A synthesis of pseudo-mauveine and a homologue

Treatment of N-phenyl-p-phenylenediamine and two equivalents of aniline with potassium dichromate in hot water acidified with a small amount of sulfuric acid gives 3-phenylamino-5-phenyl-7-aminophenazinium sulfate (pseudomauveine). The oxidation of N-phenyl-p-phenylenediamine and o-toluidine with potassium dichromate in water with a small amount of sulfuric acid gives 3-phenylamino-5-(o-toluyl)-7-amino-8-methylphenazinium sulfate. Oxidation of aniline and (o or p) toluidine only gave small quantities of mauveine chromophores. Oxidation of p-toluidine gives a known dimer which gives a purple coloured solution in acid. A hypothesis is described in which N-phenyl-p-phenylenediamine may have been involved in mauveine synthesis in the nineteenth century.