KINETICS OF THE ACID-CATALYZED REACTION OF CYCLOHEXENE WITH HYDROGEN-PEROXIDE - MECHANISTIC ASPECTS OF THE IN-SITU ACTIVATION OF H2O2

The kinetics of the reaction of cyclohexene (CH) with an excess of H2O 2 in acetonitrile (AN) at 293 K was studied at variable concentrations of H2O2 (1.7-13 M), water (1.6-13 M), acids HX (0.2-1.4 M), and salts NaX (0-1.7 M), with HX = HClO4, H2SO4, HNO3, HPF6, p-toluenesulfonic acid (TSAH), acetic acid (AH), trifluoroacetic acid (TFAH), and benzen eseleninic acid (BSAH). The solvent polarity parameter E-T(30) of AN/w ater mixtures was determined. The oxidation of CH by H2O2, monitored b y gas chromatography, was found to be acid-catalysed. The detailed inv estigation of the systems CH/HClO4/AN and CH/TSAH/AN showed that the r eaction is first-order in CH according to [CH] = [CH](0) exp(-k(exp).t ). At [H2O2] less than or equal to 3 M, the experimental rate constant k(exp) could be approximated by k(exp) = k(0)[H2O2] + k.[H2O2].[HX](2 ).[X-](tot).[H2O](-2), with k(0) = (0.93 +/- 0.7).10(-5)M(-1)s(-1) and k = (9.65 +/- 0.20).10(-3)M(-2)s(-1) for HClO4 and k = (5.96 +/- 0.10 ).10(-3)M(-2)s(-1) for TSAH ([X-](tot) = [NaX] + [HX]). GC analysis of the HClO4-catalysed reaction showed that trans-cyclohexane-1,2-diol ( CHD) is a reaction product. The order of catalytic activity of the var ious acids HX, as derived from the size of k(exp) obtained under stand ard conditions, was found to be: AH much less than HNO3 < TFAH < TSAH < HClO4 < HPF6 < H2SO4 < BSAH. A mechanistic interpretation is present ed and the synthetic potential of the acid-catalysed oxidation of olef ins by H2O2 is discussed.