HardChemistryHigh School (11–12)Organic Compounds with Functional Groups › Alcohols, Phenols and EthersNumerical
Butan-2-ol is made from ethanol in three steps on the Grignard branch: ethanol to bromoethane (88…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Butan-2-ol is made from ethanol in three steps on the Grignard branch: ethanol to bromoethane (), bromoethane to ethylmagnesium bromide (), and the reagent with ethanal in excess to butan-2-ol (, based on the Grignard reagent). Use for ethanol. Find the overall yield. Then find the amount of ethanol, for the Grignard branch only, and its mass, needed to make of butan-2-ol.
Need a reminder? The key ideaShow
Work from the target backwards. A Grignard reagent adds its R group to a carbonyl carbon. A carbocation can shift a hydrogen or a methyl group to a more stable cation. The overall yield of a route is the product of its step yields, and a count of the starting material divides by that yield.
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.
Given. Yields , and . A target of .
Step 1. Overall yield. , which is .
Step 2. Ethanol. Each ethanol that enters the branch can give at most one butan-2-ol. So .
Step 3. Mass. .
Check. The overall yield is lower than every step yield, as it must be. More ethanol is needed for the other branch, which supplies the ethanal.
Answer: , and .
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