Up Learn – A Level Chemistry (aqa) – Organic Synthesis
Organic Synthesis Reactions: Worked Example 2
How to transform bromoethane into propylamine
In a two-step synthesis, propylamine can be formed from bromoethane.
Draw the structure of compound A…
And suggest reagents and conditions for each step.
Now, to answer this question, we should first look at the functional groups of the compounds we’re given
So, here we have a…
This compound is a halogenoalkane
And this compound is an amine.
Next, we look at the number of carbons in each compound
So, this compound contains…
Our halogenoalkane contains two carbons
But our amine contains one extra carbon.
So, we know that to make this amine, we need to:
Remove this bromine atom…
Add an amine group
And add an extra carbon.
Now, we’ve seen that an easy way to add one carbon to an organic compound is to form a nitrile
So, for this step of the reaction, we could add…
To produce a nitrile, we can add either sodium cyanide or potassium cyanide to a compound
And this works, because we’ve seen that we can form nitriles from halogenoalkanes!
So, let’s say we react our halogenoalkane with sodium cyanide.
The structure of compound A must be…
When we convert a halogenoalkane to a nitrile, the halogen is substituted for a nitrile group
So, compound A must be propanenitrile!
So now we’ve got the structure of compound A…and a reagent in step 1
All we need to do now is fill in the remaining conditions for step 1…
And give reagents and conditions for step 2!
So, to carry out step 1, we also need…
To convert a halogenoalkane into a nitrile, we need our cyanide to be dissolved in ethanol.
And we need to heat the mixture.
In step 2, we’re reducing the nitrile group to an amine
So, for this reaction, we can use hydrogen gas and a nickel catalyst
And now, this is our complete synthesis!