18. Carboxylic Acids and Derivatives Flashcards
(9 cards)
What are the three methods of producing carboxylic acids?
- Oxidation of primary alcohols with acidified KMnO₄ or acified KCr₂O₇ under reflux
- Hydrolysis of nitriles with dilute acid, or dilute alkali followed by acidification
- Hydrolysis of esters with dilute acid, or dilute alkali followed by acidification
How can carboxylic acids be produced through the hydrolysis of nitriles?
Using the example of propanenitrile
- Propanenitrile is reacted with dilute acid or dilute alkali
- In the case of dilute acid, propanoic acid and an ammonium salt like ammonium chloride (if HCl is used) are formed
- In the case of dilute alkali, sodium propanoate, a carboxylate salt, and ammonia are produced
- Sodium propanoate must then be acidified to form a carboxylic acid (a proton replaces the sodium)
How can carboxylic acids be produced through the acid hydrolysis of esters?
Using the example of ethyl ethanoate
- Ethyl ethanoate is heated with dilute acid (like dilute H₂SO₄)
- The water in the aqueous environment and the acid provide the two hydrogens and oxygen needed to reform ethanol and ethanoic acid
- This reaction is reversible (the reverse is esterification) and equilibrium is established under given conditions
Like in esterification, the sulfuric acid (which could also be hydrochloric acid) is a catalyst, though it needs to be dilute, not concentrated, for hydrolysis
How can carboxylic acids be produced through the base hydrolysis of esters?
Using the example of ethyl ethanoate
- Ethyl ethanoate is heated with a dilute base like dilute NaOH
- The ester is broken down to form a carboxylate salt (sodium ethanoate if NaOH is used) and ethanol
- This reaction is not reversible as the sodium ethanoate must be acidified into ethanoic acid (proton replaces the sodium) before esterification can take place
What is the reaction of ethanoic acid with sodium?
- They react to form a carboxylate salt (sodium ethanoate) and hydrogen gas
- 2CH₃COOH + 2Na –> 2CH₃COONa + H₂
The same happens with most reactive metals
What is the reaction of ethanoic acid with sodium hydroxide?
- They react in a neutralisation reaction to form a carboxylate salt (sodium ethanoate) and water
- CH₃COOH + NaOH –> CH₃COONa + H₂O
The same happens with most bases as ethanoic acid is a weak acid
What is the reaction of carboxylic acids with carbonate salts?
- A carboxylic acid like ethanoic acid reacts with a carbonate salt like sodium carbonate in a neutralisation reaction
- A carboxylate salt will form (sodium ethanoate if using the reagents above), along with water and carbon dioxide
- 2CH₃COOH + Na₂CO₃ –> 2CH₃COONa + H₂O + CO₂
As with most of these organic reactions, the reagents react with the functional group, not the compound as a whole, so multiple reactions can occur on the same compound
What is the esterification reaction?
- A carboxylic acid and alcohol react in a condensation reaction to form an ester and water
- The reaction requires a concentrated H₂SO₄ catalyst
- It is reversible
How can carboxylic acids be reduced?
- They are usually reduced with LiAlH₄
- NaBH₄ is too weak of a reducing agent to reduce carboxylic acids
- They will be reduced into primary alcohols; for example, ethanoic acid will be reduced to ethanol
