Journal of the Chemical Society. Perkin transactions II p. 632 - 636 (1980)
Update date:2022-08-17
Topics:
Blackborow, John R.
Clifford, David P.
Hollinshead, Ira M.
Modro, Tomasz A.
Ridd, John H.
Worley, Michael C.
The rate of N-H hydrogen-isotope exchange in NN-dimethylanilinium ions has been studied in the solvents sulphuric acid and deuteriosulphuric acid using the difference in the (1)H n.m.r. absorption of the N(1+)Me2H and N(1+)Me2D groups.With the N-deuterio-NN-dimethylanilinium ion, the reaction rate decreases steadily with acidity as expected from previous studies of the reaction mechanism at lower acidities.However, the rate of N-D exchange in the N-deuterio-NN-dimethyl-3,5-xylidinium ion reaches a minimum in 83percent sulphuric aacid and then increases steadily with the acidity.Under the same conditions, hydrogen-isotope exchange occurs in the aromatic ring.The effect of methyl substituents on the rate of the acid-catalysed N-H exchange indicates that this reaction and the C-H exchange have a common initial step involving the donation of a proton or deuteron to the positions in the aromatic ring ortho or para to the nitrogen.The Wheland intermediate, so formed, is considered to be able to lose a proton from either the carbon or the nitrogen.This interpretation of the acid-catalysed exchange is supported by the effect of isotopic substitution in the aromatic ring on the rate of N-H exchange and by preliminary studies on the range of this reaction mechanism.
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