Cinnamic acid is a naturally occurring chemical and it exists in two main forms.
It's mostly used as a flavoring agent or in the perfume industry, but it's also used to make various pharmaceuticals.
The most common form of cinnamic acid is the trans form and that's what we're going to be making today.
We're going to be carrying out the Verley-Doebner modification of the Knoevenagel Condensation.
That honestly sounds like some really bad chemistry rap and it also sounds a little bit complicated,
but you'll see later in the video that it's not too bad.
The trans-cinnamic acid that I'm making this video is going to be used to make styrene and then subsequently polystyrene.
Here the chemicals that are used. From left to right at the back, we have
pyridine, benzaldehyde and beta-alanine and in the front we have malonic acid.
In total I used 50 milliliters of pyridine, 10 milliliters of benzaldehyde,
25 grams of malonic acid and 2 grams of the beta alanine.
I've made both pyridine and benzaldehyde in previous videos and if you're interested in seeing how i did this
I'll provide some links in the description.
I don't show it in the shot, but I also used about a 150 milliliters of 6 molar hydrochloric acid.
I did make up the procedure and i'm following something I found online so also provide a link to that in the description.
To get things started we add 25 grams of malonic acid to a round bottom flask.
On top of this we dumped into 2 grams of beta alanine.
Now I add the liquid ingredients and I start with 10 milliliters of benzaldehyde.
This is followed by 50 milliliters a very stinky and slightly yellow pyridine.
Pyridine is meant to be clear and colorless, so there's definitely some sort of contaminant present.
Into the mixture I drop in a stir bar and then I set things up for a reflux.
A reflux setup is pretty simple. Below the flask we have a hot oil bath and above it we have a cold water condenser.
The goal of the reflux is to increase the reaction rate by heating things up,
but to limit the loss of solvent by recondensing the solvent back into the flask.
I turn the hot plate and I heat the oil bath to about 130C.
Once it hits 130 Celsius mark, I start the timer and we keep the reflux going for an hour and a half.
Initially before things are hot we have a milky-white solution with a bunch of chunks floating around in it.
This is nothing to worry about though because as we heat things up everything will eventually dissolve.
As things get hotter and we get closer and closer to a reflux, the solution still looks opaque.
This opaqueness however is not due to the presence of undissolved starting materials and it's actually CO2 gas.
The stirring kind of increases the opaqueness of the solution so I turned it off for a second just to show you guys all the bubbling.
Here's the overall reaction that's taking place.
As I mentioned earlier, the Dr Seuss like name of this reaction, is the Veryley-Doebner modification of the Knoevenagel Condensation.
What we have is benzaldehyde reacting with malonic acid to form pyridinium trans-cinnamate, water and CO2.
Pyridine is the solvent and acts as a base catalyst and the beta alanine that we added acts as a cocatalyst.
In the normal and classic Knoevenagel condensation we use diethyl malonate
instead of malonic acid, piperidine instead of pyridine and we form diester as a product instead.
In a second step this diester can be hydrolyzed and
decarboxylated to form the same product as the Veryley-Doebner modification.
So with that being said the major benefit is that instead of having to do the reaction in two steps
with the Veryley-Doebner modification it can all be done in one shot.
The final cinemate product in this scheme is a pyridine salt
and this is because pyridines basic and it's going to pick up any acidic protons.
In general most ionic salts are not very soluble in pyridine and
I believe this is the white solid that we see precipitate at the end of the reflux
This would make sense but be aware it's more speculation and I don't really have any concrete evidence to back this up.
In terms of the mechanism this is what might be going on.
As a disclaimer though this is not a 100-percent proven mechanism and it's more just to give you guys an idea as to what might be happening.
The reaction mechanism here is circular and it's known as a catalytic cycle.
The reaction starts with our co-catalyst beta-alanine and at the end of every cycle beta alanine is regenerated
So to start things off, the beta alanine reacts with benzaldehyde to form a imine.
At the same time malonic acid is converted to its enolate form which can attack the imine.
This forms an intermediate molecule which is the combination of the benzaldehyde,
the beta alanine and the malonic acid.
The nitrogen of the beta alanine is protonated and then the decarboxylation reaction occurs.
The decarboxylation produces our CO2, our cinemate ion and regenerates the beta alanine.
The fresh and regenerated beta-alanine can then continue through with another cycle.
I should note though that the reaction can proceed without the beta alanine, it would just be a lot slower.
The beta alanine helps because the imine that's formed is a lot more reactive than the aldehyde.
And it makes it easier for the malonic acid to attack.
The bubbling really starts to die down and after 10 or 15 minutes it really isn't very interesting to look at.
When we reach the end of the reflux at the one and a half hour mark there's a bunch of precipitate in the reaction flask.
I remove the oil bath and I let the reaction mixture cool down to room temperaure.
Once it gets to around room temperature I pour the reaction mixture into about 200 milliliters of ice-cold water.
I wash the flask with about 50 milliliters of cold water and I add that to the beaker as well.
To the water down reaction mixture I then start to add some 6 molar hydrochloric acid.
The moment the hydrochloric acid is added you can see a white precipitate forming.
The white precipitate is our desired product: trans cinnamic acid
The reaction that's occurring here is pretty simple and we're just
generating cinnamic acid from its salt form.
The hydrochloric acid is a much stronger acid than both cinnamic acid and the pyridinium cation so it's able to keep both protonated.
The pyridinium salt is soluble in water so it dissolves into solution but the cinnamic acid is practically insoluble so it precipitates out.
The hydrochloric acid that's added will also react with the pyridine solvent to make more pyridinium chloride
The pyridine salt doesn't really stink so it's a nice way to clean things up and to get rid of the smelly pyridine
It should be noted though that the aqueous way still needs to be disposed of properly and just
because it doesn't stink anymore doesn't mean that it can be safely poured down the drain.
The contents of the beaker are added to a vacuum filter flask and our trans cinnamic acid is separated.
After everything is being pulled through the trans cinnamic acid is washed a few times with a little bit of water.
After the final water washing, the vacuum is kept on for something like 15 or 20 minutes to get the transatlantic acid as dry as possible.
The relatively dry powder is then dumped out onto a piece of construction paper
I was somewhat tempted to just try this and roll with the crude product but
I decided that I would actually carry out a recrystallization.
I went ahead and dumped all of the trans cinnamic acid into about two liters of distilled water.
As the solution heats up and gets closer and closer to boiling, the trans cinnamic acid slowly dissolves.
Just to get an idea of how close I was to the boiling point I added in a thermometer.
I was also losing a lot of heat and water due to the steam escaping at the
top so I just covered things up with some saran wrap.
Anyway we get to about 99 C, but there's still some undissolved trans cinnamic acid.
To remedy this we just need to keep adding small amounts of water until everything dissolves.
I'm honestly not sure exactly how much I added but eventually we get to a point where everything is dissolved.
Once we reach this point I take out the thermometer and I turn off the hot plate.
now we just wait for everything to cool down and for our trans cinnamic acid crystals to form.
It was taking a really long time to cool down so I left it out over night.
When I came back in the morning it had cooled down to room temperature and you can see that we have a lot of nice crystals.
Just like before to separate off the crystals I use a vacuum filtration.
This time takes a little bit longer though because we have to filter through so much more liquid.
I was only able to find my one liter filtration flask so throughout the filtration I had to empty a few times.
Anyway, eventually everything is added and the large beakers is washed a few
times to get out any trans cinnamic acid that might have been stuck on the sides.
Then to clean up the crystals we wash things with a little bit of distilled water.
I use the wash bottle to get the crystals off the side of the filter funnel and I used to glass rod to thoroughly mix up and wash the crystals.
Like before once I was done with the washing steps I kept the vacuum on for
15 to 20 minutes and I was eventually left with some nice fluffy crystals.
The crystals were then dumped out onto a piece of construction paper with some paper towel underneath.
And then spread the crystals out and I left them overnight to dry.
In the morning I was left with some nice dry cinnamic acid crystals and I transferred these to a bottle for storage.
The final yield of trans cinnamic acid was 12.6 grams which corresponds to a percent yield of about 87%.
I did the melting point and I found that it was something like 8 degrees lower than
theoretical, so this stuff apparently isn't super pure.
I plan to use it to make styrene which involves a pretty dirty decarboxylation, so i'm not too hung up on the purity.
If super high purity is required we'd have to just recrystallize it a few more times.
Anyway that's it for now I'm not sure which video I will posts next, but I will get at least one more out before the end of the month.
As usual I'd like to thank everybody who supported me on Patreon.
Everyone who supports me with five dollars or more per video will get their name at the end like you see here.
I've been saying forever that I would introduce some more
rewards and you know spice up my Patreon page a bit but I kind of don't really have any ideas.
If you guys have any ideas as to what might be feasible and good tier rewards, please let me know in the comments.
Also I'm trying to merchandise a little bit I'm going to be making some NileRed branded beakers, as well as lab coats.
If you think this is a cool idea let me know in the comments and maybe leave some suggestions as to how I could design things
or you know make it special better in some way.
Anyway, these are the videos that I've already filmed and the ones that I plan to film.
If you guys have any extra suggestions please let me know.