To a stirred mixture of 75 g of 5-chloro-2-(2-hydroxy-3-α-cumyl-5-tert-octyl-phenyl)-2H-benzotriazole and 105 g of N-methylpyrrolidone heated at 90° C. is added first 44.3 g of 45% aqueous potassium hydroxide solution over a 15-minute period then 20.4 g of thiophenol over another 15 minutes. The reaction mixture is then heated at 170-175° C. for four hours with water being removed by distillation. After cooling to 100° C., xylene and water are added and the resultant mixture is made acidic with 15% aqueous hydrogen chloride solution. The organic layer is separated and washed with water and then concentrated. The crude product residue is recrystallized from methanol to yield 82 g of the title compound as a pale yellow solid melting at 124-125° C.
