Oxidation to Quinoid Dyes

Isopropylidene or benzylidene 2-hydrazinoselenazole derivatives can be converted to highly colored 2.2 -dioxo-A-3,3 -biselenazol-5,5 -inylidene-bis-hydrazones (Table X-11) by oxidation with ferric chloride and hydrogen peroxide i33). 

This reaction is proof of the structure of the dye, easily obtained from the dihydro compound (3). Yields are low as a result of numerous side reactions. The stereochemical configuration of these quinoid dyes is trans. 

TABLE X-11. BIS-ISOPROPYLIDENE OR BENZYLIDENE DERTVATIX S OF 2.2-DIOXO-A-3,3-BISELENAZOL-5.S -rNYLIDENE BIS HYDRA-ZONES (33) 

Quaternarj salts are obtained by alkylation of selenazole bases, the heterocyclic nitrogen atom playing the role of nucleophile with regard to the electrophilic carbon of the alkylating, agent. 

They are used principally as intermediates for cyanine dyes that serve in photography (5, 6. 35. 36. 50-52). 3-Ethyl-2,4-dimethylselenazolium iodide (m.p. 157-8 C) was prepared as colorless crystals in 87% yield by Brooker et al. (6) by heating 2,4-dimethyls el en azole with an excess of ethyl iodide for 48 hr. 

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