Studies On Synthesis Of Bis(Benzoxazol-2-Yl) Stilbenes

Bis(benzoxazol-2-yl)stilbenes, including 4,4'-bis(benzoxazol-2-yl) stilbene and 4-(5-methylbenzoxazol-2-yl)-4'-(benzoxa zol-2-yl)stilbene, are a very important type of benzoxazolyl compounds. Bis(benzoxazol-2-yl) stilbenes are very suitable for use as optical brightener for polyesters and plastics, because of their excellent heat-resistant performance.Processes for the preparation of 4,4'-bis (benzoxazol-2-yl) stilbene and 4-(5-methylbenzoxa zol-2-yl) -4'-(benzoxazol-2-yl)stilbene are already known , However, there are some shortcomings in these processes. For example, the yield is lower, and can produce large quantity of poisonous H₂S gas and waste water containing acid or alkali.In this paper, a new synthesis process for bis(benzoxazol-2-yl)stilbene was developed by additive cyclization, esterification and Wittig-Horner condensation using 4-cyanobenzyl chloride, o-aminophenol and 4-formylphenylbenzoxazole as starting materials.4,4'-Bis(2-benzoxazolyl)stilbene was synthesized by additive cyclization, esterification and condensation. The optimum conditions of cyclization are that n(addition product) :n(o-aminophenol) is 1: 0.95, reaction temperature is 70℃ and reaction time is 1h. The optimum conditions of esterification are that n(4-chloromethylphenyl-benzoxazole) :n(triethyl phosphite) is 1: 4, reaction temperature is 165℃ and reaction time is 5h. The optimum conditions of condensation are that n(diethyl benzoxazolylbenzyl phosphate):n(p-formyl-phenylbenzoxa-zole) :n(sodium methylate) is 1:1:1.6, reaction temperature is 20℃ and the reaction time is 8h. Under the optimal conditions, the yield was over 68%.Dimethyl ester 4,4'-stilbenedicarboxylic acid was synthesized by Wittig-Horner condensation using p-chloromethylbenzoic acid and methyl p-formylbenzoate as starting materials, which was used to produce 4,4'-Bis(2-benzoxazolyI) stilbene instead of 4,4'-stilbenedicarboxylic acid. In result, this change can obviously reduce the waste gas and liquid .The optimum conditions of chlorization are that n(p-toluic acid):n(sulfonyl chloride) is 1: 1.75, reaction temperature is 90℃ and reaction time is 4h, the yield is 75%. The optimum conditions of esterification is that n(4-chloromethylbenzoic acid):n(triethylphosphate) is 1: 4, reaction temperature is 160-165°C, and the reaction time is 6h, the yield is up to 92.5%. The optimum conditions of condensation is that n(diethyl benzyl phosphate): n(methyl p-formylbenzoate):n(sodium methylate) is 1: 1: 1.6, reaction temperature is 20℃, and the reaction time is 8h, the yield is above 95%. In the cyclization, using methylnaphthalene as solvent, the yield is 88% after reflux 18h.4-(5-methyl-benzoxazol-2-yl)-4'-(benzoxazol-2-yl)stilbene wassynthesized by a new process including additive cyclization, esterification and Wittig-Horner condensation using 4-cyanobenzyl chloride, o-amino-methylphenol and 4-formylphenylbenzoxazole as starting materials.The optimum conditions of cyclization are that n(addition product) :n(o-amino-5-methylphenol) is 1: 0.95, reaction temperature is 70 ℃ and reaction time is lh, the yield is 85%. The optimal conditions of esterification is that n(4-chloromethylphenyI-5-methyl-benzoxazole): n(triethylphosphate) is 1: 4, reaction temperature is 160℃, and the reaction time is 6h, the yield is above 92%. The Optimal conditions of condensation is that n(diethyl benzoxazolylbenzyl phosphate):n(p-formyl-phenyl-benzoxazole) :n(sodium methylate) is 1: 1: 1.6, reaction temperature is 20 ℃ and the reaction time is 8h, the yield is about 90%.