Utilization of Solid Acid SO42−/TiO2 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 SO₄²⁻/TiO₂, with excellent catalytic activity, as compared to SO₄²⁻/γ-Al₂O₃ and SO₄²⁻/ZnO. To the best of our knowledge, SO₄²⁻/TiO₂ 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 SO₄²⁻/TiO₂ (prepared at 200°C) was much more than that of SO₄²⁻/TiO₂ (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 SO₄²⁻/M_xO_y. [ABSTRACT FROM AUTHOR]