The kinetics and mechanism of the electrophilic substitution of heteroaromatic compounds. Part XXVIII. The preparation and kinetic nitration of 2-, 3-, and 4-dimethylaminopyridines and their 1-oxides in sulphuric acid

Abstract

Preparative nitration of the title compounds in sulphuric acid affords products nitrated ortho or para to the dimethylamino-group in good yields for 2- and 4-dimethylaminopyridines and in poor yields for 3-dimethylaminopyridine and the 2- and 4-dimethylaminopyridine 1-oxides; a variety of demethylated and nitrosated by-products are also formed. The preparative results are rationalised from a qualitative viewpoint, and the conclusions confirmed in part by kinetic measurements at various acidities. Well established criteria show that nitration of 2- and 4-dimethylaminopyridine is occurring on the mono-protonated forms. The substitution of base-weakening nitrogroups into the aminopyridine nuclei favours free-base nitration, and the extent to which this happens is discussed.