The Research On Synthesis Of Benzoxazolyl-Stilbene Series Fluorescent Brighteners And Its Intermediates

Benzoxazolyl-stilbenes,including 4,4'-bis(benzoxazol-2-yl) stilbene and 4-(5-methylbenzoxazol-2-yl)-4'-(benzoxazol-2-yl)stilbene,are a very important type of benzoxazolyl compounds.Benzoxazolyl-stilbenes are very suitable for use as fluorescent brightener for polyesters and plastics,because of their excellent heat-resistant performance.Processes for the preparation of benzoxazolyl-stilbene are already known,However, there are some shortcomings in these processes.For example,can produce large quantity of poisonous H₂S gas,wastewater containing acid or alkali and environment pollution.So it possessed good benefit and economic value to explore a new path for synthesizing the products.This paper has reviewed the synthesis development of benzoxazolyl-stilbene in recent years,and analyzed their merits as well as shortcomings.A new synthesis process for benzoxazolyl-stilbene was developed by cyclization and Claisen-Schmidt condensation. Highlighted studying its unite reactions.Better technology conditions have been determined. The after-treatment of product is improved.Simultaneously,the intermediates had been studied also.4,4'-Bis(2-benzoxazolyl) stilbene was synthesized by condensation,cyclization and condensation using p-toluic acid,o-amino phenol and 4-formylphenylbenzoxazole as starting materials.The better conditions of cyclization are that n(o-amino phenol):n(p-toluic acid) is 1:1.093,refluxing reaction time is 5h,cyclization temperature is 200～215℃and in the presence of boric acid as catalyst.The yield of 80.8%is obtained.The better conditions of condensation are that group by group feed in raw material, w(4-formylphenylbenzoxazole):w(4-methylphenylbenzoxazole)=2.3g:2.5g,reaction time is 5h,reaction temperature is 50℃,The yield of 43.1%is obtained.4-(5-methylbenzoxazol-2-yl)-4'-(benzoxazol-2-yl)stilbene was synthesized by condensation,cyclization and condensation using p-toluic acid,o-amino-p-methyl phenol and 4-formylphenylbenzoxazole as starting materials.The better conditions of cyclization are that n(o-amino-p-methyl phenol):n(p-toluic acid) is 1:1.08,refluxing reaction time is 5h, cyclization temperature is 200～220℃and in the presence of boric acid as catalyst.The yield of 84.7%is obtained.The better conditions of condensation are that group by group feed in raw material, w(4-formylphenylbenzoxazole):w(2-(p-methylphenyl)-5-methyl-benzoxazole)=2.0g:2.3g, reaction time is 5h,reaction temperature is 50℃,The yield of 46.9%is obtained.4-(5-methylbenzoxazol-2-yl) stilbene was synthesized by condensation using 2-(p-methyl phenyl)-5-methyl-benzoxazole and benzaldehyde as starting materials.However, the synthesis of 4-(5-methylbenzoxazol-2-yl) stilbene meets much difficulty,and finally not gets better result.The obtained intermediates and products have been characterized by HPLC,UV,mass spectrum and ¹H-NMR etc.