Epoxidation of styrenes by hydrogen peroxide as catalyzed by methylrhenium trioxide

Article abstract of DOI:10.1021/ja00141a016

Methylrhenium trioxide, CH₃ReO₃, catalyzes the oxidation of styrenes by hydrogen peroxide. Kinetic studies by three methods were carried out in acidic CH₃CN/H₂O (1:1 v/v) solutions. The catalytically-active species are the mono-peroxide, CH₃Re(O)₂(C₂), A, and the bis-peroxide, CH₃Re(O)(O₂)₂, B, which epoxidize a given styrene at a similar rate. The rate constants are relatively insensitive to steric hindrance, but increase with the nucleophilicity of the styrene, electron-donating groups on the olefinic carbons or on the aromatic ring enhancing the rate. The rate constants for meta- and para-substituted styrenes follow a linear Hammett relationship; correlation with σ⁺ gave ρ + -0.93 ± 0.05. In CD₃CN, epoxides were observed by ¹H NMR spectroscopy. ais-β-Methylstyrene and transβ-methylstyrene led to the cis epoxide and the trans epoxide, respectively. In acidic CH₃CN/H₂O, the major products were 1,2-diols. In some cases C-C bond cleavage products were also observed, the extreme case being β-methoxystyrene where the C-C bond was completely cleaved to yield benzaldehyde, formaldehyde, and methanol.