Make Potassium Metal (Catalyzed Magnesium Reduction Method)

Uploaded by NurdRage on 28.12.2011

Warning: Making potassium is extremely dangerous.
Full fire safety protocols must be in place including protective clothing, goggles and face shields.
Burning potassium cannot be extinguished by conventional means
and water only serves to increase its danger.
This experiment should only be performed by an experienced chemist in a fume hood.
Greetings fellow nerds.
In this video we’re going to make potassium metal
using a lesser known chemical approach of reduction with magnesium.
First we start with 2.4g of magnesium turnings.
Now powder works better and faster but turnings can still be used.
Let me put on a funnel.
Now our next ingredient is 5g of potassium hydroxide.
There we go.
Now we need a high boiling solvent.
I’m going to use 20mL of tetrahydronapthalene.
Now I'm using this because it’s denser than potassium
and thus the potassium will float in it allowing us to see the reaction as it occurs
and to help coalesce the potassium.
You can use mineral oil instead such as the inert baby oil I showed you in a previous video.
It is critical that the solvent is high boiling at above 200 degrees Celsius, pure and inert.
Now we install a condenser so we can reflux the reaction
and prevent the loss of solvent and the catalyst we’ll put in later.
Okay, turn on the cooling water flow.
Now the reaction produces hydrogen and is inhibited by oxygen
so to reduce the diffusion of air we cover the top with aluminum foil.
Don’t seal it since the hydrogen still needs to diffuse out.
You can use a bubbler system or even a balloon to prevent air access but I find foil sufficient.
Now heat the reaction to reflux.
It might not reflux if you’re using mineral oil so just heat until the liquid reaches 200 Celsius.
As it heats up the color may change as impurities start decomposing and reacting.
This is normal.
I kept heating this for half an hour to destroy all the impurities and make it clear for the video,
but you don’t have to go that far.
As long as its refluxing or 200 degrees Celsius you can inject the catalyst.
The catalyst I'm using is tertiary amyl alcohol.
Lifting the aluminum foil we inject 0.4 mL of it into the top of the condenser and replace the foil.
Now every ten minutes,
add in an additional 0.1 mL of alcohol for a total of 0.6 mL,
or six times over an hour.
Combined with the initial injection that’s a total of 1 mL.
After all the alcohol is injected, let the mixture reflux on its own.
Now in addition to tertiary amyl alcohol, tertiary butanol can be used aswell.
Primary alcohols like methanol and ethanol do not work for this reaction
and neither does secondary alcohols like isopropanol.
Only tertiary alcohols seem to work.
Now as we wait you’ll noticed these tiny little spheres
that at first look like entrapped bubbles but never seem to pop.
As they get larger and more numerous it’ll become obvious they are spheres of potassium.
You’ll have to be patient as it can take a couple of hours before these start to appear.
What’s happening is the magnesium reacts with the potassium hydroxide
to produce potassium metal, hydrogen gas and magnesium oxide.
The alcohol catalyzes this reaction so it can proceed in a solution like this.
As the reaction progresses the alcohol may get consumed in side-reactions.
When this happens the potassium spheres will start to darken in color.
If you wait too long they’ll even go black and stop coalescing, forming a sand.
To reverse this, simply inject another 0.1mL of alcohol.
Monitor the reaction and inject alcohol in additional 0.1mL increments if you see the spheres going dark.
There we go,
I just added the alcohol and you can see the color change as operating conditions are restored.
The exact interval between alcohol injections is variable
depending on impurities and reaction conditions
and some experimenters find they don’t need additional injections at all.
You may ask why don’t I add all the alcohol at once at the beginning.
I did experimented a lot with that approach
but after getting rather poor reproducibility I determined,
after several months of research,
that sometimes the alcohol would get consumed in side reactions
at the beginning before any potassium was made.
Occasionally the potassium metal was made but would go dark as the alcohol ran out
and then would be completely destroyed again, resulting in no yield of potassium.
This problem does not occur for everyone,
likely because different reagent and solvent grades have different impurities.
So you can try and add all the alcohol at the beginning,
and if it works then go for it,
but if you’re having reproducibility issues
then it might be side reactions destroying your alcohol.
Thus I recommend going with the staggered addition as I've demonstrated in this video.
Now as we watch the reaction we see the spheres coalesce into a larger sphere.
This is a benefit of using a high density solvent like tetrahydronapthelene.
The alcohol helps the coalescence and if you see lots of spheres collecting but not coalescing
you might be able to help it along by injecting another 0.1 mL shot of alcohol.
But if you’re using a lower density mineral oil
then the spheres will just rest on top of the potassium hydroxide and only rarely come together.
Don’t worry I'll show you how to coalesce smaller spheres of potassium later.
Now the reaction is done when there is no more magnesium.
At this point turn off the heating and let it cool.
Here is the reaction mixture after everything has solidified.
You can see many small spheres of potassium resting on the byproducts
and over here is our very large sphere of potassium.
Just scope them out with a spatula or pair of tweezers.
Although if the narrow neck is giving you trouble you can dump out the mixture into some toluene.
The toluene also helps to wash the potassium
so I recommend dropping into toluene even if you can get the potassium separately.
If it's really dirty I recommend washing again with fresh toluene.
After washing with toluene,
place the potassium into a clean vial with mineral oil for short term storage.
Now before we test it,
we need to render the rest of our apparatus safe by destroying any potassium residues.
Place the flask in another beaker to contain any bubbling overflow.
And now add isopropanol to all containers that previously handled potassium.
Please do this slowly.
The isopropanol reacts with any potassium residues and forms potassium isopropoxide,
which wont catch fire when you dispose of the wastes later and clean your glassware with water.
Be sure to wait for all bubbling to cease before cleaning up your workspace.
Now I know some of you more foolish experimenters might think it would be cool
just to quench the leftovers with water directly and watch the resulting potassium fire.
But please remember we have extremely flammable solvents present,
an uncontrolled potassium fire will end very badly for you.
Okay, I’ve cleaned away all the apparatus and solvents so no flammable vapors are present.
Finally, now we can test our potassium.
With these smaller spheres we can just toss one into water.
Potassium is highly reactive and will spontaneously catch fire.
As for the larger sphere.
So that’s how you make potassium.
Now for some additional experimenter notes.
A special note about long term safety.
Do not leave potassium in storage for too long.
The potassium on the left was made today and is shiny and pure
but after storage for a month sometimes potassium will react with air and moisture
to form a coating of potassium oxides and hydroxides as seen on the right.
The color can range from dark purple to yellow.
This coating is extremely dangerous.
As it becomes thicker and thicker it becomes a highly shock sensitive explosive
and some experimenters have been seriously injured
by flaming explosions of potassium after they stored it for several months.
Therefore if you have potassium use it or destroy it within a few months or less.
Otherwise you run the risk of severe injury if your container has an air leak.
Mineral oil alone is not good for long term storage because air can still diffuse through it,
albeit slowly.
For long term storage potassium must be sealed into a glass ampoule
or kept in an inert atmosphere glove box.
You can destroy small pieces of potassium by mixing with alcohol as mentioned previously.
If you have to destroy large amounts I recommend placing it in toluene first
and adding alcohol slowly with stirring until it starts bubbling.
In this video I didn’t disturb the reaction since I wanted to film it continuously,
but occasionally stirring the mixture greatly improves the reaction speed.
Also yields are considerably improved since the magnesium metal doesn’t get cemented
into the magnesium oxide and potassium hydroxides.
Be sure to turn off the heat and wait until it stops refluxing before doing this.
On occasion, you might see tiny bits of potassium forming
even before you add the alcohol during the initial heating step.
This is because impurities are already catalyzing the reaction.
You can start adding alcohol right away if you see this.
The quality of magnesium is important for the reaction.
I found that highly oxidized magnesium as seen here on the right didn’t work to produce potassium.
Buying new magnesium, or grinding off your own from a magnesium ingot is recommended.
Another thing to do is to put the magnesium into the solvent first
without the potassium hydroxide and adding 0.1mL of alcohol and boiling for several minutes.
The alcohol helps to etch the surface and restore activity.
It doesn’t always work but it’s worth a shot.
You might be wondering if sodium can be made this way
by replacing the potassium hydroxide with sodium hydroxide.
I tried this myself and I can’t get it work, nothing seems to happen.
I don’t know if I'm doing this wrong or if I need to use a longer chain alcohol.
I’m told however that sodium should work.
If you should successfully make a sodium using this method please post a video of your process.
Anyway that’s how you make potassium using the catalyzed magnesium reduction approach.
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