Selective epoxidation of (+)-limonene employing methyltrioxorhenium as catalyst

This report presents a study of the epoxidation of limonene employing methyltrioxorhenium (MTO) as catalyst. The influence of base ligands, namely t-butylpyridine, 4,4'-dimethyl-2,2'-bipyridine and pyrazole on the catalytic activity was investigated. The choice of the oxidant (H2O2 in water or H2O2 stabilized by urea) was also examined. The effect of the solvent has been studied in order to determine optimal conditions for the epoxidation of (+)-limonene. The best result was obtained when a molar ratio (+)-limonene:MTO:H2O2:t-butylpyridine of 100:0.5:10:150 was used at 25 degrees C in dichloromethane. 1,2-Limonene oxide was formed with 77% yield and 96% selectivity after 1 h with a TOF of ca. 900 h(-1). (C) 2012 Published by Elsevier B.V.