Removing solvent under vacuum.

[Anon0631]

I hope this doesn't cross into synthesis talk. I have a feeling I'm on safe ground because freebase/salt conversions generally tend to be tolerated on BL.

I have got rather into freebasing 2c-x compounds. 15mg 2c-e freebase vaporised was extremely intense. I'm looking forward to trying 2c-b and 2c-c using the same method.

The problem is though that leaving the freebase loaded solvent to evaporate in a watchglass is producing a solid rather than a pure oil. I'm assuming its because some of the freebase is turning into the carbonate salt due to exposure to air. The answer of course is to evaporate under reduced pressure using a vacuum pump.

So here's my question: how can I do this on the cheap? I was thinking about using a hand held pump from eBay - the ones that apparently power penis pumps. I'm worried though that the dichloromethane I use will attack the piston seals like it does to the rubber bits on 3 part syringes that I sometimes use for measuring volumes.

Any comments on this or other suggestions? Obviously I'm not going to buy a rotovap just for freebasing a few mg.

 

[sekio]

a solid rather than a pure oil.

some of the 2c's are solid as free bases

don't even bother with hand pumps especially for "evaporating" solvent like you are. the dcm will just eat everything that is solvent permeable and you will have a sticky, partially molten hand vaccum pump. the chlorocarbons are terrible for this.

if you want to use a vaccum pump here are your options:
1. metal or glass water aspirator on a tap - good for maybe 50 torr on a good day. $20-250
2. electrically powered recirculating water pump - 15 torr, $200-1000
3. electrically powered oil pump - 0.1 torr, $500-2500

you would also need basically a distillation setup unless you are comfortable with generating large amounts of dichloromethane infused wastewater. a simple distilation setup could be had for maybe $150 if you shopped around. a rotary film evaporator is what you would really want though and those will run into the thousands of bucks.

realistically, if the f/bs are crystallising when you evaporate dcm in the open air, it will almost certainly crystallise when you take it out of vaccuum again and expose it to air. unless you are planning to do it in a nitrogen or argon glovebox. so solvent removal in vacuo is pretty useless for your needs unless you are in a real hurry to evaporate lots of solvent.

 

[Anon0631]

Thanks. Great info. I have been reading around. Maybe evaporating under nitrogen like this?

Edit: I wonder if argon would work equally as well? It seems easier to source in small quantities.

 

[skillet]

some of the 2c's are solid as free bases

Yeah but it usually takes time and complete removal of the solvent for them to solidify.

Why not just vapourise the salt?

 

[Anon0631]

I didn't have much luck with 2c-e HCl. The freebase on the other hand was remarkable. 15mg vaped over about 20 minutes resulted in the room falling into a drippy mess of rainbow colours.

I worked out a pretty elegant ghetto vacuum by the way. Fill one of these with water.

Then put a bung in the top with a tube leading to a bung in the flask/test tube. Open the tap and as the water drains, a vacuum is formed.

Comments?

 

[Solipsis]

Yup, I have an aspirator fitted for the tap. I guess the vacuum pulled with it is a bit inferior though but it is as you say "on the cheap".

 

[sekio]

A tap aspirator is more than sufficient for removing solvent under reduced pressure. I wouldn't use it for a vaccuum distillation though.