Heterogeneously catalyzed efficient hydration of alkynes to ketones by tin-tungsten mixed oxides.

The Sn-W mixed oxide prepared by calcination of the Sn-W mixed hydroxide precursor with a Sn/W molar ratio of 2:1 at 800 °C (SnW2-800) acts as an efficient heterogeneous catalyst for the hydration of alkynes. Structurally diverse terminal and internal alkynes, including aromatic, aliphatic, and double-bond-containing ones, can be converted into the corresponding ketones in moderate to high yields. The catalytic activity of SnW2-800 is much higher than those of previously reported heterogeneous catalysts and commonly utilized acid catalysts. The observed catalysis was truly heterogeneous, and the retrieved catalyst can be reused at least three times with retention of its high catalytic performance. The reaction rate for the SnW2-800-catalyzed hydration was decreased by addition of 2,6-lutidine and the hydration hardly proceeded in the presence of an equimolar amount of this compound with respect to that of the Brønsted acid sites in SnW2-800. Therefore, the present hydration is mainly promoted by the Brønsted acid sites in SnW2-800.