OChem 2 - LiAlH4 vs NaBH4 - Lab Question

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Discussion Overview

The discussion revolves around the differences in procedure and conditions required when using lithium aluminum hydride (LiAlH4) instead of sodium borohydride (NaBH4) for the reduction of cyclohexanone to cyclohexanol in a laboratory setting. Participants explore safety considerations and solvent choices relevant to this organic chemistry lab question.

Discussion Character

  • Homework-related
  • Technical explanation
  • Exploratory

Main Points Raised

  • One participant notes that LiAlH4 is a stronger reducing agent and more flammable and pyrophoric than NaBH4, suggesting that safety conditions would need to be amended.
  • Another participant inquires about the solvent used with NaBH4, indicating that the choice of solvent is relevant to the discussion.
  • It is mentioned that the first step with NaBH4 involved methanol, and the quenching step used NaOH/H2O.
  • A question is raised about the consequences of dissolving LiAlH4 in methanol, hinting at potential reactivity issues.
  • One participant proposes using LiAlH4 with tetrahydrofuran (THF) or an ether, followed by hydrolysis with aqueous acid (H3O+/H2O) in a second step.
  • Another participant expresses uncertainty about working with LiAlH4, indicating a lack of experience with this reagent.

Areas of Agreement / Disagreement

There is no consensus on the specific procedural changes required when substituting LiAlH4 for NaBH4, as participants present various suggestions and considerations without a definitive agreement.

Contextual Notes

Participants express uncertainty regarding the material covered in class and the time constraints they face in preparing for the lab. The discussion reflects a reliance on prior knowledge and hints rather than established facts.

Ony
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Poster has been reminded to use the HH Template in future schoolwork threads
Hey guys! New to the forum here, I've come here several times before for insight on various topics and you guys have always been so helpful!

I noticed I couldn't find anything similar to this question while I was doing my lab report and I'm quite lost, to be honest..

1) Lithium aluminum hydride would also reduce cyclohexanone to cyclohexanol. List three changes that would have to be made to the procedure/conditions to accommodate lithium aluminum hydride, instead of sodium borohydride.

I know that LiAlH4 is more flammable and pyrophoric, I know it is a much stronger reducing agent, but what would you have to change in the procedure/conditions if we were to use it instead of NaBH4? Safety conditions would have to be slightly amended, but I'm not really sure where else to go.

The lab in question was reducing a ketone ( cyclohexanone ) to an alcohol ( cyclohexanol ) using NaBH4 as your reducing agent. It was a pretty simple lab.

Thanks in advance for the help!
 
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So which solvent did you use with NaBH4?
 
DrDu said:
So which solvent did you use with NaBH4?
First step was NaBH4/methanol and quenching step was NaOH/H2O
 
What happens if you try to dissolve LiAlH4 in methanol?
 
Will it reduce the methanol?

edit: it should help to know that we haven't covered this material in class yet, unfortunately I got the bad lab schedule. This is due in 1hour and I still can't find the answer. I've been watching videos and reading but I'm still so lost :(.
 
Last edited:
Come on, I gave you a hint. I am sure you find out yourself.
 
I think I figured it out, I could use LiAlH4 with THF or an ether and then quench with H2O.
 
Sounds good, although my OC is very rusty and I never worked with LiAlH4.
 
Thanks for your help! You steered me in the right direction and got me to find the answer.

The first step you would use LiAlH4 in THF or an ether, and then you would hydrolyze that in a second step using an aq. acid, (H3O+/H2O)
 

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