Cannizzaro Reaction

The Cannizzaro reaction is an equilibrium process in which two molecules of an aldehyde combine with a hydroxyl radical to produce a primary alcohol and a carboxylic acid. This is illustrated in the example of benzaldehyde converting benzyl alcohol to benzoic acid. Examples of the Cannizzaro reaction include vanillin, benzaldehyde, syringaldehyde, and formaldehyde, which lack active hydrogen. They are subjected to an intramolecular and intermolecular strong base oxidation (NaOH) to yield carboxylic acids and alcohols.

Cannizzaro reaction mechanism:

The Cannizzaro reaction mechanism describes in detail how one molecule of  alcohol  and one molecule of carboxylic acid can be obtained from two molecules of aldehyde. Scientist Stanislao Cannizzaro obtained benzyl alcohol and potassium benzoate from benzaldehyde in 1853. An aldehyde is changed through nucleophilic acyl within the leaving institution in which the alternative aldehyde is attacked. The effect of a hydroxide assault on a carbonyl is a tetrahedral intermediate. This intermediate tetrahedral collapses and reforms the carbonyl and moves a hydride that attacks any other colony. This will exchange the ionic protons of the acid and alcohol. When supplied with a high concentration of base, the aldehyde produces an anion with a charge of 2. The hydride ion, which consists of the carboxylate and the alcohol, moves to the second molecule of the aldehyde. Alcohol ions also receive protons from the solvent for the reaction.

Steps involves in Cannizzaro reaction

Step 1. The hydroxide nucleophile is used to attack the carbonyl group of  the corresponding aldehyde, which causes an unbalanced reaction and produces an anion with two negative charges. Step 2. This intermediate  can function as a hydride reduction. The intermediate releases  hydride anions due to its unstable nature. This anion hydride attacks another aldehyde molecule. Now the divalent anion becomes the carboxylate anion  and the aldehyde becomes the alcohol anion. Step 3. In this final stage, water supplies the alcohol anions with protons to produce the final alcohol product. Alcohol is more basic than water, so reactions can occur. Here, when acid is used, carboxylation produces the final product of carboxylic acid (carboxylate is less basic than water and cannot obtain protons from water, so post-treatment with acid is required.) In general, the reaction follows a tertiary reaction rate. It is the second in aldehyde and the first in base.
Temporary rate = k[RCHO]² [OH^–]
For very high foundations, a second pass (k`) is needed. This is basically secondary.
Temporary rate = k[RCHO]<sup>2</sup>[OH<sup>−</sup>] + k`[RCHO]²[OH⁻]²
The k` orbital contains a reaction involving a divalent anion (RCHO₂^2-) and an aldehyde. The direct transfer of hydride ions is evident from the lack of deuterium attached to the alpha carbon of the recovered alcohol when the reaction was carried out when D₂O was generated.

Crossed Cannizzaro reaction

The crossed Cannizzaro reaction is not unexpected, as only 50% of the required alcohol and carboxylic acid are produced by the reaction under optimal conditions. Therefore, Cannizzaro’s crossover response is more extensive. The sacrificial aldehyde is mixed with more valuable molecules and the oxidation of sodium  is reduced by formaldehyde. The reduction of other aldehyde chemicals gives the required alcohol. If the two separate aldehydes can be completely converted to the required product, the yield of useful chemistry will increase. Finally, it can be used to imbalance aldehydes that cannot be enolated using the Cannizzaro reaction. The reaction from the crossed Cannizzaro reaction is used to increase the yield of valuable products.

Uses and applications

In  industries, polyols are produced by a combination of Cross-Cannizzaro reaction and aldol condensation. Polyol is very valuable and has many industrial uses.

• Neopentyl glycol is used in polyesters for the production of resin, paint coatings, synthetic lubricants and plasticizers for airplanes and aircraft. The structure of neopentyl provides high light resistance, heat resistance and hydrolysis resistance.
• As a raw material, pentaerythritol is explosive in the paint industry. Some esters of pentaerythritol are used as emulsifiers, including oil additives, emollients, and  higher fatty acids.
• In many applications, trimethylolpropane is used as an alternative to glycerol in the production of  alkaline resins and polyesters and polyurethanes.

Conclusion

Cannizzaro reaction is a chemical reaction named after Stanisla o Cannizzaro, in which carboxylic acid and primary alcohols are produced by the base disproportionation of two molecules of non-enolizable aldehydes. Aldehydes containing alpha hydrogen atoms were destaged and caused a potential aldol reaction with enolate by a highly alkaline reaction. This process produces only  50% alcohol and carboxylic acid under optimal conditions (two aldehydes are required to produce the acid and alcohol). Cross-Cannizzaro reactions that combine sacrificial aldehydes with  more valuable molecules can be performed more frequently to avoid low yields. In this variant, formaldehyde is a reducing agent, which is oxidized to sodium formate and alcohol is reduced to other aldehyde molecules. In this case, the aldehyde can be completely converted to its legitimate product, rather than losing 50% of a single reactant for each of the two products. Therefore,  the atom economy is still low, but the production of valuable chemicals is high.