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Separation of GBL from water

redeemer

redeemer

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Joined
Sep 14, 2003
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Hello all!

I have a question regarding the separation of GBL from water Let's say one has an amount of GBL mixed with water (the quantities of each are unknown; this is, in part, the reason a separation of the two is desired). Would it be possible to separate the water by adding iso-propanol to this mixture, which forms an azeotrope with water which boils at 80°C, and then just boiling away until the temperature starts to climb above the boiling point of water?

Since one does not know the amount of water contained in the solution, I figure it should be possible to keep adding iso-propanol and letting it boil off (with the water). If, after this has boiled off, the temperature does not rise above 100°C then water is still present and more iso-propanol is added. This is continued until the temperature rises above 100°C upon heating.

One question I'm not sure about is how much of the GBL, if any, will boil off with the water and IPA. Or if some unknown azeotrope will form with the GBL or if the GBL somehow will mess up the water-IPA-azeotrope.

All input is appreciated!
 
Why add the IPA? Just distill off the water, GBL boils at 200 degreesC. An easier way to separate them would be to make NaGHB using excess lye, get the PH down to about 8 with HCl or vinegar and then boil the liquids off.
 
Carsick said:
Will they separate over time due to the different densities? or will that take an age because they're not hugely different?
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I hadn't considered that. But as far as I can remember, I've had GBL standing for quite a while without seeing any separation. The mixture did a surfactant in it as well though, which probably would have made a difference. But I believe boiling the water off with IPA would be easier, provided it is possible of course.

ranunky said:
Why add the IPA? Just distill off the water, GBL boils at 200 degreesC. An easier way to separate them would be to make NaGHB using excess lye, get the PH down to about 8 with HCl or vinegar and then boil the liquids off.
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That was my initial notion as well, but the GBL will steam distill out with the water.

Dry GBL is interesting because of its use in the synthesis of the non-hygroscopic calcium salt of GHB. In the procedure described in US Patent 4,393,236 pure GBL is used. It is, of course, possible to use a water/GBL mixture instead, but boiling off the excess water after the reaction has finished would take ages considering it mustn't exceed 60°C.
 
^ I had considered that too, but I expect the solution to contain ~250 mL GBL and therefore about 450 mL water for the 700 mL in total. So using MgSO4 would become quite messy, I think, with such a large amount of water present.
 
distill (ie boil) it off. Water boils at 100 c and GBL boils at 200 c. Simple that.

But can I ask why you want to do this? Whats the point? You just have to water the GBL (or GHB if you convert it to that) down again before drinking.

You can still convert it in the water with a little NaOH or KaOH...
 
samadhi_smiles said:
distill (ie boil) it off. Water boils at 100 c and GBL boils at 200 c. Simple that.

But can I ask why you want to do this? Whats the point? You just have to water the GBL (or GHB if you convert it to that) down again before drinking.

You can still convert it in the water with a little NaOH or KaOH...
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As I mentioned in response to ranunky's post, boiling off the water isn't possible, the GBL will steam distill out with the water. I'll answer your second question by quoting myself in this thread :)

redeemer said:
Dry GBL is interesting because of its use in the synthesis of the non-hygroscopic calcium salt of GHB. In the procedure described in US Patent 4,393,236 pure GBL is used. It is, of course, possible to use a water/GBL mixture instead, but boiling off the excess water after the reaction has finished would take ages considering it mustn't exceed 60°C.
Click to expand...
 
You can find out how much GBL your mixture contains without seperating it from the water. You need to make a titration.

Start by adding some sort of pH-indicator (non-toxic of course) which indicates when the solution is basic. Then make a solution of the desired hydroxide (NaOH, KOH etc.) and add hydroxide-solution until the reaction-mixture is basic. Then add pure GBL until pH is neutral. As you have measured how much hydroxide you have used and how much extra GBL you have used, you can now calculate how much GBL there was in the original mixture.

Don't know if this makes sense to you? I can't really figure out why you want to remove the water when you can use this procedure. Of course you may some other agenda which I am not aware of :)
 
no, you can definitely boil the water off because people do this with nitromethane/GBL mixtures and nitromethane boils off at like 120c iirc (you have to set up a peanut oil bath).

sorry mods delete if this is inappropriate for the discussion.
 
Well, S_S, I think the whole thing about steam distillation is that the water significantly lowers the boiling point of the GBL. Basically, it interferes with the intermolecular forces that keep GBL from volatilizing and lowers the temp at which it evaporates.
 
redeemer said:
^ I had considered that too, but I expect the solution to contain ~250 mL GBL and therefore about 450 mL water for the 700 mL in total. So using MgSO4 would become quite messy, I think, with such a large amount of water present.
Click to expand...

If distillation or vacuum distillation is out of the question and dumping MgSO4 into the solution could get messy, have you considered vacuum filtration over a large surface area drying agent, like CaCl2? I'm not quite sure what amount of product you would lose, but if all else fails...
 
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