The Complexing of the Lithium Ion in Acetonitrile with Other Solvents. Investigation by the Use of a Cation-sensitive Glass Electrode

The complexing of the lithium ion with other popular solvents has been studied in acetonitrile (AN) using a monovalent cation-sensitive glass electrode. A method similar to that developed to study the complexing of the sodium ion was employed. Mono- and di-solvated species were formed for methanol, pyridine, formamide, methylfomamide, and HMPA. Tri-solvated species were also formed for DMF, DMA, and DMSO. In general, the complexing of the lithium ion with these solvents was more pronounced than that of the sodium ion. The formation constants for the mono-solvated lithium ion were 4.5 for methanol, 5.2 for pyridine, 16 for DMF, 20 for formamide, 25 for methylformamide, 49 for DMSO, 62 for DMA, and 2.1×103 for HMPA. When water was the complexing solvent, the equilibrium potential could not be obtained, probably because of the hydrolysis of the hydrated lithium ion. Prior to these experiments, the cation-sensitive glass electrode was confirmed to respond to the lithium-ion activity in different solvents by comparing its behavior with that of a lithium-amalgam electrode.