Issue 37, 2013

From molecular crystals to salt co-crystals of barbituric acid via the carbonate ion and an improvement of the solid state properties

Abstract

Co-crystals formed by neutral barbituric acid (HBA) molecules and alkaline barbiturate salts have been prepared by solvent-free mechanochemical treatment of solid HBA and alkaline carbonates or bicarbonates. During the reaction the carbonate salts release CO2 and H2O, affording the corresponding barbiturate salts which then co-crystallize with the neutral molecule. These “salt co-crystals” have the general formula Mx+(BA)x·HBA·nH2O with (M = Na and K). The compounds can be obtained in a single step, by directly grinding HBA with M2CO3 (4 : 1 ratio) or MHCO3 (2 : 1 ratio), or, alternatively, in two steps: the preparation of the BA salt followed by a further grinding process or crystallization of the resulting salts with a stoichiometric amount of neutral HBA. All compounds have been characterized by means of single-crystal and powder XRD, solid-state NMR (1H MAS, 13C and 15N CPMAS), vibrational spectroscopies and thermal methods (DSC and TGA). A series of BA salts (either hydrated or anhydrous) of formula Mx+(BA)x·nH2O (M = Na, K, Mg and Ca) have also been prepared and reported for comparison.

Graphical abstract: From molecular crystals to salt co-crystals of barbituric acid via the carbonate ion and an improvement of the solid state properties

Supplementary files

Article information

Article type
Paper
Submitted
28 May 2013
Accepted
18 Jul 2013
First published
19 Jul 2013

CrystEngComm, 2013,15, 7598-7605

From molecular crystals to salt co-crystals of barbituric acid via the carbonate ion and an improvement of the solid state properties

M. R. Chierotti, K. Gaglioti, R. Gobetto, D. Braga, F. Grepioni and L. Maini, CrystEngComm, 2013, 15, 7598 DOI: 10.1039/C3CE40938D

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