Oxidation Cannizzaro reaction

Cannizzaro reaction Two molecules of many aldehydes, under the influence of dilute alkalis, will interact, so that one is reduced to the corresponding alcohol, while the other is oxidized to the acid. Benzaldehyde gives benzyl alcohol and benzoic acid. Compare the aldol condensation. 

Action of sodium hydroxide. Does not undergo the Cannizzaro reaction. It dissolves in dil. NaOH solution, giving a yellow solution from which the aldehyde is precipitated unchanged on acidification. If heated with cone. NaOH solution, salicylaldehyde slowly undergoes atmospheric oxidation to salicylic acid. 

Furfural can be oxidized to 2-furoic acid [88-14-2] reduced to 2-furanmethanol [98-00-0] referred to herein as furfuryl alcohol, or converted to furan by decarbonylation over selected catalysts. With concentrated sodium hydroxide, furfural undergoes the Cannizzaro reaction yielding both 2-furfuryl alcohol and sodium 2-furoate [57273-36-6]. 

The base-catalyzed reaction of acetaldehyde with excess formaldehyde [50-00-0] is the commercial route to pentaerythritol [115-77-5]. The aldol condensation of three moles of formaldehyde with one mole of acetaldehyde is foUowed by a crossed Cannizzaro reaction between pentaerythrose, the intermediate product, and formaldehyde to give pentaerythritol (57). The process proceeds to completion without isolation of the intermediate. Pentaerythrose [3818-32-4] has also been made by condensing acetaldehyde and formaldehyde at 45°C using magnesium oxide as a catalyst (58). The vapor-phase reaction of acetaldehyde and formaldehyde at 475°C over a catalyst composed of lanthanum oxide on siHca gel gives acrolein [107-02-8] (59). 

Formaldehyde is readily reduced to methanol by hydrogen over many metal and metal oxide catalysts. It is oxidized to formic acid or carbon dioxide and water. The Cannizzaro reaction gives formic acid and methanol. Similarly, a vapor-phase Tischenko reaction is catalyzed by copper (34) and boric acid (38) to produce methyl formate ... 

Aldehydes 1 that have no a-hydrogen give the Cannizzaro reaction upon treatment with a strong base, e.g. an alkali hydroxide.In this disproportionation reaction one molecule is reduced to the corresponding alcohol 2, while a second one is oxidized to the carboxylic acid 3. With aldehydes that do have a-hydrogens, the aldol reaction takes place preferentially. 

The synthetic importance of the reaction is limited, because as a consequence of the disproportionation, the yield of the alcohol as well as the carboxylic acid is restricted to 50%. However good yields of alcohols can often be obtained when the reaction is carried out in the presence of equimolar amounts of formaldehyde. The formaldehyde is oxidized to formic acid and concomitantly reduces the other aldehyde to the desired alcohol. This variant is called the crossed Cannizzaro reaction. 

The Cannizzaro reaction takes place by nucleophilic addition of OH- to an aldehyde to give a tetrahedral intermediate, which expels hydride ion as a leaving group and is thereby oxidized. A second aldehyde molecule accepts the hydride ion in another nucleophilic addition step and is thereby reduced. Benzaldehyde, for instance, yields benzyl alcohol plus benzoic acid when heated with aqueous NaOH. 

The Cannizzaro reaction is a redox reaction, which requires a concentrated base and a Ccirbonyl group with no a-hydrogen atoms. Normally, the oxidation converts an aldehyde to a carboxylate (ccirboxylic acid), while the reduction generates an alcohol. Figure 11-33 shows an example of a Cannizzaro reaction. 

Cannizzaro reaction An internal oxidation-reduction reaction of aldehydes, carbamide Urea, carcinogenic Cancer causing. 

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 is an internal crossed-Cannizzaro reaction the keto group is reduced and the —CHO is oxidized. 

Cannizzaro reaction. Aromatic aldehydes (and other aldehydes in which a-hydrogen atoms arc absent, e.g., formaldehyde, trimcthylacetaldehyde, and a-hydroxy-tso-butyraldehyde) under the influence of strong aqueous or alcoholio alkali undergo simultaneous oxidation and reduction yielding the alcohol and corresponding acid. Thus —... 

The lactone 223 was isolated from 2-benzoyl-3-hydroxymethylquin-oxaline 1-oxide 221 on treatment with alkali and subsequent acidification, probably by intramolecular Cannizzaro reaction of 2-benzoyl-3-quinoxaline carboxyaldehyde (222), which in turn is obtained from 221 by a series of tautomeric shifts and 1,4-elimination.221... 

Several species of bacteria under suitable conditions cause -butyraldehyde to undergo the Cannizzaro reaction (simultaneous oxidation and reduction to butyric acid and butanol, respectively) this reaction can also be catalyzed by Raney nickel (7). The direct formation of butyl butyrate [109-21 -7] or isobutyl isobutyrate (Tishchenko reaction) from the corresponding aldehyde takes place rapidly with aluminum ethylate or aluminum butyrate... 

The apparent fickleness of the acyl-pyrroles and -indoles in their reaction with carbanions to form new C—C bonds arises from the contribution made by the zwitterionic structure, e.g. (410b), to the resonance hybrid and the choice of the reaction conditions is critical for a successful nucleophilic reaction. Thus, formyl-pyrroles and -indoles do not normally undergo the Cannizzaro reaction nor do they form stable cyanohydrins or undergo benzoin-type reactions. However, surprisingly, 2-formylpyrrole reacts with arylaldehydes in the presence of potassium cyanide to yield (428), which is easily oxidized to (429) (B-77MI30505). It is noteworthy that the presence of an ester substituent adjacent to the formyl group modifies the mesomeric interaction to such an extent to allow the formation of (430) in low yield, as a result of an initial benzoin-type self-condensation (Scheme 76) (68BSF637). 

Cyclocitral (540) behaves as a nucleophile towards benzaldehyde and in the presence of sodium hydroxide the fused pyran-2-oI (541) is formed through an aldol (Scheme 202) (81JHC549). However, when sodium ethoxide is used as the catalyst, the pyran-2-one is produced. It is proposed that oxidation arises through a crossed Cannizzaro reaction with benzaldehyde (and much benzyl alcohol is observed in support of this idea), followed by a carbanion attack on more benzaldehyde and subsequent cyclization. 

CANNIZZARO, STANISLAO (1826-1910). Born in Italy, lie extended the research of Avogadro on the molecular concentration of gases and thus was able to prove the distinction between atoms and molecules. His investigations of atomic weights helped to helped lo make possible the discovery of the periodic law hy Mendeleyev. His research in organic chemistry led to the establishment of the Cannizzaro reaction involving the oxidation reduction of an aldehyde in the presence of concentrated alkali. 

Exercise 16-33 Assume that an equimolar mixture of methanal and 2,2-dimethyl-propanal (each undergoes the Cannizzaro reaction by itself) is heated with sodium hydroxide solution. Write equations for the various possible combinations of Cannizzaro reactions which may occur. Would you expect methanal used in excess to reduce, or oxidize, 2,2-dimethylpropanal Give your reasoning ... 

---