Carboxylic acids and derivatives (A-level only)

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Question 13
Medium

This question is about esters.

The figure below shows an incomplete mechanism for the reaction of ethyl ethanoate with aqueous sodium hydroxide.

Incomplete mechanism for the alkaline hydrolysis of ethyl ethanoate with aqueous sodium hydroxide. Step 1 shows a hydroxide ion (with a lone pair and negative charge on oxygen) attacking the carbonyl carbon of ethyl ethanoate. A curly arrow goes from the lone pair on the O of OH- to the carbonyl carbon. The double bond C=O is intact, and no arrow shows its cleavage to the oxygen. Step 2 shows a tetrahedral intermediate containing CH3, OH, a single-bonded O- featuring three lone pairs and a negative charge, and an OCH2CH3 group attached to the central carbon. A curly arrow goes from one of the lone pairs on the O- to the C-O- bond to reform the carbonyl, but no arrow shows the cleavage of the C-OCH2CH3 bond. Step 3 shows ethanoic acid and an ethoxide ion (CH3CH2O- with a lone pair and negative charge on oxygen). A curly arrow goes from the lone pair on the ethoxide oxygen to the hydrogen of the OH group on ethanoic acid. No arrow is shown to break the O-H bond to the oxygen of the acid. The final products are the ethanoate ion (CH3C(=O)O-) and ethanol (CH3CH2OH).

1.

Identify where three additional curly arrows are required to complete the steps of the mechanism. Describe each missing arrow's starting position and destination.

[3]
2.

Name the type of reaction shown.

[1]
3.

Deduce the role of the CH3CH2O−\text{CH}_3\text{CH}_2\text{O}^-CH3​CH2​O−\ ion in step 3.

[1]
4.

A triester in vegetable oil reacts with sodium hydroxide in a similar way. Give a common use for the salt product of this reaction.

[1]

Carboxylic acids and derivatives (A-level only) Questions

  1. A Level
  2. /Chemistry
  3. /Carboxylic acids and derivatives (A-level only)