Carboxylic Acids, Esters, and Amides

Carboxylic Acids, Esters, and Amides Overview

Learning Goals

  • Identify features of carboxylic acids, esters, amides, lactones, and lactams
  • Provide IUPAC names for carboxylic acids, esters, and amides
  • Understand the physical properties of carboxylic acids, esters, and amides

17.1 Structures and Bonding

  • Functional groups discussed all feature an acyl group connected to a heteroatom.
  • Amides Classification:
    • Primary (1°), Secondary (2°), and Tertiary (3°) based on the number of carbons attached to nitrogen.
  • Cyclic Compounds:
    • Lactones: cyclic esters.
    • Lactams: cyclic amides (e.g., penicillin).

17.2 Nomenclature

Carboxylic Acids
  • Highest priority functional group in organic chemistry.
  • Named with the suffix “oic acid”.
  • No numbering is needed as the carboxylic acid is always at carbon 1.
    • Examples:
    • Formic acid (methanoic acid)
    • Acetic acid (ethanoic acid)
    • Benzoic acid (benzenecarboxylic acid)
  • Greek letters denote positions relative to carboxylic acid carbon:
    • Alpha-hydroxy acids (AHAs): carboxylic acids with −OH on the α-carbon.
Esters
  • Consist of acyl group and alkyl group (attached to oxygen).
  • Named with the suffix “oate” in IUPAC.
  • The alkyl group is named first, followed by the acyl chain.
Amides
  • Two parts: the acyl group derived from carboxylic acids, and the nitrogen-containing group.
  • Prefix with N- or N,N- for substituents on nitrogen.
    • Examples:
    • N,N-dimethylbenzamide, N-ethylformamide.

17.3 Physical Properties

  • Boiling Points:
    • Carboxylic acids: high boiling points due to double hydrogen bonding between molecules.
    • Esters cannot form such dimers; hence, lower boiling points.
    • Primary and Secondary amides can hydrogen bond, while Tertiary cannot.

17.4 Interesting Carboxylic Acids

  • Common Examples:
    • Formic acid: component in ant stings.
    • Acetic acid: known as vinegar.
    • Pain relievers like aspirin and ibuprofen contain a carboxylic acid group.
  • Mechanism of Action: Aspirin inhibits prostaglandin production (causes inflammation).

17.6 Acidity of Carboxylic Acids

  • Act as proton donors (H+) and increase H₃O+ in solution.
  • Acidity Equilibrium:
    Ka = \frac{[H3O^+][A^-]}{[AH]}
  • Deprotonation forms carboxylate salts (e.g., Na+ or K+ become associated with COO-).
  • Carboxylate salts, due to their charge, are more soluble in water than carboxylic acids.
  • Common bases interact with carboxylic acids to produce salts.

17.8 Ester and Amide Formation

  • Formation Process:
    • Ester: reaction between a carboxylic acid and alcohol (Fischer Esterification).
    • Amide: formed similarly but without an acid catalyst, requires heat.

17.9 Hydrolysis

  • Both esters and amides can revert to carboxylic acids via hydrolysis involving water.
  • Ester Hydrolysis: reverse of Fischer esterification produces alcohol and water.
  • Under basic conditions, hydrolysis yields carboxylate salt instead.
  • Common Application: This method forms soaps by treating fats with base.

Interesting Esters and Amides

  • Esters often provide pleasant fragrances and are present in many fruits to attract animals.
  • Melatonin: regulates sleep patterns and is used as a sleep aid.
  • Analgesics, such as acetaminophen and benzocaine, contain ester or amide functional groups.