Investigation into solid and solution properties of quinizarin

Abstract

Polymorphism, crystal shape and solubility of 1,4-dihydroxyanthraquinone (quinizarin) have been investigated in acetic acid, acetone, acetonitrile, n-butanol and toluene. The solubility of FI and FII from 20 degrees C to 45 degrees C has been determined by a gravimetric method. By slow evaporation, pure FI was obtained from n-butanol and toluene, pure FII was obtained from acetone, while either a mixture of the two forms or pure FI was obtained from acetic acid and acetonitrile. Slurry conversion experiments have established an enantiotropic relationship between the two polymorphs and that the commercially available FI is actually a metastable polymorph of quinizarin under ambient conditions. However, in the absence of FII, FI is kinetically stable for many days over the temperature range and in the solvents investigated. FI and FII have been characterized by infrared spectroscopy (IR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), transmission and ordinary powder X-ray diffraction (PXRD) at different temperatures. The crystal structure of FII has been determined by single-crystal XRD. DSC and high-temperature PXRD have shown that both FI and FII will transform into a not previously reported hightemperature form (FIII) around 185 degrees C before this form melts at 200-202 degrees C. By indexing FIII PXRD data, a triclinic P (1) over bar cell was assigned to FIII. The solubility of quinizarin FI and FII in the pure organic solvents used in the present work is below 2.5% by weight and decreases in the order: toluene, acetone, acetic acid, acetonitrile and n-butanol. The crystal shapes obtained in different solvents range from thin rods to flat plates or very flat leaves, with no clear principal difference observed between FI and FII.<p>QC 20160226</p

Thermodynamics of the Enantiotropic Pharmaceutical Compound Benzocaine and Solubility in Pure Organic Solvents

“…The solubility of benzocaine was determined in pure organic solvents using a gravimetric method described previously. 11 Solutions with excess pure FI or FII were prepared in 30 mL glass vials, each containing a PTFE-coated magnetic stirrer and sealed with a screw cap with a PTFE coated insert. The vials were placed on a magnetic stirrer plate submersed in a water bath under agitation at 600 rpm, for at least 18 h at each temperature to allow equilibrium to be reached.…”

High-Z′ structures of organic molecules: their diversity and organizing principles

“…DHXANT12); it seems likely that a transition relating them would require nucleation and growth. Careful experiments (Cheuk et al, 2015) showed that the Z 0 = 8 form is the more stable at room temperature. There are also high-Z 0 and low-Z 0 forms of 4,6-O-benzylidene--d-galactosyl azide, one with Z 0 = 6 (e.g.…”

Crystal structure and Hirshfeld surface analysis of 3,4-dihydro-2H-anthra[1,2-b][1,4]dioxepine-8,13-dione

“…Anthraquinone derivatives, which are extracted from the seeds of the Rubiaceae family of shrubs, include alizarin (1,2dihydroxyanthraquinone; C 14 H 8 O 4 ) and other polycyclic aromatic hydrocarbons. The colour of anthraquinone-based compounds can be modified by the type and position of the substituents attached to the anthraquinone nucleus (Nakagawa et al 2017;Cheuk et al, 2015;Tonin et al, 2017). Besides their application as pigments or dyes in textile, photographic, cosmetic and other industries (Wang et al, 2011), anthraquinone derivatives have been used for centuries for medical applications, for example, as laxatives (Oshio et al, 1985), antioxidants (Yen et al, 2000), antimicrobial (Xiang et al, 2008;Yadav et al, 2010) and anitiviral (Alves et al, 2004) agents.…”