The amorphous, mesoporous SiO 2 -SO 3 H catalyst with a surface area of 115 m 2 g -1 and 1.32 mmol H + per g was very efficient for the protonation of ketones on a 10% (m/m) basis, and the catalyst-bound intermediates can be trapped by polyalcohols to produce ketals in high yields or suffer aldol condensations within minutes under low-power microwave irradiation. The same catalyst can easily reverse the ketalization reaction.

This paper is dedicated to the memory of our dear co-worker Stanlei I. Klein, who passed away while this paper was being peer-reviewed.