In this video we'll be preparing diethylmelonate but starting all the way back from chloroacetic
acid.
Note we've created this video using clips from various different preparations that
we've done so we apologize if the continuity is not as easy to follow as usual.
Let's get started.
Our first minimum reactant to prepare is a strong solution of alkali cyanide.
We're using the solid melt product from the reaction we covered in a previous video, which
we find stores better over time.
Our melt product from the reaction between sodium metal and potassium peroxide.
Cyanide weighed 95 G, which in theory contains about 1.1 moles of cyanide ion which we can
use.
We've got this dissolved in about 200 mils of water, with just the fine precipitate of
iron powder remaining.
Ok let's filter this and remove the solid iron.
Here we go.
An aqueous solution containing what we'll assume is 1.1 moles of alkali cyanide.
We don't need to tell you how dangerous this is.
One milliliter of the solution contains enough to easily kill you.
Now for our second main reactant.
This is 100 grams of chloroacetic acid corresponding to approximately the same number of moles
as the cyanide.
But with the cyanide just slightly in excess.
Cyanide.
Now we're going to add 100 mils of cold water to this, and also 150 grams of ice.
Ok let's get the mixture stirring and let it chill.
We need to convert the chloroacetic acid into its sodium salt, so to do this we're going
to use 40 grams of solid sodium hydroxide, which is nearly a stoichiometric amount compared
to the chloroacetic acid.
We'll see how this goes.
We add the solid sodium hydroxide slowly to the chilled mixture and allow it to react
and dissolve.
It's very important to do this slowly and not allow the temperature to rise, or the
hydroxide will undergo a side reaction with our chloroacetic acid and produce glycolic
acid instead.
We don't want this.
Towards the end of the addition we add the chloroacetic acid.
I added some more ice in order to keep the temperature below 25 degrees C. Check the
pH at the end and then add a little more sodium hydroxide if needed in order to make the solution
slightly alkaline.
Here we go.
Our second solution.
This time of sodium chloroacetate.
Now we've got our two solutions for the first reaction which will create malonic acid.
Here's our second solution.
Set up for the reaction.
We're using the pooled water bath to cool the large beaker which is equipped with magnetic
stirrin.
And we've got the thermometer to monitor the temperature.
Okay let's add the chloroacetic solution first.
And now the cyanide.
The reaction will now kick off spontaneously.
And now we're going to add the chloroacetic solution.
We're starting at around 30 degrees C which is warm enough for this to occur quite quickly.
The temperature starts to rise.
We add cold water to the cooling bath as needed to keep this under control.
Getting up towards 60 degrees C now.
Don't allow the temperature to go above 80 otherwise dangerous cyanide gas can be produced.
produced, as well as unwanted side reactions.
We strongly recommend you use ventilation just in case.
We then stirred the mixture with the temperature slowly dropping from about 80 degrees at its
peak over the next 2 hours.
Here we've got another 45 grams of solid sodium hydroxide.
With the mixture at about 50 degrees we're now going to add this in order to start the
hydrolysis process.
Add slowly and allow to cool if boiling of the mixture occurs.
We had this happen on one run as you can see.
On complete addition, keep the mixture hot by heating it.
Ammonia gas should be evolved quite rapidly.
This is our intermediate cyanoacetate hydrolyzing to melamate.
We kept this heating and bubbling for 3 hours.
After which point no more ammonia was being emitted from the reaction mixture.
Towards the end of this period the mixture also turned milky and viscous due to the amount
of inorganic salts present in the mixture.
Ok so now our product is present in here as sodium melanate.
To get it out we need to first make the mixture acidic.
First we'll chill the mixture down again so it's at fridge temperature.
Now we slowly and carefully add concentrated hydrochloric acid to the mixture.
There's a little bit of ammonia remaining as you can see by the white ammonium chloride
smoke produced.
We added about 150 ml of acid before the pH was down to around 1 indicating complete
reaction.
On chilling this resulting mixture you can see that there's a fine white powder precipitating.
The residual color of the solution is green or even blue in some runs.
This is due to residual tiny particles of iron present from the original cyanide starting
material being added.
This is being converted into iron to chloride by the hydrochloric acid, being oxidized by
the air to iron salts, and then reacting with a very small amount of excess cyanide to create
Russian blue.
Now for the slow and boring task.
We need to evaporate the reaction mixture down to dryness, but without going over about
110 degrees C. Using a hot plate and a fan to blow air works well.
The magnetic stirrer is also helpful as without it a solid crust can form which prevents further
evaporation.
If you smell acetic acid, then the malonic acid is decomposing and the temperature is
too high.
Let's fast forward now.
We've got our solid dry product, which contains malonic acid and inorganic salts.
At this stage you can do as we did in a previous video and add diethyl ether to the solution.
in order to extract our the malonic acid, but this time we're instead going to use
ethanol to extract the malonic acid from the mixture. Hot ethanol dissolves it
better and we opted to place the mixture in a microwave which seemed to work well
as an extraction method.
Here's our hot ethanol containing some insoluble inorganic salt. Filter off the
insoluble portion while the mixture is still warm. It's worth re-extracting the
solids again with more hot ethanol in order to ensure that all the malonic
acid has dissolved.
Okay now we've got a solution of malonic acid in ethanol. We're
going to mix it now.
We're going to reflux this in order to create the diethylmelonate ester.
We're using the 500 ml flask as you can see here, and a large excess of absolute ethanol.
The reaction isn't very efficient unfortunately, and requires an acid catalyst to help things
along.
So we've measured out 7.5 ml of concentrated sulfuric acid.
We're not completely sure why, but this seems to react to some extent with the ethanol solution,
possibly because of some residual inorganic salts.
Some white precipitate is formed.
We set up the flask on a hot plate, and we're using a reflux condenser and cool water.
So let's get the mixture.
The mixture bumps slightly but not violently.
We've got a nice reflux going on now.
And now we keep this mixture refluxing for the next 5 hours.
At the end of this time we now need to distill off the excess ethanol, so we rearrange the
apparatus and set up for simple distillation.
We're using the thermometer so we can tell when the alcohol has boiled off and water remains.
Be careful not to heat too strongly because the unreacted malonic acid will decompose into
acetic acid if heated too strongly.
The distillation takes a few hours to complete.
Save the fraction of ethanol which boils off.
That exactly is the amount of ethanol that we need to distill off.
Once the temperature gets up to nearly 100 degrees C, then the alcohol distillation has
completed.
So shut off the heat and allow the mixture to cool down.
You can see two layers in the cooling mixture.
Unfortunately it seems as though malonic acid is highly soluble in diethylmelonate, so the
amount of product is less than it looks as this shows.
Once cool, we place the mixture into a separating funnel.
The top layer is organic and contains our product.
So we first drain off the bottom aqueous layer.
It's quite possible that this contains a lot of malonic acid.
So we're going to save this and see if we can evaporate it.
Next we make up a strong aqueous solution of sodium bicarbonate.
Adding this to the organic layer in the funnel produces a lot of carbon dioxide evolution.
So there's a lot of acid still present in this mixture.
Unshaking.
Our product separates from the aqueous layer has oily droplets.
The bubbles of CO2 gas generate a rather nice lava lamp type effect in the separating
funnel.
After a white we end up with a distinct top layer of product.
So we drain off the bottom aqueous layer.
The bubbles of CO2 gas generate a rather nice lava lamp type effect in the separating funnel.
and then separate our product it does have a beautiful sweet tropical fruit
aroma which is fresh like right sweet green apples but also with an undertone
of pineapple as well we dried the product quickly using a small amount of
anhydrous calcium chloride and here we go
crude diethyl melonate will purify this using distillation before we use it in
another reaction the yield is low though this is just 14 grams of product
obtained from using about half of our original chloroacetic acid reaction
mixture batch this is only a 17% yield from starting
chloroacetic acid but it is enough for us to experiment and do some interesting
reactions with for better yields we think that the
intermediate malonic acid would need to be purified and made
for better yields we think that the intermediate malonic acid would need to be purified and made
completely dry before esterification but this overall process is long and
arduous enough as it is so we didn't do this maybe in the future thanks for
watching and stay tuned for diethyl melonate reactions
watching and stay tuned for diethyl melonate reactions