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Ethanol reacts with potassium cyanide, followed by dilute acid, to form 2-hydroxypropanenitrile - AQA - A-Level Chemistry - Question 4 - 2019 - Paper 3
Question 4
Ethanol reacts with potassium cyanide, followed by dilute acid, to form 2-hydroxypropanenitrile. Name the mechanism for the reaction between potassium cyanide and... show full transcript
Worked Solution & Example Answer:Ethanol reacts with potassium cyanide, followed by dilute acid, to form 2-hydroxypropanenitrile - AQA - A-Level Chemistry - Question 4 - 2019 - Paper 3
Step 1
Step 2
Step 3
Explain how the structure of ethanol leads to the formation of two isomers.
Answer
Ethanol has a chiral center due to the presence of the hydroxyl group (-OH) and the carbon chain, allowing for equal chances of attack from either side by the nucleophile. This leads to the formation of two isomers that are mirror images of each other, known as enantiomers.
Step 4
Draw 3D representations of the two isomers to show the relationship between them.
Answer
The two isomers can be represented in 3D as:
-
Structure of (R)-2-hydroxypropanenitrile:
H OH | | C---C | / \ H CN -
Structure of (S)-2-hydroxypropanenitrile:
OH H | | C---C / \ CN HThe representations show how the -OH and -CN groups are positioned differently around the chiral center.
Step 5
Suggest a suitable reagent and conditions for the conversion of 2-hydroxypropanenitrile into acrylonitrile.
Answer
A suitable reagent for this conversion is concentrated sulfuric acid (H₂SO₄) or concentrated phosphoric acid (H₃PO₄). The conditions typically involve heating the reaction mixture to a temperature of about 170°C.
Step 6
Draw a section of the polymer polyacrylonitrile, showing three repeating units.
Answer
The structure of polyacrylonitrile can be represented as follows:
-[-CH₂-CH(CN)-]-
-[-CH₂-CH(CN)-]-
-[-CH₂-CH(CN)-]-
This notation indicates that each repeating unit consists of a vinyl group with a nitrile substituent.