Greetings fellow nerds.
In this video we're going to examine a specialized piece of lab equipment called a Soxhlet extractor.
Now first let's consider a common lab issue.
You have a mixture of chemicals that you want to separate.
The answer is usually to find a solvent that one dissolves in but the others do not.
Filter it out and distill off the solvent and now you've separate them.
But what about the case where you're separating insoluble from very slightly soluble compounds?
Assuming other methods like trying different solvents, temperatures,
or performing reactions to alter one can't be used,
you're going to have a difficult time.
If the chemicals you're trying to separate only dissolve slightly then you'll need huge amounts of solvent.
It might take thousands of liters of expensive solvent just to leach out a gram of chemical.
Additionally if the solvent isn't perfectly pure it can add its own impurities to your process.
If you have 1 mg of impurity per liter of solvent
and you're using a thousand liters then you've just added a gram of impurity to you product.
One thing you could do is treat your mixture with the solvent, filter it off,
then distill the filtrate so you have fresh solvent again and retain the recovered chemical.
Now you add your solvent back to the residue to dissolve more of the chemicals,
filter again, and then distill again.
If the process is repeated enough times you can recycle the same small quantity of solvent over and over again
and completely carry out a weakly soluble chemical this way.
The problem is that distillations are slow
and if you need to do this a thousand times then you can be at this for days, even months.
A soxhlet extractor fully automates this whole process so you can separate slightly soluble chemicals
from totally insoluble chemicals using a small amount of solvent and repeated distillations.
When you buy one it usually comes with the condenser as well and fits on top of the extractor like this.
Here in the extractor is where you put your mixture of chemicals.
Now the extractor looks like the large main body is open right through but it's actually closed with glass.
It's just connected for structural support.
The vapors and liquids can only travel through these two side tubes.
This outer tube is where the vapors from your boiling flask travel.
They rise up and into the main body where they condense on the condenser and fall into the trap.
Because it's closed the solvent accumulates and dissolves the chemicals.
Eventually the trap overflows and activates this siphon tube which quickly siphons out the solution and dumps it into the boiling flask.
Of course talking about it is one thing.
Let me actually show you.
So here is the soxhlet extractor setup.
Down here is the boiling flask containing our solvent
and this is where all of the soluble chemicals will end up as the extraction progresses.
On top we have the soxhlet extractor.
Mine is empty but you would fill it with chemicals.
On top of that we have the condenser.
Now all we do is turn on the heating and let it boil.
As you can see the vapors rise up through the outer tube and condense inside the extractor.
Any chemicals would get dissolved
and as the extractor fills it eventually overflows and the siphon tube pulls out all the solution.
The process repeats without any intervention and you can leave this running indefinitely.
Let's see that again but this time close up.
Now the Soxhlet extractor is extensively used to separate and analyze the components in food and other natural products.
It can be used to analyze fats, extract essential oils,
you can even use it to clean things by placing them in the body and having the solvent wash over it.
Almost every chemical glassware supplier sells a soxhlet extractor.
It's even more common than the dean-stark apparatus.
Now so far i've just been showing you an empty soxhlet extractor so you can see how it works.
To fill it you need to remember to put your chemicals in some type of restraint like filter paper and make a tea bag out of it.
Then you can put into the extractor.
You can also buy special filter thimbles made of filter paper especially for this purpose.
Alternatively you can stuff the extractor with glass wool
and put your chemicals on top or buy a special fritted glass extraction tube.
You cannot put powdered or granular chemicals into the extractor because they'll clog the thin siphon tube.
Getting it unclogged is extremely difficult since it's in such an awkward place.
Only in rare circumstances like if you're dissolving coatings or extracting leaves
can you place items naked into the extractor. Always teabag it.
Now soxhlet extractors aren't cheap.
While you may occasionally be in dire need of one.
It may not be often enough to justify the expenditure.
Fortunately, similar to my dean-stark video, we can jury-rig a working,
albeit poorly performing, version for those occasions when you are in dire need of one.
All you need is a pressure equalized separatory funnel with ground glass joints
and matching boiling flask and reflux column.
Most labs already have these parts.
You place your teabagged chemicals into the separatory funnel,
install the rest of the parts along with the solvents and begin boiling with the valve closed.
The vapors will travel up the pressure equalizing tube and into the reflux condenser.
They'll distill and accumulate inside the funnel.
Now wait until it overflows.
Without a siphon tube it'll never completely empty out.
Now very carefully open the valve just a crack until starts to drip.
But don't open it far enough that it empties.
I know it's hard to see through the ground glass joint but it's dripping.
What we want is for the rate of dripping to be just below the rate of condensation.
So most of the solvent drips out and a small amount overflows out.
This ensures the chemicals are always covered in solvent.
At the same time the constant dripping drains away whatever chemicals have dissolved
and replaces the solvent with fresh solvent from the condenser.
We can't open the valve all the way because the solvent will drain out
leaving some of the chemicals uncovered and thus undissolved.
And we can't keep it closed because the solvent at the bottom of the funnel will be stagnant
and never get mixed with the solvent at the top that constantly overflows.
Overall we get essentially the same function as a Soxhlet extractor.
A way of keeping our chemicals soaking in solvent
while at the same time removing the dissolved chemicals and replacing them with fresh solvent.
It's not quite as fast as an actual soxhlet extractor but far cheaper.
Especially since most labs already have these components.
And there you have it, the Soxhlet extractor.
Now i'm going to leave you with a time lapsed video of me actually using a Soxhlet extractor
in one of those rare cases where you can indeed put something naked in.
This is also one of those less common cases where it's the insoluble component i want to keep and not the soluble one.
I find it fascinating to watch when it's sped up like this.
Now this actually took 12 hours to run, but only about half an hour to set up.
Thus freeing me up to focus on much more important work like the next step of the pyrimethamine synthesis.
Anyway, i'll let you watch it.
Oh by the way, if you want to actually buy the soxhlet extractor for your lab I got mine from alchemy lab supply.
The link is in the video description.