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Unraveling the Chemistry and Applications of Cannizzaro Reaction

Cannizzaro reaction, also known as the Cannizzaro disproportionation, is an organic reaction where an aldehyde without an active hydrogen reacts with a strong base to form an alcohol and a carboxylic acid. The reaction was first observed by a chemist named Stanislao Cannizzaro in 1853, who used grass ash to produce benzyl alcohol and benzaldehyde through a unique process that he discovered.

In this article, we will discuss the history, mechanism, and examples of Cannizzaro reaction and how it has been used in organic chemistry.

History of Cannizzaro Reaction

In the mid-19th century, the understanding of chemical reactions was still in its nascent stage. Cannizzaro, an Italian chemist, performed his experiments to unravel the reaction mechanism of benzaldehyde.

He used grass ash, a crude form of potassium carbonate, to cause benzaldehyde to undergo a unique reaction that produced benzyl alcohol and benzoic acid. This discovery threw light on the importance of understanding the difference between chemical elements, which led to the development of the concept of chemical atomicity.

Examples of Cannizzaro Reaction

There are various examples of Cannizzaro reaction. In one example, vanillin, a phenolic aldehyde, undergoes a Cannizzaro reaction in the presence of a strong base to yield vanillic acid and vanillyl alcohol.

Similarly, syringaldehyde reacts with a strong base to form syringic acid and syringol. These examples show how aldehydes without active hydrogen undergo Cannizzaro reaction to form an alcohol and a carboxylic acid.

Another example of Cannizzaro reaction is the reaction of benzaldehyde and formaldehyde. Benzaldehyde reacts with formaldehyde in the presence of a strong base to form benzyl alcohol and formic acid.

The reaction also takes place if the aldehydes are different; for example, when p-nitrobenzaldehyde and formaldehyde are used in the reaction, p-nitrobenzyl alcohol and formic acid are formed.

Mechanism of Cannizzaro Reaction

The Cannizzaro reaction takes place when an aldehyde reacts with a strong base such as sodium hydroxide or potassium hydroxide. The aldehyde is reduced to an alcohol while another molecule of the same aldehyde is oxidized to a carboxylic acid.

The overall reaction comprises two half-reactions that take place simultaneously. The first half-reaction involves the reduction of the aldehyde to an alcohol by donating an electron.

The second half-reaction involves the oxidation of the same aldehyde to a carboxylic acid by losing an electron. The mechanism of the Cannizzaro reaction involves the formation of a stable intermediate called an aldehyde anion, which is formed by the reaction between a base and the aldehyde.

The aldehyde anion can either react with another molecule of aldehyde to give the alcohol and carboxylic acid or undergo further protonation to give the corresponding alcohol and carboxylic acid.

Conclusion

In conclusion, Cannizzaro reaction is a fundamental organic reaction that has been used in organic chemistry for decades. The reaction involves the use of aldehydes without active hydrogen and strong bases to yield an alcohol and a carboxylic acid.

The history of the reaction dates back to the 19th century when Stanislao Cannizzaro discovered it. In modern times, the reaction has become an essential tool in organic chemistry for synthesizing various compounds.

With the help of the examples and mechanisms, we have provided in this article, readers will have a better understanding of the Cannizzaro reaction. 3)

Mechanism of Cannizzaro Reaction

The Cannizzaro reaction involves the transfer of electrons from an aldehyde’s carbonyl group to a strong base, usually a hydroxide (-OH) ion.

This transfer results in the formation of two products: a carboxylic acid and an alcohol.

Steps involved in Cannizzaro reaction:

1.

The hydroxide ion attacks the carbonyl carbon, resulting in the formation of a dianion intermediate.

2.

The dianion intermediate undergoes an intramolecular proton transfer, resulting in the formation of an alkoxide and a carboxylate anion.

3.

Another molecule of the aldehyde reacts with the alkoxide to form a secondary alcohol product.

4.

Finally, the carboxylate anion is protonated with acid workup, forming the carboxylic acid product.

In the Cannizzaro reaction, the hydride anion (negative hydrogen ion) is not involved in the reaction, contrary to earlier understanding.

Instead, the reaction involves a transfer of electrons from the carbonyl carbon to the base. The transferred hydride then reduces another molecule of the aldehyde to an alcohol.

Acid workup and final product formation:

Acid workup is a common technique in organic chemistry that is used to terminate a reaction. It involves the addition of an acid to a reaction mixture, which neutralizes any base present and protonates any acidic groups.

In the case of the Cannizzaro reaction, acid workup is used to protonate the carboxylate anion formed during the reaction, resulting in the formation of the carboxylic acid product. The final product of the Cannizzaro reaction depends on the aldehyde used.

If the aldehyde has no other functional groups, such as vanillin and benzaldehyde, it yields an alcohol and a carboxylic acid. If the aldehyde has other functional groups, such as formaldehyde, the reaction results in the formation of the corresponding methyl alcohol and formic acid.

4) Crossed Cannizzaro Reaction

The crossed Cannizzaro reaction involves the reaction of two different aldehydes in the presence of a strong base, resulting in the formation of an alcohol and a carboxylic acid. The reaction is named “crossed” because it involves two cross-coupling reactions that yield different products.

One aldehyde undergoes the Cannizzaro reaction while the other aldehyde undergoes oxidation to formic acid.

The reaction products of crossed Cannizzaro reaction:

When formaldehyde and benzaldehyde are used in a crossed Cannizzaro reaction, benzyl alcohol and formic acid are formed.

The formaldehyde undergoes Cannizzaro reaction, forming methyl alcohol and formic acid, while the benzaldehyde undergoes reduction to yield benzyl alcohol. The reaction equation for this reaction is as follows:

HCHO + C6H5CHO + 2NaOH C6H5CH2OH + HCOOH + CH3OH

Usefulness of crossed Cannizzaro reaction in synthesizing alcohol:

The crossed Cannizzaro reaction is useful in synthesizing primary alcohols that can be difficult to obtain.

The reaction has a higher yield than other methods such as Grignard reaction and sodium borohydride reduction. The reaction is also useful because it can be used to access chiral alcohols.

In conclusion, Cannizzaro reaction is a fundamental organic reaction that involves the use of aldehydes without active hydrogen. The reaction is facilitated by a strong base, and the final products include an alcohol and a carboxylic acid.

The mechanism of the Cannizzaro reaction involves several steps, including hydroxide attack, alkoxide and carboxylate anion formation, and acid workup. The crossed Cannizzaro reaction is a variant of the reaction that involves the use of two different aldehydes to yield alcohols and carboxylic acids.

This reaction has a high yield and is useful in synthesizing primary alcohols.

5) Intramolecular Cannizzaro Reaction

Intramolecular Cannizzaro reaction is a variant of Cannizzaro reaction that involves the reaction of a single molecule. This reaction occurs when one carbonyl group reacts with another carbonyl group in the same molecule.

The reaction results in the formation of a carboxylic acid and an alcohol, as seen in the traditional Cannizzaro reaction.

Significance of intramolecular Cannizzaro reaction as model reactions

Intramolecular Cannizzaro reaction is important because it serves as a model reaction for the study of enzyme-substrate complexes. This reaction is very similar to the biological function of enzymes and their substrates.

By studying this reaction, scientists can gain a deeper understanding of enzyme-substrate interactions and use the knowledge to develop new drugs and treatments.

Examples and details of intramolecular Cannizzaro reaction

An example of intramolecular Cannizzaro reaction is phenylglyoxal. Phenylglyoxal is an aromatic aldehyde that undergoes an intramolecular Cannizzaro reaction to form benzyl alcohol and benzoic acid.

The reaction is facilitated by a strong base such as sodium hydroxide, resulting in the formation of the carboxylic acid and alcohol products. The intramolecular Cannizzaro reaction is also observed in the reduction of carbonyl groups by dihydroxyacetone.

Dihydroxyacetone is a ketone that is used in the production of diols. During the reaction, the hydroxyl group takes a hydride ion from the carbonyl group, forming the diol.

6) Uses and Applications of Cannizzaro Reaction in Industry

Combination of crossed Cannizzaro reaction and aldol condensation for preparing polyols

The Cannizzaro reaction, specifically the crossed Cannizzaro reaction, is used in combination with aldol condensation to produce polyols. Polyols are essential building blocks in the production of polymers, including polyurethanes and resins.

The use of the Cannizzaro reaction in combination with aldol condensation allows for the preparation of polyols in high yields and with high selectivity. Industrial applications of neopentyl glycol, pentaerythritol, and trimethylolpropane

The Cannizzaro reaction is widely used in the production of industrial chemicals such as neopentyl glycol, pentaerythritol, and trimethylolpropane.

These chemicals are used in the production of resins, lubricants, and plasticizers.

Neopentyl glycol is produced through the Cannizzaro reaction of formaldehyde and isobutyraldehyde.

This reaction is used to produce high purity neopentyl glycol, which is used in the production of resins, coatings, and plasticizers.

Pentaerythritol is produced through the Cannizzaro reaction of formaldehyde and acetaldehyde.

Pentaerythritol is used in the production of resins, coatings, and plasticizers.

Trimethylolpropane is produced through the Cannizzaro reaction of formaldehyde and isobutyraldehyde.

This chemical is used in the production of lubricants, resins, and coatings.

In summary, the Cannizzaro reaction has numerous uses and applications in industrial chemistry.

It is used in the synthesis of industrial chemicals such as neopentyl glycol, pentaerythritol, and trimethylolpropane, which play vital roles in the production of resins, lubricants, and plasticizers. The reaction is also used in the preparation of polyols through the combination of the crossed Cannizzaro reaction and aldol condensation.

The intramolecular Cannizzaro reaction is important as it serves as a model reaction in the study of enzyme-substrate complexes. Cannizzaro reaction is a fundamental organic reaction that involves the use of aldehydes without active hydrogen and strong bases to yield an alcohol and a carboxylic acid.

The mechanism of the reaction involves hydroxide attack, alkoxide and carboxylate anion formation, and acid workup. The Cannizzaro reaction has numerous uses and applications in industry for producing various chemicals used in the production of resins, lubricants, and plasticizers.

Intramolecular Cannizzaro reactions serve as model reactions for studying enzyme-substrate complexes. A takeaway from this article is the importance of understanding the Cannizzaro reaction and its applications to advance organic chemistry in several fields.

FAQs:

– What is the Cannizzaro reaction? The Cannizzaro reaction is an organic reaction that involves the use of aldehydes without active hydrogen and strong bases to yield an alcohol and a carboxylic acid.

– What are some examples of Cannizzaro reaction? Vanillin and syringaldehyde are examples of aldehydes without active hydrogen that undergo Cannizzaro reaction.

Benzaldehyde and formaldehyde result in alcohol and carboxylic acids.

– What is the importance of the Cannizzaro reaction in industry?

The Cannizzaro reaction is critical for producing various chemicals used in the production of resins, lubricants, and plasticizers.

– What is an intramolecular Cannizzaro reaction?

Intramolecular Cannizzaro reaction involves the reaction of a carbonyl group with another carbonyl group within the same molecule, yielding a carboxylic acid and an alcohol.

– What are the uses of Cannizzaro reaction in organic chemistry?

Cannizzaro reaction plays an important role in producing industrial chemicals such as neopentyl glycol, pentaerythritol, and trimethylolpropane that are used to produce various items from resins to lubricants.

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