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

The addition of molecular iodine to solutions of te rtiary aliphatic amines in liquid sulphur dioxide is found to result in the formation of stable free radical oxidation in te r­ mediates. In triethylam ine solutions, oxidised under these conditions, arom atisation appears to take place to produce a pyridinyl radical. Radicals formed from N-ethyldim ethylam ine, N ,N -diethylm ethylam ine and tri-n-propylam ine on the other hand appear to be essentially aliphatic in character, w ith two of the N-alkyl groups in tact. The m agnitude of the measured coupling constants however, implies some delocali­ sation in the “ dam aged” alkyl group, possibly via a tautom eric mechanism. A num ber of mechanistic possibilities are explored to account for the roles played by iodine and sulphur dioxide in these reactions.