Study Of A Clean Process For Synthesis Of Benzotriazole Ultraviolet Absorber

Currently there are some problems in the industrial producing benzotriazole UV absorbers such as complex process, serious environmential pollution, poor quality of the products. In this paper,2-(2’-hydroxy-5’-methylphenyl)-benzotriazole (UV-P),2-(2’-hydroxyl-3’,5’-di-tertbutylphenyl)-benzotriazole (UV-320),2-(2’,4’-dihydroxylphenyl)-benzotriazole and2-(2’-hydroxyl-4’-amino-phenyl)-benzotriazole were synthesized by diazotization, coupling and reduction reaction with o-nitroaniline,p-cresol,2,4-di-tertbutyl-phenol, resorcinol,3-amino-phenol as raw material. Clean and efficient processes for preparation of them were studied and the main reaction mechanism were discussed. The target compounds were characterized by1H NMR, MS and IR and the ultraviolet performance were tested.2-Nitro-(2’-hydroxyl-5’-methylphenyl)-azobenzene,2-nitro-(2’,4’-dihydroxylphenyl)-azobenzene and2-nitro-(2’-hydroxyl-4’-aminophenyl)-azobenzene were prepared by emulsion coupling process with sodium dodecylbenzenesulfonate and2-nitro-(2’-hydroxyl-3’,5’-ditert-butylphenyl)-azobenzene was prepared in ethanol-water system while n(o-nitroaniline): n(phenol)=1:1and the temperature is0-5℃. When the2-nitro-(2’-hydroxyl-5’-methyl-phenyl)-azobenzene and2-nitro-(2’-hydroxyl-3’,5’-di-tertbutylphenyl)-azobenzene were synthesized the pH is7-9and the yields were higher than95%and82%with purities of more than96%(by HPLC). When the2-nitro-(2’,4’-hydroxylphenyl)-azobenzene and2-nitro-(2’-hydroxyl-4’-aminophenyl)-azobenzene were synthesized the pH value is less than1and the yields were higher than92%with the purities of more than95%and more than80%(by HPLC). After the coupling wastewater was cyclic used3times there is no significant change in the yield and the purity of the azo intermediates; the sodium sulfate should be filtered out after the coupling wastewater was cyclic used3-5times.UV-P,2-(2’-hydroxy-4’-aminophenyl)-benzotriazole and UV-320were prepared by two-step process using glucose-zinc powder while n(NaOH):n(glucose):n(azo intermediate)=2.5:1.2:1and the temperature is55～60℃. In the process of alkaline zinc powder reduction, n(NaOH):n(oxygen intermediates):n(powder)=1.8:1:1.2and the temperature is85～90℃. The yields were separately higher than80%,60%and71%and the purities were heigher than96%(by HPLC) after purification. Ethanol was required in the preparation of UV-320. Thiourea dioxide was used in the80℃aqueous alkaline solution to prepared2-(2’,4’-dihydroxyphenyl)-benzotriazole with feeding by batches and the yield was above70%and the purity was above97%(by HPLC) after purification. The target products were prepared by catalytic hydrogenation with1%Pd/C as a catalyst while the hydrogen pressure was2.5MPa and the stirring speed was350-400r/min and the temperature was55～65℃. After9h, the process give the product UV-P with the yield of above74%and purity of above98%(by HPLC) and2-(2’-hydroxyl-4’-aminophenyl)-benzotriazole with yield of above56%, purity of above99%after purification and UV-320with yield of above66%, purity of above99%(by HPLC). The hydroxyl was protected before hydrogenation in the preparation of2-(2’,4’-dihydroxylphenyl)-benzotriazole. The intermediate was hydrolyzed in the alkaline solution to deprotection after hydrogenation reaction to get the product with the yield of above56%and purity of above98%. There is no significant change in the yield and the purity of the targets after the hydrogenation catalyst was cyclic used twice.