Solvent effect and proton inventory in the hydrolysis of p-methylphenyl trichloroacetate

Hydrolysis of p‐methylphenyl trichloroacetate in water–acetonitrile mixtures was studied as a function of water concentration in the range 5.5–55.5 M. The proton inventory technique, in H2O–D2O mixtures, shows, for a value of D atom fraction in the solvent n = 0.5, deviations from the expected value...

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Bibliographic Details
Published in:Journal of physical organic chemistry 2006-02, Vol.19 (2), p.143-147
Main Authors: Frasson, Cléa M. L., Brandão, Tiago A. S., Zucco, César, Nome, Faruk
Format: Article
Language:English
Subjects:
hydrolysis
kinetics
p-methylphenyl trichloroacetate
proton inventory
transition state
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Summary:Hydrolysis of p‐methylphenyl trichloroacetate in water–acetonitrile mixtures was studied as a function of water concentration in the range 5.5–55.5 M. The proton inventory technique, in H2O–D2O mixtures, shows, for a value of D atom fraction in the solvent n = 0.5, deviations from the expected value (for a reaction with one proton being transferred) of 7.5 and 12.3%, for experiments in the presence of 16.6 and 33.3 M L2O (L = H or D), respectively. Theoretical treatment of the data obtained at [L2O] = 16.6 M using the Gross–Butler equation are consistent with a cyclic transition‐state structure with three protons involved. Conversely, similar experiments in the presence of [L2O] = 33.3 M show that multiple water molecules are involved in the transition state of the reaction. Copyright © 2006 John Wiley & Sons, Ltd. Hydrolysis of p‐methylphenyl trichloroacetate in water–acetonitrile mixtures shows that the structure of the transition state depends on solvent composition. Two transition‐state structures may be drawn for this ester hydrolysis, one with three water molecules and the other with multiple water molecules involved in the transition state of the reaction.
ISSN:0894-3230
1099-1395
DOI:10.1002/poc.1009