Abstract The thermal decomposition of a series of cyclic α-azo hydroperoxides (3, 3, 5-R 1, R 2, R 3-4, 4-dimethyl-4, 5-dihydro-5-hydroperoxy-3H-pyrazoles; 2a R 1= R 2= R 3= Ph; 2b R 1= R 3= Ph, R 2= Me; 2c R 1= R 3= p-Anisyl, R 2= Me; 2d R 1= R 2= Me, R 3= Ph; 2e R 1= R 3= Me, R 2= Ph), synthesized by oxidation of the corresponding 3, 4-dihydro-2H-pyrazoles, proceeded smoothly with evolution of nitrogen. The relative stability series was found to ...