Application of hollow silica spheres with radially oriented mesopores to microreactors for two-phase reactions heated by microwave irradiation

Abstract

Hollow silica spheres with radially oriented mesopores were used as microreactors for the two-phase reaction of the aldol condensation of butanal. The hollow spheres filled with 2 M sulfuric acid as a catalyst, which served as an aqueous phase, were added to the heptane solution of butanal, which served as an organic phase, and the mixture was heated at 95ºC. The reaction rate was higher than that of the emulsive two-phase reaction without the use of the hollow spheres because the droplets in the emulsion were larger than the hollow spheres. When microwave heating was used, the reaction rate increased compared with that when conventional heating was applied at the same temperature of the reaction mixture. Only the aqueous phase in the hollow spheres, where the reaction proceeded, was selectively heated by microwave irradiation because water effectively absorbs microwaves, whereas heptane cannot.