Modulating Catalytic Selectivity by Base Addition in Aqueous Reductive Amination of 1,6-Hexanediol Using Ru/C

Efficient base-modulated product selectivity in the aqueous-phase Ru/C-catalyzed reductive amination of 1,6-hexanediol (HDO) was reported by performing the reaction at mild conditions (463 K, 25 bar H2). High selectivity of amines could be controlled by the addition of different bases; for example, Cs2CO3 addition gave a high yield of 6-amino-1-hexanol (AH, 26%). However, the addition of Ba(OH)2 resulted in the formation of high yield of secondary amination products, hexamethylenediamine (HMDA, 34%) and azepane (26%). The hydroxide base, especially Ba(OH)2, aids in the initial conversion of HDO to AH by significantly decreasing the apparent activation energy from 68 to 48 kJ mol–1. A closer analysis of the formation of secondary products (azepane and HMDA) revealed a faster reaction between NH3 and the carbonyl-containing intermediate by the addition of Ba(OH)2 into the reaction solution.