RING-OPENING HYDROGENATION REACTIONS OF MONOALKYL-SUBSTITUTED CYCLOBUTANES OVER NI SIO2 CATALYST/

The hydrogenative ring-opening reactions of methyl- and propylcyclobut ane were studied over Ni/SiO2 catalyst in wide temperature and hydroge n pressure ranges. Firstly, the temperature dependence of ring opening was determined and maximum curves were observed for both reactants. O n the basis of the temperature dependence curves, various temperatures were selected for hydrogen pressure studies. At both 523 and 573 K, o nly hydrogenative ring opening occurred, and the ring opened mostly in the sterically less hindered direction in the case of methylcyclobuta ne over clean as well as working catalysts. However, for propylcyclobu tane the selectivity was close to statistical or opposite to that for methylcyclobutane, especially at lower hydrogen pressures over the ini tial catalyst. At the lowest temperature at which ring opening occurre d at all, exclusive heptane formation (ring opening in the more hinder ed direction) was observed. The hydrogen pressure dependence curves ov er the initial and working catalysts were used to draw mechanistic inf erences concerning the ring-opening reactions. (C) 1995 Academic Press , Inc.