Cannizzaro Reaction

The Cannizzaro reaction is a chemical reaction that involves the disproportionation of an aldehyde in the presence of a strong base, such as potassium hydroxide $\ce{(KOH)}$ or sodium hydroxide $\ce{(NaOH)}$. In this reaction, one aldehyde molecule is oxidized to form a carboxylic acid, while another aldehyde molecule is reduced to form an alcohol.

Cannizzaro Reaction Mechanism

The Cannizzaro reaction is a chemical reaction that involves the disproportionation of an aldehyde in the presence of a strong base to form an alcohol and a carboxylic acid. The reaction is named after the Italian chemist Stanislao Cannizzaro, who first reported it in 1853.

Mechanism

The Cannizzaro reaction proceeds via a nucleophilic addition mechanism. The reaction is initiated by the attack of a hydroxide ion on the carbonyl group of the aldehyde, forming a tetrahedral intermediate. This intermediate then collapses, expelling the hydroxide ion and forming a carboxylate anion. The carboxylate anion is then protonated by water to form the carboxylic acid.

The overall reaction scheme for the Cannizzaro reaction is as follows:

$\ce{RCHO + KOH → RCOO^-K^+ + RCH2OH}$

Reaction Conditions

The Cannizzaro reaction is typically carried out in a polar protic solvent, such as water or ethanol. The reaction is also catalyzed by a strong base, such as potassium hydroxide or sodium hydroxide. The reaction temperature is typically between room temperature and 100 °C.

Examples

Some examples of the Cannizzaro reaction include:

• The reaction of benzaldehyde with potassium hydroxide to form benzyl alcohol and potassium benzoate.
• The reaction of formaldehyde with sodium hydroxide to form methanol and sodium formate.
• The reaction of acetaldehyde with potassium hydroxide to form acetic acid and potassium ethoxide.

Cross Cannizzaro Reaction

The Cross Cannizzaro reaction is an organic reaction in which an aldehyde and a ketone react in the presence of a base to form an alcohol and a carboxylic acid. The reaction is named after the German chemist Richard Anschütz, who first reported it in 1881.

Scope and Limitations

The Cross Cannizzaro reaction is a versatile reaction that can be used to synthesize a variety of alcohols and esters. However, the reaction is limited to aldehydes and ketones that are not too hindered. If the aldehyde or ketone is too hindered, the reaction will not proceed.

Uses of Cannizzaro Reaction

The Cannizzaro reaction is an organic reaction in which an aldehyde that lacks an alpha-hydrogen atom is disproportionated into an alcohol and a carboxylic acid. The reaction is named after the Italian chemist Stanislao Cannizzaro, who first reported it in 1853.

The Cannizzaro reaction is a useful method for synthesizing alcohols and carboxylic acids from aldehydes. It is particularly useful for synthesizing aromatic alcohols and carboxylic acids, which are often difficult to prepare by other methods.

Applications of the Cannizzaro Reaction

The Cannizzaro reaction has a number of applications in organic synthesis, including:

• The Cannizzaro reaction can be used to synthesize a variety of alcohols, including primary, secondary, and tertiary alcohols. Primary alcohols are formed from aldehydes that have one hydrogen atom on the alpha-carbon. Secondary alcohols are formed from aldehydes that have two hydrogen atoms on the alpha-carbon. Tertiary alcohols are formed from aldehydes that have three hydrogen atoms on the alpha-carbon.

• Synthesis of carboxylic acids:** The Cannizzaro reaction cannot be used to synthesize carboxylic acids. The Cannizzaro reaction is used to convert aldehydes into carboxylic acids and alcohols under basic conditions. Aliphatic carboxylic acids are formed from aldehydes that have no alpha-hydrogen atoms. Aromatic carboxylic acids are formed from aldehydes that have an aromatic ring adjacent to the alpha-carbon atom.

• Synthesis of other organic compounds:** The Cannizzaro reaction cannot be used to synthesize esters, amides, or nitriles. Esters are formed by the reaction of an alcohol and a carboxylic acid. Amides are formed by the reaction of an amine and a carboxylic acid. Nitriles are formed by the reaction of an aldehyde or ketone with ammonia.

Advantages of the Cannizzaro Reaction

The Cannizzaro reaction has a number of advantages over other methods for synthesizing aldehydes and carboxylic acids, including:

• The Cannizzaro reaction is a reaction between aldehydes that lack alpha hydrogens, leading to disproportionation into a carboxylic acid and a primary alcohol.

• The Cannizzaro reaction can be used to synthesize a wide variety of alcohols but not carboxylic acids.

• The Cannizzaro reaction is a relatively inefficient reaction that produces low yields of products.

• Green chemistry: The Cannizzaro reaction is a reaction that does not produce any harmful byproducts.

The Cannizzaro reaction is a versatile and useful reaction for synthesizing alcohols and carboxylic acids. It is a simple, efficient reaction that has a number of applications in organic synthesis.

Cannizzaro Reaction FAQs

What is the Cannizzaro reaction?

The Cannizzaro reaction is a chemical reaction in which an aldehyde that lacks an alpha-hydrogen atom is disproportionated into an alcohol and a carboxylic acid. The reaction is named after the Italian chemist Stanislao Cannizzaro, who first reported it in 1853.

What are the conditions for the Cannizzaro reaction?

The Cannizzaro reaction is typically carried out in a polar protic solvent, such as dimethylformamide (DMF) or acetonitrile, in the presence of a base, such as potassium hydroxide or sodium hydroxide. The reaction is usually performed at room temperature, but it can also be carried out at higher temperatures.

What are the products of the Cannizzaro reaction?

The products of the Cannizzaro reaction are an alcohol and a carboxylic acid. The alcohol is formed by the reduction of the carbonyl group, while the carboxylic acid is formed by the oxidation of the carbonyl group.

What are some examples of the Cannizzaro reaction?

Some examples of the Cannizzaro reaction include:

• The reaction of benzaldehyde with potassium hydroxide in DMF to form benzyl alcohol and potassium benzoate.
• The reaction of formaldehyde with sodium hydroxide in water to form sodium formate and methanol.
• The reaction of acetaldehyde with potassium hydroxide in ethanol to form acetic acid and potassium ethoxide.

What are the applications of the Cannizzaro reaction?

The Cannizzaro reaction is used in a variety of applications, including:

• The production of alcohols and carboxylic acids.
• The synthesis of fine chemicals and pharmaceuticals.
• The purification of aldehydes.
• The detection of aldehydes.

What are the limitations of the Cannizzaro reaction?

The Cannizzaro reaction is limited to aldehydes that lack an alpha-hydrogen atom. Aldehydes that have an alpha-hydrogen atom will undergo the aldol condensation reaction instead of the Cannizzaro reaction.

What are the safety considerations for the Cannizzaro reaction?

The Cannizzaro reaction should be carried out in a well-ventilated area. The reactants and products of the reaction are corrosive and can cause skin and eye irritation. The reaction should be carried out under the supervision of a qualified chemist.