Separation of polar and steric effects in the oxidation of <em>ortho</em>-substituted benzaldehydes by ethyl chlorocarbamate

Abstract

Kinetics of oxidation of twelve <em>ortho</em>-substituted benzaldehydes by ethyl chlorocarbamate (ECC) to the corresponding benzoic acids have been studied. The reaction is first order each in [aldehyde],[ECC] and [H⁺]. Addition of ethyl carbamate has no effect on the reaction rate. (EtOC(OH)NHCl)⁺ has been postulated as the reactive oxidizing species. The correlation of rates with single substituent parameter equations is poor. The correlation with Charton's equation of inductive, resonance and steric parameters is satisfactory. However, excellent correlations are obtained, when Charton's steric parameter is used along with Taft's or and &sigma;substituent constants. The polar reaction constants have negative values. The reaction is subject to steric hindrance by the <em>ortho-</em> substituents. Mechanistic aspects are discussed.