33 Hydroxy Compounds and their derivatives

33.1 Carboxylic Acids:

1. Production of Benzoic Acid:
   1. Benzoic acid can be produced by the oxidation of an alkylbenzene, such as methylbenzene (toluene), using hot alkaline potassium permanganate (KMnO4) followed by dilute acid.
2. Reaction of Carboxylic Acids with PCl3, PCl5, or SOCl2:
   1. Carboxylic acids can react with phosphorus trichloride (PCl3) and heat, phosphorus pentachloride (PCl5), or thionyl chloride (SOCl2) to form acyl chlorides (acid chlorides).
   2. The general reaction equation is:

R-COOH + PCl₅ → R-COCl + PCl₃ + HCl

3R-COOH + PCl₃ → 3R-COCl + H₃PO₃

R-COOH + PCl₅ + SOCl₂ → R-COCl + SO₂ + HCl

1. For example, ethanoic acid (acetic acid) reacts with PCl5 to form ethanoyl chloride (acetyl chloride):

CH₃COOH + PCl₅ → CH₃COCl + POCl₃ + HCl

1. Further Oxidation of Carboxylic Acids:
   1. Some carboxylic acids can be further oxidized under specific conditions:

(a) Methanoic acid (formic acid) can be oxidized with Fehling's reagent, Tollens' reagent, or acidified potassium permanganate (KMnO4) or potassium dichromate (K₂Cr₂O₇) to carbon dioxide (CO₂) and water (H₂O).

(b) Ethanedioic acid (oxalic acid) can be oxidized with warm acidified KMnO₄ to produce carbon dioxide (CO₂).

1. Relative Acidities of Carboxylic Acids, Phenols, and Alcohols:
   1. Carboxylic acids are more acidic than phenols and alcohols due to the presence of the carboxyl group (–COOH).
   2. The resonance stabilization of the carboxylate ion (–COO^-) contributes to the increased acidity compared to phenols and alcohols.
2. Relative Acidities of Chlorine-Substituted Carboxylic Acids:
   1. The presence of electron-withdrawing chlorine substituents in carboxylic acids increases their acidity.
   2. The electron-withdrawing effect of chlorine enhances the stability of the carboxylate ion and facilitates proton donation.

33.2 Esters:

1. Production of Esters:
   1. Esters can be produced by the reaction of alcohols with acyl chlorides (acid chlorides).
   2. The general reaction equation is:

R'-COCl + R''-OH → R'-COOR'' + HCl

1. For example, the reaction between ethanol and ethanoyl chloride (acetyl chloride) forms ethyl ethanoate (ethyl acetate).

CH₃COCl + CH₃CH₂OH → CH₃COOCH₂CH₃ + HCl

33.3 Acyl Chlorides:

1. Production of Acyl Chlorides:
   1. Acyl chlorides can be produced by the reaction of carboxylic acids with PCl3 and heat, PCl5, or SOCl2.
   2. The reaction involves the replacement of the hydroxyl group in the carboxylic acid with a chlorine atom.
2. Reactions of Acyl Chlorides:
   1. Acyl chlorides undergo various reactions, including:

(a) Hydrolysis with water at room temperature to form the corresponding carboxylic acid and hydrogen chloride (HCl).

(b) Reaction with alcohols at room temperature to produce esters and HCl.

(c) Reaction with phenol at room temperature to produce esters and HCl.

(d) Reaction with ammonia at room temperature to produce amides and HCl.

(e) Reaction with primary or secondary amines at room temperature to produce amides and HCl.

1. Addition-Elimination Mechanism of Acyl Chlorides:
   1. The reactions of acyl chlorides follow an addition-elimination mechanism.
   2. In the addition step, a nucleophile attacks the acyl chloride, forming an acyl-oxygen bond.
   3. In the elimination step, chloride ion is expelled, resulting in the formation of the desired product.
2. Relative Ease of Hydrolysis:
   1. Acyl chlorides are more reactive towards hydrolysis compared to alkyl chlorides and aryl chlorides (halogenoarenes).
   2. The high reactivity of acyl chlorides is attributed to the presence of a polarized carbonyl group, which facilitates nucleophilic attack.