Catalytic Decomposition of t-Butyl Hydroperoxide over Boron Trioxide under Vacuum

Abstract

The conversion rate and yields of products in the decomposition of t-butyl hydroperoxide over boron trioxide under vacuum have been studied over the temperature range of 200 to 310 C, in order to clarify the mechanism of boric acid catalyzed autoxidation of tertiary aliphatic hydrocarbons. A novel procedure has been devised where t-butyl hydroperoxide was transfered from trap to trap through boron trioxide under vacuum (Fig.1). Under these conditions, primary products were transfered immediately from the catalyst surface to a trap, so that the secondary reactions of primary products could be suppressed and the boron trioxide was kept at its initial state throughout the reaction. Boron trioxide was quite effective in the decomposition of t-butyl hydroperoxide, and the major products were isobutene, water, acetone, and methanol (Fig.2). Isobutene was supposed to be produced by the thermal decomposition of t-butyl metaborate formed directly from the interaction of t-butyl hydroperoxide and boron trioxide. Therefore, little t-butanol was formed under the reaction conditions employed. Boron trioxide was also effective as a Lewis acid to give equimolar amount of acetone and methanol. The thermal decomposition of t-butyl hydroperoxide was completely suppressed by the boron trioxide below 250 C (Table 1, Fig.2). At higher temperature than 280 C, however, both the rate of esterification and acid-catalyzed decomposition decreased rapidly and that of thermal decomposition increased. A comprehensive mechanism has been proposed.