Selective Catalytic Synthesis of Mixed Alkylamines and Polyfunctional Amines
Lower alkylamines are typically produced by reaction of an alcohol with ammonia or an amine in the presence of either acidic or supported metal catalysts. However, this technology is not suitable for the synthesis of unsymmetric (mixed) amines and polyfunctional amines. In the latter instances, selectivities to desired products are often low, owing to fast equilibration of the products of the initial alkylation reaction. To circumvent this problem, mixed amines and polyfunctional amines are currently prepared by alternate, more expensive routes, such as reductive amination of carbonyl compounds or amination of alkyl polyhalides. In this chapter, we describe a new approach to amine synthesis. A catalyst system has been developed which does not catalyze product equilibration under the conditions of product formation. Depending on the structure of the starting amine and alcohol components, group IIA and/or group IIIB metal acid phosphates selectivity catalyze amine formation. Specifically, selective syntheses of mixed alkyl amines have been achieved by amine-alcohol reactions over strontium hydrogen phosphate. In addition, strontium hydrogen 220phosphate catalyzes formation of more complex polyfunctional amines in high selectivity. Under appropriate conditions, strontium hydrogen phosphate, lanthanum hydrogen phosphate, or phosphoric acid on silica also catalyzes vapor phase production of noncyclic polyethylene amines from ethylenediamine, ethanolamine, and, optionally, ammonia. In all instances, products appear to be generated via initial formation of a phosphate ester on the catalyst surface with subsequent nucleophilic displacement of phosphate by the reactant amine.