Palladium-based catalysts are widely used in cross-coupling reactions, which is a type of chemical reaction by which two hydrocarbon molecules are bound together through the carbon atoms to form a new molecule with the help of a catalyst composed of transition metals. This type of chemical reaction is widely used in the pharmaceutical industry, the problem is that in this type of reaction the palladium catalyst cannot be reused.
To solve this problem, scientists at RUDN University have proposed a new type of palladium catalyst, made from soluble biopolymers with modified chitin as a support, which, together with palladium, formed effective catalysts for cross-linking organic reactions and can be reused more than 10 times. The results were published in the journal Carbohydrate polymers.
Chitin is a polysaccharide composed of N-acetylglucosamine units that forms part of the shells and exoskeleton of marine life arthropods, and is the second most abundant natural polymer after cellulose.
Chitin molecule. Source: Wikipedia.com.
Modification of chitin for use as a catalyst support is difficult to achieve, however, scientists at RUDN University have succeeded in sintering chitin suitable for these purposes. To do this, they mixed chitin powder from crab shells with water and with 1-azide-3-chloropropan-2-ol and subjected it to ultrasonic treatment. The polymer obtained was an extremely rare case of a chitin derivative that proved to be soluble in both water and organic solvents. Treatment of that derivative with a Pd(II) complex solution resulted in a chitin-supported Pd(II) complex.
Palladium chitin catalyst. Image edited by the author.
The catalytic activity of the palladium-chitin complex was measured in cross-coupling reactions, in which fragments of two classes of substances were combined: aryl halides and alkynes, carried out in different organic solvents, water and various bases. As a result, the scientists found that the new catalyst when used in the form of 30 nanometer particles when it reacts with water in the presence of potassium carbonate. On the other hand, the scientists also tested whether the catalyst could be reused by giving the same performance for the same reaction parameters; and after first use, the nanoparticles were separated from the reaction product in a centrifuge and washed with water, then the reaction was repeated. The scientists found that after 10 repetitions the yield did not decrease and the catalyst nanoparticles were not degraded.
This is a great advance in the development of catalysts, since this material is vital for many industries, especially medical chemistry, being used in large quantities, so being able to obtain an effective and reusable catalyst for organic synthesis is a great advantage, helping to minimize production costs of pharmaceuticals and also reduce the waste of catalysts containing valuable transition metals such as palladium.
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