AMMONIUM AZONIUM TAUTOMERISM IN SOME N,N-DIALKYLAMINOAZODYES .2. COMPOUNDS CONTAINING MORE THAN 2 PROTONATION SITES

The UV-vis properties in neutral and acidic media of some N,N-dialkyl- aminoazo dyes containing strong electron donor substituents or an exte nded conjugated system, leading to more than two protonation sites, ar e investigated in order to clarify the influence of these structural c hanges on the position of the ammonium-azonium tautomeric equilibrium. The observed absorption maxima associated with the colour changes of neutral and protonated molecules are assigned within the charge-transf er (CT) model. The tautomeric equilibrium constants K-T and pK(a) valu es of the ammonium and azonium tautomeric forms of N,N-dialkylaminoazo benzenes containing strong electron donor substituents are evaluated. Copyright (C) 1996 Elsevier Science Ltd