Application Of Photocatalytic Technology In Clean Organic Synthesis

Because of the extensive mode of economic development, our country has made significant economic benefits.However, at the same time it caused a lot of environmental problems. Especially when it comes to organic synthesis. The traditional technical route brought a large amount of organic solvent pollution and energy consumption. How to use clean renewable energy in organic synthesis has to be an effective and green economy route which can reduce environmental risks from the source.Photocatalytic technology has many green, non-polluting characteristics.We can just use solar energy to produce the redox electrons and holes. Photocatalytic technology has been widely used in many areas such as degrading, self-cleaning materials, hydrogen production, reducing CO2 etc. But the application in organic synthesis is still rare. From the current studies, the photocatalytic organic synthesis had the following aspects: 1) the photocatalytic organic reduction reaction, such as nitrobenzene reduction, reduction of aldehydes and ketones, benzene reduction etc;(2) the photocatalytic organic oxidation, such as oxidation of alcohols to aldehydes, amino oxidation to imine, dehydration of the alcohol oxidase ester;(3)the photocatalytic dehydrogenation reactions. Such reactions are rare, such as Academician Li Can who decomposed glycerol to hydrogen and hydroxyl acetaldehyde; other groups removed hydrogen of cyclohexane to benzene and hydrogen. The advantages of photocatalysis technology in organic synthesis are as followed(1) energy savings;(2) mild reaction conditions;(3) reactions can be controlled by the light. The disadvantages are that(1) the types of the photocatalytic reactions are still rare;(2) most of them just use photo-generated electrons or holes;(3) the adaptation of each photocatalytic reaction is relatively settled;(4) the reaction will be sacrificed organic hydrogen resources.For the above shortcomings, we intend to introduce metal ions redox duplet in the photocatalytic process.We can realize the dehydrogenation oxidation in the aqueous phase and the toluene dehydrogenation coupling reaction controlled by external conditions. The advantages are that(1) using the ion redox duplet as the intermediary replaced the traditional photocatalytic process which the organic reactions and photocatalytic reaction substrate contacted with each other directly.It improved the capacity of photogenerated carriers to contact with the organic substrates by the effect of the ion redox duplet’s mass and charge transfer.(2) the solvent is water which is green to the environment.(3)we can control the capacity of the oxidizable species by control the species of the redox duplet which helps to achieve the better control of the product’s selectivity.(4) when the toluene dehydrogenating p-toluene coupling, toluene is a solvent and also is a reactant,The unreacted toluene can be recycled and the reaction is simple, the condition is mild.In order to expand the photocatalytic technology in cleaning organic synthesis,we carried out two main aspects. 1. By photoelectrocatalysis technology, we used photocatalyst film as positive electrode which can oxidate alkyl aromatics to the corresponding aldehydes / ketones and the cathodic can reduce the water to hydrogen. We studied the different reaction conditions which affected our activities, including the species and concentration of metal ions, the species and concentration of the acid, the reaction bias, reaction time etc. The results showed that:(1) under certain conditions, we can make the alkyl aromatic hydrocarbons including toluene, p-methoxy toluene, p-chloro-toluene, ethylbenzene, to the corresponding aldehyde / ketone and hydrogen the selectivity of benzaldehyde reached to 86.5%.(2) the reaction is easy to control, has low energy consumption and is clean to environment, besides you can use atoms completely.(3) the reaction not only use the photo-generated electrons but also the photo-generated holes which better reflect the advantage of photocatalytic technology.2.By the photocatalytic technology,we transformed the toluene to dibenzyl.We made the C-C coupling reaction into reality under the photocatalytic conditions firstly. We studied the different reaction conditions which affected our activities, including the proportion of the water and oxygen, the effect of noble metal catalysts and we also discussed the reaction mechanism. The results showed that:(1) the optimal amount of Pt loaded on the P25 was 2.0%.The product is dibenzyl, the quantum yield is 0.29% and the selectivity is 93.4%.(2) when the reaction system contains oxygen, the product is benzaldehyde.The innovation of our work are as followed:(1) in terms of the photocatalytic selective oxidation,we introduced metal ion redox couple in improving our activities while increasing the selectivity of the intermediate product(organic aldehyde).(2) We made the C-C coupling reaction into reality under the photocatalytic conditions firstly and further expanded the scope of application of photocatalytic technology in organic reactions, besides we offered experience about the design of more complex organic synthesis routes.