Kinetics of the Acid‐Catalysed Reaction of Cyclohexene with Hydrogen Peroxide: Mechanistic Aspects of the “In Situ” Activation of H 2 O 2

The kinetics of the reaction of cyclohexene (CH) with an excess of H 2 O 2 in acetonitrile (AN) at 293 K was studied at variable concentrations of H 2 O 2 (1.7–13 M ), water (1.6–13 M ), acids HX (0.2–1.4 M ), and salts NaX (0–1.7 M ), with HXHClO 4 , H 2 SO 4 , HNO 3 , HPF 6 , p ‐toluenesulfonic acid (TSAH), acetic acid (AH), trifluoroacetic acid (TFAH), and benzeneseleninic acid (BSAH). The solvent polarity parameter E T ( 30 ) of AN/water mixtures was determined. The oxidation of CH by H 2 O 2 , monitored by gas chromatography, was found to be acid‐catalysed. The detailed investigation of the systems CH/HClO 4 /AN and CH/TSAH/AN showed that the reaction is first‐order in CH according to [CH][CH] 0 exp(– k exp · t ). At [H 2 O 2 ] ⩽ 3 M , the experimental rate constant k exp could be approximated by k exp = k 0 [H 2 O 2 ] + k ·[H 2 O 2 ]·[HX] 2 · [X − ] tot ·[H 2 O] −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 HClO 4 and k = (5.96 ± 0.10)·10 −3 M −2 s −1 for TSAH ([X − ] tot = [NaX] + [HX]). GC analysis of the HClO 4 ‐catalysed reaction showed that trans ‐cyclohexane‐1,2‐diol (CHD) is a reaction product. The order of catalytic activity of the various acids HX, as derived from the size of k exp obtained under standard conditions, was found to be: AH ≪ HNO 3 < TFAH < TSAH < HClO 4 < HPF 6 < H 2 SO 4 < BSAH. A mechanistic interpretation is presented and the synthetic potential of the acid‐catalysed oxidation of olefins by H 2 O 2 is discussed.