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Chemguide: Support for CIE A level Chemistry Learning outcome 34: Nitrogen compounds 34.1: Primary and secondary amines Learning outcome 34.1.1 This statement is about making primary amines by various methods. I suggest you read the statements in your copy of the syllabus as you go along. Background work Start by reading the page introducing amines. The syllabus talks about primary amines and secondary amines. You can ignore tertiary amines. It is important that you are familiar with this sort of basic background material before you go any further. Statements 34.1.1(a) and 34.1.1(b) These statements deal with making amines from halogenoalkanes. In statement 34.1.1(a) the syllabus talks about reacting a halogenoalkane with a solution of ammonia in ethanol heated under pressure to produce a primary amine. In statement 34.1.1(b) the syllabus talks about reacting a halogenoalkane with a primary amine in ethanol heated under pressure to produce a secondary amine. Basically, these are part of the same reaction which gives you a mixture of types of amine. This is a seriously messy bit of chemistry. For statement 34.1.1(a) start by reading the beginning of the page about making amines, stopping when you get to the end of the bit about making primary amines. At the end of the section on making primary amines, you will find a green box with a link to a page about the products of the reaction. Follow that link, and look at the various ways that you might come across for writing an overall equation for the reaction. In all the question papers from CIE up to the time of writing (April 2020), there is no clear indication of which of these ways of writing the equation CIE are looking for. There was one question where they talked about using an excess of ammonia, so I suspect that they might be content with the second possibility for writing a single equation for the reaction, and there was one question which just asked for the conditions. Personally, I don't believe that you can write a single meaningful equation for this reaction, and you will find wherever this reaction comes up on Chemguide that I have used the two equation version discussed at the bottom of the page. Don't worry too much about this. In principle, they should accept any accurate version. If you are asked for a single equation, use either the first or second possibility on that page. For statement 34.1.1(b) continue reading the page about making amines, stopping when you get to the end of the bit about making secondary amines. Then skip through the bits about tertiary amines and quaternary ammonium salts, and read the section "What do you actually get when you react bromoethane with ammonia?". If you start with a halogenoalkane and ammonia you get a mixture of everything. If you use a large excess of ammonia, you will increase your chances of getting a majority of a primary amine formed. If you wanted a secondary amine, you could do what it suggests in the syllabus statement and start with a primary amine instead of ammonia. If you used a large excess of this, then that would increase your chances of getting a majority of secondary amine. In both of these cases, the large excess cuts down the chances of the product molecule you want finding an unreacted halogenoalkane molecule to react with further. Secondary amines have made their first appearance in a CIE syllabus with the current one. I have no idea what exactly they are likely to ask, but past experience with primary amines suggests that it isn't likely to be much more than conditions for the reactions. Reduction of an amide You will find this at the bottom of the page about other reactions of amides. You won't have met amides yet, and this statement is repeated in statement 34.3.2(b) in the section about amides. You might want to leave this until then. Reduction of a nitrile You will find this at the very bottom of the page you have already been using about making amines.
© Jim Clark 2020 |