Carboxylic Acids and Derivatives

• Carboxylic acids and their derivatives are the lesson's topic.

Carboxylic Acids

• An instructional situation involves a student learning about carboxylic acid in vinegar and its importance in product synthesis.
• The class decides to identify carboxylic acids and derivatives and write equations for their conversion, under supervision.

Carboxylic Acids: Definitions

• They are organic compounds containing oxygen.
• General formula: R-COOH, where R is a hydrogen atom, alkyl, or aryl group.
• The functional group is called a carboxyl group.
• The general gross formula for monocarboxylic acids is CnH2nO2.

Carboxylic Acids: Nomenclature

• Add "acid" to the name of the corresponding hydrocarbon chain.
• Replace the final "e" with the suffix "oic."
  • CH3 - CH2-COOH: propanoic acid
  • CH3-CH2-CH2-COOH: butanoic acid

Carboxylic Acids: Chemical Properties

• Carboxylic acids are weak
• Reaction with water is reversible, causing partial dissociation. $$R-COOH + H_2O \rightleftharpoons H_3O^+ + R-COO^-$$

Derivatives of Carboxylic Acids: General Formula

• General formula is: R-COZ, where Z can vary to give different derivatives.

Derived Functions and Their Nature

• Chlorure d'acyle: Cl (Chlorure)

• Anhydride d'acide: COO-R' (Anhydride)

• Ester: O-R' (Ester)

• Amide: NH2 (Amide)

Conversion of a Carboxylic Acid to its Derivative

Acyl Chlorides

Preparation

• React with thionyl chloride (SOCl2) to yield $$R-COOH + SOCl_2 \rightarrow R-COCl + SO_2 + HCl$$
• React with phosphorus pentachloride ($PCl_5$) $$R-COOH + PCl_5 \rightarrow R-COCl + POCl_3 + HCl $$

Nomenclature

• Replace "acid" with "chloride of" and "oic" with "oyl"

Acid Anhydrides

Preparation

• Acid anhydride results from the elimination of a water molecule between two carboxylic acid molecules.
  • Achieved by heating with a dehydrating agent like tetraphosphorus decaoxide ($P_4O_{10}$). $$2RCOOH \xrightarrow{P_4O_{10}} R(CO)_2O+H_2O$$

Nomenclature

• Replace "acid" with "anhydride" in the name of the corresponding acid.

Amides

Preparation

• React a carboxylic acid and ammonia in two steps
  • Step 1: Acid-base reaction forms an ammonium carboxylate. $$R-COOH + NH_3 → R-COO^- + NH_4^+$$
  • Step 2: Ammonium carboxylate dehydrated by heating. $$R-COONH_4 \xrightarrow{\Delta} RCONH_2 + H_2O$$
• React an acyl chloride and ammonia.
  • The reaction is fast, complete, and occurs in one step.
  • $R-COCl + NH_3→ R-CO-NH_2 + HCl$
• With primary and secondary amines, secondary and tertiary amides are obtained respectively.

Amide Nomenclature

• Replace the final "e" of the corresponding hydrocarbon with "amide".
• Precede with "N" before each substituent name on the nitrogen atom.

Esters

Preparation

• Direct esterification is the reaction between a carboxylic acid and an alcohol.
  • It is slow, athermic, reversible, and limited $$R-COOH + R’OH \rightleftharpoons RCOOR’ + H_2O$$
• The reverse reaction is called ester hydrolysis
  • It shares the same characteristics.
• Indirect esterification is a fast, complete, and exothermic reaction between an acid derivative (acyl chloride or acid anhydride) and an alcohol.

Ester Nomenclature

• Drop the word "acid."
• Replace the suffix ”oïque“ with ”oate“.
• Add the preposition "of" followed by the name of the alkyl group linked to the oxygen atom.

Applications of Carboxylic Acids

• Carboxylic acids have uses in manufacturing paints, solvents, shampoos, candles, and textiles.
• Acetylsalicylic acid is known as aspirin.
• Ethanoic acid is found in vinegar and is produced on a large scale.
• High-quality fatty acids have served in candle making.
• Their sodium or potassium salts form soaps.
• Reduced fatty acids create detergents.
• Esters of medium or aromatic acids are used in perfumery.
• Derivatives of benzoic acid are in pharmaceuticals.
• Acetic has varied uses as pigment, mordant, and antiseptic.