The main products of hexane H isomerization on HZSM-5 at 1608C in liquid phase are the isomers 2-methylpentane Ž . Ž . 2MP and 3-methylpentane 3MP , accompanied by cracking and disproportionation products, but no alkenes. 2MP and Ž . 3MP are not formed by a simple carbocationic isomerization of H, because the 2MPr3MP ratio, 6-7 r1 is higher than the equilibrium ratio of 2.1 and does not change with conversion between 1 and 10%. The same observation applies to the small Ž . amounts of 2,3-dimethylbutane formed. Methylcyclopentane MCP has a minor accelerating effect on the conversion of H Ž .
Ž . only at ratios 1:1. No hydride transfer catalysis operates. At the same ratio 1:1 , cyclopentane CP has a somewhat greater effect than MCP on the conversion of H. The redistribution of the label in the conversion of H-u-d containing 4-5% MCP 4.3 and of H containing 5% MCP-1-d showed that the products were formed from alkenes, which are the major intermediates of the reaction, even though none of them is found in the products desorbed. Each alkene exchanges hydrogen with the catalyst Ž . several times before being desorbed. The direct HrD exchange between the alkene or its mechanistic equivalent and the alkane, if it occurs, is less important. Thus, the usual mechanistic representation for alkane conversion, borrowed from reactions in superacid solutions, does not apply to the reaction with the zeolite catalyst.