Cannizzaro oxidation

CANNIZZARO Oxidation - Redtjction A redox reaction between two aromatic aldehydes (or an aromatic aldehyde and formaldehyde) to a mixture ol alcohol and acid... 

Since the enolization is not restricted to the 2 and 3 positions, a number of products are formed that undergo subsequent aldol condensations and the Cannizzaro oxidation. They are all 2-hydroxy-3-methyl, 3,4-dimethyl-2-hydroxy, 3,5-dimethyl-2-hydroxy, and 3-ethyl-2-hydroxy-2-cyclopenten-l-ones sugar acids acetic acid hydroxyacetone three isomeric hydroxy-2-butanones y-butyrolactone and such furan derivatives as furyl alcohol, 5-methyl-2-furyl alcohol, and 2,5-dimethyl-4-hydroxy-3(2H)-furanone. They are food flavoring agents. 

CANNIZZARO Oxidation-reduction 58 CARROLL Allylalion 59 Castro 363... 

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 ... 

In contrast with the well-known Embden-Meyerhof-Pamass glycolysis pathway for the conversion of hexose sugars to alcohol, the steps in conversion of ethanol to acetic acid remain in some doubt. Likely, ethanol is first oxidized to acetaldehyde and water (39). For further oxidation, two alternative routes are proposed more likely, hydration of the acetaldehyde gives CH2CH(OH)2, which is oxidized to acetic acid. An alternative is the Cannizzaro-type disproportionation of two molecules of acetaldehyde to one molecule of ethanol and one molecule of acetic acid. Jicetobacter... 

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... 

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