Tetrazole, 5-phenyl-, thermolysis

These intermediates have been intensively studied and characterized by the addition to reactive multiple bonds giving 5-membered heterocyclic adducts . The decomposition of 2,5-diphenyltetrazole follows first order kinetics, with a rate nearly independent of the nature of the solvent . This precludes an interaction with the medium prior to elimination of the nitrogen molecule and confirms that the nitrile imine is an intermediate. Alkylated tetrazoles also undergo elimination of nitrogen on heating. With 2-methyl-5-phenyl-tetrazole however, thermolysis does not occur below about 220 °C and proceeds in competition with a second mode of decomposition which leads to benzonitrile and methylazide , viz. 

A similar transformation occurs during the thermolysis of l-thiacarbamyl-5-phenyl tetrazole (286) to give 5-amino-3-phenyl-1,2,4-thiadiazole (287) (Equation (43)) <92JPR283>. 

A well-known reaction of tetrazoles is the thermolysis of 2,5-disubstituted tetrazoles to give nitrilimines by loss of N2 an example is shown in Scheme 4. The reaction is used not only for its synthetic potential but also as a source of nitrilimines for direct observation and exploration of their behavior. The first direct detection of a thermally generated nitrilimine was the species (31) produced by flash vacuum pyrolysis of 5-phenyl-2-trimethylsilyltetrazole (85AG(E)56). The parent nitrilimine, HCNNH, has been generated by file photolysis of tetrazole (96LA1041). 

Gas-phase thermolysis of 5-methyl- and 5-phenyl-2-(trimethylsilyl)-tetrazole (47) has been studied by real-time PE spectroscopy by Bock et al. (87TL617). N2 is split off quantitatively at the spectroscopically optimized temperatures of 750 K (R = CH3) and 770 K (R = C6H5), and the substituted nitrile imines are generated exclusively. 

Reactivity with Tetrazoles. Reactive tetrazoles were used for the synthesis of rubbers having an appreciable ageing protection [237]. 2-(Subst.)phenyl -5-(3,5-di-tert-butyl-4-hydroxyphenyl)tetrazole (181) can be compounded without thermolysis with BR or IR. At vulcanization temperatures, 181 is thermolysed and reactive nitrileimine 182 undergoes 1,3-dipolar addition to C = C double bonds. 183 is formed with yields from 70 to 85%, depending on the character of R in 181 (the activity series R = CH3 < H < Cl). Mechanistic model experiments were performed with 181 (R = Cl) and styrene, the latter was isued as a model instead of IR [237]. l-(3-Chloro-phenyl) -3-(3,5-di-/ert-butyl-4-hydroxyphenyl)-5-phenyl-2-pyridazoline was isolated in 44% yield and medhanism of the attachement of 183 to IR was thus confirmed. 

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