Substituted phenyl benzoates hydrolysis

The influence of temperature on the ortho effect has been evaluated in the alkaline hydrolysis in aqueous DMSO solutions of ortho-, meta- and para-substituted phenyl benzoates (26). The alcoholysis of phthalic anhydride (27) to monoalkyl phthalates (28) occurs through an A-2 mechanism via rate-determining attack of the alcohol on a carbonyl carbon of the anhydride (Scheme 4). Evidence adduced for this proposal included highly negative A 5 values and a p value of 4-2.1. In the same study, titanium tetra-n-butoxide and tri-n-butyltin ethanoxide were shown to act as effective catalysts of the half-ester formation from (27), the mechanism involving alkoxy ligand exchange at the metal as an initial step. ... 

Complexation with caffeine and theophylline-7-acetate depresses the rate of alkaline hydrolysis of substituted phenyl benzoates and is consistent with the formation of molecular complexes with 1 1 stoichiometry between the hosts and esters stacking of the xanthines is excluded as an explanation in the range of concentrations studied. Inhibition of hydrolysis is attributed to repulsion of the hydroxide ion from the host-ester complex by the extra hydrophobicity engendered by the xanthine host, as well as by the weaker binding of the transition state to the host compared with that in the host-ester complex. ... 

Alkaline Hydrolysis Rates of Acyl- and Aryl-Substituted Phenyl Benzoates... 

Kirsch, J. F., W. Clevell, and A. Simon, Multiple structure-reactivity correlations. The alkaline hydrolysis of acyl- and aryl-substituted phenyl benzoates , J. Org. Chem., 33,127-132 (1968). 

Generally, the rate of alkaline hydrolysis of a series of substituted phenyl benzoates was decreased in the presence of 0.5 m BiuNBr, the retardation being larger for esters with electron-donating substituents. The data from 22 esters were fitted to a multiparameter equation, the results showing that solvent electrophilicity was the main factor responsible for changes in the ortho, para and meta polar substituent effects with medium.15... 

The influence of temperature on the ortho effect has been evaluated in the alkaline hydrolysis in aqueous DMSO solutions of ortho-, meta- and para-substituted phenyl benzoates (26). The alcoholysis of phthalic anhydride (27) to monoalkyl phthalates... 

Pirinccioglu, N., Williams, A. Studies of reactions within molecular complexes alkaline hydrolysis of substituted phenyl benzoates in the presence of xanthines. J. Chem. Soc. Perkin Trans. 2. 1998, 37 0. 

Rate-decreasing effects of the concentration of caffeine and theophylline-7-acetate (the additives) have been observed for the alkahne hydrolysis phenyl and substituted phenyl benzoates. ... 

Perhaps the most informative studies (Anvia and Bowden, 1990) of leaving groups are of the alkaline hydrolysis of 3-substituted phenyl 2-acetyl- and 2-benzoyl-benzoates [20], The Hammett reaction constants p are ca. 0.50 and 1.48 for the 2-acetyl and 2-benzoyl esters respectively, as. shown in Table 2. These were compared with various limiting models in a similar manner to the effective charge model (Williams, 1984,1992). This comparison indicates that all simple phenyl esters of the latter types hydrolyse by a mechanism... 

Hubbard and Kirsch (1972) have recently proposed that histidine may act as a nucleophile in a-chymotrypsin acylation reactions of esters having a good leaving group (jO-nitrophenol). This suggestion was based on a similarity in p-value for acylation by p-substituted nitrophenyl and dinitrophenyl benzoates and nucleophilic attack on these compounds by imidazole, in contrast with less positive p-values for hydroxide ion catalysis. Hammett p-values for hydrolysis of substituted phenyl esters are given in Table 6 and show little apparent trend. The values for hydroxide ion and alcoholate ions are... 

The rates and mechanisms of hydrolysis and transesterification of phenyl benzoate in aqueous ethanolic KOH solution were determined by non-linear least-squares regression.4 Kinetic studies of the transesterification of a series of 4-nitrophenyl 3- and 4-substituted benzoates by 4-chlorophenol in DMF in the presence of potassium carbonate at various temperatures were reported.5... 

The most widely applied of these relationships is the Hammett equation which relates rates and equilibria for many reactions of compounds containing substituted phenyl groups. It was noted in the 1930s that there is a relationship between the acid strengths of substituted benzoic acids and the rates of many other chemical reactions, for instance, the rates of hydrolysis of substituted ethyl benzoates. The correlation is illustrated graphically in Fig. 4.2, which shows log k/ko, where fco is the rate constant for hydrolysis of ethyl benzoate and k is the rate constant for the... 

Slightly smaller p values are obtained with more polar solvents, where the medium is able to stabilize the transition state more effectively, and thus the response to the electronic effects of substituents is less critical. For the alkaline hydrolysis of the phenyl esters of substituted benzoates in 33% aqueous acetonitrile Kirsch et al.235 find p = 1.98. The value is not significantly different for more or less reactive leaving groups under the same conditions... 

Exercise 26-40 Explain why p for ionization of benzoic acids is larger than p for phenylethanoic acids. Estimate a value ofp for the ionization of substituted 4-phenyl-butanoic acids. Why should we expect the value of p for alkaline hydrolysis of ethyl benzoates to be larger than for acid ionization and to have the same sign ... 

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