Clean synthesis of furfural oxime through liquid-phase ammoximation of furfural over titanosilicate catalysts

The clean synthesis of furfural oxime (FO) has been realized through titanosilicate-catalyzed liquid-phase ammoximation of furfural with ammonia and hydrogen peroxide. A detailed investigation of furfural ammoximation over three representative titanosilicates Ti-MOR, TS-1 and Ti-MWW reveals that the reaction involves the hydroxylamine route and the imine route. The hydroxylamine route accounts for the formation of the target product (FO), while the imine route leads to the formation of undesired products such as 2-furylamide and 2-furoic acid. With a high efficiency for hydroxylamine formation, Ti-MOR proves to be superior to TS-1 and Ti-MWW. The catalytic performance of Ti-MOR depends greatly on the operating conditions of the reaction, which is closely related to its activity in catalyzing hydroxylamine decomposition. The decomposition of hydroxylamine and the non-catalytic oxidation of furfural can be effectively suppressed in Ti-MOR-catalyzed ammoximation when employing water as the solvent and adding H₂O₂ dropwise into the reaction system. Under optimized conditions, Ti-MOR is capable of providing furfural conversion and oxime selectivity both above 97%.