Chemguide: Support for CIE A level Chemistry

This statement is about the formation of amides from the reactions between acyl chlorides and ammonia or primary amines.

Before you go on, you should find and read the statement in your copy of the syllabus.

This statement will be examined at the end of the first year of a two year course. It could also come up again in the final exam of your course.

Important background

The way this is expressed in the syllabus statement is potentially confusing. The content section of the syllabus talks about "Amides (exemplified by ethanamide)" but the learning outcomes section asks for the reaction between RNH₂ and R'COCl.

The symbol R is usually taken to mean an alkyl group. R' also means an alkyl group which can be the same as, or different from, the other one.

If you interpret R and R' in this way, you can't make ethanamide. What you would get is a product with the formula R'CONHR, whereas ethanamide is CH₃CONH₂.

So, in this case, it is important to realise than R and R' can be either alkyl groups or hydrogen.

So ethanamide, CH₃CONH₂, would be made from ethanoyl chloride, CH₃COCl, and ammonia, NH₃. In other words, in the RNH₂ that the syllabus is talking about, the R can be a hydrogen atom.

Where the product molecule contains the -CONH₂ group, you have a simple amide such as ethanamide, CH₃CONH₂.

We will start with this relatively easy case before we look at somewhat more complicated molecules.

So start by reading the page introducing amides.

Making amides from an acyl chloride

In previous syllabuses, CIE had this bit of chemistry left until the second half of the course. I have no idea what the logic is of moving it forward to the first half.

You will probably have come across acyl chlorides when you were looking at the chemistry of carboxylic acids. You should know how they are made from carboxylic acids - see statement 10.6(b).

Read the page the reaction of acyl chlorides with ammonia and primary amines.

In the first instance, stop when you get to the end of the section about the reaction of an acyl chloride with ammonia. You will need to know the overall equation for the reaction. Make sure you understand the formation of simple amides like ethanamide before you go on to the rest of the page.

Now continue to the reactions with methylamine and phenylamine to produce N-substituted amides.

My feeling is that you are more likely to be asked about the formation of these than about simple amides. You must expect to be given a formula for a complicated molecule which may contain one or more amino groups. You will then be asked to draw the structure of the product after reaction with ethanoyl chloride.

Provided you understand what is happening with methylamine or phenylamine, there is no real problem about this, even though the molecules look more scary. All you are doing is replacing a hydrogen atom in the amine by a CH₃CO group.

If you have more than one amino group in your molecule, you mustn't forget to do this with all of them.

Go to the Section 10.7 Menu . . .

To return to the list of learning outcomes in Section 10.7

Go to the CIE Main Menu . . .

To return to the list of all the CIE sections

Go to Chemguide Main Menu . . .

This will take you to the main part of Chemguide.