IT1071652B - 2-Aryl 2H-benzotriazole derivs. prepn. - by reductive cyclization of 2-nitro azabenzene derivs. (BE161176) - Google Patents

Abstract

2-Aryl-2H-benzotriazole derivs. of formula (I): (where R1 is H or Cl, R2 is H, Cl, 1-4C alkyl, 1-4C alkoxy, 2-9C carbaloxy, COOH or SO3H, R3 is 1-12C alkyl, 1-4C alkoxy, phenyl, phenyl substd. by 1-8C alkyl, 5-6C cycloalkyl, 2-9C carbalkoxy, Cl, carboxyethyl or 7-9C aralkyl, R4 is H 1-4C alkyl, 1-4C alkoxy, Cl or OH, and R5 is H 1-12C alkyl, Cl, 5-6C cycloalkyl, or 7-9C aralkyl), e.g 2-(2-hydroxy-5-methylphenyl)-2H-benzotriazole, are prepd. by reducing and cyclizing a corresp. o-nitro-azobenzene with hydrogen at ca 20-100 degrees C and ca 1-66 atmospheres in admixture with an aq. alkaline/organic medium at pH >10 in the presence of gp. VIII noble metal hydrogenation catalyst being other than Pd when R1, R2, R3, R4 or R5 is Cl), and isolating the desired 2-aryl-2H-benzotriazole. The 2-aryl-2H-benzotriazoles are extensively used as dyestuff intermediates, optical brightening agents, blue fluorescent agents and selective UV - absorbing stabilizers for fibres, films and various polymeric structures subject to destruction by UV radiation. The new process gives (I) in high yields and avoids pollution problems associated with known processes.