Molybdenum oxides catalyzed the <i>N</i>,<i>N</i>‐dimethylamination of alcohols with <i>N</i>,<i>N</i>‐dimethylformamide for direct synthesis of tertiary amines

Abstract

Molybdenum oxides (MoO 3 − x , x = 1, 2, and 3) with three types of morphologies were prepared and applied to the reaction of benzyl alcohol with dimethylformamide (DMF) for synthesis of tertiary amines. The MoO 3 − 1 catalyst prepared by direct calcination exhibited high activity and tertiary amines selectivity in the N , N ‐dimethylamination of benzyl alcohol under the reaction conditions at 150°C for 12 h using DMF as a methylating agent and solvent, as compared to MoO 3 − 2 and MoO 3 − 3 catalysts. This feature was ascribed to the high proportion of surface chemisorbed oxygen for MoO 3 − 1 sample, which can promote the adsorbed benzyl alcohol transformation into benzaldehyde. The MoO 3 − 1 catalyst was also found to be reusable in five consecutive runs without a significant decrease in catalytic activity. In addition, control experiments showed two parallel reaction routes in this catalytic system. One route is the reaction of benzaldehyde intermediate and DMF to form tertiary amines (Route I); the other route is that benzyl formate intermediate reacted with DMF (Route II), which has not been reported before and specifically involves the esterification of benzyl alcohol with formic acid from DMF decomposition to form benzyl formate.