Laser‐flash photolysis study of dithiobis (tetrazole); reactivities of tetrazole‐thio radical

The photo-cleavage of SS bond of 5,5′-dithiobis (1-phenyl-1H-tetrazole) has been studied by the nanosecond-laser flash photolysis method. The transient absorption band at ca. 430 nm was attributed to 1-phenyl-1H-tetrazole-5-thio radical forming by the SS bond fission. For the reaction with conjugated dienes, an addition reaction takes place forming the SC bond, suggesting that unpaired electron of the radical localizes mainly on the S-atom. From the decay rates of the radical, the addition reaction rate constant for 2-methyl-1,3-butadiene is evaluated to be 5.5 × 109 M−1 s−1 in THF at 23°C, which is as fast as diffusion controlled limit. The reactivity of the radical is ca. 100 times higher than that of the PhS˙. The reactivity of the thio radical to O2 was too low to evaluate, which is one of the characteristics of a S-centered radical. The rate constant for 1,4-cyclohexadienene (1.4 × 108 M−1 s−1) is larger than that of cyclohexene (2.8 × 107 M−1 s−1) suggesting the hydrogen abstraction is a main reaction. The MO calculations have been performed for these radicals to reveal the reason of the high reactivity of the radical. © 1996 John Wiley & Sons, Inc.