PROTONATION CONSTANTS OF SOME SUBSTITUTED SALICYLIDENEANILINES IN DIOXAN-WATER MIXTURES

Sixteen Schiff's bases have been prepared from salicylaldehyde and substituted anilines and their stoichiometric protonation constants have been determined in dioxan-water mixtures of 30, 40, 50 and 60% dioxan (v/v) using a combined pH electrode at 25 degrees C, under nitrogen atmosphere. The calculation of the constants has been carried out using a PKAS computer programme. The effects of the substituents on the protonation constants and the additivities of these effects are discussed. Furthermore, it was found that the log K-OH value increases but the log K-NH value decreases for all Schiff's bases if the percentage of dioxan is increased.