Try it on paper first. A hint, the key idea and the worked solution are here when you need them.
A chemist has of 1-chlorobutane () and wants an amine. Chemists compare routes by the amount of product as well as by the number of steps. Assume that the potassium cyanide and the reducing agent are used in excess. Route 1 treats the halide with potassium cyanide to give pentanenitrile in a yield of , and then reduces the nitrile with lithium aluminium hydride to pentan-1-amine in a yield of . Route 2 is the Gabriel synthesis of butan-1-amine, with an overall yield of . The route 1 amine has one carbon more than the halide. Use pentan-1-amine and butan-1-amine . Find the amount of nitrile formed in route 1, the amount and the mass of pentan-1-amine, and the mass of butan-1-amine from route 2. Then say, in the solution, why a student who wanted butan-1-amine could not use route 1.
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Halide. .
Step 2. Nitrile. .
Step 3. Pentan-1-amine. , and .
Step 4. Route 2. of butan-1-amine, which is .
Answer: , , and .
The amount is about the same, but the amines are different. The two routes give almost the same number of moles of amine, and . Route 1 gives pentan-1-amine, since the carbon of the cyanide group joins the four carbons of the halide. A student who wanted butan-1-amine would use route 2, or would start from 1-chloropropane and use the nitrile route.
Check. The mass from route 1 is larger only because pentan-1-amine has a larger molar mass.
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Silver cyanide gives an isocyanide and potassium cyanide gives a nitrile. A nitrile is reduced to a primary amine with one more carbon than the halide. An isocyanide is hydrolysed by acid to a primary amine and formic acid, and is reduced to a secondary amine. Nitrobenzene takes 6, 4 or 5 electrons in an acidic, neutral or alkaline medium, and each atom of zinc or tin gives 2 electrons.