The Complexing of the Ammonium Ion in Acetonitrile with Other Solvents. Investigation Using a Cation-sensitive Glass Electrode

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Abstract
As a part of potentiometric studies of the complexing of univalent cations in acetonitrile with other solvents by the use of a cation-sensitive glass electrode, investigations were carried out of the complexing of the ammonium ion in acetonitrile with such solvents as water, methanol, N-methylformamide, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, 1-methyl-2-pyrrolidone, and hexamethylphosphoric triamide, and also with dibenzo-18-crown-6. Prior to the study of the complexing, the cation-sensitive glass electrode was confirmed to respond in a Nernstian way to the change in the ammonium-ion activity which occurs due to the change of the solvent (solvent effect). The ammonium ion in acetonitrile formed complexes of mono- and di-solvated species with methanol and water. Formations of up to tri-solvated species were formed with DMF, DMA, and DMSO, and up to tetra-solvated species with 1-methyl-2-pyrrolidone and NMF. With HMPA, even penta-solvated species were formed. The complex formation constants of the mono-solvated ammonium ion, β1 (mol −1 dm3), were 1.7 with methanol, 5.6 with DMF, 14 with DMSO, 17 with DMA, 31 with 1-methyl-2-pyrrolidone, 3.0×102 with NMF, and 1.2×103 with HMPA. The association constant of ammonium perchlorate in acetonitrile was determined conductometrically to be 25 mol −1 dm3.