Mechanochemical synthesis of pyrazine: dicarboxylic acid cocrystals and a study of dissociation by quantitative phase analysis

Cocrystals of pyrazine with dicarboxylic acids were synthesised by mechanochemical methods. Crystal structure determination was performed by single crystal and powder X-ray diffraction (PXRD). The cocrystals consist of infinite 1D hydrogen-bonded chains exploiting the familiar pyridine-carboxylic acid synthon. The kinetics of dissociation of the pyrazine: phthalic acid cocrystal was studied at non-ambient conditions using PXRD and quantitative Rietveld phase analysis. We show that the dissociation process is both temperature and humidity dependent providing useful information about a possible dissociation mechanism.