Synthesis and crystal structures of two purpurin derivatives: 1,4-dihy-droxy-2-propoxyanthra-quinone and 2-but-oxy-1,4-di-hydroxy-anthra-quinone.

The title compounds were obtained by deprotonation of 1,2,4-tri-hydroxy-anthra-quinone (purpurin) using sodium hydride followed by reaction with either 1-bromo-propane or 1-bromo-butane. 1,4-Dihy-droxy-2-propoxyanthra-quinone crystallizes as a 1:1 solvate from aceto-nitrile, C(17)H(14)O(5)·CH(3)CN. The anthra-quinone core of the mol-ecule is essentially planar and both hy-droxy groups participate in intra-molecular O-H⋯O (carbon-yl) hydrogen bonds. The propyl chain is angled slightly above the plane of the anthra-quinone moiety with a maximum deviation of 0.247†(2)†à above the plane for the terminal carbon atom. In contrast, 2-but-oxy-1,4-di-hydroxy-anthra-quinone, C(18)H(16)O(5), crystallizes from nitro-methane with two independent mol-ecules in the asymmetric unit. The anthra-quinone core of each independent mol-ecule is essentially planar and both hy-droxy groups on both mol-ecules participate in intra-molecular O-H⋯O(carbon-yl) hydrogen bonds. The butyl chain in one mol-ecule is also angled slightly above the plane of the anthra-quinone moiety, with a maximum deviation of 0.833†(5)†à above the plane for the terminal carbon atom. In contrast, the butyl group on the second mol-ecule is twisted out of the plane of the anthra-quinone core with a torsion angle of 65.1†(3)°, resulting in a maximum deviation of 1.631†(5)†à above the plane for the terminal carbon atom.