The role of amide-type solvents, particularly DMF, was studied in the epoxidation of styrene over Co2+-exchanged hydroxyapatite. Even under relatively mild conditions, DMF is autoxidized with molecular oxygen to N-(hydroperoxymethyl)-N-methylformamide, which acts as an oxygen-transfer agent in the epoxidation of styrene, thereby producing N-formyl-N-methylformamide in considerable amounts. In addition, the drastic effect of reactor operation mode (open and closed systems) on the catalyst performance reveals the formation of another, volatile byproduct from DMF that inhibits the reaction in closed reactors (autoclaves). (c) 2006 Elsevier Inc. All rights reserved.