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Kinetics of oxidation of phenoxyacetic acids by pyridinium hydrobromide perbromide
Author(s) -
Karunakaran K.,
Elango K. P.
Publication year - 1996
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/(sici)1099-1395(199602)9:2<105::aid-poc758>3.0.co;2-a
Subject(s) - chemistry , hydrobromide , pyridinium , kinetics , substituent , reaction rate constant , hydride , acetic acid , aqueous solution , decomposition , medicinal chemistry , inorganic chemistry , organic chemistry , hydrogen , physics , quantum mechanics
The oxidation of several monosubstituted phenoxyacetic acids by pyridinium hydrobromide perbromide (PHPB) was studied in aqueous acetic acid. The reaction is first order with respect to PHPB. Michaelis‐Menten‐type kinetics are observed with respect to phenoxyacetic acids. The oxidation of [2,2‐ 2 H 2 ]phenoxyacetic acid exhibits a substantial kinetic isotopic effect. The effect of solvent composition indicates that the transition state is more polar than the reactants. The formation constants of the intermediate phenoxyacetic acid‐PHPB complexes and the rates of their decomposition were determined at different temperatures. The rates of oxidation of para ‐ and meta ‐substituted phenoxyacetic acids were correlated with Hammett's substituent constants. The ρ value is −2·59 at 35°C. The rates of oxidation of ortho ‐substituted compounds are correlated with Charton's triparametric equation. A mechanism involving transfer of a hydride ion from the substrate to the oxidant is proposed.