Titrations in non-aqueous media. Part IX. Potentiometric titrations of symmetrical aliphatic diamines and their Schiff bases in different solvents

Abstract

Four aliphatic symmetrical diamines (1,2-diaminoethane, 1,3-diaminopropane, 1,4-diaminobutane and 1,6-diaminohexane) plus hydrazine and their Schiff bases with salicylaldehyde were titrated potentiometrically with perchloric acid in acetonitrile, nitrobenzene and acetic acid solvents. 1,2-Diaminoethane and 1,3-diaminopropane were titrated stepwise in acetonitrile, but not in nitrobenzene and acetic acid solvents. An increase in the number of methylene groups between the two amino groups increased the basicity. The basicity order of these diamines, extracted from the second half of the titration curves in all solvents, and also for their Schiff bases, was 1,6-diaminohexane > 1,4-diaminobutane > 1,3-diaminopropane > 1,2-diaminoethane > hydrazine. Among the Schiff bases, only N,N′-bis(salicylidene)-1,2-diaminoethane could be titrated differentially in acetonitrile and nitrobenzene solvents. N,N′-Bis(salicylidene)hydrazine could not be titrated even in acetic acid. However, the same compounds could be titrated in acetonitrile and nitrobenzene. Acetic acid had a very strong levelling effect on the basicity on both sides of the potential range.