Selective and Waste-Free Isolation of High Purity Primary Amines from Amine and Reaction Mixtures by Selective Ammonium Carbamate Crystallization.

The isolation of primary amines from secondary and tertiary amines presents a significant challenge in their sustainable production, and existing strategies are either multistep, energy-demanding, or waste-intensive. We present an efficient process that utilizes the distinct solubility profiles of ammonium carbamate species formed through waste-free and reversible salt formation of primary amines and CO2. This selective ammonium carbamate crystallization (SACC) enables the purification of challenging amine mixtures. Starting from 35% initial primary amine purity, SACC achieves very high isolated yields of up to 94% and excellent purities exceeding 99%. Additionally, the separation of secondary from tertiary amines with 86% yield and 91% purity and the fractional crystallization of primary, secondary, and tertiary amines with yields ranging from 83% to 94% and purities from 90% to > 99% were successfully achieved. SACC was also successfully employed in the alcohol amination with ammonia/ammonia alkylation to isolate primary amines with high yields of up to 84% and excellent purities exceeding 99% using a homogeneous Ru/xantphos catalyst system. The observed average metal and phosphorus losses were at a minimal level of < 1 wt% of the initial amounts. Based on this high catalyst retention, the additional potential of SACC for recycling the homogeneous catalyst was demonstrated.