[ih]

So I'm doing a grignard reaction with ethylmagnesium bromide and propionaldehyde which will make 3-pentanol. I need it to be as pure as possible my question is how do I make this as pure as possible? I know I will have MgBr and tetrahydrofuran in solution with the 3-pentanol and I will have to get rid of these. Will cooling the solution cause the MgBr to crystallise? This would leave 3-pentanol and THF in solution. Would I heat this to remove the THF because the boiling point of THF is 66°C and 3-pentanol is 115.3°C.

All help will be appreciated.
ih

[Archer]

Usually, once the reaction has been quenched, ether is added as THF is water soluble. This should leave the inorganics in the aqueous phase.

[ih]

How would I remove the inorganic's if they are in aqueous phase? I need to do a Williamson Ether Synthesis after this and methylate the OH group that's why I think I have to remove everything else. I have to end up with a pure compound by the end of the experiment.

[Archer]

What happens when you mix ether and water?

[ih]

You get a layer of ether on water, so I can use a seperatory funnel and remove the water. So will my MgBr be in the water too with the THF?

But where did the water come from? Do I add it or am I missing something from my equations?

So then would I have ether and the 3-pentanol? I need to do a Williamson ether synthesis to the pentanol after this, will the ether interfere with methyl iodide? And how would I eventually remove the ether to have a pure product?

[Archer]

You get a layer of ether on water, so I can use a seperatory funnel and remove the water. So will my MgBr be in the water too with the THF?

The THF will be partitioned across both layers, as will your product so you will need to wash the aqueous layer several times with clean ether and pool the washings.

How do you intend to quench this reaction?

[ih]

Sorry, I don't understand. If the product I want and the impurities will be in both the layers why am I doing this? Would the way I had this in my first post work?

I'm not familiar with quenching, we haven't been taught this yet. I assume that because we only need a small amount that we would just let the reaction finish.

[ih]

What happens.when you mix ether and water?

Where did the water come from in this too?

[Archer]

Can you draw the mechanism for a Grignard Reaction for us please?

[Archer]

Where did the water come from in this too?

All in good time, first I need to be sure that you understand what you are doing. Grignard reagents are extremely dangerous if handled improperly.

[ih]

[Archer]

I can't see your attachment, please use the "Additional Options" function below the box which you type in to upload the scheme.

[ih]

Can you see this? I think my reaction will stop at the O- stage

[Archer]

Thanks, this is good but there are a couple of minor points which make me thing that you should look this mechanism up in a couple of other sources. Don't forget that this reaction is taking place in an organic solvent.

Now look at the last step, this is the quenching step. What is H₃O⁺?

[ih]

Hydronium. So are you saying that by adding water the reaction finishes?