33.1 A2 Level

Carboxylic acids

8 flashcards to master this topic

Definition Flip

How is benzoic acid commonly produced in the lab?

Answer Flip

Benzoic acid is produced by the oxidation of alkylbenzenes, such as toluene, using hot alkaline potassium manganate(VII) (KMnO₄) as the oxidising agent. The alkyl group is oxidised to the carboxyl group.

Key Concept Flip

What products are formed when a carboxylic acid reacts with PCl₃ and heat?

Answer Flip

A carboxylic acid reacts with PCl₃ and heat to form an acyl chloride, phosphorus acid (H₃PO₃), and HCl.

Example: 3RCOOH + PCl₃ → 3RCOCl + H₃PO₃.
Calculation Flip

Write the balanced equation for the oxidation of methanoic acid (HCOOH) with acidified potassium permanganate (KMnO₄).

Answer Flip

2KMnO₄ + 5HCOOH + 3H₂SO₄ → K₂SO₄ + 2MnSO₄ + 5CO₂ + 8H₂O. Methanoic acid is oxidised to carbon dioxide and water.

Key Concept Flip

Describe the reaction of ethanedioic acid (HOOCCOOH) with warm acidified KMnO₄.

Answer Flip

Ethanedioic acid is oxidised to carbon dioxide by warm, acidified potassium permanganate (KMnO₄). The purple colour of the KMnO₄ decolourises as MnO₄⁻ is reduced to Mn²⁺.

Key Concept Flip

Explain the relative acidities of carboxylic acids, phenols, and alcohols.

Answer Flip

Carboxylic acids are generally more acidic than phenols, which are more acidic than alcohols. This is because the negative charge on the carboxylate ion (RCOO⁻) is delocalised over two oxygen atoms, making it more stable than the phenoxide ion (delocalised over the benzene ring). Alkoxide ions are the least stable.

Key Concept Flip

How does the presence of chlorine substituents affect the acidity of carboxylic acids? Explain why.

Answer Flip

Chlorine substituents increase the acidity of carboxylic acids. This is because chlorine is electron-withdrawing, which stabilises the carboxylate anion by dispersing the negative charge, making the acid more likely to donate a proton.

Definition Flip

Write the general equation for the reaction of a carboxylic acid with thionyl chloride (SOCl₂).

Answer Flip

RCOOH + SOCl₂ → RCOCl + SO₂ + HCl. This reaction produces an acyl chloride, sulfur dioxide, and hydrogen chloride gas.

Definition Flip

What is the product formed when ethanoic acid reacts with phosphorus pentachloride (PCl₅)?

Answer Flip

The reaction of ethanoic acid (CH₃COOH) with phosphorus pentachloride (PCl₅) forms ethanoyl chloride (CH₃COCl), phosphorus oxychloride (POCl₃), and hydrochloric acid (HCl).

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32.2 Phenol 33.2 Esters