Acrolein is a simple unsaturated aldehyde with a piercing and overall bad smell.
It can be produced accidentally by overheating things like carbohydrates or fat,
but the most common form of human exposure is cigarettes.
Acrolein is strongly irritating to the skin, eyes, and respiratory tract.
And for this reason it was actually used as a tear gas in WWI.
On top of being extremely irritating, it's also toxic and it readily reacts with things like DNA or proteins.
When the acrolein reacts with them, it can disrupt their function
which can lead to bad things like you know, mutations or altered gene expression.
Anyway all this is to say that it's a dangerous chemical and should be handled with extreme care.
Personally, I think it's one of the worst things that I've ever worked with and I really don't want to ever work with it again.
I need the acrolein to make 1-octen-3-ol which is a chemical attractant for biting insects.
Industrially, acrolein is used to make acrylic acid, which is an important precursor to many plastics, adhesives, polishes, etc.
I honestly looked into making some of these things, but I decided that I only wanted to use acrolein for one reaction and then be done with it.
It really was too irritating for my liking.
I mentioned at the beginning of the introduction that acrolein can be produced
by burning animal fats and this is kind of how we're going to be producing it in this video.
Most animal fat is stored as triglycerides which comprises of a glycerol backbone and three fatty acids.
When the animal fat is heated, the triglyceride splits into the fatty acids and the glycerol
and it's the glycerol that breaks down to form the acrolein.
So in theory we could do the synthesis using animal fat
but it makes much more sense to just go to the pharmacy and buy glycerol directly.
So here's what we need to prepare the acrolein.
On the left we have our glycerol and on the right we have anhydrous magnesium sulfate.
The magnesium sulfate in this reaction acts as a catalyst and I'll explain later on what it's really doing.
Both the glycerol and the magnesium sulfate can be bought from the pharmacy
except the magnesium sulfate has to be dried first in the oven.
I actually prepared glycerol myself in a previous video and I also dried Epsom salt
so if you're interested in seeing either of these, I'll provide links to them in the description.
This is what the entire apparatus looked like and you can see that it's a little bit complicated.
On the far left, we have our flasks where the reaction is going to take place,
in the middle, we have a flask with some regular salt in it with an oil bath underneath,
and on the far right, we have our receiving flask.
As we continue with the preparation, you'll see why the middle flask was really necessary.
To start things off, I added about 54g of the powdered magnesium sulfate.
On top of the magnesium sulfate, I poured in about 67g of glycerol and in hindsight,
I probably should have done this the other way around.
Since I added the powder first, the glycerol kind of just sat on top and I need to use a glass stir rod to mix things around.
To the flask, I attach an addition funnel and I add about 100g of glycerol to it.
The glycerol from the addition funnel is going to be added slowly over the course of the reaction.
To our middle flask that's sitting above the oil bath, I add about 50g of regular table salt.
This is what the entire setup looks like prior to running it and there's just one last thing we need to do.
Both of the condensers are protected with aluminum foil which should limit how much acrolein polymerizes in them.
It's not shown here but I did eventually go further and I covered the entire apparatus in aluminum foil
just to prevent any polymerization in general.
Before turning on the heating mantle and starting the reaction, the oil bath under the middle flask is preheated to about 110°C.
To start things off, we can crank the heat up a little bit and initially we really don't see much of anything happening.
However as things heat up, a lot of water condensation will start to come off and the flask will get cloudy.
When we look at the flask from the side, we can see that it's producing a lot of white vapor.
At this point, some liquid starts to come over into our salt flask and I decided to cover it with aluminum foil just to limit any polymerization.
We wait a little bit and not too long afterwards, we actually start to collect some stuff in our receiving flask.
I don't show it here but I covered the entire bowl with aluminum foil to again prevent polymerization.
After we started to collect some stuff in the receiving flask,
I open up the addition funnel and I start to slowly add more glycerol.
In theory we should add things at the same rate that we're collecting our acrolein in the final flask,
but I found this really hard to do.
Glycerol is really viscous and with the addition funnel I found that the drip rate was either way too fast or way too slow.
I think I gave up trying to add it at a constant drip rate and i just added it in portions
by opening the addition funnel to max for a little bit and then closing it.
As we heat our mixture of magnesium sulfate and glycerol,
our glycerol is catalytically broken down into acrolein and water.
The reaction is catalyzed by our slightly acidic magnesium sulfate salt
and it proceeds in two distinct dehydration steps.
The first thing that happens is the middle hydroxyl group is protonated to form H₂O which is a good leaving group.
A random water molecule then comes along and picks up the hydrogen marked in blue.
The electrons in the carbon-hydrogen bond then moved to form a double bond and the water marked in red is kicked off.
This intermediate molecule then undergoes something called a keto-enol tautomerization.
I don't really want to go into much detail on how this transition happens
but I will provide a link in the description for those who are interested in seeing the mechanism.
Anyway, after it changes from the enol to the keto form, it can undergo its second dehydration reaction.
Just like before, the hydroxyl is protonated to form water
and the hydrogen is taken away by another random water molecule.
The electrons from the hydrogen moved to form a double bond,
the water is kicked off and we generate our final acrolein molecule.
This reaction takes place at a temperature that is much higher than the boiling point of both water and acrolein.
For this reason both the water and the acrolein boil out of the flask almost immediately after they form.
When we take a look at the intermediate flask, we should notice that it is collected a lot of water.
The salt helps to hold back the water and we only heat the oil bath up to about 110°C
which is almost not enough to boil off the water but more than enough to boil off the acrolein.
Eventually we'll have added all of our glycerol but we will reach a point where we stop collecting any acrolein in the final flask.
The reaction flask is taken off heat and when we look at it it's kind of just a tarry mess.
When we uncover the middle flask, we can see that it's collected a lot of water and it looks pretty messy.
if we didn't use this intermediate flask, this is what our final distillate would look like and I wouldn't really be happy with it.
Anyway, now that the reaction is done, I take the apparatus apart and I do a little bit of a workup on the acrolein that we've collected.
This is the acrolein that I collected and it's evidently much cleaner than the stuff that was in the intermediate flask.
The intermediate flask helped to stop a lot of the water from coming over but
nonetheless we still had a little bit of water there at the bottom.
Instead of using a separatory funnel, I decide to remove the lower water layer just by using a pipette.
All of the water that's removed is heavily contaminated with acrolein
and this is neutralized in the basic solution you see on the right.
One very important thing though is to not let the pipette tip touch the sodium hydroxide solution.
If the pipette get some sodium hydroxide on it and we actually introduce it into the acrolein,
it can all start to polymerize.
After removing the water, I dumped in a bunch of sodium bicarbonate to get rid of any acid that might be present.
I swirled the flask around a bit to mix it and then I let it sit for a little while before I filtered it.
I really do want to mention how horrible these steps are and just how terrible it is to work with acrolein without a proper fume hood.
Even with decent ventilation it will burn your eyes pretty quickly and respirators don't stop it
so don't think you're immune if you wear one.
On top of burning your eyes and your respiratory tract, it also smells terrible, so it's just all together a horrible thing to work with.
So now we move on to our filtering step where the acrolein is filtered into a flask containing about 0.1g of hydroquinone.
Hydroquinone is a stabilizer and it's important to mix it with the acrolein to prevent it from polymerizing.
After everything have filtered through, the funnel was removed and a greased stopper was used to seal the flask.
I ran out of time and it was getting late so instead of doing the second distillation right away,
I opted to cover it with aluminum foil and do it the next day.
The next morning, I set up my distillation apparatus and you can see what it looks like here.
The receiving flask is a pre-weighed bottle that contains about 1g of hydroquinone.
The goal here is to distill all the acrolein directly into the bottle and then immediately seal it
so we don't have to worry about any transferring steps.
You should also notice that the condenser has ice-cold water running through it and the receiving bottle is chilled with ice.
And just like before, we cover everything with aluminum foil to try to limit the polymerization.
When we're ready, we place the heating mantle under the flask, we start our stirring and we heat things up.
As we heat things up, we'll start to collect the acrolein at around 50-51°C.
The temperature slowly rose a couple of degrees and we collected the bulk of the acrolein at around 52-53°C.
As we continue boiling things, the stuff in the distillation flask will darken and eventually become a caramel color.
The temperature of the stuff that we're collecting will also start to rise and I stopped collecting things at around 55°C.
The heating mantle was removed and the distillation flask was allowed to cool
and you can see there's still actually quite a bit of stuff left over.
At the right side, our receiving bottle is removed and it's immediately capped.
I take the final acrolein product inside and I remove the aluminum foil just to see visually what we got.
And what we see visually is pretty anticlimactic because acrolein is just a colourless liquid.
Anyway, the bottle is still a little bit wet from the ice bath so I dried it off and covered it again with aluminum foil.
As an added safety precaution, I stored the bottle of acrolein in a sealed jar.
The final yield that I got was about 25g which corresponds to a percent yield of about 25%.
The procedures that I was following did this on a much larger scale and their yields varied between 30% and 50%.
Considering this was done on a small scale, I think the yield is okay and in the end I got way more than I actually need.
On a very sad note, when I tried to use the acrolein something like a week later, I found out that it all polymerised.
I really did plan to use it the day after I made it but due to some complications I couldn't, and now I guess I never will.
Despite having the hydroquinone present, it's still polymerised into this nice glass.
After making the acrolein once, I vowed I'd never do it again and now that it's all useless,
I have to use a different pathway to get to my 1-octen-3-ol.
Luckily there is another pathway that I can follow and that's the aldol condensation between formaldehyde and 2-heptanone.
This aldol condensation is followed by something very interesting called the MPV reduction and I'm going to do this in a future video.
Anyway, now I want to talk about how I cleaned all of my glassware.
After each distillation, the first thing that I did was I left all of my glass were open to air and light so that all of the acrolein could polymerize.
In the first part when we were actually carrying out the reaction, we're left with the hard crusty mess at the bottom of the flask.
I first added a little bit of water to dilute everything, and then I added a little bit of sodium hydroxide solution to destroy any acrolein that might remain.
I followed this up with several warm water washings but in the end I was still left with a hard black residue at the bottom.
To get rid of this, I decided that I would use piranha solution.
By mixing sulfuric acid drain cleaner and 35% hydrogen peroxide,
we make a very strongly oxidizing solution which should destroy almost all organic material.
After swirling it around for a little bit and occasionally adding a little bit of peroxide, I was able to get rid of the majority of the black stuff.
Eventually though, it seemed like the piranha was losing its potency so I made a new fresh batch just to get rid of the last stubborn stuff.
In the end, when I was finally done cleaning it with the piranha, I was left with a relatively clean flask.
For pretty much all of the glassware, I threw it into a base bath to destroy any of the acrolein that might remain.
After sitting in the base bath for a little while, I took it out and I had to manually scrape off all of the acrolein polymer.
It doesn't really stick too well on the glass though so it wasn't very hard to do.
At the end of the second distillation, I removed all of the aluminum foil and I poured a bunch of sodium hydroxide solution into the distillation flask.
I use the sodium hydroxide solution that I had earlier and you can see that when I add it to the distillation flask,
the acrolein that's present immediately starts to polymerize.
Once it's all been added, I let it sit there for a little bit to fully react and I come back later.
When we look closer at the condenser column, we can actually see a pretty exothermic reaction happening
between the sodium hydroxide and the acrolein that was still present.
Anyway, the rest of the apparatus was dismantled and the contents of the distillation flask was poured into an acrolein waste container.
I scraped out the acrolein from the condenser column and it had formed a nice hard plastic.
Anyway, as usual I'd like to extend a big thanks to all of my supporters on Patreon and especially those who donate $5 or more.
Anyone who donates and supports me on Patreon gets to see my videos 24 hours before I release it to YouTube,
and if you donate five dollars or more you get your name at the end of the video like you see here.
In the next few months though, I want to work on my Patreon page a lot and I want to get more rewards going
and maybe even get some higher tier ones and I want to also offer some Patreon exclusive content.
Also, as usual, here's the videos that I've currently filmed and the ones that plan to work on.
If you have any suggestions or ideas, please feel free to leave them in the comments.