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Issue 18, 2019
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Investigation of solid–liquid phase diagrams of the sulfamethazine–salicylic acid co-crystal

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Abstract

The influence of temperature and solvent on the solid–liquid phase diagram of the 1 : 1 sulfamethazine–salicylic acid co-crystal has been investigated. Ternary phase diagrams of this co-crystal system have been constructed in three solvents: methanol, acetonitrile and a 7 : 3 (v/v) dimethylsulfoxide–methanol mixture, at three temperatures. The system exhibits congruent dissolution in acetonitrile and the co-crystal solubility has been determined by a gravimetric technique. The Gibbs energy of co-crystal formation from the respective solid components has been estimated from solubility data, together with the corresponding enthalpic and entropic component terms. The Gibbs energy of formation ranges from −5.7 to −7.7 kJ mol−1, with the stability increasing with temperature. In methanol and the DMSO–methanol mixture, the co-crystal dissolves incongruently. It is shown that the solubility ratio of the pure components cannot be used to predict with confidence whether the co-crystal will dissolve congruently or incongruently. The size of the region where the co-crystal is the only stable solid phase is inversely related to the pure component solubility ratio of salicylic acid and sulfamethazine.

Graphical abstract: Investigation of solid–liquid phase diagrams of the sulfamethazine–salicylic acid co-crystal

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Supplementary files

Article information


Submitted
23 Jan 2019
Accepted
12 Mar 2019
First published
02 Apr 2019

This article is Open Access

CrystEngComm, 2019,21, 2863-2874
Article type
Paper

Investigation of solid–liquid phase diagrams of the sulfamethazine–salicylic acid co-crystal

D. Ahuja, M. Svärd and Å. C. Rasmuson, CrystEngComm, 2019, 21, 2863 DOI: 10.1039/C9CE00124G

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