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Cannizzaro first accomplished this transformation in 1853, when he obtained benzyl alcohol and potassium benzoate from the treatment of benzaldehyde with potash (potassium carbonate). More typically, the reaction would be conducted with sodium hydroxide or potassium hydroxide , giving the sodium or potassium carboxylate salt of the carboxylic ...
Benzaldehyde undergoes disproportionation upon treatment with concentrated alkali (Cannizzaro reaction): one molecule of the aldehyde is reduced to the benzyl alcohol and another molecule is simultaneously oxidized to benzoic acid. With diols, including many sugars, benzaldehyde condenses to form benzylidene acetals.
In this reaction, one aldehyde donates a proton and one aldehyde accepts a proton. Some aldehydes can only donate protons, such as 4-dimethylaminobenzaldehyde, whereas benzaldehyde is both a proton acceptor and donor. In this way it is possible to synthesise mixed benzoins, i.e. products with different groups on each half of the product.
Stanislao Cannizzaro FRS (/ ˌ k æ n ɪ ˈ z ɑːr oʊ / KAN-iz-AR-oh, [1] US also /-ɪ t ˈ s ɑːr-/-it-SAR-, [2] Italian: [staniˈzlaːo kannitˈtsaːro]; 13 July 1826 – 10 May 1910) was an Italian chemist. He is famous for the Cannizzaro reaction and for his influential role in the atomic-weight deliberations of the Karlsruhe Congress ...
Usually, the crossed product is the major one. Any traces of the self-aldol product from the aldehyde may be disallowed by first preparing a mixture of a suitable base and the ketone and then adding the aldehyde slowly to the said reaction mixture. Using too concentrated base could lead to a competing Cannizzaro reaction. [12]
Another route entails hydrogenation of benzaldehyde, a by-product of the oxidation of toluene to benzoic acid. [5] For laboratory use, Grignard reaction of phenylmagnesium bromide (C 6 H 5 MgBr) with formaldehyde and the Cannizzaro reaction of benzaldehyde also give benzyl alcohol.
The reaction is named after Russian organic chemist Vyacheslav Tishchenko, who discovered that aluminium alkoxides are effective catalysts for the reaction. [1] [2] [3] In the related Cannizzaro reaction, the base is sodium hydroxide and then the oxidation product is a carboxylic acid and the reduction product is an alcohol.
Aside from the inherent reversibility of the reaction (or "retro–Henry") that can prevent the reaction from proceeding, the β-nitro alcohol also has the potential to undergo dehydration. For sterically hindered substrates, it is also possible for a base-catalyzed self-condensation (Cannizzaro reaction) to occur. A general scheme of the ...