Crystal structures of 1-hydroxy-4-propyloxy-9,10-anthraquinone and its acetyl derivative

The title compounds were synthesized from the commercially available dye quinizarin. In both compounds, the anthraquinone frameworks are close to planarity but there is a large difference in the conformation of the propyloxy group.

1. Chemical context 9,10-Anthraquinone and its derivatives are important molecules as dyes and pigments. As a part of a project on the study of the substitution effects of the anthraquinone ring on optical properties in solution as well as in the solid state, we have been synthesizing new anthraquinone derivatives. Recently, we found that the recrystallization of 1,4-dipropyloxy-9,10anthaquinone from hexane solution afforded two polymorphs, red prisms and yellow needles, whose crystal structures were different from each other (Kitamura et al., 2015b). Then we became interested in the effect of the asymmetric substitution pattern of 9,10-anthraquinone because 1,4-dipropyloxy-9,10anthraquinone is a symmetric molecule along the direction of the molecular short axis. We thought that mono-alkoxylation from quinizarin (1,4-dihydroxy-9,10-anthraquinone) should be effective to gain asymmetric 9,10-anthraquinones along the molecular short axis. We report herein the synthesis and crystal structures of 1-hydroxy-4-propyloxy-9,10-anthraquinone (I) and its acetyl derivative, 1-acetyloxy-4-propyloxy-9,10-anthraquinone (II). ISSN 2056-9890

Figure 1
Molecular structure of compound (I), showing the atom labelling and 50% probability displacement ellipsoids. The intramolecular hydrogen bond is indicated by a dashed line.

Figure 3
Packing of the unit cell of (I), showing short C-HÁ Á ÁO contacts as blue lines.
anthraquinone ring systems is observed for compound (II), on the other hand, compound (I) scarcely shows any overlap.

Figure 5
Top view of two neighboring molecules of compound (I) along the stacking direction.

Figure 6
Top view of two neighboring molecules of compound (II) along the stacking direction.

Figure 8
Side view of two neighboring molecules of compound (II).
Compound (II): A mixture of compound (I) (132 mg, 0.47 mmol), K 2 CO 3 (137 mg, 0.99 mmol) in acetic anhydride (5 mL) was stirred at 383 K for 3 h under air. After cooling to room temperature, water (50 mL) was added into the resulting mixture, then the mixture was stirred for 20 min at room temperature. The mixture was extracted with CH 2 Cl 2 . The

Figure 9
Reaction scheme for the synthesis of compounds (I) and (II).
organic layer was washed with 10% NaHCO 3 solution and then brine, and dried over Na 2 SO 4 , and evaporated under reduced pressure. The residual yellow solid was purified by recrystallization from a hexane-toluene (>v:v = 3:1) solution to provide title compound (II) as a yellow solid (128 mg, 84%

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. The hydroxyl H atom, H1 of compound (I), was refined isotropically. All other H atoms were positioned geometrically and treated as riding atoms: C-H = 0.95-0.99 Å with U iso (H) = 1.5U eq (C) for CH 3 and 1.2U eq (C) for CH 2 and aromatic C-H.

Computing details
For both structures, data collection: PROCESS-AUTO (Rigaku, 1998); cell refinement: PROCESS-AUTO (Rigaku, 1998); data reduction: PROCESS-AUTO (Rigaku, 1998); program(s) used to solve structure: SIR2004 (Burla et al., 2005); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: Mercury (Macrae et al., 2008); software used to prepare material for publication: WinGX (Farrugia, 2012) and publCIF (Westrip, 2010). Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )