Cannizzaro dismutation

In the same way, the replacement of sodium hydroxide by potassium hydroxide leads to bad results (ref. 7), especially because consumption of glyoxylic acid by the Cannizzaro dismutation (ref. 8). 

This dismutation or disproportionation reaction is known as the Cannizzaro reaction. 

The analogous dismutation of furfural is described in Section V,8. For crossed Cannizzaro reaction , see discussion following Section IV,199. 

Phytochemical reduction must be regarded as a special case of oxidation-reduction. Since it is enzymatically conducted it should be distinguished from the analogously formulated Cannizzaro reaction. For this reason Neuberg, Hirsch and Reinfurth suggested the name dismutation for the physiological process, and in the last 25 years... 

This dismutation or disproportionation reaction is known as the Cannizzaro reaction. The mechanism of the reaction involves the production of the anion (1) which may transfer a hydride ion to a carbonyl carbon atom in another aldehyde molecule. The reaction sequence is completed by a proton transfer to yield the carboxylate anion and the alcohol. 

Dismutations of the same type, but involving two unlike aldehyde molecules, will be classed as crossed Cannizzaro reactions. The reduction of benzaldehyde to benzyl alcohol by means of formaldehyde and alkali is an example. 

Oxidation-reduction reactions similar to the Cannizzaro process are brought about in the living cell by certain enzyme systems. Numerous exanfples 7-8- 10 of these have been studied in vitro by the aid of tissue preparations, and certain of them 6 suggest possible application in preparative methods. The dismutation. of aldehydes in basic or neutral solution also has been effected by catalytic metals, such as nickel and platinum.11 12 It seems likely that there is a closer analogy between... 

It has been shown by Kharasch and Foy22 and confirmed by Urushi-bara and Takebayashi28 that the presence of peroxides markedly accelerates the heterogeneous Cannizzaro reaction. Highly purified benzaldehyde undergoes dismutation to the extent of only 2-4% under conditions which result in 25-80% reaotion with ordinary benzaldehyde. 5-Bromofurfural dismutates only slowly with 30% sodium hydroxide in ether, but the reaotion is accelerated markedly by the addition of a trace of hydrogen peroxide.24 Variousjexplanations have been advanced to account for the effect of peroxides,26 260 but the problem is still obscure-. 

The only useful Cannizzaro reactions involving the use of aldehydes having one or two a-hydrogen atoms are those already described, in which the aldehyde first undergoes an aldol condensation. The direct dismutation of aldehydes of these types has been carried out successfully only by means of enzyme systems or catalytic metals (p. 95). Such reactions do not represent the true Cannizzaro reaction and as yet have found little practical use. The smooth and practically quantitative dismutation of straight-chain aliphatic aldehydes of four to seven carbon atoms under the influence of the enzymes of hog-liver mash 6 suggests that practical applications of this method may be found. 

The Cannizzaro reaction of heterocyclic aldehydes has been examined in a few cases only. Furfural,83 a-thiophenealdehyde,84 and a-pyridylal-dehyde 86 undergo the reaction normally to give the expected products. 3-Formyl-l,2,5,6-tetrahydro-l-ethylpyridine resinifies upon treatment with potassium hydroxide,86 a behavior consistent with the observation that it is structurally similar to an a,/3-unsaturated alicyclic aldehyde. 3,4-Dibromothiophene-2,5-dialdehyde undergoes a complex series of reactions, involving both cleavage (loss of —CHO) and dismutation, when treated with alkali.87 Of particular interest in this connection is the fact that under certain conditions the ester composed of the usual... 

Studies of the crossed Cannizzaro reaction have not embraced so wide a variety of structural modifications as the examples discussed above in connection with the normal dismutation. There is reason to believe,... 

Disproportionation (or dismutation) — Reaction in which species with the same oxidation state react with each other to yield one species of higher oxidation state and one of lower oxidation state, e.g., 3Au+ -> Au3+ + 2Au, or 4KCIO3 -> KC1 + 3KCIO4, or the d. reaction of an aldehyde in alkaline medium into the respective carboxylic acid and alcohol compounds, known as Cannizzaro reaction 2R - CHO + NaOH - R - COONa + R-CH2OH. In practice, d. happens rarely spontaneously, but is usually achieved by a catalyst application. 

The reaction is most important for the preparation of carbinols from certain aromatic and heterocyclic aldehydes and for the preparation of several aliphatic polyhydroxy compounds. In the normal Cannizzaro reaction the theoretical yield of alcohol is only 50% because half of the aldehyde is converted to the acid. A mixture of an aldehyde with excess formaldehyde, however, results in a dismutation in which most of the higher aldehyde is reduced formaldehyde is oxidized to sodium formate, viz., ... 

On treatment with aqueous or alcoholic aLkah solutions aromatic and aliphatic aldehydes 11 lacking a-hydrogens undergo dismutations (Cannizzaro reactions) to give the corresponding carboxylic acid salts 12 and alcohols 13 [Eq. (6)] [146,147]. 

Intramolecular Cannizzaro reactions can occur when two aldehyde functionahties are in close proximity to each other. Then, dismutation followed by ring-closure leads to lactones [151]. 

---