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1-Bromobutane from 1-Butanol

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Homework Statement



The lab is to create 1-Bromobutane from 1-Butanol. Dibutyl ether is a side product you want to remove.

Homework Equations



N/A

The Attempt at a Solution



9M H2SO4, KBr and 1-Butanol are refluxed for 45 mins. After distillation, you place 10 ml of cold 1M H2SO4 acid into the distillate. The organic layer contains 1-Bromobutane and the dibutyl ether in the aqueous layer is removed. Why do you need to treat the 1-Bromobutane with NaOH to purify the solution? Wouldn't NaOH do an Sn2 reaction and get us right back to the starting point?
 
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Answers and Replies

  • #2
chemisttree
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You wash with H2SO4. NaOH neutralizes it. I agree it is a dangerous step. Better to use bicarb wash.

Why do you think dibutyl ether is extracted into the aqueous layer?

Hint: Williamson Ether Synthesis.
 
  • #3
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Sn2 reactions are very solvent dependent. The rate of an Sn2 reaction in a polar, protic solvent is so slow that it's safe to say it "doesn't happen"--at least on the time your lab will take!

That said, I will second what chemisttree is: double check which phases your 1-bromobutane and your dibutyl ether will be in.
 
  • #4
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Based on your feedback, 1-bromobutane and dibutyl ether must both be in the organic layer (Very little dibutyl ether however after distillation) . I'm still confused though. Williamson Ether Synthesis creates the ether we want to eliminate by reacting the 1-bromobutane with the alcohol in the presence of a base. This process of adding an acid then base is used to get rid of alkenes. Do you think this process was to get rid of the alkenes that maybe formed E2 reaction at start?
 
  • #5
chemisttree
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I think I misunderstood your question. I thought you distilled again after treating with NaOH.

Did you distill from the 9M H2SO4 solution or did you do a preliminary workup and distill that?
 
  • #6
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The NaOH was removed using a separatory funnel. The only distillation that occured was after 45mins of a reflux containing 9M H2SO4, KBr and 1-butanol.
 
  • #7
chemisttree
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OK then. You have the right idea. I thought you were distilling directly after washing with NaOH. That would have produced butanol and when the distillation got further along you would have a Williamson product to consider.
 

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