Ethanol reacts with potassium cyanide, followed by dilute acid, to form 2-hydroxypropanenitrile - AQA - A-Level Chemistry - Question 4 - 2019 - Paper 3

The mixture is referred to as a racemic mixture, which indicates that it contains equal amounts of both isomers.

The structure of ethanol has a chiral center due to the presence of the hydroxyl (-OH) group attached to a carbon atom that is also bonded to other distinct groups. This chiral center allows for the formation of two different spatial arrangements (isomers), as the cyanide ion can attack the carbon atom from either side. The result is two stereoisomers, which are mirror images of each other.

The 3D representations of the two isomers show that one isomer has the CN group above the plane of the molecule while the other has it below. This can be represented in diagrammatic form:

• Isomer 1: $\text{C} ext{H}_2 \text{OH} \text{C} \text{H} | \text{C} \text{N}$
• Isomer 2: $\text{C} \text{H}_2 \text{OH} \text{C} \text{H} | \text{C} \text{N}$

A suitable reagent for converting 2-hydroxypropanenitrile into acrylonitrile is concentrated sulfuric acid (H₂SO₄) or phosphoric acid (H₃PO₄) with heat at temperatures ranging from 170°C to 190°C.

The section of the polymer polyacrylonitrile showing three repeating units can be illustrated as follows:

  --(CH₂--CH)---
     |         |
     CN       CN
  --(CH₂--CH)---
     |         |
     CN       CN
  --(CH₂--CH)---
     |         |
     CN       CN

This depicts the repeating unit of polyacrylonitrile with the nitrile groups incorporated.