Preparation and thermal reactivity of hydrazinium 2,n-pyridinedicarboxylates (n=3, 4, 5 and 6)

Hydrazinium 2,n-pyridinedicarboxylates of general compositions N₂H₅HA, (N₂H₅)₂A·H₂O and N₂H₅HA·H₂A, where H ₂ A=2,n-pyridinedicarboxylic acid (n=3, quinolinic acid;n=4, lutidinic acid; n=5, isocinchomeronic acid and n=6, dipicolinic acid) have been prepared by the neutralisation of aqueous solution of hydrazine hydrate with the respective acids, in stoichiometric ratios. Formation of these hydrazinium derivatives has been confirmed by analytical, IR spectral and thermal studies. Among these, the monohydrazinium salts are anhydrous whereas the dihydrazinium salts are monohydrated. While lutidinic and dipicolinic acids form all the three types of salts, the quinolinic and isocinchomeronic acids do not form N₂H₅HA·H₂A and N₂H₅HA, respectively, except the other two types. Infrared spectra of these salts reveal N-N stretching frequencies of the hydrazinium ion in the region 970-950 cm^-1. The simultaneous TG and DTA of these salts show that all of them decompose without clear melting and lose hydrazine endothermically between 200 and 280°C, except dihydrazinium isocinchomeronate monohydrate in which half of the hydrazine molecule is lost exothermically, to give pyridinemono- or dicarboxylic acid intermediate which further decomposes exothermically to gaseous products. This revised version was published online in August 2006 with corrections to the Cover Date.