Aldehydes, Ketones & Carboxylic Acids

  • Physical Properties of Carbonic Compounds

Introduction

  • Aldehydes, ketones, and carboxylic acids are important classes of organic compounds.
  • They contain the carbonyl functional group (-C=O).
  • This functional group imparts unique physical properties to these compounds.

Solubility

  • Aldehydes and ketones are generally soluble in water.
  • Carboxylic acids, on the other hand, have significantly higher solubility in water.
  • This is due to the presence of a polar -COOH group, which can form hydrogen bonds with water molecules.

Boiling Points

  • Aldehydes, ketones, and carboxylic acids have higher boiling points compared to hydrocarbons of similar molecular weight.
  • This is due to the polarity of the carbonyl group and the ability to form dipole-dipole interactions between molecules.

Odor

  • Aldehydes and ketones often have pleasant or pungent odors.
  • Carboxylic acids generally have a sour odor.

Reactivity with Oxidizing Agents

  • Aldehydes are easily oxidized to carboxylic acids.
  • Ketones, on the other hand, are relatively resistant to oxidation.
  • Carboxylic acids can also be further oxidized to form carbon dioxide and water.

Reduction Reactions

  • Aldehydes and ketones can be reduced to primary and secondary alcohols, respectively.
  • Carboxylic acids can be reduced to primary alcohols or even aldehydes under suitable conditions.

Acidic Nature

  • Carboxylic acids are acidic in nature due to the presence of the -COOH group.
  • They can donate a proton and behave as acids in various chemical reactions.
  • Aldehydes and ketones, on the other hand, are relatively neutral compounds.

Schiff’s Test

  • Aldehydes can be detected using the Schiff’s test.
  • Schiff’s reagent, a pink-colored solution of fuchsin sulfurous acid, turns colorless when exposed to aldehydes.
  • This test is based on the reaction between the aldehyde and the sulfur dioxide group present in the Schiff’s reagent.

Tollens’ Test

  • Tollens’ test is used to distinguish aldehydes from ketones.
  • The silver mirror test is a positive indicator for aldehydes.
  • In this test, Tollens’ reagent, which contains silver ions, reacts with aldehydes to form a silver mirror on the inner side of the test tube.

Iodoform Test

  • The iodoform test is used to identify compounds containing the -COCH3 group.
  • In this test, compounds such as methyl ketones react with iodine and sodium hydroxide to give a yellow precipitate of iodoform.

Slide 11

  • Oxidation of Aldehydes
    • Aldehydes can be oxidized to carboxylic acids using oxidizing agents such as potassium permanganate (KMnO4) or chromic acid (H2CrO4).
    • Example: Oxidation of formaldehyde (CH2O) gives formic acid (HCOOH).
    • Equation: CH2O + 2[O] → HCOOH Slide 12
  • Oxidation of Ketones
    • Ketones are resistant to oxidation due to absence of an easily oxidizable hydrogen atom.
    • They do not undergo oxidation with mild oxidizing agents.
    • However, strong oxidizing agents like chromic acid (H2CrO4) can oxidize highly reactive ketones.
    • Example: Oxidation of acetone (CH3COCH3) gives acetic acid (CH3COOH).
    • Equation: CH3COCH3 + 2[H2CrO4] → CH3COOH Slide 13
  • Esterification Reaction
    • Esterification is a reaction between an alcohol and a carboxylic acid.
    • It forms an ester and water as byproducts.
    • The reaction is catalyzed by an acid or base.
    • Example: Ethanol reacts with acetic acid to form ethyl acetate and water.
    • Equation: CH3COOH + CH3CH2OH → CH3COOCH2CH3 + H2O Slide 14
  • Hydrolysis Reactions
    • Hydrolysis is the reverse of esterification.
    • It involves the reaction of an ester with water to form a carboxylic acid and an alcohol.
    • The reaction can be acid or base catalyzed.
    • Example: Hydrolysis of ethyl acetate gives acetic acid and ethanol.
    • Equation: CH3COOCH2CH3 + H2O → CH3COOH + CH3CH2OH Slide 15
  • Reduction of Carboxylic Acids
    • Carboxylic acids can be reduced to primary alcohols using reducing agents such as LiAlH4.
    • Example: Reduction of acetic acid gives ethanol.
    • Equation: CH3COOH + 2[H] → CH3CH2OH Slide 16
  • Reduction of Aldehydes and Ketones
    • Aldehydes can be reduced to primary alcohols and ketones can be reduced to secondary alcohols using reducing agents such as NaBH4 or LiAlH4.
    • Example: Reduction of butanal (CH3CH2CH2CHO) gives 1-butanol (CH3CH2CH2CH2OH).
    • Equation: CH3CH2CH2CHO + 2[H] → CH3CH2CH2CH2OH Slide 17
  • Aldol Condensation
    • Aldol condensation is a reaction between two molecules of an aldehyde or ketone to form a β-hydroxy carbonyl compound.
    • The reaction can be either an acid- or base-catalyzed.
    • Example: Condensation of propanal (CH3CH2CHO) gives 3-hydroxybutanal (CH3CH(OH)CH2CHO).
    • Equation: CH3CH2CHO + CH3CH2CHO → CH3CH(OH)CH2CHO Slide 18
  • Cannizzaro Reaction
    • Cannizzaro reaction is a disproportionation reaction in which one molecule of an aldehyde is reduced to an alcohol and another molecule is oxidized to a carboxylic acid in the presence of a strong base.
    • Example: Benzaldehyde (C6H5CHO) undergoes Cannizzaro reaction to give benzyl alcohol (C6H5CH2OH) and benzoic acid (C6H5COOH).
    • Equation: C6H5CHO + C6H5CHO → C6H5CH2OH + C6H5COOH Slide 19
  • Nucleophilic Addition Reactions
    • Aldehydes and ketones undergo nucleophilic addition reactions with nucleophiles such as water, alcohols, ammonia, and amines.
    • Example: Addition of water to propanal gives propan-1-ol.
    • Equation: CH3CH2CHO + H2O → CH3CH2CH2OH Slide 20
  • Formation of Acetals and Ketals
    • Aldehydes and ketones react with alcohols in the presence of an acid catalyst to form acetals and ketals, respectively.
    • This reaction is useful in protecting carbonyl groups in organic synthesis.
    • Example: Acetal formation from propanal and ethanol gives 1,1-diethoxyethane.
    • Equation: CH3CH2CHO + 2CH3CH2OH → CH3CH(OCH2CH3)2 Slide 21
  • Nomenclature of Aldehydes and Ketones
    • Aldehydes are named by replacing the -e ending of the corresponding alkane with -al.
    • Ketones are named by replacing the -e ending of the corresponding alkane with -one.
    • Example: Methanal (formaldehyde), Ethanal (acetaldehyde), Propanone (acetone) Slide 22
  • Nomenclature of Carboxylic Acids
    • Carboxylic acids are named by replacing the -e ending of the corresponding alkane with -oic acid.
    • The carbon atom of the carboxyl group is assigned the number 1.
    • Example: Methanoic acid (formic acid), Ethanoic acid (acetic acid), Propanoic acid (propionic acid) Slide 23
  • Preparation of Aldehydes
    • Aldehydes can be prepared by the oxidation of primary alcohols in the presence of suitable oxidizing agents.
    • Example: Oxidation of ethanol gives ethanal.
    • Equation: CH3CH2OH + [O] → CH3CHO + H2O Slide 24
  • Preparation of Ketones
    • Ketones can be prepared by the oxidation of secondary alcohols in the presence of suitable oxidizing agents.
    • Example: Oxidation of 2-propanol gives propanone.
    • Equation: CH3CH(OH)CH3 + [O] → CH3COCH3 + H2O Slide 25
  • Preparation of Carboxylic Acids
    • Carboxylic acids can be prepared by the oxidation of primary alcohols or aldehydes using strong oxidizing agents.
    • Example: Oxidation of ethanol gives ethanoic acid.
    • Equation: CH3CH2OH + [O] → CH3COOH + H2O Slide 26
  • Reactions of Aldehydes
    • Aldehydes undergo a variety of reactions.
    • They can undergo nucleophilic addition reactions, oxidation reactions, and condensation reactions.
    • Example: Aldehydes react with ammonia to form imines.
    • Equation: RCHO + NH3 → RCH=NH2 + H2O Slide 27
  • Reactions of Ketones
    • Ketones also undergo nucleophilic addition reactions and condensation reactions.
    • They are resistant to oxidation due to the absence of easily oxidizable hydrogen atoms.
    • Example: Ketones react with phenylhydrazine to form crystalline derivatives.
    • Equation: R2C=O + C6H5NHNH2 → R2C=NNHC6H5 + H2O Slide 28
  • Reactions of Carboxylic Acids
    • Carboxylic acids undergo a variety of reactions due to their acidic nature.
    • They can undergo esterification, hydrolysis, and decarboxylation reactions.
    • Example: Carboxylic acids react with alcohols to form esters.
    • Equation: RCOOH + R’OH → RCOOR’ + H2O Slide 29
  • Uses of Aldehydes and Ketones
    • Aldehydes and ketones find numerous applications in industry and laboratories.
    • They are used in the production of plastics, solvents, and pharmaceuticals.
    • Example: Acetone is commonly used as a solvent in nail polish removers. Slide 30
  • Uses of Carboxylic Acids
    • Carboxylic acids have diverse uses in various fields.
    • They are used as preservatives, flavoring agents, and intermediates in organic synthesis.
    • Example: Acetic acid is widely used in the production of vinegar and as a solvent in the chemical industry.