Science of Synthesis

Favre-Réguillon, A., Science of Synthesis Knowledge Updates, (2024) 3, 259.

Historically, the oxidation of aldehydes to carboxylic acids has been performed using stoichiometric metallic oxidants. In the late 19th century, Fehling’s solution and Tollens’ reagent were used to detect and differentiate between reducing and nonreducing sugars. Both methods used stoichiometric metallic oxidants [i.e., copper(II) and silver(I), respectively] in a basic aqueous solution. Every type of aldehyde (aromatic, aliphatic, unsaturated, and even reducing sugars) was efficiently and selectively oxidized to the corresponding carboxylic acid. Introduced in the 1940s, oxidation with inorganic chromium(VI) reagents (Jones oxidation) and, in the 1970s, oxidation with chromium(VI) complexes (Sarett reagent, Collins reagent, pyridinium chlorochromate, and pyridinium dichromate) have been successfully used for the oxidation of aldehydes because of the mild conditions, good functional-group tolerance, and effectiveness. Even if effective and selective, these methods generate stoichiometric portions of toxic metallic wastes that are environmentally unfriendly and their use is now prohibited. Furthermore, methods involving classical/stoichiometric reagents were well described in the previous Science of Synthesis article on this topic (Section 20.2.1.3).[‌1‌]

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