Ketalization of Ketones to 1,3-Dioxolanes and Concurring Self-Aldolization Catalyzed by an Amorphous, Hydrophilic SiO2-SO3H Catalyst under Microwave Irradiation

Sandro Barbosa,Myrlene Ottone,Guilherme Lage,Norberto Lopes,David Nelson,Giuliano Clososki,Lucas Zanatta,Melina Almeida,Wallans Dos Santos,Mainara De Almeida,Stanlei Klein

doi:10.21577/0103-5053.20180039

Abstract

The amorphous, mesoporous SiO2-SO3H catalyst with a surface area of 115 m2 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.

Highlights

Sulfuric acid can be considered to be the standard acid for all organic reactions that are catalyzed by strong BrønstedLowry acids, but its anti-Green-Chemistry nature impairs its widespread use: its residues are highly acidic and its corrosiveness is widely avoided
We report that reactions such as equation 3 can be greatly enhanced by microwave irradiation using our hydrophilic catalyst and that the procedure can be extended to other polyols such as trimethylol propane, neopentyl glycol and crude glycerol
One might assume that the enhancement of the Si–O–Si longitudinal-transverse optical vibration (LO) absorption at 1210 cm-1 and the transversal optical (TO) rocking of the Si–O–Si bonds at 592 cm-1 may be due to the presence of the –OSO3H groups of the catalyst.[7]

Summary

Introduction

Sulfuric acid can be considered to be the standard acid for all organic reactions that are catalyzed by strong BrønstedLowry acids, but its anti-Green-Chemistry nature impairs its widespread use: its residues are highly acidic and its corrosiveness is widely avoided. This protection is accomplished by the reaction of the carbonyl compound with ethylene glycol in the presence of an acid catalyst.[9] The products are usually referred to as an acetal if prepared from an aldehyde, or ketal, if formed from a ketone.

Results

Conclusion