Important factors affecting photochemical synthesis reaction

Due to thermodynamic limitations, the traditional organic synthesis steps are often complicated. The reaction process requires a large amount of energy and organic solvents, and the product selectivity is not high. The generated byproducts are harmful to the environment. For some organic reactions with special structures in the total synthesis process, if the photocatalytic reaction is adopted, the reaction steps can be greatly shortened, energy consumption can be reduced and side reactions can be reduced at the same time, making the reaction more green and economic.

In recent years, with the rapid development of photocatalysis in organic synthesis, photocatalytic organic synthesis has gradually developed into an important branch in the field of photocatalysis.

At present, relevant researches mainly involve the following important organic reactions: coupling reaction, polymerization reaction, oxidation reaction of functional groups, reduction reaction of functional groups, synthesis of chiral molecules, etc.

With the development of research, photocatalysts are no longer limited to traditional semiconductor photocatalysts. Other commonly used photocatalysts include ruthenium, iridium metal organic complexes, dyes and so on.

Photocatalytic organic synthesis has attracted more and more attention mainly because the application of photocatalytic technology in organic synthesis has the following advantages:

• Using the inexhaustible solar energy as an energy source can save the waste of traditional energy and the pollution caused by the use of it.

• The reaction condition is mild, can be carried out under normal temperature and pressure conditions, reduce the use of toxic and corrosive reagents, and low temperature is more conducive to the synthesis of chiral compounds;

• Through the design of photocatalyst, the selectivity of target products can be improved effectively, the generation of by-products can be reduced, and atomic economy can be improved.

• The free radical reaction mechanism of photocatalytic organic synthesis can break through the limitation of thermodynamic reaction in traditional organic synthesis, simplify the traditional multi-step reaction into a one-step reaction, and greatly reduce the consumption of energy, solvents, reaction reagents and the generation of synthetic wastes.

There are many important factors affecting photochemical synthesis reaction, the main ones are as follows:

1. Selection of catalyst and wavelength of light

The photocatalyst absorbs photons of different wavelengths to generate different excitation states, and its REDOX energy is different, so the chemical reactions may also be different. The selection of appropriate wavelength light source can effectively reduce the occurrence of side reactions and improve the product selectivity.

• PerfectlightLED light source255~940 nm multi-wavelength optional

• Blue light absorption area λ/nm:450, 460, 475, 485, 505

• Green light absorption area λ/nm:520、525、535、550、575

2. Light intensity and light efficiency

When the light intensity is much higher than the concentration of the photocatalyst, the concentration of the photocatalyst in the excited state increases, and the excited photocatalyst can absorb the second photon to generate the excited state of higher energy or the high-energy electron overflow leads to a new reaction. The type of reaction can be regulated by appropriate light intensity.

• Perfectlight Optical power of LED light source100~450 mW/cm²adjustable.

3. Reaction device

The traditional reactor reaction is convenient to operate, but the light penetration efficiency limits the reaction rate, and the low mass and heat transfer efficiency leads to the reaction time length and low selectivity. The new flow chemical reaction can effectively improve the light efficiency, accelerate the mass and heat transfer rate, thus improving the yield and selectivity, and the flow reaction is easier to scale up production.

• PerfectlightPLR-SMCR1000 Multiphase microchannel reaction systemSmall photocatalytic flow experiments can be realized.

4. Dwell time

Dwell time is the illumination time of the reaction liquid in flow chemistry. If the time is too short, the reaction is not complete. Too much time may cause side effects. Proper dwell time can improve raw material conversion rate and reduce side reactions.

• Perfectlight PLR-SMCR1000 The multiphase microchannel reaction system can provide 5 mL, 10 mL volume reaction tubes and 1.5~8.5 mL/min flow rate control to meet the requirements of different dwell times.

5. Flow rate and mixing efficiency of reaction liquid

The flow reaction can mix the reactant and catalyst quickly and improve the mixing efficiency. The gas-liquid and liquid-liquid Taylor fluids can further promote the in-phase mixing rate, improve the interface of the two phases, and accelerate the reaction rate. 

• Perfectlight Multiphase microchannel reaction systems can introduce gas-liquid and liquid-liquid Taylor fluids to further promote the in-phase mixing rate, especially for gas/liquid and liquid/liquid heterogeneous reaction systems.