New insight into the mechanism of zeolite catalyzed nucleophilic amination Via In Situ infrared spectroscopy

Amination of alcohols over Brønsted acidic molecular sieves such as H-mordenites proceeds via a bimolecular precursor consisting of an ammonium ion and an alcohol molecule. The rate of transformation of that complex into a sorbed alkyl ammonium ion is fast. Desorption of the formed amines, however, is difficult under reaction conditions (633K) and only proceeds in the presence of excess ammonia. Two mechanisms are proposed for the release of the alkylamines in the gasphase, i.e., adsorption assisted desorption and alkyl scavenging by ammonia. The vast majority of the alkylamines are formed by scavenging alkyl groups of chemisorbed alkyl ammonium ions by ammonia. A linear relation of the initial rate of monomethylamine formation and the total surface concentration of methyl groups (present as mono-up to tetramethylammonium ions) inside the pores of the mordenites was found.