Unit 5: Carboxylic Acids & Aliphatic Amines

February 20, 2026

Semester 2
BP202T

Introduction to Carboxylic Acids & Aliphatic Amines

Unit 5 closes the course by covering two very important classes of compounds. Carboxylic Acids are weakly acidic and their strength is influenced by substituents (Inductive Effect). Aliphatic Amines are weakly basic. Both classes contain many crucial pharmaceuticals: Aspirin, Citric Acid, Benzoic Acid, and Ethanolamine are all covered here.

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Syllabus & Topics

  • 1Carboxylic Acids: Acidity of carboxylic acids.
  • 2Effect of substituents on acidity: Inductive effect (electron-withdrawing increases acidity, electron-donating decreases acidity).
  • 3Qualitative tests for carboxylic acids, amides, and esters.
  • 4Structure and uses of Acetic acid (Solvent, pharmaceutical).
  • 5Structure and uses of Lactic acid.
  • 6Structure and uses of Tartaric acid and Citric acid (effervescent formulations).
  • 7Structure and uses of Succinic acid and Oxalic acid.
  • 8Structure and uses of Salicylic acid (Keratolytic).
  • 9Structure and uses of Benzoic acid (Antifungal/Preservative).
  • 10Structure and uses of Benzyl benzoate (Scabicide), Dimethyl phthalate, Methyl salicylate.
  • 11Structure and uses of Acetyl salicylic acid (Aspirin – Analgesic, Antipyretic, Antiplatelet).
  • 12Aliphatic Amines: Basicity and effect of substituents on basicity.
  • 13Qualitative tests for aliphatic amines.
  • 14Structure and uses of Ethanolamine, Ethylenediamine, and Amphetamine.

Learning Objectives

Explain Acidity: Rank a series of substituted acetic acids in order of increasing acidity using the Inductive Effect.
Pharmaceutical Knowledge: State the therapeutic uses of Aspirin and Salicylic Acid.
Explain Basicity: Explain why Aliphatic Amines are more basic than Aromatic Amines.
Apply Qualitative Tests: Describe the test used to identify a carboxylic acid.
Know Formulations: Explain the role of Citric Acid and Tartaric Acid in effervescent formulations.

Frequently Asked Questions (FAQs)

Q1. How do electron-withdrawing groups affect acidity of carboxylic acids?

Electron-withdrawing groups (EWGs) such as –Cl and –NO₂ increase the acidity of carboxylic acids by stabilizing the carboxylate anion (conjugate base) through the inductive effect.
In contrast, electron-donating groups (EDGs) like –CH₃ destabilize the conjugate base, thereby decreasing acidity.

Q2. What are the uses of Aspirin (Acetyl Salicylic Acid)?

Aspirin (Acetyl Salicylic Acid) is used as:

  • Analgesic (pain relief)

  • Antipyretic (reduces fever)

  • Anti-inflammatory agent

  • Antiplatelet drug (in low doses, to prevent heart attacks and strokes)

Q3. Why is Benzoic acid used as a preservative?

Benzoic acid possesses antibacterial and antifungal properties. It is most effective in acidic conditions (low pH) and is used as a food preservative (E210) as well as in pharmaceutical formulations.

Q4. What is the difference between an Amine and an Amide?

  • Amine (R–NH₂): Derived from ammonia (NH₃), contains nitrogen attached to alkyl or aryl groups.

  • Amide (R–CO–NH₂): Contains a carbonyl group (C=O) directly attached to a nitrogen atom.

Q5. What is the pharmaceutical use of Ethanolamine?

Ethanolamine is used as a surfactant and emulsifying agent in cosmetic and pharmaceutical preparations. It also acts as a weak base for pH adjustment.