97% sodium hydroxide 9.6 g was added to methanol 100 ml, and was stirred at 65° C. for 30 minutes. After cooling to 50° C., 2-nitro-4-chloro-2'-hydroxy-3'-t-butyl-5'-methylazobenzene 11.6 g was added to the resultant mixture over 30 minutes, and thereafter 2,3-dichloro-1,4-naphthoquinone 0.7 g was added. Glucose 8 g was added to the resultant mixture at 40° to 45° C. over one hour, and the mixture was stirred for one hour at 40° to 45° C. As this result, almost all of the azobenzenes disappeared to produce 2-(2'-hydroxy-3'-t-butyl-5'-methylphenyl)-5-chlorobenzotriazole-N-oxide, thus the reaction of Process (b) being completed.
