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) which acts as a catalyst for the dehydration reaction.

For step 2, the reagent needed is bromine in water, which adds across the double bond of the alkene formed in step 1. The equation is:

Compound G is the product formed after step 2, which, after bromination, can be represented structurally as:

     Br   Br
      |   |
 H2C--C   C--CH2
      |   |
     H2C--C   CH2

(Exact distribution depends on the structure of cyclohexanol used).

The mechanism for this reaction is known as nucleophilic addition-elimination, as it involves nucleophilic attack followed by elimination of a leaving group.

In the first step of the reaction, the mechanism can be illustrated as follows:

1. The nucleophile attacks the carbonyl carbon, and a tetrahedral intermediate is formed showing the negative charge on oxygen.
2. The intermediate collapses, leading to the elimination of the leaving group (Cl), resulting in the formation of the ester link. The mechanism can be summarized as:

   OH  OH
    |   |
C---C---C
    |   |   Cl 
    `"/   
    O    C=O

Fewer steps in a production method minimize cost, time, and resource expenditure, leading to more efficient synthesis processes. Additionally, reducing the number of steps can decrease the risk of side reactions, ultimately enhancing yield.

A high percentage atom economy indicates that a larger proportion of reactants are converted into the desired product, which is beneficial for sustainability. It reduces waste and conserves resources as all atoms from reactants are effectively utilized in the final product.