Substituted phenyl benzoates

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. ... 

Table 4 Relative Quantum Yield in the PFR of Several 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... 

In a reaction similar to that shown above for aliphatic esters [Eq. (13)], it has been reported that aromatic esters may also be reduced to the corresponding diketone provided the reduction is carried out using a cadmium cathode and magnesium anode [60]. Earlier work demonstrated that phenyl benzoate anion radical cleaves to form phenolate in good yield and presumably benzoyl radical, which leads to dibenzoyl [16]. Nitro-substituted phenyl benzoates are similarly cleaved on reduction to give phenolate [62,63]. 

J.F. Kirsch et al.. Multiple Structure-Reactivity Correlations. The Alkaline Hydrolyses of Acyl- and Aryl-Substituted Phenyl Benzoates, J. Org. Chem., 1968, 33, 127. 

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... 

The reactions of phenyl Y-phenyl carbonates (12) with Z-phenoxides in (4 1) H2O DMSO at 278 K were found to be concerted, in contrast to previously reported studies with Y-substituted phenyl benzoates (13) where the reactions were stepwise (and about two orders of magnitude slower). 

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 Hammett p-value for cleavage of the exocyclic bond of 2-methoxy-2-substituted-phenyl-l,3-dioxolans (—1.58 + 0.06) is a little larger than that for cleavage of the endocyclic C— bond of 2-hydroxy-2-substituted-phenyl-l,3-dioxolans (—1.24 + 0.04) (Table 9) (Chiang et al., 1983). A direct comparison between the p-values for C—OMe bond cleavage of trimethyl orthobenzoates and dimethyl hemiorthobenzoates is not possible at present since they have not been measured in the same solvent. However, that based on H+ for the breakdown of the hemiorthobenzoates (— 1.58) is less than that based on the equilibrium constants for their conversion into methyl benzoates and methanol which is —1.9 (derived from the equilibrium constants for formation of the hemiorthobenzoates, McClelland and Patel, 1981b). This implies that the development of positive charge in the transition state is less than in the final product, the ester. 

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... 

An oxygen substituent directly attached to the ring strongly activates it toward electrophilic aromatic substitution. Phenyl acetate is much more reactive than benzene or methyl benzoate. 

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