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.

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

CHIEROTTI, Michele Remo;GAGLIOTI, KATIA;GOBETTO, Roberto;
2013-01-01

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.
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http://pubs.rsc.org/en/Content/ArticleLanding/2013/CE/c3ce40938d#!divAbstract
Michele R. Chierotti;Katia Gaglioti;Roberto Gobetto;Dario Braga;Fabrizia Grepioni;Lucia Maini
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2318/141217
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