Hydrogenation of biphenyl using a hydrogen storage alloy as a hydrogenation reagent

A detailed investigation of the hydrogenation reaction of biphenyl with MmNi(3.5)Co(0.7)Al(0.8)H(4.2) [Mm: mixture of La, Ce, Pr, and Nd (30:52:5:13 wt ratio)] to give either cyclohexylbenzene or bicyclohexyl was performed. Time profiles of the amounts of hydrogen evolved from the alloy and that introduced into biphenyl during the reaction were measured; it was suggested that the hydrogen absorbed by the alloy could predominantly react with the substrate, and the hydrogen released into the gas phase played only a minor role in the reaction. The deuteration of biphenyl with the deuterated alloy, MmNi(3.5)Co(0.7)Al(0.8)D(3.5), was also examined; a GC-MS analysis of the reaction mixture indicated that a H-D exchange between the hydrogen in the substrate and the deuterium in the alloy took place as a parallel reaction to hydrogenation of the aromatic rings, and, as a result, the product cyclohexylbenzene appeared to contain 3-9 deuterium atoms.