Warning: This experiment may produce small amounts of toxic and volatile acrolein.
Work outside or in a fume hood.
Formic acid is corrosive, wear gloves when handling it.
Greetings fellow nerds.
Some years ago i showed how to make silver conductive ink and one of key ingredients was formic acid.
In this video we'll make formic acid from glycerol and oxalic acid.
The overall idea is that oxalic acid is essentially formic acid with carbon dioxide in it.
So we're going to break that off by heating.
But we can't do this with pure oxalic acid because it will mostly sublime and decompose.
So to stabilize it against unwanted reactions we're going to esterify with glycerol.
Then we're going to heat it up and convert it formic acid.
Afterward we'll hydrolyze it again to separate the formic acid from glycerol and collect it.
So let's get stared.
Get an erlenmeyer flask with 100 mL of glycerol also known as glycerine.
This can found at pharmacies or from soap making companies.
I recommend soap companies as it's cheaper.
Now add 100g of oxalic acid dihydrate.
Set up a distillation apparatus around it and warm up the mixture.
Now it's important to keep the temperature of the mixture in between 105 and 120 celsius.
If it goes too high it will decompose the reactants.
Normally you do this by immersing a thermometer but all of mine were broken so i'm just eyeballing this by gradually raising the temperature until it begins to distill.
I'm likely going too hot and decomposing some but i'm not too worried.
Glycerol is very cheap.
It's actually a waste product from making biodiesel so it can be extremely cheap.
Looks like the water is condensing inside the flask.
I don't want refluxing, i want distillation.
So I'm putting on this shroud of aluminum foil to keep the flask warm and help the water distill over.
Okay, so what's happening chemically.
First the excess water from both the glycerol and the oxalic acid distills over.
Then as the mixture loses water the oxalic acid reacts with the glycerol to produce glyceryl oxalate ester.
As the heating continues the glycerol oxalate decomposes into glyceryl monoformate and carbon dioxide.
This is where we're essentially producing formic acid.
Although it's still esterified with the glycerol.
Now if there was some water present it would hydrolyze with the glyceryl monoformate to produce glycerol and formic acid.
But most of that water has already boiled off so we need to put some back in.
Wait until the bubble starts tapering off indicating most of the carbon dioxide has been released and the reaction is nearly complete.
Now let it cool and then add in another 100g portion of oxalic acid dihydrate.
Now replace the condenser apparatus and start heating again.
Oxalic acid dihydrate has water in it and that will cause hydrolysis of the glyceryl monoformate.
The formic acid will now distill over.
Essentially this step is where we are releasing and collecting our formic acid.
The oxalic acid will go onto make more glyceryl oxalate and eventually more glyceryl monoformate.
You can then add in more oxalic acid and repeat the cycle.
We're essentially converting oxalic acid into formic acid using glycerol as our catalyst.
I'm doing about 4 cycles but you can do as many as you want.
Just keep an eye on how much volume of liquid you have.
If it decreases significantly as you progress then the glycerol is actually being decomposed and you'll need to add in more.
If it turns black from impurities then the decomposition has gone too far and you'll need to discard and start again.
Anyway, when you're done, for your last cycle, instead of adding oxalic acid add about 50ml of water instead.
This will hydrolyze off the remaining formic acid without generating more glyceryl oxalate.
Now you have a crude mixture of formic acid and a lot of water.
To purify and concentrate it, we set up for fractional distillation and start distilling.
If you kept the original reaction temperature in the right range, the first liquid you'll distill should be water.
But if you notice anything below 100 celsius then it's impurities formed from the decomposition of the glycerol esters.
Two of the main ones are acrolein that boils at around 51 to 53 degrees celsius.
and allyl alcohol with azetrope around 88 degrees celsisus.
Acrolein in particular is a rather volatile toxic irritant.
Fortunately the amount produced is very little and they're easy to separate by fractional distillation like this.
Oh crap i got a bug here.
Okay bug, I'm going to call you Gary.
I'll give you twenty bucks if you don't do what i think you're going to do... no... No... NO...
Ugh...
you just lost twenty bucks Gary.
Okay, let me pour the distillate back in and start all over again.
And here we are again.
Assuming everything goes smoothly and nothing interrupts you like stupid bugs named Gary,
continue distilling off the water at around 100 celsius and switch out the receivers at 104 celsius.
At 107 celsius we'll be collecting a high boiling azeotrope formic acid.
And there you have it, an azeotropic mixture of 77.5% formic acid and water.
Now some of you might want to dry it further and get pure formic acid but i recommend against that.
Formic acid has a tendency to generate small amounts of carbon monoxide when you attempt to dehydrate it.
Especially if you use sulfuric acid as the dehydrating agent.
I thus recommend storing it and using it as the azeotrope.
For most amateur uses some water isn't a problem anyway.
Anyway formic acid can be used to make silver conductive ink as i've shown in a previous video.
Thanks for watching.
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