Formation of Radical Intermediates in Sulphur Dioxide Solutions of Tertiary Aliphatic Amines

Abstract

The addition of molecular iodine to solutions of tertiary aliphatic amines in liquid sulphur dioxide is found to result in the formation of stable free radical oxidation intermediates. In triethylamine solutions, oxidised under these conditions, aromatisation appears to take place to produce a pyridinyl radical. Radicals formed from N-ethyldimethylamine, Ν,Ν-diethylmethylamine and tri-n-propylamine on the other hand appear to be essentially aliphatic in character, with two of the N-alkyl groups intact. The magnitude of the measured coupling constants however, implies some delocalisation in the “damaged” alkyl group, possibly via a tautomeric mechanism. A number of mechanistic possibilities are explored to account for the roles played by iodine and sulphur dioxide in these reactions.