Preparation, spectral and thermal studies of pyrazinecarboxylic acids and their hydrazinium salts

Abstract. Some new hydrazinium 2-pyrazinecarboxylate and 2,3-pyrazinedicarboxylate salts of the formulae N2H5pc, N2H5pc.H2O (Hpc = 2-pyrazinecarboxylic acid), N2H5Hpdc, (N2H5)2pdc.H2O and N2H5(Hpdc).H2pdc (H2pdc = 2,3-pyrazinedicarboxylic acid) have been prepared by neutralization of aqueous hydrazine hydrate with the respective acids in appropriate molar ratios. The free acids and their hydrazinium salts have been characterized by analytical, IR spectroscopic and thermal studies. IR spectra of all the salts show N–N stretching frequencies of the N2H5 + ion in the region 975–960 cm–1. The thermoanalytical behaviour of the free acids and their salts has been investigated by simultaneous TG and DTA. While pyrazinecarboxylic acid shows single-step endothermic (229C) complete decomposition, pyrazindicarboxylic acid shows exothermic decarboxylation followed by identical endothermic decomposition as that of the former. Similarly, salts of the monocarboxylic acid show endothermic effects during pyrolysis, whereas salts of the dicarboxylic acid show endothermic followed by exothermic decomposition. The acids and their salts both undergo complete decomposition to gaseous products.