Micellar solutions hydrolysis

Surfactants have also been of interest for their ability to support reactions in normally inhospitable environments. Reactions such as hydrolysis, aminolysis, solvolysis, and, in inorganic chemistry, of aquation of complex ions, may be retarded, accelerated, or differently sensitive to catalysts relative to the behavior in ordinary solutions (see Refs. 205 and 206 for reviews). The acid-base chemistry in micellar solutions has been investigated by Drummond and co-workers [207]. A useful model has been the pseudophase model [206-209] in which reactants are either in solution or solubilized in micelles and partition between the two as though two distinct phases were involved. In inverse micelles in nonpolar media, water is concentrated in the micellar core and reactions in the micelle may be greatly accelerated [206, 210]. The confining environment of a solubilized reactant may lead to stereochemical consequences as in photodimerization reactions in micelles [211] or vesicles [212] or in the generation of radical pairs [213]. 

R = Et) were hydrolysed in micellar solutions of the prepared ketoximes under pseudo-first-order reaction conditions.In the alkaline hydrolysis of / -nitrophenyl ethyl chloromethylphosphonate (254), micellar catalysis by cetylpyridinium bromide is much reduced when KCl and KBr are present. ... 

Gonzalez, J. and Ukrainczyk, L. Transport of nicosulfuron in soil columns. J. Environ. Qua ., 28(1) 101-107, 1999. Gonzalez, V., Ayala, J.H., and Afonso, A.M. Degradation of carbaryl in natural waters enhanced hydrolysis rate in micellar solution. Bull. Environ. Contam. Toxicol, 42(2) 171-178, 1992. 

With respect to the reduced water concentration (1), it seems as if all but one of the hydrolysis reactions following the mechanism shown in Scheme 10 are retarded in micellar solutions (the exception being the hydrolysis of 4-nitrophenyl chloroformate la in cationic micelles ) and the lower water concentration in the micellar Stern region (estimated to be 45 mol dm for and 33 mol dm for SDS ) will... 

The alcohol formed on hydrolysis of a betaine ester surfactant has strong effects on the shape of its aggregates and its phase behavior. In a micellar solution of dodecyl betainate, addition of 10 to 20% of dodecanol causes a significant aggregate growth (higher additions cause phase separation) [29]. In... 

Three new macrocyclic ligands (187) when complexed with zinc(II) could promote ester hydrolysis and a kinetic study of the hydrolysis of 4-nitrophenyl acetate in Tris buffer at pH 8.63 in 10% (v/v) MeCN was earned out with these.153 The hydrolysis of lipophilic esters is also catalysed by zinc(H) in a complex of a long alkyl-pendant macrocyclic tetraamine (188) in micellar solution.154 A study with a copper chloride-containing micelle has compared its effectiveness in the hydrolysis of esters and amides.155... 

Alkaline hydrolysis rates of a series of thiophenyl 4-X-benzoates (47 X = H, Me, N02) was significantly enhanced in the presence of cyclodextrins (CDs), and this was attributed to strong binding of the benzoyl moiety within the CD cavity and covalent catalysis by secondary hydroxy groups of the CDs (48).63 The effect of MeCN and MeOH on the alkaline hydrolysis of acetylsalicylic acid in aqueous micellar solutions was reported.64 Butylaminolysis of p-nitrophenyl acetate in chlorobenzene in the presence of different kinds of phase-transfer catalysts (crown ethers and gly-mes) supported the existence of a novel reaction pathway exhibiting a first-order dependence on the concentration of the phase-transfer catalyst and a second-order... 

Recently, Bunton et al. synthesized the Ci6H33-attached triamine copper(II) complex 8b [26], which promoted the hydrolysis of diphenyl 4-nitrophenyl phosphate (DNP) at alkaline pH. The catalytic activity was almost the same as that for Menger s previously reported comicellar system with 3b. The active species was proposed to be the hydroxide-bound copper(II) complex 8b. The pvalue of the copper(II)-bound water molecule was speculated to be about 8 from the fact that the nonalkylated and tetradecyl homologous copper(II) complexes have a pvalue of 8 (determined by DNP hydrolysis kinetics). Since the micellar metal complex 8b was not fully characterized either in the solid state or in a micellar solution, its hydrolysis mechanism remains to be elucidated. 

Consequently, new investigations dealing with reactions in micellar solutions composed of functional surfactants, or mixtures of inert and functional surfactants, continue to appear in the literature. An interesting study of acid-catalyzed hydrolysis of 2-(p-tetradecyloxyphenyl)-l,3-dioxolane (p-TPD) in aqueous sodium dodecyl sulfate (SDS) solutions has been reported [13]. In this case,/ -TPD behaves as a non-ionic functional surfactant and apparently forms non-ideal mixed micelles with the anionic surfactant (SDS). Based on the observed kinetic data, the authors propose that, at elevated temperatures, the thermodynamic non-ideality results in the manifestation of two populations of micelles, one rich in SDS and the other rich in/>-TPD. 

The redox stability of the various model complexes was examined in aqueous Triton X-100 solutions. Only [Fe(Z-cys1-Pro-Leu-cys-OMe)2]2 exhibits a quasireversible redox couple at — 0.37 V versus SCE, which is considered to simulate closely the value of native rubredoxin, although a small difference (0.1 V) still remains (7). Other model peptide complexes are rapidly decomposed by hydrolysis in an aqueous micellar solution and do not exhibit even an oxidation peak. The simple alkythiolate model [Fe(S2-o-xyl)2]2 exhibits a quasireversible redox couple at —1.0 V versus SCE in an aqueous micellar solution. Therefore, macro-ring peptide chelation with some hydrophobic side chains, is required in order to induce redox stability (reversibility of cyclic voltammogram measurements) of the Fe(III/II) couple. 

The effect of micellar solutions of sodium dodecanoate (laurate) and n-dodecyltrimethylammonium bromide on the rate of alkaline hydrolysis of p-nitrophenyl acetate, mono-p-nitrophenyl dodecanedioate, and p-nitrophenyl octanoate has been investigated by Menger and Portnoy... 

The values of the observed rate constants and, where specified, the activation energy, for the hydrolysis of micellar solutions of the surfactants are given in the cited reference, but no data are available for solutions below the CMC. 

Anionic micellar systems were found to increase the rate of the acid catalyzed hydrolysis of acetylsalicylic acid (Nogami et al., 1962), methantheline bromide (Nogami and Awazu, 1962), n-butyl acetate, t-butyl acetate, ethyl p-aminobenzoate, and ethyl o-aminobenzoate (Sakurada et al., 1967), but decreased that of methyl benzoate slightly (Sakurada et al., 1967). The acid catalyzed hydrolysis of anionic amphi-philes also generally tend to be accelerated by micellization (Table 5). The rates of the acid catalyzed hydrolyses of sodium sulfoethyl do-decanoate, sodium undecanoate, and sodium sulfobutyl caprylate are significantly greater in micellar than in non-micellar solutions while that of sodium dodecyl sulfoacetate is unaffected by micelle formation (Meguro and Hikota, 1968). 

The activation parameters for the acid-catalyzed hydrolysis of long chain alkyl sulfates compared to those for non-micellar ethyl sulfate calculated from potentiometric data indicate that the rate acceleration accompanying micellization is primarily a consequence of a decrease in the enthalpy of activation rather than an increase in the entropy (Kurz, 1962). However, the activation energies for the acid-catalyzed hydrolysis of sodium dodecyl sulfate calculated from spectrophotometric data have been reported to be identical (Table 8) for micellar and non-micellar solutions, but the entropy of activation for the hydrolysis of the micellar sulfate was found to be 6 9 e.u. greater than that for the non-micellar system (Motsavage and Kostenbauder, 1963). This apparent discrepancy may be due to the choice of the non-micellar state as the basis of comparison, i.e. ethyl sulfate and non-micellar dodecyl sulfate, to temperature dependent errors in the values of the acid catalyzed rate constant determined potentiometrically, or to deviations in the rate constants from the Arrhenius equation. 

Xiancheng Z, Xiaonan C, Ziming Q, Qian W. The alkaline hydrolysis of ethyl acetate and ethyl propionate in single and mixed micellar solutions. J Disper Sci Technol 1996 17(3) 339-348. 

Many dmgs associate to form micelles in aqueous solution (see section 6.3) and several smdies have been reported of the effect of this self-association on stability. In micellar solutions of benzylpenicillin (500 000 units cm ) the apparent rate of the hydrogen-ion-catal-ysed degradation was increased twofold, but that of water- and hydroxide-ion-catalysed hydrolysis was decreased twofold to threefold. Consequently, the pH profile was shifted to higher pH values and the pH of minimum degradation was found to be 7.0 compared to 6.5 for monomeric solution (8000 units cm ). When compared at the respective pH-rate profile minima, micellar benzylpenicillin was reported to be 2.5 times as stable as the monomeric solutions under conditions of constant pH and ionic strength. 

From Fig. 5, we can see that samples prepared without template have a lower specific surface area than those obtained with a surfactant / zirconium molar ratio lower than 5. A beneficial effect of the template on the specific surface area is thus observed. All these results led us to propose the mechanism represented in Fig. 6. When- zirconium propoxide is added to the micellar solution, its rapid polymerization will disturb the micellar array. Furthermore, the large amount of propanol produced during the hydrolysis of Zr(OPr)4 will provoke a change of organisation of the surfactant molecules in solution. This variation in organisation of the surfactant molecules associated with the high... 

The second objective Is to examine the Influence of reversed micellar solution parameters, Including the Interaction of substrates with the surfactant Interface, on observed Initial rate kinetics. This Is of Interest because a number of reports have Indicated that enzymes In reversed micellar solutions exhibit an enhanced reactivity, or "super-activity" (7-9I. As a model system, the hydrolysis reactions of synthetic substrates of a-chymotrypsln were studied In a reversed micellar solution. Nuclear magnetic resonance was used to examine the Interactions between these substrates and the micellar environment. 

Methods. Z-Tyr-Gly-NH2 was synthesized from Z-Tyr-OMe and Gly-NH2 In reversed micellar solutions containing 0.15 M DTAB as the surfactant In a 1 5 volume mixture of n-hexanol and n-octane. Hexanol acts as a cosurfactant and aids In solubilizing the Z-Tyr-OMe. Initial rate kinetic studies employed the hydrolysis of the synthetic substrates GPANA and BTPNA In reversed micelles of CTAB In a... 

The rate of a-chymotrypsin-catalyzed hydrolysis as a function of overall GPANA concentration in CTAB reversed micelles and in aqueous solution are shown in Figure 5. It is apparent that the reaction rate in the reversed micellar solution is on the order of 50 times more rapid than in the aqueous system. Furthermore, in the reversed micellar system there is no indication of enzyme saturation as the reaction is first order in substrate concentration. As enzyme saturation kinetics are not observed, it is impossible to differentiate between the parameters kcat and Kg. Instead a second order bimolecular rate constant for both the micelle interior ( micelle) and for what is experimentally observed ( observed) is defined. 

Enantioselective hydrogenation of imines in aqueous systems generated much research interest, partly because of the practical value of the product amines, partly due to the unusual kinetic observations. Imines, such as N-benzylacetophenone-imine, are relatively stable to hydrolysis, and could be reduced either in a water/ ethyl acetate two-phase solvent mixture [93, 130, 131], or in a benzene-AOT-water reverse micellar solution (AOT = bis(2-ethylhexyl)sulfosuccinate). With catalysts, prepared from [Rh(cod)Cl]2 and the products of the stepwise sulfonation of... 

J. M. Patel and D. E. Wurster, Catalysis of carbaryl hydrolysis in micellar solutions of cetyltrimethylam-monium bromide, Pharm. Res. 8, 1155-1158 (1991). 

The first six-membered iodine(III) heterocycle, the cyclic tautomer of 2-iodosylphenylacetic acid, 221, was reported in 1963 by Leffler and coauthors [342]. This compound was synthesized by chlorination of 2-iodophenylacetic acid (220) followed by hydrolysis of the initially formed, unstable 2-(dichloroiodo)phenylacetic acid (Scheme 2.67). Compound 221 is stable at room temperature but decomposes in solution at 80-100 °C the proposed cyclic structure 221 is in agreement with its relatively low acidity (pXa = 7.45) [342]. 8-Iodosyl-l-naphthoic acid (222) was prepared by the peracetic oxidation of 8-iodo-1-naphthoic acid [343]. Anions of 2-iodosylphenylacetic acid (221) [328] and 222 [343] have a moderate reactivity in the cleavage of phosphate esters in aqueous micellar solution. The chiral, enantiomerically pure substituted 2-iodosylphenylacetic acid derivatives 223 and 224 were synthesized from the corresponding aryl iodides by oxidation with dimethyldioxirane [344]. 

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