The formation, under kinetic control, of a new monoacetal (2,3-O-butylidene-D-glucitol) from D-glucitol and n-butyraldehyde

Abstract

D-Glucitol and n-butyraldehyde in aqueous acid rapidly form an intermediate product of relatively large negative optical rotation which has been separated and identified as 2,3-O-butylidene-D-glucitol. Examination of the products throughout reaction by g.l.c. analysis of the O-trimethylsilyl derivatives shows that the subsequent disappearance of the intermediate product as equilibrium is approached is accompanied by the appearance of the 2,4-O-butylidene acetal but there is no evidence for intramolecular conversion.

Aqueous acid hydrolysis of the 2,3-acetal leads to fission of the acetal ring, with the D-glucitol and n-butyraldehyde subsequently recombining to form the 2,4-acetal. Kinetic measurements of hydrolysis rates show that the 2,3-acetal is much more rapidly hydrolysed than the 2,4-acetal. In anhydrous NN-dimethylformamide in the presence of hydrogen chloride, the 2,3-acetal appears to undergo intramolecular rearrangement to the 2,4-acetal.