Experimental investigation of the primary and secondary deuterium kinetic isotope effects for epoxidation of alkenes and ethylene with m- chloroperoxybenzoic acid

Article abstract of DOI:10.1021/jo981652x

The secondary deuterium kinetic isotope effect (DKIE) for the epoxidation of ethylene and d₄-ethylene by m-chloroperoxybenzoic acid (MCPBA) is determined to be 0.83, or 0.95/α-H. The second-order rate constants for MCPBA and MCPBA-O-D epoxidation of a variety of alkenes that differ in the steric access to the double bond (anti-sesquinorbornene (2), tetramethylethylene (3), adamantylideneadamantane (4), 7-norbornylidene-7'- norbornane (5), bis(bicyclo[3.3.1.]non-9-ylidene) (6), bis(homoadamantane) (7), cyclohexene (8), 1-octene (9), trans-5-decene (10) and 2-methyl-1- pentene (11)) have been determined in dichloroethane at 25°C using UV kinetics, and the primary DKIE, k(OH)/k(OD), is 1.05 ± 0.05 in all eases. By comparison of the rates of epoxidation of sterically encumbered alkenes, it is suggested that the spiro epoxidation transition state is favored over a planar one. The products of the epoxidation of anti-sesquinorbornene are determined to be the epoxide and a cis-hydroxy ester, the latter most probably being formed by acid-catalyzed ring opening of the epoxide by in situ-produced m-chlorobenzoic acid produced in situ to form a β-hydroxy carbocation and carboxylate ion pair that collapses to product.