Heterocyclic compounds from alloxan and amines. XIII. Phenazine freeradical betaines and their dehydro dimers derived from alloxan and 2-aminodiphenylamines

2-Amino-N-alkydiphenylamines and 2-aminotriphenylamines react with alloxan at room temperature to give green, intensely coloured, stable, free-radical betaines (dihydrophenazinioylbarbiturates). Heating the free-radical betaines alone or in a solvent gives rise to blue dimers. 3,7-Disubstitution of the phenazinioyl nucleus by methyl groups prevents formation of the blue dimers, which are therefore considered to arise by dimerization at the 3-position, followed by dehydrogenation. Dimerization of 3,7- dimethyldihydrophenazinioylbarbi- turates gives deep green 3,3?-dimers in which the 3,3?-methyl substituents prevent the dehydrogenation step entailed in the formation of the blue dehydro dimers. ��� A violent explosion occurred in two instances during preparation of phenazine by oxidative sublimation of crude dihydrophenazine by Morley's method (J. chem. Soc., 1952, 4008).