The reaction of glycerol carbonate with primary aromatic amines in the presence of Y- and X-faujasites: the synthesis of N-(2,3-dihydroxy)propyl anilines and the reaction mechanism

Abstract

At 140 °C, in the presence of alkali metal exchanged faujasites, preferably NaY, as catalysts, glycerine carbonate (GlyC) is an efficient and green alkylating agent of primary aromatic amines (p-XC₆H₄NH₂, X = H, OMe, OH, Cl): the reaction takes place with a high conversion (∼90%) and a good selectivity (80–90%) for the formation of N-(2,3-dihydroxy)propyl anilines (p-XC₆H₄NHCH₂CH(OH)CH₂OH). The alkylation process does not proceed through an exclusive nucleophilic substitution of anilines at the C5 position of GlyC. Evidence proves that a dehydrative condensation of anilines with GlyC produces intermediate species, and both transesterification and hydrolysis reactions are involved to obtain the final N-alkyl derivatives. A mechanism is proposed accordingly. Experiments show that faujasites are recyclable catalysts on condition that they are exposed to a mild thermal activation (70 °C, 18 mbar) prior to their re-use. Otherwise, if zeolites are calcined (400 °C, air), both the catalyst activity and the reaction selectivity drop. Isolated yields (60–65%) of N-(2,3-dihydroxy)propyl anilines are somewhat limited by the difficult separation of the unreacted GlyC and of the by-product glycerine. Nonetheless, the overall efficiency of the method is comparable to that of alternative routes based on highly toxic reagents (glycidol and aryl halides).