Issue 23, 2011

Influence of impurities on the crystallisation of 5-X-aspirin and 5-X-aspirin anhydride polymorphs (X = Cl, Br, Me)

Abstract

Crystallisation of 5-X-aspirin (X = Cl, Br) by ambient evaporation from organic solvents commonly yields a mixture of polymorphs I and II for X = Cl, but only polymorph I for X = Br. Addition of 5-X-aspirin anhydride (5–20 mol %) leads to sole production of polymorph II for X = Cl, and new production of polymorph II for X = Br. Slurry experiments show that polymorph I transforms to polymorph II for X = Cl, while polymorph II transforms to polymorph I for Br. Thus, addition of the anhydride during crystallisation apparently accelerates the I → II transformation for X = Cl, and inhibits the II → I transformation for X = Br. 5-X-Aspirin anhydride can be produced as a by-product during heating of 5-X-aspirin in organic solvents, or during synthesis from 5-X-salicylic acid, and the duration of the heating step in such a synthesis can therefore change the polymorphic form of the synthesised product. The 5-X-aspirin anhydrides (X = Cl, Br, Me) are also polymorphic. Crystallisation of the pure compound from organic solvents yields only polymorph I, while polymorph II can be obtained by heating in ethanol or acetone. For X = Cl or Br, the heating step produces significant quantities of 5-X-aspirinin situ, while for X = Me, it is necessary also to add 5-X-aspirin (5–20 mol %) to obtain polymorph II.

Graphical abstract: Influence of impurities on the crystallisation of 5-X-aspirin and 5-X-aspirin anhydride polymorphs (X = Cl, Br, Me)

Supplementary files

Article information

Article type
Paper
Submitted
17 Aug 2011
Accepted
30 Sep 2011
First published
13 Oct 2011

CrystEngComm, 2011,13, 6991-6996

Influence of impurities on the crystallisation of 5-X-aspirin and 5-X-aspirin anhydride polymorphs (X = Cl, Br, Me)

K. A. Solanko and A. D. Bond., CrystEngComm, 2011, 13, 6991 DOI: 10.1039/C1CE06065A

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