Why is NaOH used to purify 1-Bromobutane in 1-Butanol synthesis?

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Discussion Overview

The discussion centers on the use of NaOH in the purification process of 1-Bromobutane synthesized from 1-Butanol, particularly addressing the role of NaOH in removing dibutyl ether and the implications of potential side reactions during the synthesis.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions the necessity of NaOH for purification, suggesting it might lead to a reverse reaction to the starting material through an Sn2 mechanism.
  • Another participant proposes that NaOH neutralizes sulfuric acid, indicating a preference for using bicarbonate instead due to safety concerns.
  • It is noted that Sn2 reactions are solvent-dependent, with one participant asserting that the reaction rate in a polar, protic solvent is slow enough to suggest it may not occur during the lab timeframe.
  • A participant expresses confusion regarding the role of Williamson Ether Synthesis in the context of removing dibutyl ether, questioning whether the acid-base treatment was intended to eliminate alkenes formed during the reaction.
  • Clarification is sought about the sequence of distillation and treatment with NaOH, with one participant confirming that distillation only occurred after the reflux with sulfuric acid.
  • Another participant acknowledges the correct understanding of the phases of 1-Bromobutane and dibutyl ether, emphasizing the need to consider the products of potential Williamson reactions.

Areas of Agreement / Disagreement

Participants express differing views on the role of NaOH in the purification process, with some questioning its necessity and others supporting its use for neutralization. The discussion remains unresolved regarding the implications of Sn2 reactions and the role of Williamson Ether Synthesis in this context.

Contextual Notes

There are uncertainties regarding the phases of the organic and aqueous layers, the potential for side reactions during the synthesis, and the specific role of NaOH in the purification process. The discussion reflects a lack of consensus on these points.

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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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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.
 
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.
 
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?
 
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?
 
The NaOH was removed using a separatory funnel. The only distillation that occurred was after 45mins of a reflux containing 9M H2SO4, KBr and 1-butanol.
 
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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