Cannizzaro’s reaction

Benzyl Alcohol, CeH5CH20H, and Benzoic Acid, CaHsCOOH. (Cannizzaro s Reaction). 

This reaction is given by most aromatic aldehydes having the aldehyde group directly joined to the benzene ring it is also given by formaldehyde, with the formation of methanol and formic acid. Other aliphatic aldehydes do not give Cannizzaro s reaction under these conditions. 

Undergoes Cannizzaro s reaction, giving benzyl alcohol and benzoic acid (p. 229). Warm gently for several minutes, cool, add a few ml. of water and then cone. HCl, and cool again. Crystals of benzoic acid separate out on scratching the sides of the tube with a glass rod. 

A) most aromatic aldehydes giving Cannizzaro s reaction. 

Salicylaldehyde gives a yellow coloration and forms salicylic acid very slowly. Cannizzaro s reaction is also given by formaldehyde but, owing to the difficulty in isolating the products, is not used as a test. 

Reacts slowly on heating without evolution of gas. Esters some acid chlorides and anhydrides benzaldehyde (undergoes Cannizzaro s reaction, p. 342). 

NaOH Cannizzaro s reaction < yellow resin > chloroform on heating Cannizzaro s reaction yellow coloration... 

Cannizzaro s Reaction.—On this reaction, which may be represented thus—... 

CANNIZZARO S REACTION. BENZOIC ACID AND BENZYL ALCOHOL FROM BENZALDEHYDE 1... 

Cannizzaro s reaction probably proceeds in such a way that two molecules of aldehyde condense to form an ester which is then hydrolysed to alcohol and acid ... 

Afterwards the pentaerythrose reacts with a fourth molecule of formaldehyde according to Cannizzaro s reaction ... 

The presence of the double bond (carbonyl group C 0) markedly determines the. chemical behavior of the aldehydes. The hydrogen atom connected directly to the carbonyl group is not easily displaced. The chemical properties of the aldehy des may be summarized by (1) they react with alcohols, with elimination of H2O, to form ace t i (2) they combine readily with HCN to form cyanohydrins, (3) they react with hydroxylamine to yield aldoximes (4) they react with hydrazine to form hydrazones (5) they can be oxidized lulu fatty acids, which contain die same [lumber of carbons as in the initial aldehyde 5) they can be reduced readily to form primary alcohols. When bcnzaldchydc is reduced with sodium amalgam and HjO, benzyl alcohol C,f l - -C f I Of I is obtained. The latter compound also may be obtained by treating benzaldehyde with a solution of cold KOH in which benzyl alcohol and potassium benzoate are produced. The latter reaction is known as Cannizzaro s reaction. 

Dodge has proposed another method for the quantitative estimation of benzaldehyde. This is based upon Cannizzaro s reaction — 2CeH5CHO + KOH = O HjCOOK -i- CgHjCHjOH. 

Stanislao Cannizzaro (Palermo, Sicily, 1826-Rome, 10 May 1910) studied in Palermo and Naples. In 1847 he took part in the Rebellion. In 1850 he became Piria s assistant in Paris and in 1851 published his first research, on cyanogen chloride and cyanamide, done jointly with Cloez in Chevreul s laboratory. In 1852 he was appointed in Alessandria and in 1853 published an important researdi on the action of caustic potash on benzaldehyde, obtaining potassium benzoate and benzyl alcohol ( Cannizzaro s reaction ) 2C,H5CHO+KOH=C.HsCOOK+C,H8CH,OH. In 1855 he became professor in G noa, where at fimt there was no laboratory, and there he wrote his famous pamphlet. In i860 he joined Garibaldi at Palermo. In 1861 he became professor in Palermo and in 1870 in Rome, where he was created senator. ... 

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