Aldehydes, Ketones & Carboxylic Acids

  • Carbonyl compounds are organic compounds that contain the C=O functional group.
  • Aldehydes have the carbonyl group at the end of a carbon chain.
  • Ketones have the carbonyl group placed between two carbon atoms.
  • Carboxylic acids have the carbonyl group attached to a hydroxyl group. Examples:
  • Methanal (formaldehyde) is an aldehyde.
  • Propanone (acetone) is a ketone.
  • Ethanoic acid (acetic acid) is a carboxylic acid. Chemical Equations:
  • Aldehydes: RCHO (R = alkyl group)
  • Ketones: RCOR’ (R = alkyl group, R’ = alkyl group)
  • Carboxylic acids: RCOOH (R = alkyl group) Properties of Aldehydes:
  • Boiling point and melting point increase with increasing molecular weight.
  • Aldehydes have a characteristic odor.
  • Most aldehydes do not mix completely with water. Properties of Ketones:
  • Boiling point and melting point increase with increasing molecular weight.
  • Ketones are generally less reactive than aldehydes.
  • Ketones do not undergo oxidation easily. Properties of Carboxylic Acids:
  • Carboxylic acids can form hydrogen bonds with water.
  • They have higher boiling points compared to aldehydes and ketones.
  • Carboxylic acids are weak acids and ionize partially in water. Functional Group Reactions:
  • Aldehydes and ketones undergo nucleophilic addition reactions.
  • Reduction of aldehydes and ketones gives corresponding alcohols.
  • Carboxylic acids undergo esterification reactions with alcohols. Applications of Aldehydes:
  • Formaldehyde is used in the production of plastics and resins.
  • Glucose, an aldehyde, is a major energy source for living organisms. Applications of Ketones:
  • Acetone is commonly used as a solvent and for nail polish remover.
  • Some ketones have medicinal uses, such as the anesthetic methoxyflurane. Applications of Carboxylic Acids:
  • Acetic acid is widely used as a preservative and a solvent.
  • Aspirin is a derivative of salicylic acid, which is a carboxylic acid.
  1. Types of carbonyl compounds:
  • Aldehydes have the carbonyl group (-C=O) at the end of a carbon chain.
  • Ketones have the carbonyl group placed between two carbon atoms.
  • Carboxylic acids have the carbonyl group attached to a hydroxyl (-OH) group.
  1. Aldehydes:
  • Examples: Methanal (formaldehyde), Ethanal (acetaldehyde), Propanal.
  • Aldehydes have the general formula RCHO (R = alkyl group).
  • The carbonyl group in aldehydes is always at the end of a carbon chain.
  • Aldehydes can be oxidized to carboxylic acids.
  • Aldehydes undergo nucleophilic addition reactions.
  1. Ketones:
  • Examples: Propanone (acetone), Butanone (methyl ethyl ketone), Hexan-3-one.
  • Ketones have the general formula RCOR’ (R = alkyl group, R’ = alkyl group).
  • The carbonyl group in ketones is placed between two carbon atoms.
  • Ketones do not undergo oxidation easily.
  • Ketones undergo nucleophilic addition reactions.
  1. Carboxylic Acids:
  • Examples: Ethanoic acid (acetic acid), Propanoic acid, Benzoic acid.
  • Carboxylic acids have the general formula RCOOH (R = alkyl group).
  • The carbonyl group in carboxylic acids is attached to a hydroxyl (-OH) group.
  • Carboxylic acids are weak acids and ionize partially in water.
  • Carboxylic acids can undergo esterification reactions.
  1. Physical properties of Aldehydes:
  • Boiling point and melting point increase with increasing molecular weight.
  • Aldehydes have a characteristic odor, some have pleasant smells.
  • Most aldehydes do not mix completely with water due to their polar nature.
  • Aldehydes with lower molecular weight are highly volatile.
  1. Physical properties of Ketones:
  • Boiling point and melting point increase with increasing molecular weight.
  • Ketones are generally less reactive than aldehydes.
  • Ketones do not undergo oxidation easily due to the absence of a hydrogen atom attached to the carbonyl group.
  • Ketones with lower molecular weight are highly volatile.
  1. Physical properties of Carboxylic Acids:
  • Carboxylic acids can form hydrogen bonds with water due to the presence of a hydroxyl (-OH) group.
  • Carboxylic acids have higher boiling points compared to aldehydes and ketones.
  • Carboxylic acids are usually colorless liquids or crystalline solids at room temperature.
  • Carboxylic acids have a sour taste and a sharp odor.
  1. Chemical reactions of Aldehydes:
  • Aldehydes undergo nucleophilic addition reactions with nucleophiles such as water, alcohols, and amines.
  • Reduction of aldehydes gives primary alcohols.
  • Oxidation of aldehydes gives carboxylic acids.
  • Aldehydes can undergo condensation reactions to form larger compounds.
  1. Chemical reactions of Ketones:
  • Ketones undergo nucleophilic addition reactions similar to aldehydes.
  • Reduction of ketones gives secondary alcohols.
  • Ketones are less prone to oxidation compared to aldehydes.
  • Ketones can undergo condensation reactions to form larger compounds.
  1. Chemical reactions of Carboxylic Acids:
  • Carboxylic acids undergo esterification reactions with alcohols in the presence of an acid catalyst.
  • Reduction of carboxylic acids gives primary alcohols.
  • Carboxylic acids can be converted to acyl chlorides, anhydrides, and esters.
  • Carboxylic acids undergo decarboxylation reactions to form carbon dioxide and an alkane.
  1. Common Reactions of Aldehydes:
  • Aldehydes undergo oxidation reactions in the presence of oxidizing agents such as Tollens’ reagent and Fehling’s solution.
  • Aldehydes can be reduced to primary alcohols using reducing agents like NaBH4 or LiAlH4.
  • Aldehydes react with ammonia to form imines.
  • Aldehydes undergo nucleophilic addition reactions with Grignard reagents to form alcohols.
  1. Common Reactions of Ketones:
  • Ketones can be oxidized to produce carboxylic acids using strong oxidizing agents like KMnO4 or K2Cr2O7.
  • Ketones undergo reduction to form secondary alcohols using reducing agents like NaBH4 or LiAlH4.
  • Ketones react with hydrazine to form hydrazones.
  • Ketones undergo nucleophilic addition reactions with organometallic reagents like Grignard reagents to form alcohols.
  1. Common Reactions of Carboxylic Acids:
  • Carboxylic acids react with bases to form carboxylate salts and water.
  • Carboxylic acids undergo esterification reactions with alcohols in the presence of an acid catalyst.
  • Carboxylic acids can be converted to acid chlorides using thionyl chloride or phosphorus pentachloride.
  • Carboxylic acids react with ammonia or a primary amine to form amides.
  1. Importance of Aldehydes:
  • Formaldehyde is commonly used in the production of plastics, resins, and textiles.
  • Benzaldehyde is used in the synthesis of various pharmaceuticals and perfumes.
  • Glucose, an aldehyde, is a major source of energy for living organisms.
  1. Importance of Ketones:
  • Acetone is widely used as a solvent in various industries, as well as in nail polish remover.
  • Methyl ethyl ketone (MEK) is used as a solvent in paints, adhesives, and coatings.
  • Some ketones have medicinal uses, such as the anesthetic methoxyflurane.
  1. Importance of Carboxylic Acids:
  • Acetic acid is commonly used as a preservative in food and as a solvent.
  • Formic acid is used as a coagulant in the rubber industry and as a preservative in livestock feed.
  • Salicylic acid is used in the production of aspirin and other pharmaceuticals.
  1. Industrial Importance of Carbonyl Compounds:
  • Carbonyl compounds are used in the production of plastics, resins, and fibers.
  • They are important intermediates in the synthesis of various pharmaceuticals and agrochemicals.
  • Carbonyl compounds are used as solvents, preservatives, and flavoring agents in various industries.
  1. Common Methods of Preparation of Aldehydes:
  • Oxidation of primary alcohols using mild oxidizing agents such as pyridinium chlorochromate (PCC).
  • Oxidation of primary amines using mild oxidizing agents like hypochlorous acid (HOCl).
  • Reduction of nitriles using reducing agents like lithium aluminum hydride (LiAlH4).
  1. Common Methods of Preparation of Ketones:
  • Oxidation of secondary alcohols using strong oxidizing agents like Jones reagent (CrO3 in H2SO4).
  • Friedel-Crafts acylation of aromatic compounds using acid chlorides.
  • Reaction of acid chlorides with organometallic reagents like Grignard reagents.
  1. Common Methods of Preparation of Carboxylic Acids:
  • Oxidation of primary alcohols using strong oxidizing agents such as potassium permanganate (KMnO4) or potassium dichromate (K2Cr2O7).
  • Oxidation of aldehydes using mild oxidizing agents like Tollens’ reagent or Fehling’s solution.
  • Hydrolysis of nitriles using either acid or base catalysis.