Recrystallizations

[Arcee]

Crystallization and recrystallization is a great method for purifying substances in and outside the lab. HCl bubbling in particular is used to precipitate methamphetamine from a solution as a hydrochloride salt.

Of course in gram quantities recrystallization from supersaturated solutions is unrealistic for purifying substances.

I think basifying and acidifying to produce crystals is a decent method though for smaller quantities to rid of things like baby formula or whatever else is cut into it, but it's a little dangerous to bubble HCl if you don't know what you're doing. Muriatic acid eats skin pretty well.

Citric acid, which can come as a pure solid (I'm not talking about lemon juice!), is often used by European heroin users to create water-soluble heroin. I wonder why I've never heard of it used in lieu of hydrochloric acid for certain things, as it would reduce the harm associated with operating a bubbler, and also make purifications more accessible to the lay user.

Perhaps there's some chemistry explanation that I've not been made aware of. I do understand it has its limitations, as it is a solid and dissolving it in water defeats certain purposes, but I suppose it should have a niche use at the very least.

 

[pasha]

homeless -> other drugs

 

[sekio]

Acid/base extraction is too much work for pretty much everyone, unfortunately. Especially if it needs solvents more complex than water and naptha... And it takes some care with compounds that are at all acid or base-sensitive - heroin and cocaine being two big ones - or you'll destroy product trying to purify it.

Gaseous hydrogen chloride is a whole different level of nasty from muriatic acid. At least concentrated hydrochloric acid is a liquid; you can dump a bunch of vermiculite on it to sop it up if need be. Gas HCl in any quantity bigger than a little whiff will burn and destroy any exposed tissue that is wet - eyes, nasal passages, lungs, mouth, etc - and can do things like convert all your steel equipment to a rust-coated mess. Nobody should generate hydrogen chloride without a well-equipped and tested fume hood...

Citric acid is a perfectly fine food-safe acid to use, I believe it's soluble in a few organic solvents - THF and the alcohols, at least.

If you find the right solvent, recrystallizing from a hot saturated solution is pretty useful. Doubly so if you use a co-solvent to force your goodies out. Even if the yield is poor you can concentrate the mother liquor and re-crystallize over and over.

 

[granddeception2]

What's the real question

 

[Chakakali]

recrystallization is also a way to make something look pure when it isnt. most organize compounds will recrystalize if they are purified.

 

[Arcee]

Sadly using two solvents isn't helpful in cases where a compound is an oil at STP.

I have a small personal project going that relates to all this--not going to go into detail though.

If citric acid is even marginally soluble in acetone that could be something terribly useful--simultaneous salting and washing, and then it evaporates so quickly!

 

[Arcee]

Chakakali, I think you have things a little backwards.

Recrystallization is useful for separating enantiomers. If done properly, it can create a rather pure product, albeit not quite in the league of capillary electrophoresis.

What do you even mean by "most organize compounds will recrystalize if they are purified."

 

[sekio]

capillary electrophoresis.

I don't think anyone uses that to separate drugs. Column chromatography is the tool of choice for separating complex mixtures (on silica or alumina) or optical isomers (on a chiral phase).

Usually nobody recrystallizes to separate isomers, because you need to start with crystals enriched in the isomer you want, and not all compounds can be seperated by hand like potassium sodium tartrate (classical example, the stuff Pasteur used). You'd instead selectively form the salt of one isomer with a chiral acid (d- or l- tartaric acid usually), which will precipitate/crystallize, leaving the other in solution. This is how people used to separate d- from l-amphetamine. Or you can derivatize the chiral function with another chiral reagent, forming a mixture - the "matched pair" (say, S,S) and the "unmatched pair". (say R,S), which will have different boiling points. And there's also chromatography over a chiral stationary phase.

recrystallization is also a way to make something look pure when it isnt.

Don't confuse recrystallization with melting and reforming crystals - the shady shit that MDMA dealers do to make stuff look better and make "moon rocks". A proper recrystallization from saturated solution will purify whatever substance you're working with if you find the right solvent system. It isn't 100% yield but you can drive purities up quite rapidly. It also takes more effort than adding solvent and stripping it back off, or just heating the stuff.

Sadly using two solvents isn't helpful in cases where a compound is an oil at STP.

If you're lucky you can just stick it in a freezer, those usually are -10 to -20C. If you don't have a freezer, crush a bunch of ice really finely and mix it with about 1/3 its weight in salt... instant -20C cold-bath. If you live near a gas distributor you could see about grabbing a few litres of liquid nitrogen, or some dry ice, too...

BTW: If you can get a hold of it, glacial acetic acid will dissolve in stuff like hexane a little. It's probably a nicer reagent system than acetone and citric.

As a general rule of thumb, acetone is a poor choice of solvent to dissolve any more than traces of acid or base in. If you're going to use it anyway, work quickly. Acetone undergoes self-condensation to form aldol products like mesityl oxide, (which are less volatile and smell kind of minty), as well as water. This happens faster with stronger acid/base and especially if heated. It's hard to dry it for the same reason, it's also hygroscopic and will absorb water out the air unless you live in Nevada.

 

[trippy888]

I don't think anyone uses that to separate drugs. Column chromatography is the tool of choice for separating complex mixtures (on silica or alumina) or optical isomers (on a chiral phase).

Usually nobody recrystallizes to separate isomers, because you need to start with crystals enriched in the isomer you want, and not all compounds can be seperated by hand like potassium sodium tartrate (classical example, the stuff Pasteur used). You'd instead selectively form the salt of one isomer with a chiral acid (d- or l- tartaric acid usually), which will precipitate/crystallize, leaving the other in solution. This is how people used to separate d- from l-amphetamine. Or you can derivatize the chiral function with another chiral reagent, forming a mixture - the "matched pair" (say, S,S) and the "unmatched pair". (say R,S), which will have different boiling points. And there's also chromatography over a chiral stationary phase.



Don't confuse recrystallization with melting and reforming crystals - the shady shit that MDMA dealers do to make stuff look better and make "moon rocks". A proper recrystallization from saturated solution will purify whatever substance you're working with if you find the right solvent system. It isn't 100% yield but you can drive purities up quite rapidly. It also takes more effort than adding solvent and stripping it back off, or just heating the stuff.



If you're lucky you can just stick it in a freezer, those usually are -10 to -20C. If you don't have a freezer, crush a bunch of ice really finely and mix it with about 1/3 its weight in salt... instant -20C cold-bath. If you live near a gas distributor you could see about grabbing a few litres of liquid nitrogen, or some dry ice, too...

BTW: If you can get a hold of it, glacial acetic acid will dissolve in stuff like hexane a little. It's probably a nicer reagent system than acetone and citric.

As a general rule of thumb, acetone is a poor choice of solvent to dissolve any more than traces of acid or base in. If you're going to use it anyway, work quickly. Acetone undergoes self-condensation to form aldol products like mesityl oxide, (which are less volatile and smell kind of minty), as well as water. This happens faster with stronger acid/base and especially if heated. It's hard to dry it for the same reason, it's also hygroscopic and will absorb water out the air unless you live in Nevada.

What is a good solvent system for MDMA? acetone and isopronanol?