A chemist makes butan-1-amine, C₄H₉NH₂, by the Gabriel synthesis…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A chemist makes butan-1-amine, , by the Gabriel synthesis. This route is chosen when a clean primary amine is needed, because the other routes give mixtures. The chemist must also weigh out the reagents carefully, so that none is wasted. Potassium phthalimide, , reacts with 1-bromobutane, , to give N-butylphthalimide, and alkaline hydrolysis then frees the amine. The chemist starts with of 1-bromobutane. The potassium phthalimide is supplied in the exact amount needed. Use C = 12, H = 1, N = 14, O = 16, K = 39 and Br = 80 in g/mol. The two steps together give the amine in an overall yield of . Find the molar mass of 1-bromobutane, the amount of it, the minimum mass of potassium phthalimide, and the mass of butan-1-amine collected. Explain in your solution why this route would fail with bromobenzene.
Need a reminder? The key ideaShow
The nitro group, the nitrile group and the amide group are reduced to a primary amine. A nitrile adds one carbon to the halide it came from. The Hofmann bromamide degradation removes one carbon: . The Gabriel synthesis makes pure primary aliphatic amines.
The worked solution
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. Molar mass of the halide. .
Step 2. Amount. .
Step 3. Potassium phthalimide. Its molar mass is . The 1 : 1 reaction needs , which is .
Step 4. Amine. Butan-1-amine has . At a yield of 100 % the mass is . At 60 %, .
Answer: , , and .
Why bromobenzene fails. The phthalimide ion has to attack the carbon that holds the halogen. In an aryl halide that carbon is and part of the ring, and the C-Br bond has some double-bond character. The ion cannot reach it from behind. No reaction occurs, so no aniline forms.
Check. Only 1 mol of amine per mol of halide, so the amine mass can never exceed .
Discussion (0)
Log in to join the discussion.
Loading…