Identification of robust synthon in the molecular salts of 2-aminothiazole with substituted benzoic acids: A case study

Abstract

Six new salts of an API intermediate 2-aminothiazole with different carboxylic acid coformers were synthesized and characterized by IR (Infrared spectroscopy), 1H-NMR, DSC (Differential scanning calorimetry), XRPD (X-ray powder diffraction) and single crystal XRD. The crystal structure of the salts with benzoic acid, 2,3-, 2,4-, 2,5-, 2,6- dihydroxybenzoic acids and 2,4-dinitrobenzoic acid were determined. The thiazole moiety exhibited solvent (polarity) assisted tautomerism in all reported salts and proton transfer was noticed to the ring N of thiazole due to which two point supramolecular synthon N+-H(thiazole)⋯O-(acid), N-H(amine)⋯O-(acid) was observed. The crystal structures were studied with respect to the positional effect of the competing functional groups like hydroxyl (-OH) and nitro (-NO2) as well as their donor and acceptor abilities for hydrogen bonding. The presence of the non-conventional hydrogen bond (C-H⋯O) has been found to play a critical role in the formation of secondary supramolecular architectures.