TRANSFORMATION OF CIS-2,3-DIMETHYLOXIRANES AND TRANS-2,3-DIMETHYLOXIRANES ON A PD SIO2 CATALYST/

The transformation of cis- and trans-2,3-dimethyloxiranes on a Pd/SiO2 catalyst, leading to the formation of 2-butanone and 2-butanol, was s tudied in hydrogen and deuterium atmosphere. The effect of hydrogen pr essure (1.3-100 kPa) and temperature (323-423 K) on the reaction rate was also measured. The transformation of the two stereoisomers involve s different mechanisms. In the case of the cis-isomer, hydrogen partic ipates in the cleavage of the C-O bond and different surface species b elong to the two products. In the case of the trans-isomer, ring openi ng by hydrogen (the formation of 2-butanol) is less significant and th e main reaction is intramolecular hydrogen migration leading to the fo rmation of 2-butanone. Considering the geometry of the adsorbed specie s, cis-2,3-dimethyloxirane is most probably adsorbed on the surface of the Pd catalyst in a planar manner, while the adsorption of the trans -isomer is intermediate between edgewise and planar adsorption mode. ( C) 1997 Academic Press.