Triple ion formation ability of picrate in protophobic aprotic solvents with very low basicity

Abstract

The conditions for the formation of species from monovalent salts in protophobic aprotic solvents have been examined for lithium, triethylammonium and 1,3-diphenylguanidinium picrates (2,4,6-trinitrophenolates) by means of conductometry. The molar conductivities of lithium picrate (Li + Pic −, (0.4–4.0) × 10 −3 mol dm −3) in nitromethane were explained by assuming the formation of “symmetrical” triple ions ((Li +) 2Pic − and Li + (Pic −) 2) in addition to ion pairs. However, triethylammonium picrate formed only the ion pair in the same solvent. Symmetrical triple ion formation from lithium picrate was also observed in benzonitrile. The formation of the triple cation (Li +) 2 Pic − in benzonitrile was proved by spectrophotometry. Both conductometry and spectrophotometry confirmed that in acetonitrile the lithium salt formed only the ion pair. Distinct triple ion formation was observed for 1,3-diphenylguanidinium picrate ((0.4–6.0) × 10 −3mol dm −3) in nitrobenzene, but was not so apparent in benzonitrile. The ability of the picrate ion to form triple ions was found to be as low as that of SCN − or I −.