Towards a more sustainable production of triacetoneamine with heterogeneous catalysis

tThe acid-catalyzed condensation of acetone and ammonia to directly produce 2,2,6,6-tetramethy-4-piperidone (triacetonamine) was studied under both homogeneous and heterogeneous catalysis. Theselectivity to the desired product was affected by the presence of a complex reaction network involvingseveral kinetically parallel and consecutive reactions, leading to by-products such as diacetonealcohol,diacetoneamine, mesityl oxide, acetonine, and 2,2,4,6-tetramethyl-2,5-dihydropyridine. The latter wasthe most undesired by-product, since its formation was irreversible. Key elements in achieving high selec-tivity in the direct synthesis of triacetonamine were the molar feed ratio between acetone and ammonia,and the amount of water in the reaction medium; in fact, water was found to play an important rolein the transformation of the intermediate acetonine into triacetonamine. Compared with homogeneouscatalysis, the selectivity achieved by the use of the heterogeneous H-Y zeolites was controlled by meansof a proper selection of the zeolite features. In fact, the use of a highly hydrophilic H-Y zeolite made it pos-sible to achieve the same selectivity as that obtained under homogeneous catalysis conditions, with theadditional advantage of using an easily separable and reusable catalyst, which showed no deactivation.