Co-crystallised alpha- and beta-Anomers of 2,3,4,6-Tetra-acetyl-D-glucopyranose, in which the alpha- and beta-Anomers are Randomly Distributed in the Hydrogen-bonded Chains of Molecules

A co-crystallised sample of alpha- and beta-2,3,4, 6-tetra-O-acetyl-D-glucopyranose [alpha:beta = 1: 2.86(8)], (alpha, beta-1), has been isolated from a solution of 2,3,4,6-tetra-O-acetyl-D- glucopyranose in moist ethyl acetate/diethyl ether. In contrast, pure b-2,3,4,6-tetra-O-acetyl-D- glucopyranose, (beta-1) was isolated on crystallisation from diethyl ethyl/petroleum ether. Species (alpha,beta- 1) is a solid solution in which approximately one in four of the molecules in the b- form is randomly substituted by a molecule of the a- anomer. The hydrogen bonded zig-zag chain connectivity of the pure b- anomer is maintained in the solid solution along the b direction. Since the parent D-glucopyranose compounds differ in their molecular packing and, therefore in structure, the solid solution phenonmenon in the case of their tetraacetyl derivatives is unexpected. Compound (beta- 1) and the (alpha, beta-1) solid solution crystallize in the orthorhombic space group P2(1)2(1)2(1):a = 7.8612( 4) angstrom, b = 10.2045( 5) angstrom, c = 20.7362( 11) angstrom, and Z = 4 for (alpha- 1) at 120( 2) K; and a = 7.9674(5) A, b = 10.2547( 4) angstrom, c = 21.1565( 10) angstrom, and Z = 4 for ( alpha, beta-1) at 291(2) K.