This question is about making a diester from cyclohexanol - AQA - A-Level Chemistry - Question 8 - 2021 - Paper 2

The reagent needed for step 1 is concentrated sulfuric acid (H₂SO₄).

For step 2, the reagent needed is an alkoxide, typically generated from sodium hydroxide (NaOH).

The equation for step 2 can be represented as:

In step 3, the reagent needed is ethanedioyl dichloride (also known as oxalyl chloride).

The equation for step 3 can be represented as:

The structure of Compound G can be represented as follows:

       O
      ||
C-O-C
      |    
     O

This indicates the presence of the ester link from the cyclohexyl group connected to the carbonyl groups.

The mechanism for this reaction is known as nucleophilic addition-elimination.

The mechanism will involve the nucleophile attacking the carbonyl carbon of ethanedioyl dichloride, followed by the departure of the leaving group (Cl⁻), leading to the formation of an ester link:

1. The alkoxide ion attacks the electrophilic carbon in the carbonyl.
2. A tetrahedral intermediate forms.
3. The intermediate collapses, expelling Cl⁻ and forming the ester link.

Chemists aim for fewer steps to reduce costs and increase efficiency in synthetic processes. Fewer steps often lead to shorter reaction times, reduced labor, and minimized consumption of reagents. Moreover, simpler processes generally diminish the risk of side reactions and improve yields.

A high percentage atom economy is desirable as it indicates that most of the reactants are converted into useful products rather than waste. This efficiency minimizes environmental impact by reducing the generation of by-products and the need for excessive purification processes.