Solid–gas reactions between 1,3-dimethylbarbituric acid and amines. A structural and spectroscopic study

Abstract

The reactions of solid 1,3-dimethylbarbituric acid (DMBA) with vapours of NH3 and of the volatile amines NH2(CH3) and NH(CH3)2 have been investigated. The barbiturate salts (DMB) [NH4]DMB (1), [NH3(CH3)]DMB (2) and [NH2(CH3)2]DMB (3) have been characterized by X-ray powder diffraction, differential scanning calorimetry and thermogravimetric analysis. The solid–gas reactions were monitored by UV–Vis spectroscopy in the solid state. Single crystal X-ray diffraction was used to characterize compounds 1, obtained by recrystallization from methanol, and 3, obtained by direct reaction of DMBA with aqueous NH(CH3)2. In the case of 3, recrystallization from methanol yields the salt [NH2(CH3)2][DMB]·2[DMBA] (3a), while recrystallization of 2 yields both the dimerization product [NH3(CH3)][(C6O3N2H6)2-OH]·2H2O (2a) and the hydurilate salt [NH3(CH3)]2[(C6O3N2H6)2] (2b), i.e. the product 2 is only accessible via the solid–gas reaction.