THE KINETICS, KINETIC ISOTOPE EFFECTS, AND SUBSTRATE SELECTIVITY OF ALKYLBENZENE OXIDATION IN PERMANGANATE AQUEOUS-SOLUTIONS .1. REACTIONS WITH MNO4(-) ANION

The kinetic distribution method is used to study the kinetics of benzene and alkylbenzene oxidation in aqueous solutions of permanganate, with the MnO4- anion being the active reagent, at 70-degrees-C and pH 5 - 7. The kinetic equation -d[ArH]/dtau = k[ArH][MnO4-] is valid. The following kinetic isotope effects are measured: C6H6/C6D6 = 1.0; C6H5CH3/C6D5CH3 = 1.0; 1,3-(CH3)2C6H4/1,3-(CD3)2C6D4 = 11.3, and 1,4-(CH3)2C6D4/1,4-(CD3)2C6D4 = 16.8. For the C6H5CH3/CfD5CD couple, k(H)/k(D) = 13.6; E(a)D - E(a)H = 9.9 kJ/mol, and A(H)/A(D) = 0.40. The reaction rate increases in the series: PhH < PhC(CH3)3 < PhCH3 < PhCH2CH3 less-than-or-equal-to PhCH(CH3)2 and, in the case of methylbenzenes, it grows with the increase in the number of methyl substituents. The interaction of MnO4- with arenes studied is found to occur via two parallel routes: through attack at the C-H bond in alkyl substituents (in the case of iso-Pr-, Et-, Me-, and polymethylbenzenes) and through attack at the ring (in the case of benzene and, evidently, tert-butylbenzene). The reaction rates of these routes are estimated.