Meloxicam hydro-chloride.

The title salt, CHNOS ·Cl [systematic name: 2-(4-hy-droxy-2-methyl-1,1-dioxo-1,2-benzo-thia-zine-3-amido)-5-methyl-1,3-thia-zol-3-ium chloride] is the hydro-chloride derivative of meloxicam, a drug used to treat pain and inflammation in rheumatic disorders and osteoarthritis. Although its mol-ecular structure is similar to that previously reported for the hydro-bromide analogue, both salts are not isomorphous. Different crystal structures originate from a conformational modification, arising from a degree of rotational freedom for the thia-zolium ring in the cations.

One mol-ecule, three crystal structures: conformational trimorphism of -[(1)-1-phenyl-eth-yl]benzamide.

The title compound, CHNO, is an enanti-opure small mol-ecule, which has been synthesized many times, although its crystal structure was never determined. By recrystallization from a variety of solvent mixtures (pure aceto-nitrile, ethanol-water, toluene-ethanol, THF-methanol), we obtained three unsolvated polymorphs, in space groups 2 and 222. Form is obtained from aceto-nitrile, without admixture of other forms, whereas forms and are obtained simultaneously by concomitant crystallizations from alcohol-based solvent mixtures.