Which of the following conditions are necessary for the preparation of alkanoates from alkanols and alkanoic acid?

Analyze the question: You are asked for the conditions needed to make an ester (an alkanoate) from an alkanol (alcohol) and an alkanoic acid (carboxylic acid). This reaction is called esterification.

Concept: Esterification is a reversible, condensation reaction:

RCOOH + R'OH ⇌ RCOOR' + H₂O

• Concentrated H₂SO₄ acts as a catalyst. It also acts as a dehydrating agent: it absorbs the water formed, which pushes the equilibrium toward the ester.
• Heat (reflux) speeds up the reaction, because it is slow at room temperature.

Step-by-step check of the options:

• A. Water and NaOH: NaOH is a base. It would neutralise the acid to form a salt and would hydrolyse any ester formed (saponification). Water also pushes the equilibrium backward. ❌
• B. Conc. H₂SO₄ and heat: This is the standard catalyst and condition for esterification. ✅
• C. NaOH and heat: This is the condition for alkaline hydrolysis of an ester, which is the reverse of what we want. ❌
• D. Water and aqueous HCl: This is a dilute acid medium, which favours hydrolysis of esters, not their formation. ❌

Example: CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O (conc. H₂SO₄, heat)

Here, ethanoic acid and ethanol give ethyl ethanoate.

Answer: B. Conc. H₂SO₄ and heat

Exam tip: Remember "Esterification = Acid + Alcohol + conc. H₂SO₄ + heat". If you see NaOH or lots of water, think of hydrolysis or saponification, which breaks esters down instead of making them.