Proton-transfer equilibria for N-base–trimethyl-N-oxide cation systems in acetonitrile

Abstract
The electrometric behaviour of homo- and hetero-complexes, (Me3NOHONMe3)+ and (Me3NOHB)+(where B is an N-base), in acetonitrile have been investigated by e.m.f. measurements. The N-bases, B. studied were: 2-chloropyridine, 3-chloropyridine, pyridine, quinoline, N-methylimidazole, morpholine, N-methylpiperidine, triethylamine and trimethyl-N-oxide. The formation constant, Kf, and the proton-transfer equilibrium constant, KPT, for the reactions (Me3NO + BH+) and (B + Me3NOH+) have been evaluated. The sigmoidal titration curve for (Me3NOH++Me3NO) and some (Me3NOH++B) suggest that (—OHO—)+ and (—OHN)+ hydrogen bridges are very strong. The experimental formation constants of the complexes (Me3NO)2H+, log Kf= 5.51, and (Me3NOHB)+, log Kf=≈ 4.0, with (NHN)+ bridges showing weaker interaction, log Kf≈ 2.0.

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