Transformation of 4-hydroxybutanal over porcelain

The transformation of 4-hydroxybutanal (4-HB) in the presence of pretreated porcelain (molar ratio SiO2:Al2O3 = 6:1) as catalyst has been investigated in a micropulse reactor at 230-300 degrees C in a gas phase. The main reaction of the alcanol was cyclodehydration resulting in 2,3-dihydrofuran (2,3-DHF) formation. Under the conditions studied the significant irreversible adsorption of 4-HE on porcelain is observed, amounting to 1.1 x 10(20) molecules/g at 240 degrees C. The experiments with the mixture of 4-HE and 1,4-butanediol (1,4-BD) indicate that the dehydration reaction of these compounds is of a competitive character. The presence of 4-HE essentially diminishes the 1,4-BD conversion. A theoretical description of 4-HE cyclodehydration and its tautomeric cyclic form at the solid-gas interface is under discussion. The reaction mechanism has been proposed on the basis of the quantum chemical calculations. The conversion of 4-HE and its cyclic form 2-hydroxytetrahydrofuran (2-HTHF) can be interpreted by assuming the concert mechanisms. It is suggested that the Bronsted acidic and basic Si(OH)(3)O- sites take part in the reactions. (C) 1999 Elsevier Science B.V. All rights reserved.