The initial stages of the liquid-phase oxidation of 1-octene and cyclooctene by molecular oxygen in the presence of transition metal borides and MoO3 are investigated. The investigated compounds influence the oxidation process only in the presence of hydroperoxide in the reaction system. The most active in this process is vanadium diboride. The molybdenum compounds activate the oxidation process of 1-octene and inhibit the oxidation of cyclooctene. (c) 2006 Elsevier B.V. All rights reserved.