Ar. Katritzky et Sa. Belyakov, A DIRECT ONE-STEP PREPARATION OF TRIARYLVERDAZYLIUM SALTS FROM THE CORRESPONDING TRIARYLFORMAZANS, Synthesis, (1), 1997, pp. 17
6-(4-Substituted-phenyl)-2,4-diphenylverdazylium salts 2 (8 examples,
55-93 %) were prepared by the reaction of 3-(4-substituted-phenyl)-1,5
-diphenylformazans 1 with formaldehyde and different organic and inorg
anic acids in a two-phase chloroform/water medium by brief and gentle
heating. Self-phase-transfer catalysis is apparently involved. Subsequ
ent reductions of the salts 2 with excess ascorbic acid in the two-pha
se system give the corresponding verdazyl radicals, while in methanol
the reduction proceeds to form leuco-verdazyls.