Nickel-catalyzed amination of 1,3-propanediols differently substituted at C2-position: influence of reactant structure on diamine production

The heterogeneously catalyzed amination of 2,2'-dimethyl-1,3-propanediol, 2-methyl-1,3-propanediol and 1,3-propanediol over a commercial silica supported Ni catalyst has been studied in a continuous fixed-bed reactor using supercritical ammonia at 135 bar in the temperature range 180-235 degrees C. The amination of 2,2'-dimethyl-1,3-propanediol afforded as main products the corresponding diamine (70%) and the amino alcohol (7%) resulting in a cumulative selectivity of 77% at 75% conversion. The application of supercritical ammonia and an ammonia excess favoured the desired reactions. At temperatures > 210 degrees C the amination selectivity decreased due to the formation of iso-butylamine. The amination of the structurally related 2-methyl-1,3-propanediol and 1,3-propanediol under similar reaction conditions afforded much lower amination selectivities (< 20%) mainly due to degradation products formed by water elimination. Direct elimination of water is not possible for 2,2'-dimethyl-1,3-propanediol. (C) 1999 Elsevier Science B.V. All rights reserved.