Aldehydes, Ketones & Carboxylic Acids - Special Preparation of Ketones

  • Ketones can be prepared by the oxidation of secondary alcohols.
  • The oxidation of secondary alcohols to ketones is known as dehydrogenation.

Example:

  • Oxidation of Isopropanol (secondary alcohol) to form Acetone (ketone)

Equation:

$$\ce{CH3-CHOH-CH3 ->[\text{KMnO4}] CH3-CO-CH3}$$

Aldehydes, Ketones & Carboxylic Acids - Reactions of Ketones

Ketones undergo various reactions, including:

  1. Nucleophilic addition reactions
  1. Oxidation reactions
  1. Reduction reactions
  1. Condensation reactions

Aldehydes, Ketones & Carboxylic Acids - Nucleophilic Addition Reactions

Ketones undergo nucleophilic addition reactions at the carbonyl group (C=O). Some common nucleophiles include:

  • Grignard reagents
  • Cyanide ions
  • Hydrazine
  • Alcohols

Example:

Reaction of Acetone (ketone) with Grignard reagent (RMgX)

Equation:

$$\ce{CH3-CO-CH3 + RMgX -> CH3-COMgX + H2O}$$

Aldehydes, Ketones & Carboxylic Acids - Oxidation Reactions of Ketones

Ketones are not easily oxidized under normal conditions. Strong oxidizing agents are required for the oxidation of ketones to carboxylic acids.

  • Mild oxidation reagents, such as Tollen’s reagent (Ag(NH3)2OH), do not oxidize ketones.

Example:

Oxidation of Acetone (ketone) using Sodium hypochlorite (NaOCl)

Equation:

$$\ce{CH3-CO-CH3 + NaOCl -> CH3-COOH + HCl}$$

Aldehydes, Ketones & Carboxylic Acids - Reduction Reactions of Ketones

Ketones can be reduced to secondary alcohols by various reducing agents.

  • Sodium Borohydride (NaBH4) is a commonly used reducing agent for the reduction of ketones.

Example:

Reduction of Acetone (ketone) using Sodium Borohydride (NaBH4)

Equation:

$$\ce{CH3-CO-CH3 + 4H -> CH3-CHOH-CH3}$$

Aldehydes, Ketones & Carboxylic Acids - Condensation Reactions of Ketones

Ketones can undergo condensation reactions to form larger molecules such as aldol condensation and Cannizzaro reaction.

  • Aldol condensation: Formation of beta-hydroxy ketone through the reaction of two molecules of ketones.
  • Cannizzaro reaction: Reaction of a non-enolizable aldehyde or ketone with a strong base to form a carboxylic acid and alcohol.

Example:

Aldol condensation of Acetone (ketone)

Equation:

$$\ce{2CH3-CO-CH3 -> CH3-CO-CH2-CO-CH3 + H2O}$$

Aldehydes, Ketones & Carboxylic Acids - Special Reaction in Ketones: Haloform Reaction

Ketones containing a methyl group adjacent to the carbonyl group undergo the Haloform reaction.

  • In the Haloform reaction, ketones react with halogens (chlorine, bromine, or iodine) in the presence of a strong base to form a haloform.

Example:

Haloform reaction of Acetone (ketone) with Chlorine

Equation:

$$\ce{CH3-CO-CH3 + 3Cl2 + 4OH- -> CHCl3 + CH3COONa + 3H2O}$$

Aldehydes, Ketones & Carboxylic Acids - Special Reaction in Ketones: Clemmensen Reduction

Ketones can be reduced to alkanes by Clemmensen reduction.

  • Clemmensen reduction is carried out using zinc amalgam (Zn(Hg)) and concentrated hydrochloric acid (HCl).

Example:

Clemmensen reduction of Acetone (ketone)

Equation:

$$\ce{CH3-CO-CH3 + 2Zn(Hg) + 2HCl -> CH3-CH3 + ZnCl2 + 2H2O}$$

Aldehydes, Ketones & Carboxylic Acids - Special Reaction in Ketones: Wolff-Kishner Reaction

Ketones can be converted to alkanes by Wolff-Kishner reduction.

  • Wolff-Kishner reduction is carried out using hydrazine (N2H4) and strong base (KOH or NaOH) in the presence of heat.

Example:

Wolff-Kishner reduction of Acetone (ketone)

Equation:

$$\ce{CH3-CO-CH3 + 2N2H4 + KOH -> CH3-CH3 + N2 + KOH + H2O}$$

Special Preparation of Ketones:

  • Ketones can also be prepared by the ozonolysis of alkenes.
  • Ozonolysis is the cleavage of alkenes using ozone (O3) followed by reduction with zinc dust (Zn).

Example:

  • Preparation of Propanone (ketone) from Propene (alkene)

Equation:

$$\ce{CH2=CH-CH3 + 3O3 -> CH3-CO-CH3 + 3O2}$$

Special Preparation of Ketones (continued):

  • Ketones can also be synthesized by the reaction of acid chlorides with organometallic compounds.
  • This method is known as the Corey-Kim oxidation.

Example:

Preparation of Acetone (ketone) from Acetyl chloride and Phenyl magnesium bromide

Equation:

$$\ce{CH3COCl + C6H5MgBr -> CH3-CO-CH3 + C6H5OH + MgBrCl}$$

Reactions of Ketones - Nucleophilic Addition Reactions:

  • Ketones undergo nucleophilic addition reactions at the carbonyl group (C=O).
  • Nucleophiles attack the electrophilic carbon of the carbonyl group, resulting in the formation of a new bond.

Example:

  • Reaction of Acetone (ketone) with Sodium Cyanide (NaCN)

Equation:

$$\ce{CH3-CO-CH3 + NaCN -> CH3-CO-CN + NaOH}$$

Reactions of Ketones - Nucleophilic Addition Reactions (continued):

  • Another example of nucleophilic addition is the reaction of ketones with Grignard reagents.
  • The Grignard reagent acts as a nucleophile attacking the carbonyl carbon.

Example:

  • Reaction of Propanone (ketone) with Methyl Magnesium Bromide (CH3MgBr)

Equation:

$$\ce{CH3-CO-CH3 + CH3MgBr -> CH3-COMgBr + CH3OH}$$

Reactions of Ketones - Oxidation Reactions:

  • Ketones are not easily oxidized under normal conditions.
  • Strong oxidizing agents are required for the oxidation of ketones to carboxylic acids.

Example:

  • Oxidation of Butanone (ketone) using Potassium Permanganate (KMnO4)

Equation:

$$\ce{CH3-CO-CH2-CH3 + 2KMnO4 -> CH3-COOH + CH3COOH + 2MnO2 + 2KOH}$$

Reactions of Ketones - Oxidation Reactions (continued):

  • Mild oxidation reagents, such as Tollen’s reagent (Ag(NH3)2OH), do not oxidize ketones.
  • Tollen’s reagent is commonly used for the oxidation of aldehydes to carboxylic acids.

Example:

  • Reaction of Acetone (ketone) with Tollen’s reagent

Equation:

$$\ce{2Ag(NH3)2OH + 2CH3-CO-CH3 + 3OH- -> 2Ag + 2NH4+ + 2CH3-COO- + 4H2O}$$

Reactions of Ketones - Reduction Reactions:

  • Ketones can be reduced to secondary alcohols by various reducing agents.
  • Sodium Borohydride (NaBH4) and Lithium Aluminum Hydride (LiAlH4) are commonly used reducing agents for the reduction of ketones.

Example:

  • Reduction of Propanone (ketone) using Sodium Borohydride (NaBH4)

Equation:

$$\ce{CH3-CO-CH3 + 2H2 + NaBH4 -> CH3-CHOH-CH3 + NaOH}$$

Reactions of Ketones - Reduction Reactions (continued):

  • Reduction of ketones with LiAlH4 leads to the formation of the corresponding alcohols.
  • LiAlH4 is a stronger reducing agent compared to NaBH4.

Example:

  • Reduction of Butanone (ketone) using Lithium Aluminum Hydride (LiAlH4)

Equation:

$$\ce{CH3-CO-CH2-CH3 + 4[H] -> CH3-CH2-CH2-CH3}$$

Reactions of Ketones - Condensation Reactions:

  • Ketones can undergo condensation reactions to form larger molecules.
  • Aldol condensation is a common condensation reaction of ketones.

Example:

  • Aldol condensation of Propanone (ketone)

Equation:

$$\ce{CH3-CO-CH3 -> CH3-CH(OH)-CH2-CO-CH3}$$

Reactions of Ketones - Condensation Reactions (continued):

  • In the aldol condensation reaction, two molecules of ketones react to form a beta-hydroxy ketone or an aldol.

Reactions of Ketones - Condensation Reactions (continued):

  • Claisen condensation is another type of condensation reaction of ketones.
  • Claisen condensation involves the reaction between the alpha-carbon of one ketone and the carbonyl group of another ketone.

Example:

  • Claisen condensation of Ethyl Acetate (ketone)

Equation:

$$\ce{CH3-CO-OEt + CH3-CO-K -> CH3-CO-CH2-CO2Et + KOEt}$$

Reactions of Ketones - Special Reaction: Haloform Reaction

  • Ketones containing a methyl group adjacent to the carbonyl group undergo the Haloform reaction.
  • This reaction is useful for the identification of such ketones.

Example:

  • Haloform reaction of Ethyl Acetone (ketone) with Chlorine

Equation:

$$\ce{CH3-CO-CH2-CO-CH3 + 3Cl2 + 4NaOH -> CHCl3 + CH3COONa + 2Na2CO3 + 3H2O}$$

Reactions of Ketones - Special Reaction: Clemmensen Reduction

  • Ketones can be reduced to alkanes by Clemmensen reduction.
  • Clemmensen reduction is carried out using zinc amalgam (Zn(Hg)) and concentrated hydrochloric acid (HCl).

Example:

  • Clemmensen reduction of Butanone (ketone)

Equation:

$$\ce{CH3-CO-CH2-CH3 + 2Zn(Hg) + 2HCl -> CH3-CH2-CH2-CH3 + ZnCl2 + 2H2O}$$

Reactions of Ketones - Special Reaction: Wolff-Kishner Reaction

  • Ketones can be converted to alkanes by Wolff-Kishner reduction.
  • Wolff-Kishner reduction is carried out using hydrazine (N2H4) and strong base (KOH or NaOH) in the presence of heat.

Example:

  • Wolff-Kishner reaction of Butanone (ketone)

Equation:

$$\ce{CH3-CO-CH2-CH3 + 2N2H4 + KOH -> CH3-CH2-CH2-CH3 + N2 + KOH + H2O}$$

Reactions of Ketones - Special Reaction: Cannizzaro Reaction

  • A non-enolizable aldehyde or ketone reacts with a strong base to form a carboxylic acid and alcohol.
  • This reaction is known as the Cannizzaro reaction.

Example:

  • Cannizzaro reaction of Benzaldehyde (aldehyde) with Sodium Hydroxide (NaOH)

Equation:

$$\ce{2C6H5CHO + 2NaOH -> C6H5COONa + C6H5CH2OH}$$

Reactions of Ketones - Special Reaction: Aldol Reaction

  • The aldol reaction involves the condensation of an aldehyde or ketone with an enolate ion or another carbonyl compound.
  • It leads to the formation of a beta-hydroxy aldehyde or ketone called an aldol.

Example:

  • Aldol reaction of Acetone (ketone) with Propanal (aldehyde)

Equation:

$$\ce{CH3-CO-CH3 + CH3CHO -> CH3-CH(OH)-CH2-COH}$$

Reactions of Ketones - Special Reaction: Perkin Reaction

  • The Perkin reaction involves the reaction of an aromatic aldehyde with an acid anhydride and anhydrous alkali.
  • It leads to the formation of an unsaturated acid known as a perkin acid.

Example:

  • Perkin reaction of Benzaldehyde (aldehyde) with Anhydride (RCO) and Anhydrous Alkali (KOH)

Equation:

$$\ce{C6H5CHO + RCOO + KOH -> C6H5-CH=CH-COOH + RCOOK}$$

Reactions of Ketones - Special Reaction: Kiliani-Fischer Synthesis

  • Kiliani-Fischer synthesis involves the conversion of a straight-chain aldehyde to L-glyceraldehyde, which can be further converted to D-glyceraldehyde.
  • This synthesis is used for the preparation of sugars.

Example:

  • Kiliani-Fischer synthesis of Butanal (aldehyde)

Equation:

$$\ce{CH3CH2CH2CHO + NaCN -> CH3CH2CH(OH)CN -> CH3CH(OH)CH(OH)CN -> CH3CH(OH)CH(OH)CHO}$$

Reactions of Ketones - Special Reaction: Fisher Esterification

  • Fisher esterification involves the reaction of an alcohol with an acid in the presence of an acid catalyst to form an ester.

Example:

  • Fisher esterification of Acetic Acid and Methanol

Equation:

$$\ce{CH3COOH + CH3OH -> CH3COOCH3 + H2O}$$

Summary:

  • Ketones can be prepared by various methods such as oxidation of secondary alcohols and ozonolysis of alkenes.
  • Ketones undergo nucleophilic addition reactions, oxidation reactions, reduction reactions, and condensation reactions.
  • Special reactions of ketones include the Haloform reaction, Clemmensen reduction, Wolff-Kishner reaction, Cannizzaro reaction, aldol reaction, Perkin reaction, Kiliani-Fischer synthesis, and Fisher esterification.
  • These reactions play a significant role in organic synthesis and have various applications in the industry.