Лако-красочные материалы — производство

Solutions of tetrazolium salts, e. g., 53, have been reported to both become colored and bleached under the influence of both UV and visible light. Several workers have attributed this phenomenon to photoreduction to the corresponding formazan (51) and the formation of a fluorescent colorless compound (152) through photooxidation.240- 243 The reduction of 152 under UV or blue light to the intense green radical structure (153) has also been reported (Scheme 21).244 A one-electron reduction product (154) is proposed as a short-lived intermediate in the photoreduction.245

This reaction is influenced by solvent. Thus, in aqueous solutions 2,3,5- triphenyltetrazolium chloride yields 1,3,5-triphenylformazan (51), while in ethanol 152 is obtained. The mechanism of this reaction is not well understood.246 — 254

In a related manner, gamma radiolysis of tetrazolium salts also yields formazans.256,257 Pulse radiolysis in aqueous solutions leads to tetrazole

O-cj

(152)

Colorless, fluorescen

Reduction

Scheme 21

radicals which can then disproportionate to formazan anions and tetra — zoliumsalts.258-260

Unlike others, the 5-isopropyl tetrazoliums (155) undergo photode­protonation to 156 which then yields the aziridimine (157) with the elimination of nitrogen (Scheme 22).254

Scheme 23