Tetrachlorobenzotriazole is readily prepared in 87% yield by heating a solution of benzotriazole in a mixture of hydrochloric and nitric acids . 5,6-Dibromobenzotriazole is prepared in 62% yield by treatment of benzotriazole with bromine and silver sulfate in concentrated sulfuric acid . Under more forcing conditions, when the reaction is run in refluxing nitric acid, 4,5,6,7-tetrabromobenzotriazole is formed () . 1-Ethylbenzotriazole , is chlorinated by refluxing in a mixture of concentrated hydrochloric and nitric acids to give 1-ethyl-4,5,6,7-tetrachlorobenzotriazole in 81% yield . A reaction of derivative with bromine in refluxing concentrated nitric acid provides 1-ethyl-4,5,6,7-tetrabromobenzotriazole in 68% yield .