Fotooxidación sensibilizada de furfural en medio n-butanólico. II. Efecto de la presencia de agua en la reacción

Abstract

The photosensitized oxidation of furfural in butano] at 60 ºC has been performed with addition or not of water at the beginning of the reaction. In both cases 2,5-dihidro-5-hidroxi-2-furanone (I) (in equilibrium with its non cyclic form, the β-formilacrylic acid) and 2,5-dihidro-5-butoxi-2-furanone (II) were the main reaction products, showing the reaction with initially added water a higher selectivity toward the second product. This behavior is surprising since the presence oflarge amounts of water should dificult the reaction with n-butanol of che first mcntioned product. The reaction of (1) with butano! giving (II) occurs under mild conditions and the withdrawal of water from the final reaction mixture through azeotropic destilation with n-butanol at low vacnum and 60- 80 ºC favored the obtaining of higher yields of (II). When the azeotropic dis­tillaton was performed at more severe temperature conditions (at atmosferic pressure), butyralization reactions lowered strongly the yield of (II). Formic acid, expected to be from literature reports an important product of the photosensi­tized oxidation of furfural, is oxidized under the reaction conditions and there­fore constitutes a source of water formation. This could explain the formation of (I)in experiments without addition of water.