Open AccessOxygenation of Substituted (Phenylthio)acetic Acids by Acidic Bromate: A Kinetic and Mechanistic Study and Validity of Linear Free-Energy Relationships
Author(s) -
B. Suresh Babu,
Padma Sunitha Manjari,
Ch. Sanjeeva Reddy
Publication year - 2022
Publication title -
asian journal of chemistry/asian journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.145
H-Index - 34
eISSN - 0975-427X
pISSN - 0970-7077
DOI - 10.14233/ajchem.2022.23509
Subject(s) - chemistry , bromate , ionic strength , reaction rate constant , reactivity (psychology) , free energy relationship , acetic acid , reaction mechanism , order of reaction , substrate (aquarium) , substituent , reaction rate , kinetics , moiety , activation energy , inorganic chemistry , medicinal chemistry , stereochemistry , organic chemistry , catalysis , aqueous solution , bromide , medicine , physics , alternative medicine , oceanography , quantum mechanics , pathology , geology
Kinetics and mechanistic investigations on the oxygenation of (phenylthio)acetic acid and its substituted compounds using bromate inacid medium have been carried out. The reaction exhibited first-order in [bromate], 1.6 order in [H2SO4], less than one order in [substrate]and displayed solvent isotopic effect of 1.75 (kD2O/kH2O). The reaction rate is not affected by ionic strength variation, however, enhancedby lowering dielectric constant of the medium. Structural modifications in the aryl moiety of the substrate resulted in a change ofreactivity, where electron-seeking substituents decreased the reaction rate. The order of reactivity among the studied substrates is paramethoxy> para-methyl > -H > para-chloro ≈ para-bromo > para-nitro(phenylthio)acetic acid and showed an excellent correlationbetween rate constant and the Hammett substituent constant (σ value). The reaction constant (ρ) value is negative (-1.37 at 303 K) anddecreased by increase in the reaction temperature. Proposed mechanism involves decomposition of the complex formed between acidbromate and the substrate. Based on the proposed mechanism, an appropriate rate law has been derived and tested for its validity.Activation parameters and isokinetic temperature have been evaluated and discussed. The validity of linear free-energy relationships havebeen discussed thoroughly.