Mechanistic Studies on the Oxidation of Naphthalenes and Methylbenzenes to Quinones with H₂O₂ in the Presence of Pd(II) Catalysts

Abstract

The oxidation of naphthalenes and methylbenzenes to quinones with aqueous 60% hydrogen peroxide in the presence of a 0.24% Pd(II)-sulfonated polystyrene-type resin catalyst was studied. The presence of electron-donating substituents on carbon-2 of naphthalenes accelerated the oxidation. A reaction path by way of hydroxylated intermediates to the quinones is proposed.By using the MINDO/3 method, quantum chemical indices such as the superdelocalizability for electrophilic species (S^E_r) and for radical species (S^R_r), and the net charge (Q_r) of naphthalenes, methylbenzenes, and naphthols were calculated. The activity in the above reaction could be explained in terms of bothe Q_r and S^E_r. The decrease of the selectivity was correlated with side reactions by radical species attacking the sites of largest S^R_r.