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Gleichgewichte der Protonenaddition an 1, 1‐Bis‐(4′, 4″‐dimethylaminophenyl)‐äthylen in Methanol und in Dimethylsulfoxid
Author(s) -
Bernasconi Claude F.,
Iijima Toshiro,
Koch Werner,
Wakae Masao,
Zollinger Heinrich
Publication year - 1973
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19730560750
Subject(s) - chemistry , tautomer , methanol , equilibrium constant , adduct , solvent , dissociation constant , acid dissociation constant , ion , dissociation (chemistry) , ammonium , medicinal chemistry , organic chemistry , aqueous solution , biochemistry , receptor
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: K 1 (CH 3 OH) = 8.3 (± 0.9) · 10 −6 M, K 2 (CH 3 OH) = 1.22 (± 0.06) · 10 −4 M, K 1 (DMSO) = 2.3 (± 0.9) · 10 −3 M, K 2 (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 K 23 = [3]/[2] ≅ 23). The tautomer 2 cannot be detected in dimethylsulfoxide. The possible causes of these solvent effects are discussed.