Study Of Reaction Behavior With Photocatalytic Synthesis Of Aromatic Acetalization

Aromatic acetals as a specific kind of fine chemicals has very significant appli-cation value in organic synthesis and industrial production.In this paper, heterogene-ous photocatalytic technology is firstly applied to the acetal reaction in a self-designed constant temperature quartz-glass photocatalytic reactor with UV-LED as light source. Different kinds of TiO2photocatalysis have been prepared and their photocatalysis properties were evaluated.Benzaldehyde Diethyl Acetal (BDA) has been high selec-tively synthesized.the condition of acetal reaction has been optimized. The photocata-lytic acetal reaction of benzaldehyde with different substitutions have also been rese-arched and the mechanism was discussed.Pure TiO2,N/TiO2,Pt/TiO2and PtN/TiO2were prepared by sol-gel method with tetrabutyltitanate[Ti(OC4H9)4] as a precursor,ammonia(NH3)as nitro source,and six hydration chlorine platinum acid(H2PtCl6·6H2O) as platinuim source respectively.The properties of the various kinds of TiO2were studied by different technologies, such as XRD,XPS and TEM.X-ray diffraction(XRD) and Transmission Electorn Microscope (TEM) showed that the self-synthesized TiO2by sol-gel method mainly are composed with anatase globular particles,and average particle size is less than20nm.The photo-catalytic activities of self-synthesized TiO2and commercial mixed crystal-Degussa P25were evaluated by photo-degradation of methylene blue solution and the result showed that all catalysts demonstrated good capacity of photodagradation,in which mixed crystal-Degussa P25is the best.We have designed the photocatalytic reaction system equipped with adjustable light intensity UV-LED array light source and constant temperature quartz glass reactor. Based on the system, photocatalytic synthetic reaction behavior of Benzaldehyde Diethyl Acetal(BDA) is studied in anhydrous alcohol with Degussa P25as a catalyst from benzaldehyde. The effects of reaction solution pH, light intensity, reaction time, concentration of substrate, loading of TiO2and dimension of the reactor on reaction rate and yield of BDA were evaluated. Several alcohols such as methanol. ethanol and isopropanol as reactant of the acetal reaction with benzaldehyde were also studied. The yield of BDA could reach high up to100%under the condition of solution pH7.86, TiO2concentration:5.0g/L,benzaldehyde initial concentration:0.05mol/L, light intensity:0.6mw/cm2,temperature:30℃.reaction time:15min. Additionally,the reaction rate was also related to the pKa of the alcohols, the smaller pKa value, the more lively alcohol, the higher the reaction activity.Furthermore, we investigated the synthesis of aromatic aldehyde with different substitutions under the optimized conditions mentioned above. The results showed that benzaldehyde with EDG substitutions in/P-phenyl ring have good efficiency in the photocatalytic acetal reaction, acetal yield is in the range of83.89%-58.20%,. Chlorine substituted benzaldehyde showed high reaction activity as the lone-electron pair on Chlorine atom give strong electrophobic effect on the phenyl ring, the yield of acetal product reached to96.84%. While acetal reactions of benzaldehyde with EDG substitutions in P-phenyl ring were relatively difficult to take place. The mechanism of the photocatalytic acetal reaction was discussed based on the facts mentioned above.In addition, benzaldehyde photocatalytic reaction behavior and acetal reaction in ethanol with self-made photocatalytic micro reactors was studied in this paper. The effects of light intensity, reaction time and the size of photocatalytic reactor on benzaldehyde acetal reaction was investigated. The results showed that not only benzaldehyde acetal but reduction of benzaldehyde were produced. The greater the light intensity and the longer reaction time is, the more tendency benzaldehyde reduction would occur. And when the reactor size is larger, photocatalytic acetal reaction is more likely to take place.our study indicates that photocatalysis is a novel, green and effective method for acetalization of Benzaldehyde and have good prospect in acetal synthesis.