The title compounds were obtained by deprotonation of 1,2,4-trihydroxyanthraquinone (purpurin) using sodium hydride followed by reaction with either 1-bromopropane or 1-bromobutane. 1,4-Dihydroxy-2-propoxyanthraquinone crystallizes as a 1:1 solvate from acetonitrile, C 17 H 14 O 5 ÁCH 3 CN. The anthraquinone core of the molecule is essentially planar and both hydroxy groups participate in intramolecular O-HÁ Á ÁO (carbonyl) hydrogen bonds. The propyl chain is angled slightly above the plane of the anthraquinone moiety with a maximum deviation of 0.247 (2) Å above the plane for the terminal carbon atom. In contrast, 2-butoxy-1,4-dihydroxyanthraquinone, C 18 H 16 O 5 , crystallizes from nitromethane with two independent molecules in the asymmetric unit. The anthraquinone core of each independent molecule is essentially planar and both hydroxy groups on both molecules participate in intramolecular O-HÁ Á ÁO(carbonyl) hydrogen bonds. The butyl chain in one molecule is also angled slightly above the plane of the anthraquinone moiety, with a maximum deviation of 0.833 (5) Å above the plane for the terminal carbon atom. In contrast, the butyl group on the second molecule is twisted out of the plane of the anthraquinone core with a torsion angle of 65.1 (3), resulting in a maximum deviation of 1.631 (5) Å above the plane for the terminal carbon atom. Chemical contextPurpurin, 1,2,4-trihydroxy anthraquinone, is a major component of the dye extracted from madder root (Schweppe & Winter, 1997). The extract from madder root has been used to dye wool and other fabrics since antiquity. Purpurin is commercially available and we here report two derivatives, 1,4-dihydroxy-2-propoxy anthraquinone and 2-butoxy-1,4-dihydroxy anthraquinone, prepared by selective deprotonation of purpurin followed by alkylation with the either 1-bromopropane or 1-bromobutane. Structural commentaryThe asymmetric unit of 1,4-dihydroxy-2-propoxy anthraquinone (1), crystallized from acetonitrile solvent, contains a single anthraquinone molecule and one acetonitrile solvate molecule as shown in Fig. 1. The two intramolecular hydrogen bonds (Table 1) are typical for the 1,4-dihydroxy anthraquinones and 1-hydroxyanthraquinones. These hydrogen bonds are maintained in chloroform solution, as shown by the chemical shift of 13.47 and 13.56 ppm for the two hydroxyl protons. The anthraquinone moiety is planar, with an average root mean square (r.m.s.) deviation of atoms C1 to C14 of 0.021 Å , in which the maximum deviation from the plane defined by atoms C1 to C14 is 0.044 (1) Å for C9. The propyl chain is angled slightly above the plane of the anthraquinone moiety, with deviations of 0.043 (2), 0.143 (2) and 0.247 (2) Å for atoms C15, C16 and C17, respectively, from the plane defined by atoms C1-C14. The acetonitrile is angled towards H10 with a N1Á Á ÁC10 distance of 3.401 (2) Å . The final difference map shows several peaks of 0.2 to 0.7 e Å À3 in the anthraquinone plane that suggest the presence of minor whole-molecule disorder in which the anthraquinone is ...
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