Verdazylium salts

The reaction of verdazyls (111) with diacyl peroxides, such as benzoyl peroxide, dilauroyl peroxide, perbenzoic acid and substituted perbenzoic acids has received considerable attention (76TL1893, 78ZOR2471, 78MI22101). One mole of the radical always consumes three moles of the peroxide. The first product is the verdazylium salt (113) which is then transformed into the Af-formylformazan (112). 

Verdazylium salts 13 can be obtained in high yield by reacting the corresponding triphenylformazans with formaldehyde in acid media in a two phase system (CHCV HjO). The reduction of the salts with ascorbic acid in the two phase system gives the verdazyl radicals, whereas in methanol leucoverdazyls are obtained <97S 17>. 

In general, C3-saturated verdazyls 1 are prepared via oxidation of the readily prepared leucoforms 2 (1963AGE155), and less commonly via the reduction of verdazylium salts 3 using excess ascorbic acid as a mild one-electron reductant (Scheme 1) (1997S17). 

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