Experimental Investigation of the Primary and Secondary Deuterium Kinetic Isotope Effects for Epoxidation of Alkenes and Ethylene with m-Chloroperoxybenzoic Acid
- 17 December 1998
- journal article
- research article
- Published by American Chemical Society (ACS) in The Journal of Organic Chemistry
- Vol. 64 (1) , 196-201
- https://doi.org/10.1021/jo981652x
Abstract
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, kOH/kOD, is 1.05 ± 0.05 in all cases. 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.Keywords
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