ific c

ondu

ctiv

ity (m

S cm

minus1)





119900profile






119900= 20sim50 the



119900for CTAB1-


119900 The larger


Refr

activ

e ind

ex

142

141

140

139

138

137

136












119900= 364 (119889=




30

25

20

15

10

05

000 20 40 60 80

Microemulsions


wo

BC

ow

Z-av

erag

e dia

met

erd

(nm

)

(a)

140

120

100

80

60

40

20

00


wo

BC

ow

Reverse micelles

Z-av

erag

e dia

met

erd

(nm

)

(b)







119900






119900


119900


4 Conclusions










Acknowledgments




References
























































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


(sminus1)

28

24

20

16

12

08

04

[CTAB] (mM)00 200 400 600 800 1000

[H+] (M) = 0001[H+] (M) = 0010

k998400times103

(sminus1)

24

20

16

12

[CTAB] (mM)00 02 04 06




infin)] = 119896

1015840119905 here 1198961015840 is


0and 119860
















1198961015840=119896119882[H+] + (119896

119872119870119878minus 119896119882)119898H [119872]

1 + 119870119878[119872]

(1)


119872refers to


1198982

H + 119898H [H+] + 119870HBr [Br

minus]


120573 [H+](119870HBr minus 1) [119872]

= 0

(2)










119900)




119900(gt50)







[H+] (M) 119896119872(sminus1) 119870

HBr 119870

119878(Mminus1)

0010 0016 100 2000001 0370 100 187

k998400times103

(sminus1)

120

80

40

00


a

b

c

d






119900






(sminus1)

120

80

40



119900= 709) and 119908119900 (119908

119900= 364) micro-

emulsions























119900 CTAB







119900)

respectively




119900 The



119900


119900= 20sim50 and119908

119900gt 50 cor-


119900causes change





CTAB

1-Butanol

BzBr N

NNH O

+

Br

NN

NH O

Br

NN

NH O

Br

NN

NH O

Br

NN

NH O

H+H+

H+ H+

H+

+

+

+

(c)

Br

NNNH

OBr

NNNH

O

Br

NNNH

O

Br

NNNH

OH+

H+

H+

H+

H+

H+

H+

H+

+

+

++++

+

+

+

+

+

+

(a)

Br

NNNH

OBr

NNNH

O

Br

NNNH

O

Br

NNNH

O

Br

NNNH

OH+

H+

H+ H+

H+

H+

+

+

+

+

+

+

+

(b)



Visc

osity

(MPa

s)

80

70

60

50

40


Microemulsions

wo

BC

ow

(a)

Visc

osity

(MPa

s)

80

70

60

50

40


wo BC

ow

Reverse micelles

(b)


micelles


20

16

12

8

4

0



Spec

ific c

ondu

ctiv

ity (m

S cm

minus1)





119900profile






119900= 20sim50 the



119900for CTAB1-


119900 The larger


Refr

activ

e ind

ex

142

141

140

139

138

137

136












119900= 364 (119889=




30

25

20

15

10

05

000 20 40 60 80

Microemulsions


wo

BC

ow

Z-av

erag

e dia

met

erd

(nm

)

(a)

140

120

100

80

60

40

20

00


wo

BC

ow

Reverse micelles

Z-av

erag

e dia

met

erd

(nm

)

(b)







119900






119900


119900


4 Conclusions










Acknowledgments




References
























































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



1198961015840=119896119882[H+] + (119896

119872119870119878minus 119896119882)119898H [119872]

1 + 119870119878[119872]

(1)


119872refers to


1198982

H + 119898H [H+] + 119870HBr [Br

minus]


120573 [H+](119870HBr minus 1) [119872]

= 0

(2)










119900)




119900(gt50)







[H+] (M) 119896119872(sminus1) 119870

HBr 119870

119878(Mminus1)

0010 0016 100 2000001 0370 100 187

k998400times103

(sminus1)

120

80

40

00


a

b

c

d






119900






(sminus1)

120

80

40



119900= 709) and 119908119900 (119908

119900= 364) micro-

emulsions























119900 CTAB







119900)

respectively




119900 The



119900


119900= 20sim50 and119908

119900gt 50 cor-


119900causes change





CTAB

1-Butanol

BzBr N

NNH O

+

Br

NN

NH O

Br

NN

NH O

Br

NN

NH O

Br

NN

NH O

H+H+

H+ H+

H+

+

+

+

(c)

Br

NNNH

OBr

NNNH

O

Br

NNNH

O

Br

NNNH

OH+

H+

H+

H+

H+

H+

H+

H+

+

+

++++

+

+

+

+

+

+

(a)

Br

NNNH

OBr

NNNH

O

Br

NNNH

O

Br

NNNH

O

Br

NNNH

OH+

H+

H+ H+

H+

H+

+

+

+

+

+

+

+

(b)



Visc

osity

(MPa

s)

80

70

60

50

40


Microemulsions

wo

BC

ow

(a)

Visc

osity

(MPa

s)

80

70

60

50

40


wo BC

ow

Reverse micelles

(b)


micelles


20

16

12

8

4

0



Spec

ific c

ondu

ctiv

ity (m

S cm

minus1)





119900profile






119900= 20sim50 the



119900for CTAB1-


119900 The larger


Refr

activ

e ind

ex

142

141

140

139

138

137

136












119900= 364 (119889=




30

25

20

15

10

05

000 20 40 60 80

Microemulsions


wo

BC

ow

Z-av

erag

e dia

met

erd

(nm

)

(a)

140

120

100

80

60

40

20

00


wo

BC

ow

Reverse micelles

Z-av

erag

e dia

met

erd

(nm

)

(b)







119900






119900


119900


4 Conclusions










Acknowledgments




References
























































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


(sminus1)

120

80

40



119900= 709) and 119908119900 (119908

119900= 364) micro-

emulsions























119900 CTAB







119900)

respectively




119900 The



119900


119900= 20sim50 and119908

119900gt 50 cor-


119900causes change





CTAB

1-Butanol

BzBr N

NNH O

+

Br

NN

NH O

Br

NN

NH O

Br

NN

NH O

Br

NN

NH O

H+H+

H+ H+

H+

+

+

+

(c)

Br

NNNH

OBr

NNNH

O

Br

NNNH

O

Br

NNNH

OH+

H+

H+

H+

H+

H+

H+

H+

+

+

++++

+

+

+

+

+

+

(a)

Br

NNNH

OBr

NNNH

O

Br

NNNH

O

Br

NNNH

O

Br

NNNH

OH+

H+

H+ H+

H+

H+

+

+

+

+

+

+

+

(b)



Visc

osity

(MPa

s)

80

70

60

50

40


Microemulsions

wo

BC

ow

(a)

Visc

osity

(MPa

s)

80

70

60

50

40


wo BC

ow

Reverse micelles

(b)


micelles


20

16

12

8

4

0



Spec

ific c

ondu

ctiv

ity (m

S cm

minus1)





119900profile






119900= 20sim50 the



119900for CTAB1-


119900 The larger


Refr

activ

e ind

ex

142

141

140

139

138

137

136












119900= 364 (119889=




30

25

20

15

10

05

000 20 40 60 80

Microemulsions


wo

BC

ow

Z-av

erag

e dia

met

erd

(nm

)

(a)

140

120

100

80

60

40

20

00


wo

BC

ow

Reverse micelles

Z-av

erag

e dia

met

erd

(nm

)

(b)







119900






119900


119900


4 Conclusions










Acknowledgments




References
























































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


CTAB

1-Butanol

BzBr N

NNH O

+

Br

NN

NH O

Br

NN

NH O

Br

NN

NH O

Br

NN

NH O

H+H+

H+ H+

H+

+

+

+

(c)

Br

NNNH

OBr

NNNH

O

Br

NNNH

O

Br

NNNH

OH+

H+

H+

H+

H+

H+

H+

H+

+

+

++++

+

+

+

+

+

+

(a)

Br

NNNH

OBr

NNNH

O

Br

NNNH

O

Br

NNNH

O

Br

NNNH

OH+

H+

H+ H+

H+

H+

+

+

+

+

+

+

+

(b)



Visc

osity

(MPa

s)

80

70

60

50

40


Microemulsions

wo

BC

ow

(a)

Visc

osity

(MPa

s)

80

70

60

50

40


wo BC

ow

Reverse micelles

(b)


micelles


20

16

12

8

4

0



Spec

ific c

ondu

ctiv

ity (m

S cm

minus1)





119900profile






119900= 20sim50 the



119900for CTAB1-


119900 The larger


Refr

activ

e ind

ex

142

141

140

139

138

137

136












119900= 364 (119889=




30

25

20

15

10

05

000 20 40 60 80

Microemulsions


wo

BC

ow

Z-av

erag

e dia

met

erd

(nm

)

(a)

140

120

100

80

60

40

20

00


wo

BC

ow

Reverse micelles

Z-av

erag

e dia

met

erd

(nm

)

(b)







119900






119900


119900


4 Conclusions










Acknowledgments




References
























































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


20

16

12

8

4

0



Spec

ific c

ondu

ctiv

ity (m

S cm

minus1)





119900profile






119900= 20sim50 the



119900for CTAB1-


119900 The larger


Refr

activ

e ind

ex

142

141

140

139

138

137

136












119900= 364 (119889=




30

25

20

15

10

05

000 20 40 60 80

Microemulsions


wo

BC

ow

Z-av

erag

e dia

met

erd

(nm

)

(a)

140

120

100

80

60

40

20

00


wo

BC

ow

Reverse micelles

Z-av

erag

e dia

met

erd

(nm

)

(b)







119900






119900


119900


4 Conclusions










Acknowledgments




References
























































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


30

25

20

15

10

05

000 20 40 60 80

Microemulsions


wo

BC

ow

Z-av

erag

e dia

met

erd

(nm

)

(a)

140

120

100

80

60

40

20

00


wo

BC

ow

Reverse micelles

Z-av

erag

e dia

met

erd

(nm

)

(b)







119900






119900


119900


4 Conclusions










Acknowledgments




References
























































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



References
























































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of
























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

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