On the Basicity of Triarylmethylamines in Solution

Article abstract of DOI:10.1002/hlca.19800630405

The pK_a^* of 11 triarylmethylamines (tritylamines), eight of which are new, and some related bases were measured in methylcellosolve/water 80:20 (MCS); some were also measured in dioxane/water 60:40 (Dx), acetonitrile (An), nitrobenzene (Nb) and acetic acid (Ac). 1) The influence of the aryl groups on the basicity is essentially additive; 2) In different solvents, similar linear free energy relationships were found, with differences in ρ^* characteristic of solvation; 3) The influence on basicity of substituents of the aryl groups follows Hammett's relationship.These results indicate a preponderance of inductive effects.N,N-Dimethyltritylamine (3b) pK_a^MCS = 3.40) shows a marked crowding effect, absent in the isomeric tertiary amines 13 and 14.Tri-p-nitrotritylamine (10a) 8pK_a^MCS = 3.10), N,N-dimethyl-tri-p-nitrotritylamine (10b) (pK_a^Ac = 0.50), and 3b are particularly weak bases; the baseweakenning effect of the trinitrotrityl group is similar to that of the cyanomethyl and trifluoroethyl groups.