Aldehydes, Ketones & Carboxylic Acids - An introduction

• Aldehydes, Ketones, and Carboxylic Acids are important classes of organic compounds.
• They contain the functional groups:
  • Aldehydes (-CHO)
  • Ketones (R-CO-R')
  • Carboxylic Acids (R-COOH)
• They have significant applications in various industries and biological processes.

Key Concepts

1. Nomenclature of Aldehydes, Ketones, and Carboxylic Acids.

2. Structural characteristics and properties of each class of compounds.

3. Preparation methods for aldehydes, ketones, and carboxylic acids.

4. Chemical reactions and functional group transformations.

5. Identification tests for aldehydes, ketones, and carboxylic acids.

Nomenclature of Aldehydes

• Aldehydes are named using the suffix “-al” or “-aldehyde.”
• The parent chain is numbered to give the carbonyl group the lowest possible number.
• Common names are also used for some aldehydes.

Examples:

• Methanal (formaldehyde)
• Ethanal (acetaldehyde)
• Propanal
• Butanal

Nomenclature of Ketones

• Ketones are named using the suffix “-one.”
• The parent chain is numbered to give the carbonyl group the lowest possible number.
• Common names are also used for some ketones.

Examples:

• Propanone (acetone)
• Butanone
• Pentan-3-one
• Cyclohexanone

Nomenclature of Carboxylic Acids

• Carboxylic acids are named using the suffix “-oic acid.”
• The parent chain is numbered to give the carboxyl group the lowest possible number.
• Common names are also used for some carboxylic acids.

Examples:

• Methanoic acid (formic acid)
• Ethanoic acid (acetic acid)
• Propanoic acid
• Butanoic acid

Structural Characteristics of Aldehydes

1. Aldehydes have a carbonyl group (-CHO) attached to at least one hydrogen atom.

2. The carbonyl carbon is sp2 hybridized, resulting in a trigonal planar geometry.

3. Aldehyde groups are more reactive compared to ketones due to their higher electrophilic nature.

4. The carbonyl group can be located anywhere along the carbon chain.

Example:

Structural Characteristics of Ketones

1. Ketones have a carbonyl group (C=O) bonded to two carbon groups.

2. The carbonyl carbon is sp2 hybridized, resulting in a trigonal planar geometry.

3. Ketones are less reactive compared to aldehydes, but certain reactions are specific to ketones.

4. The carbonyl group is always present within the carbon chain.

Example:

Structural Characteristics of Carboxylic Acids

1. Carboxylic acids have a carboxyl group (-COOH) attached to a carbon chain.

2. The carbonyl carbon is sp2 hybridized, while the carboxyl carbon is sp3 hybridized.

3. The presence of a hydroxyl group makes carboxylic acids polar and capable of hydrogen bonding.

4. The carboxyl group is always at the end of the carbon chain.

Example:

Sure! Here are slides 11 to 20 on the topic of “Aldehydes, Ketones & Carboxylic Acids”:

11. Preparation Methods for Aldehydes

• Oxidation of primary alcohols: Primary alcohols can be oxidized using mild oxidizing agents such as PCC (pyridinium chlorochromate) to form aldehydes.
• Oxidation of alkylbenzenes: Alkylbenzenes can be oxidized using potassium permanganate (KMnO4) or chromic acid (H2CrO4) to yield aldehydes.

12. Preparation Methods for Ketones

• Oxidation of secondary alcohols: Secondary alcohols can be oxidized using stronger oxidizing agents such as Jones reagent (CrO3 + H2SO4) or potassium dichromate (K2Cr2O7) to form ketones.
• Friedel-Crafts acylation: Aromatic compounds can be acylated using acyl halides in the presence of Lewis acids like aluminum chloride (AlCl3) to yield ketones.

13. Preparation Methods for Carboxylic Acids

• Oxidation of primary alcohols: Primary alcohols can be further oxidized using stronger oxidizing agents such as potassium permanganate (KMnO4) or potassium dichromate (K2Cr2O7) to form carboxylic acids.
• Hydrolysis of nitriles: Nitriles can be hydrolyzed using acidic or basic conditions to yield carboxylic acids.

14. Reactions of Aldehydes

• Nucleophilic addition reactions: Aldehydes undergo nucleophilic addition reactions to form alcohols when treated with nucleophiles such as water, alcohols, or cyanide ions.
• Oxidation: Aldehydes can be further oxidized to carboxylic acids using strong oxidizing agents like potassium permanganate (KMnO4) or Tollens’ reagent (Ag(NH3)2OH).

15. Reactions of Ketones

• Nucleophilic addition reactions: Ketones undergo nucleophilic addition reactions to form alcohols when treated with nucleophiles such as water, alcohols, or cyanide ions.
• Keto-enol tautomerism: Ketones can exist in equilibrium with their enol forms, which have a hydroxyl group (-OH) attached to a carbon-carbon double bond.

16. Reactions of Carboxylic Acids

• Acid-Base reactions: Carboxylic acids can donate a proton (H+) to act as acids or accept a proton to act as bases.
• Esterification: Carboxylic acids react with alcohols in the presence of an acid catalyst to form esters and water.

17. Identification Tests for Aldehydes

• Tollens’ Test: Aldehydes react with Tollens’ reagent (Ag(NH3)2OH) to produce a silver mirror.
• Fehling’s Test: Aldehydes react with Fehling’s reagent (CuSO4 + sodium potassium tartrate) to form a brick-red precipitate of copper(I) oxide.

18. Identification Tests for Ketones

• Iodoform Test: Ketones react with iodine (I2) and sodium hydroxide (NaOH) to form a yellow precipitate of iodoform (CHI3).
• Lucas Test: Ketones do not react with Lucas reagent (conc. HCl + ZnCl2), hence showing no change in appearance.

19. Identification Tests for Carboxylic Acids

• Sodium Bicarbonate Test: Carboxylic acids react with sodium bicarbonate (NaHCO3) to produce carbon dioxide gas, which results in effervescence.
• Esterification Test: Carboxylic acids react with alcohols in the presence of an acid catalyst to form esters, which have a fruity smell.

20. Applications of Aldehydes, Ketones & Carboxylic Acids

• Aldehydes like formaldehyde are widely used as preservatives, disinfectants, and in the production of resins and plastics.
• Ketones like acetone are used as solvents, paint thinners, and in the synthesis of various pharmaceuticals.
• Carboxylic acids are important in the food industry as flavoring agents, acidifiers, and preservatives. They are also used in the production of polymers and pharmaceuticals.

21. Reactions of Aldehydes:

• Reduction: Aldehydes can be reduced to primary alcohols using reducing agents such as lithium aluminum hydride (LiAlH4) or sodium borohydride (NaBH4).
• Cannizzaro Reaction: Certain aldehydes undergo self-oxidation and self-reduction simultaneously in the presence of concentrated alkali to yield a carboxylic acid and an alcohol.

22. Reactions of Ketones:

• Reduction: Ketones can be reduced to secondary alcohols using reducing agents such as lithium aluminum hydride (LiAlH4) or sodium borohydride (NaBH4).
• Haloform Reaction: Ketones react with halogens (chlorine, bromine, or iodine) in the presence of a strong base, such as sodium hydroxide (NaOH), to form a haloform and a carboxylic acid.

23. Reactions of Carboxylic Acids:

• Ester Hydrolysis: Carboxylic acids can undergo hydrolysis in the presence of water and an acid or base catalyst to yield an alcohol and a carboxylic acid salt.
• Decarboxylation: Certain carboxylic acids undergo decarboxylation upon heating to produce carbon dioxide and an alkane.

24. Physical Properties of Aldehydes, Ketones & Carboxylic Acids:

• Lower molecular weight aldehydes and ketones are highly soluble in water due to the presence of hydrogen bonding with water molecules.
• As the carbon chain length increases, the solubility in water decreases.
• Carboxylic acids have higher boiling points compared to aldehydes and ketones due to their ability to form intermolecular hydrogen bonds.

25. Chemical Properties of Aldehydes, Ketones & Carboxylic Acids:

• Nucleophilic Addition Reactions: Aldehydes, ketones, and carboxylic acids undergo nucleophilic addition reactions with various nucleophiles, such as water, alcohols, and amines.
• Acidity and Basicity: Carboxylic acids are acidic due to the presence of the carboxyl group, which can donate a proton. Aldehydes and ketones are neutral compounds.

26. Uses of Aldehydes:

• Formaldehyde is used in the production of plastics, resins, and textiles.
• Acetaldehyde is used as a precursor in the production of various chemicals, including acids, esters, and polymers.
• Benzaldehyde is used as a flavoring agent in food and beverages.

27. Uses of Ketones:

• Acetone is widely used as a solvent in many industries and as a nail polish remover.
• Cyclohexanone is used as a solvent for paint and varnish removers and in the production of nylon.
• Methyl ethyl ketone (MEK) is used as an industrial solvent, especially in the production of adhesives and coatings.

28. Uses of Carboxylic Acids:

• Acetic acid is used in the production of vinegar, solvents, and various synthetic chemicals.
• Citric acid is widely used in the food and beverage industry as an acidulant and flavor enhancer.
• Salicylic acid is used in the production of aspirin and other pharmaceuticals.

29. Key Terminologies:

• Carbonyl Group: A functional group consisting of a carbon-oxygen double bond (C=O).
• Nucleophile: A species that donates an electron pair to form a new chemical bond with an electron-deficient carbon atom.
• Electrophile: A species that accepts an electron pair to form a new chemical bond with an electron-rich atom.
• Tautomerism: The phenomenon where a compound exists in equilibrium between two isomeric forms.

30. Summary:

• Aldehydes, ketones, and carboxylic acids are important classes of organic compounds.
• They have distinctive structural features, characteristic properties, and specific nomenclature rules.
• These compounds undergo various reactions, such as addition reactions, oxidation, reduction, and hydrolysis.
• Identification tests can be performed to distinguish between aldehydes, ketones, and carboxylic acids.
• These compounds find diverse applications in industries, medicine, and the food and beverage sector.