Gleichgewichte der Protonenaddition an 1, 1-Bis-(4′, 4″-dimethylaminophenyl)-äthylen in Methanol und in Dimethylsulfoxid |
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Authors: | Claude F Bernasconi Toshiro Iijima Werner Koch Masao Wakae Heinrich Zollinger |
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Abstract: | The first and second proton addition equilibrium constants of 1,1-bis-(4′, 4″-dimethylaminophenyl)-ethylene ( 1 ) have been measured by the spectrophotometric method in methanol and in dimethylsulfoxide. Defined as acid dissociation constants of the mono- and diprotonated adduct they are: K1 (CH3OH) = 8.3 (± 0.9) · 10?6M, K2 (CH3OH) = 1.22 (± 0.06) · 10?4M, K1 (DMSO) = 2.3 (± 0.9) · 10?3M, K2 (DMSO) ≥ 1M. The evaluation of the electronic and the NMR. spectra demonstrates that the equilibrium of the two monoprotonated tautomers 2 (methyl-carbenium ion) and 3 (ammonium ion) is, in methanol to about 96% on the side of the ammonium ion (tautomeric equilibrium constant K23 = 3]/2] ? 23). The tautomer 2 cannot be detected in dimethylsulfoxide. The possible causes of these solvent effects are discussed. |
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