PROTONATION CONSTANTS OF SOME SUBSTITUTED 2-HYDROXY-1-NAPHTHALIDENEANILINES IN DIOXAN WATER MIXTURES

The protonation constants of ten Schiff's bases synthesized by the con densation of 2-hydroxy-1-naphthaldehyde with aniline and o-, m-, and p -substituted methylanilines, ethylanilines and methoxyanilines in vari ous dioxan-water mixtures have been determined potentiometrically usin g an electrode system calibrated in concentration units of the hydroge n ion. The influence of substituents in the molecular structure on the protonation constants is discussed. The log K-2 values relating to th e protonation of imine nitrogen atoms are in accordance with the Hamme tt relationship for all solvent compositions. A reverse relationship i s observed between log K-2 for all Schiff's bases and the mole fractio n of dioxan. However, the log K-1 values corresponding to the protonat ion of naphtholate O-ions have been found to increase with the increas e in concentration of dioxan. Both electrostatic and non-electrostatic contributions influencing these constants are briefly discussed.