Butanol dehydration

[FriendlyFinger]

Is it ok to salt out water saturated butanol with Potasium Carbonate and then fractionally distill it?

Thanks,
FF

[foxy2]

Is it ok to salt out water saturated butanol with Potasium Carbonate and then fractionally distill it

Yea its ok, but what are you trying to do?


Salt it out, then separate with a seperatory funnel.
Then dry it with a drying agent(dry MgSO4).
This will give you dry butanol.

If your worried about other contaminates then distill, but if I was you I would dry it before distilling.

What butanol do you have?
normal, secondary or tertiary?

[FriendlyFinger]

I'm using butan-1-ol straight from MeNH₂ recrystalisation. Wanted to see what would happen to all the yellow stuff If I washed it with water a few times. I know that water dissolves around 8g of the alcohol per 100g if I remember right, but I wasn't sure how much water the alcohol would dissolve. Anyway I found out when I fractionally distilled.

So I assume that it's now dry after removing the azeotrope.
I guess that salting out would be more convienient. What I'm trying to do is recycle the butanol and get it as dry as I can for purer MeNH₂ Vogles 5th Ed. suggests using Calcium Sulphate and distilling. Why do you have to distill it. Does the sulphate go right through the filter paper?

Also I read a post where some guy says that he takes care of any water in the alcohol, when recystalising the amine by placing some Calcium Chloride in the mix. Doesn't Calcium Chloride react with amines? And since I'm asking tones of questions, Why does Organic Synthesis suggest recrystalising MeNH₂ with Butanol at tempretures between 90-100°C when other references say reflux? That means 118°C right?.

My lab grade n-Butanol has 0.1% water. That's alot when you consider how much you have to use to clean up 3 or 4 hundred grams of amine.

Thanks heaps.
FF

[foxy2]

If your going to distill it anyways I would just dry it then distill it.  The water wash is most likely unnecessary.  Or else just do the water wash and don't distill.  Did the water wash out the yellow?

[FriendlyFinger]

Yes it did and after 3 washes the alcohol still had only the faintest hint of yellow. When I did distill it, the azeotrope came over at 93°C and then the butanol at around 118°C but I had to be very careful. there was some yellow stuff that was coming over at higher temps but I stopped. What is this stuff?

I tend to agree with you. Just distill without washing. Too much trouble.