Potassium Iodide → 5-n-Dodecylthio-2-(2-hydroxy-3,5-di-tert-butylphenyl)-2H-benzotriazole

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To a 3-liter three-necked flask equipped with stirrer, thermometer, nitrogen inlet and distillation set-up are charged 357.8 g (1 mole) of 5-chloro-(2-hydroxy-3,5-di-tert-butyl-phenyl)-2H-benzotriazole, available from CIBA-GEIGY Corp. as TINUVIN® 327, 216.8 g (1.05 mole) of n-dodecyl mercaptan and 600 mL of N,N-dimethylformamide (DMF). Then 73.9 g (0.54 moles) of potassium carbonate and 2 g of potassium iodide are added and the mixture heated for 20 hours at 150° C. under a nitrogen atmosphere. Any water which is liberated as a result of the reaction distills off as an azeotrope until the head-temperature reaches 132° C. After 20 hours at 150° C. the starting 2H-benzotriazole is totally consumed. With partial vacuum at 80°-100° C., most of the DMF is distilled off. To the resulting oil is added at 80° C. 1 L of toluene and 500 mL of water. The aqueous phase is drained off. The toluene solution is washed twice more with 500 mL water containing 1 mL of acetic acid. The organic solution is freed from residual water by azeotropic distillation until a clear solution is obtained. Under partial vacuum all but about 100 mL of toluene is distilled off at 70° C. The residue is diluted at 60° C. with 2 L of isopropanol and some product seeds are added The product gradually crystallizes and the mixture is slowly cooled to 10° C. The product is filtered off and washed with 300 mL of isopropanol to yield 490.4 g (93.6% of theory) of the title compound, mp. 62°-64° C.

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