Catalytic activity of niobium phosphate in the benzylation of anisole with styrene, benzyl alcohol and benzyl chloride

Abstract

The catalytic activity of niobium phosphate was evaluated in the benzylation of anisole with three alkylating agents. Niobium phosphate was characterized by N2 adsorption, X-ray diffraction (XRD), solid state 31P NMR, NH3-TPD, structural FTIR and FTIR after adsorption of pyridine in order to determine its physico-chemical properties. The influence of catalyst calcination in the benzylation conversion was studied. A comparison between the benzylation with benzyl alcohol, benzyl chloride and styrene was done. The results indicated that the conversion of the benzyl alcohol and styrene on niobium phosphate was extremely dependent on the pre-treatment temperature. The catalyst calcined at 773 K showed high activity and selectivity to benzylated products in the benzylation with all alkylating agents and the conversion order was benzyl chloride > styrene > benzyl alcohol. Competitive reactions were also performed with two alkylating agents simultaneously. In the reaction of anisole with both benzyl alcohol and benzyl chloride, the alcohol was consumed faster than the chloride. The behavior indicates a phenomenon related to preferential adsorption, in which the alkylating agents compete for the sites, mainly Lewis sites, on the niobium phosphate. In the reaction of anisole with both styrene and benzyl alcohol, there was also an inversion of the relative reactivity, the alcohol was consumed faster, and in the reaction of anisole with styrene and benzyl chloride, both of them have presented similar conversions probably because HCl formed in the reaction with benzyl chloride catalysis the reaction of styrene.