Utilization of Solid Acid SO 4 2 − /TiO 2 as Catalyst to the Three‐Component Mannich Reaction at Ambient Temperature

The three‐component Mannich reaction of among dimethyl malonate, aromatic primary amine, and aromatic aldehyde was made successfully in the presence of solid acidic catalyst SO 4 2 − /TiO 2 , with excellent catalytic activity, as compared to SO 4 2 − /γ‐Al 2 O 3 and SO 4 2 − /ZnO. To the best of our knowledge, SO 4 2 − /TiO 2 prepared at varied calcination temperatures can perform different intensities of Lewis and Brønsted acidities. Because of this point, under the optimum conditions, the effect of SO 4 2 − /TiO 2 (prepared at 200°C) was much more than that of SO 4 2 − /TiO 2 (prepared at 300°C or 400°C) in the three‐component Mannich reaction. In observing ionization activation mode of the three‐component Mannich reaction, it disclosed that the plausible mechanism possibly undergoes formation of aldimines and transformation of aldimines into β ‐amino esters by applying solid acidic catalyst SO 4 2 − /M x O y .