Linear free energy relationship in naphthalene system. Kinetics of oxidation of 4-substituted 1-naphthyl methyl sulphides with peroxoanions

Abstract

The kinetics of the oxidation of several 4-substituted 1-naphthyl methyl sulphides and methyl 2-naphthyl sulphide with potassium peroxodisulphate and potassium peroxodiphosphate have been studied in 70% acetic acid–30% water (v/v) mixture. The results are in accord with rate-limiting electrophilic attack of the oxidants on the sulphide. The applicability of the Hammett equation to the rate data employing naphthalene and benzene substituent constants has been critically examined. Excellent results emerge in the correlation of rate constants with σ_p⁺ constants in both oxidations. The diminution in the electron-withdrawing ability of the acetyl group present in the 4-position of the naphthyl ring has been attributed to the steric inhibition of resonance of the acetyl group by the proximate peri-hydrogen. The reactivity order of methyl phenyl, methyl 1-naphthyl, and methyl 2-naphthyl sulphides (2-C₁₀H₇SMe > C₆H₅SMe > 1-C₁₀H₇SMe) found in these oxidations has been explained on the basis of polar and steric effects.