The hydrogenation of alkadienes. Part V. The hydrogenation of trans- and of cis-penta-1,3-diene catalysed by cobalt, nickel, copper, palladium, and platinum

Abstract

The gas-phase hydrogenation of trans-penta-1,3-diene and of cis-penta-1,3-diene has been investigated with use of alumina-supported cobalt (99–156 °C), nickel (50–86 °C), copper (72–154 °C), palladium (20 °C), and platinum (94 °C) as catalysts. Reactant isomerisation was very fast over copper and over one form of cobalt, but it was relative slow over the other catalysts. All three isomers of n-pentene were formed over each catalyst; pentene yields were small of zero. Some catalysts exhibited a marked selectivity of the formation of one particular pentene isomer; e.g., 90% yields of trans-pent-2-ene were recorded in some cobalt-catalysed reactions, 70% yields of pent-1-ene were observed in reactions over copper.

The isomeric compositions of the pentene are compared with expectation based on the mechanisms of buta-1,3-diene hydrogenation over these metals developed in parts III and IV. The relative importance of 1,2-, 3,4-, and 1,4-addition of hydrogen to penta-1,3-diene is determined. 3,4-Addition is more important than 1,2-addition over all catalysts except one form of cobalt. The fraction of the product formed by 1,4-addition in penta-1,3-diene hydrogenation and in buta-1,3-diene hydrogenation is similar.