Study On The Photoisomerization Of Norbornadiene

The phtotsensitized isomerization of norbornadiene to quadricyclane was investigated using 4,4'-bis(diethylamino)benzophenone as triplet sensitizer.The effects of reaction conditions,such as concentration of sensitizer,initial concentration of norbornadiene,reaction time and solvents on conversion and selectivity were discussed.And the optimal conditions of this reaction were obtained.The results show that the conversion increases with the increase of the concentration of sensitizer till it reaches 1.86%(wt).After that the concentration of sensitizer has no significant effect on the conversion.In our work,the conversion of norbornadiene increases with the increase of initial concentration of norbornadiene.The optimal concentration of nonbornadiene is 0.8 mol·L^-1.The conversion of norbornadiene increases as the reaction time increases,with a steep gradient at initial stage,which is gradually stablized as the time beyond 12 hours.In different solvents,the conversion of norbomadiene,as well as the selectivity of quadricyclane,is different.The conversion of this reaction depends on the polarity of solvents.The solvents of weak polarity are preferable for the conversion of this reaction.The selectivity is independent on the polarity of solvents.Since the photolytic products of halohydrocarbon will react with both norbornadiene and its photolytic products,the selectivity of quadricyclane decreases.So the halohydrocarbon is not suitable for this reaction.The Y zeolites catalysts were produced via ion-exchanging or impregnating method.The characters of zeolites in photoisomerization of norbornadiene is studied. The results of XRD,EDS,²⁹Si-NMR,²⁷Al-NMR,UV-VIS and FT-IR showed that the ion-exchanging method can move the metal ion into the cage of zeolites.The method of "twice exchanging and twice calcination" can improve the exchanging degree.The biggest exchanging degree is 88.85%.The ions of metal in the cage of zeolites are benefit to the reaction of photoisomerization.And La³⁺is the best catalysts.As the enhancement of exchanging degree,the conversion of photoisomerization is increased.The photoisomerization of norbornadiene catalyzed by zeolites have better selectivity.The selectivity of quadricyclane is 100%in weak polority solvents.