Synthesis of 2,4-dihydro-6-methyl-4-phenyl-2-(4-substituted phenyl)pyrazolo[3,4-d]-1,2,3-triazole derivatives and their use as fluorescent whitener

Diazotised arylamines ( 2a – 2c ) were coupled with 5-amino-3-methyl-1-phenylpyrazole 1 to give 5-amino-4-arylazo-3-methyl-1-phenylpyra-zoles ( 3a – 3c ) which were then oxidised, using cupric acetate and DM F in a current of air, to the 2,4-dihydro-6-methyl-4-phenyl-2-(4-substituted phenyl)pyrazolo[3,4-d]-],2,3-triazoles( 4a – 4c ).The carboxylic acid group in 4c was further converted to the corresponding 2-[4-(benz-imidazol-2-yl)phenyl], 2-[4-(benzoxazol-2-yl)phenyl] and 2-[4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl]-derivatives( 6a , 6b and 8 respectively). 2-Hydro-2-(4-aminophenyl)naphtho[1,2-d]-1,2,3-triazole ( 9 ) was diazo-tised and similarly converted to 2,4-dihydro-6-methyl-4-phenyl-2-[4-(2-hydronaphtho[1,2-d]-1,2,3-triazol-2-yl) phenylpyrazolo [3,4-d]-1,2,3-triazole ( 10 ). Benzidine ( 11 ) as tetrazotised and similarly converted to 2,2'-(1,1'-biphenyl-4,4'-diyl)bis(2,4-dihydro-6-methyl-4-phenylpyrazolo-[3,4-d]-1,2,3-triazole) ( 12 ),using 2 moles of 1 . The 2,4-dihydro-6-methyl-4-phenyl-2-(4-substituted phenyl) pyrazolo[3,4-d]-1,2,3-triazole derivatives ( 4a – 4b , 6a – 6b , 8 and 10 ) and 2,2'-1,1'-biphenyl-4,4' -diyl)-bistriazole ( 12 ) were applied as fluorescent whiteners on polyester fibres and gave excellent results.