Chemistry of Carboxylic Acids, Esters, Amines, and Amides

IUPAC Names for Carboxylic Acids

• The IUPAC naming convention for carboxylic acids involves replacing the -e in the alkane name with -oic acid.

  • Example:
    • Methane → Methanoic acid
    • Ethane → Ethanoic acid

• Substituents are numbered starting from the carboxyl group (C-1), similar to aldehyde nomenclature.

  • Example:
    • ➜ 3-Methylbutanoic acid
    • ➜ 2,3-Dichlorobenzoic acid

Common Names of Carboxylic Acids

• Selected carboxylic acids and their common names:
  • Methanoic acid: Formic acid
  • Ethanoic acid: Acetic acid
  • Propanoic acid: Propionic acid
  • Butanoic acid: Butyric acid

Properties of Carboxylic Acids

• Polarity: Carboxylic acids are highly polar due to the presence of
  • Hydroxyl group (-OH)
  • Carbonyl group (C=O)
• This results in the ability to form hydrogen bonds.

Solubility in Water

• Carboxylic acids with 1 to 5 carbon atoms are very soluble in water due to extensive hydrogen bonding.
• However, solubility decreases with increased carbon chain length.
• Example:
  • Methanoic acid and Ethanoic acid are highly soluble.
  • Hexanoic acid and Benzoic acid are slightly soluble.

Acidity of Carboxylic Acids

• Carboxylic acids are weak acids that can ionize in water, producing carboxylate ions and hydronium ions:
  $ext{RCOOH} + ext{H}<em>2 ext{O} \rightarrow ext{RCOO}^- + ext{H}</em>3 ext{O}^+$
• The stability of the carboxylate ion (due to resonance) aids in the loss of a proton.

Neutralization of Carboxylic Acids

• Carboxylic acids can react with strong bases like NaOH or KOH to form carboxylic acid salts.
  • Example:
    $ext{HCOOH} + ext{NaOH} \rightarrow ext{HCOONa} + ext{H}_2 ext{O}$
• Important salts: Sodium benzoate (fruit juices), Sodium propionate (cheeses).

Esters

• Esters are formed from the reaction between carboxylic acids and alcohols, typically characterized by pleasant smells.
  • Example:
  • Ethanoic acid + Methanol forms Methyl acetate:
    $ext{CH}<em>3 ext{COOH} + ext{CH}</em>3 ext{OH} \xrightarrow{H^+, heat} ext{CH}<em>3 ext{COOCH}</em>3 + ext{H}_2 ext{O}$

Naming Esters

• The name of an ester comprises two parts:
  1. The alkyl part (from the alcohol)
  2. The carboxylate name (from the acid)
• Example:
  • Ethyl acetate (from acetic acid and ethanol).

Acid Hydrolysis and Base Hydrolysis of Esters

• Acid hydrolysis reverses the esterification process, yielding a carboxylic acid and an alcohol.
  • Example:
    $ext{RCOOR'} + ext{H}_2 ext{O} \rightarrow ext{RCOOH} + ext{R'OH}$
• Base hydrolysis (saponification) produces the salt of the acid and alcohol:
  $ext{RCOOR'} + ext{NaOH} \rightarrow ext{RCOONa} + ext{R'OH}$

Amines

• Amines, derivatives of ammonia (NH₃), replace hydrogen atoms with alkyl or aromatic groups.
• Classified as:
  • Primary (1°): One carbon group attached to nitrogen.
  • Secondary (2°): Two carbon groups attached.
  • Tertiary (3°): Three carbon groups attached.

Solubility of Amines

• Primary and secondary amines containing fewer than six carbons are generally soluble in water due to hydrogen bonding.
• Tertiary amines have lower solubility due to lack of hydrogen bonding capability.

Properties of Ammonium Salts

• Ammonium salts are formed when amines react with acids, resulting in ionic compounds that are solids at room temperature and typically soluble in water.

Amides

• Amides are formed when the hydroxyl group (-OH) of carboxylic acids is replaced by an amine or ammonia, leading to compounds with a nitrogen atom bonded to a carbonyl carbon.
  • Example: Ethanoic acid forms Ethanamide:
    $ext{CH}<em>3 ext{COOH} + ext{NH}</em>3 \rightarrow ext{CH}<em>3 ext{CONH}</em>2 + ext{H}_2 ext{O}$
• Amides can be hydrolyzed back into carboxylic acids and amines/ammonium salts by acid/base hydrolysis.

• Chemistry Link to Health:
  • Salicylic Acid from willow tree reacts with acetic acid to form Aspirin (acetylsalicylic acid).
  • Alkaloids in plants, such as Nicotine and Caffeine, have physiological effects.