In a research published in Science recently, it shows that the free radical is highly adaptable and convenient to handle, which represents a “Great Holy” in organic synthesis, while on the other hand it is put under pressure by the “big mountain” of the carboxyl group. According to scientists, carboxylic acid compounds is responsible for producing a lot of well-known as well as significant substances in our life and industrial production, like the amino acids, acetic acid, and vinegar.
The free radical portion that is freed from the carboxylic acid compounds is highly useful in the industry of the materials, pharmaceuticals, and a number of other fields. Conventional decarboxylation processes are over and over again carried out at raised temperatures, which turn out a large number of various unfamiliar products, thereby restraining their industrialisation.
Of late, researchers have endeavoured to use photocatalytic reaction to attain decarboxylation conversion, by deploying light to stimulate electron transitions to produce free radical fragments for chemical bond cleavage and recombination under mild conditions. When contrasted with the traditional heating method, photocatalysis proves to have a lot of edge, including simple operation, easy control, economy of energy and environmental safety. So far the photocatalytic system has shown great success when applied to the combination of a variety of complex functional molecules, showing exceptional catalytic synthesis value and the prospects of industrial application.
On the other hand, most photoredox catalysts presently in use are made up of precious metal complexes – like Iridium and ruthenium, or are unnaturally complicated organic dyes with complex structures. This results in making the photocatalytic industrial system rather expensive, complex in process, and complicated to manage. As a result, the development of new low-priced and multifunctional photocatalytic systems has become a vital direction for future development. The current most important types of photocatalytic systems are complicated in nature and expensive. The new catalyst comes with a novel approach to applying a new method to combine the inexpensive catalyst with the carboxyl group, push the redox reaction cycle, and without difficulty freely salvage the “free radicals”.
The study team working at the University of Science and Technology of China came up with a suggestion of a novel idea based on visible light excitation for intermolecular charge transfer to create a catalytic redox cycle for organic synthesis. An uncomplicated, easy to obtain, very efficacious and non-metallic anionic complex photocatalytic system was revealed for decarboxylative reaction of carboxylic acid derivative.
The catalytic system they suggested simultaneously drives a redox cycle, makes the photocatalytic method very easy while bringing down the financial implication of the photocatalyst, avoiding the usual constraints of traditional heating method, and lending solutions to the issue of transition metals being retained in the synthesis of efficient compounds and medicines. Applying this system, redox-active esters gotten from a range of natural and artificial amino acids were able to activate decarboxylative coupling reactions with great effectiveness and gram scale production successfully, which signifies that industrialisation is very possible. In addition, it is hoped that it would promote the level of industrialisation of photocatalytic technology in the production of very vital and efficient molecules, with significant synthetic chemical value as well as a bright future for first-rate industrial application.
The work scored a high mark in a peer review as well: “The results are interesting, and may initiate a new area of research in photoredox catalysis by introducing a tricomponent system based on a salt, a phosphine and an electron- acceptor to access redox active complexes without the need for traditional transition metal or complex dye catalysts.
“This work gives us a very interesting concept; decarboxylative alkylation is accomplished without precious transition metals or organic dyes, which may be good news for many synthetic chemists.”
By Sally Ahmed