If you're following closely you'll know that we recently ordered a bottle of
monochloroacetic acid from our supplier.
They very helpfully shipped us a bottle of trichloroacetic acid.
Oh well.
So we've been trying to find some interesting things to do with it and we recently did a
video on reducing it to dichloroacetic acid using zinc metal.
But on reading about trichloroacetic acid, we learned that it's not very stable with
respect to temperature, especially in aqueous solution.
One of the products of the reaction is apparently chloroform.
So we figured let's give it a go and see if we can actually prepare chloroform starting
with trichloroacetic acid.
So here's our starting material.
80 grams of trichloroacetic acid crystals.
They've got a strange slightly sweet sickly slightly fruity aroma.
Take care with the crystals, and with strong aqueous solutions because they'll badly
burn your skin if you splash in.
And if you don't, they'll burn your skin and your skin won't get any on you.
Those three chloro groups transform the normally mild acetic acid into a very strong acid indeed.
Well this is a pretty simple reaction to try out.
First of all we're going to dissolve the trichloroacetic acid crystals in water in order to make up
a solution.
We're starting with 100 mils of water.
So let's get this into the beaker with the acid.
There's no noticeable temperature change on adding the trichloroacetic acid crystals.
So this seems to be one case where you can break the acid to water rule.
It dissolves pretty easily with a few minutes of stirring with a glass rod.
And here we go.
About 150 mils of total volume now.
Apparently the decomposition is accelerated by the presence of the sodium salt of the
acid.
We'll explain why we think this is later on.
So what we're going to do next is convert some of the acid in the solution into the
sodium salt by neutralizing it.
Here we've weighed out 10 grams of solid sodium hydroxide.
This should be enough to neutralize approximately half of the trichloroacetic acid and convert
it into the sodium salt.
We'll add this to the acid solution slowly and carefully because it's likely to be
exothermic.
Okay, that was pretty boring.
Let's try more.
It sits there for a while, presumably heating up as a surface reaction occurs, then erupts
after 20 seconds.
Okay.
Simple pleasures.
That was very meditational.
We've now got a clear, approximately half-neutralized solution of our trichloroacetic acid.
It's warm, but not overly so.
So here's our setup for the actual reaction.
We're using a 500 ml 2-neck flask, and we're going to heat this using a heating mantle.
We've got a thermometer in the sidearm so that we can monitor the temperature of the reaction mixture inside.
We've then got an adapter set up, leading to a Liebig condenser.
And this then leads down to a receiving adapter, and a small flask which will collect the distillate in.
Pretty standard.
The only specific thing we've ensured is that we've using ice-cold water in the condenser.
Chloroform boils at about 60 degrees C, but it evaporates quite easily so we'll use ice-cold water to maximize the yield.
We've temporarily removed the adapter, and we'll now get our partially neutralized trichloroacetic acid solution into the flask.
Now we wash out the BPA.
We're going to heat this up in a double beaker with a further 100 mils of water, and add this to the flask as well.
So we've not got 200 mils of water in total in the mixture.
Let's set the adapter up again.
And we'll start the cooling water aquarium pump.
And heat on.
Now at 50 degrees C.
And there's a surprising amount of condensation inside the flask.
We're going to watch the temperature closely and see if we can see if there's a point at which an obvious reaction starts.
Lots of condensation now.
And at around 90 degrees C we can see that something is happening in the flask.
So the mixture is boiling.
And this increases in intensity.
And pretty soon a vigorous reaction is taking place, with the temperature now at about 95 degrees C.
And the vapors start to condense.
For a moment we're worried that this might go out of control, but it doesn't.
It boils away vigorously and the temperature settles at about 98 degrees C.
And we start to collect the distilling vapors.
It looks as though we've got two different layers collecting in the receiving flask.
This is a good sign.
So let's explore what's going on.
In the solution we've got the trichloroacetate ion.
Looking at this you can imagine that it's quite possible for a decarboxylation reaction to occur, whereby carbon dioxide is produced.
This happens especially easily in the case of trichloroacetic acid because of the electron withdrawing effect of the chloro groups on the adjacent layer.
What's left behind after carbon dioxide is generated is actually a stabilized anion, a carbon with three chloro groups on it.
But with all the water around this is going to want to pick up a hydrogen ion and be converted into our product, chloroform.
This rapidly boils off and is eliminated from the reaction mixture.
The hydroxyl ion left behind effectively becomes sodium hydroxide in solution.
Sodium hydroxide will first of all react with any residual trichloroacetic acid to reform the sodium salt again.
It will also react with the carbon dioxide produced, forming sodium carbonate, and eventually sodium hydrogen carbonate.
So if the reaction goes anywhere near completion, we should actually see the acidity disappearing, and eventually perhaps even an alkali solution remaining.
We keep the heating going and let the reaction continue, with the distillate slowly coming off.
Definitely two layers in there.
The temperature very slowly rises during the course of the reaction.
Now at 99 degrees C.
Once the flask is relatively full, we separate the contents into a measuring cylinder, so we can see the progress.
About 10 ml of a lower dense layer, and about 40 ml in total collected so far.
We keep the reaction boiling and distilling for two hours in total.
So sit back and relax, and watch the rest of the process.
Time for more...
chakra part 7
chakra part 17
chakra part 18
chakra part 19
chakra part 21
chakra part 23
Towards the end we've got a white deposit building up inside the flask.
And with about 130 mils of distillate in total now collected, there's not much of a lower
layer now collecting.
So we switch off the heat and allow the apparatus to cool down.
Still a few small bubbles coming off as it cools.
Let's first take a look at the contents of the boiling flask.
Slight effervescence as we pour it into the beaker.
So let's test the pH.
That's pretty alkali.
As we suspected it was.
But it might be due to a buildup of sodium hydroxide and sodium carbonate.
So let's add a little dilute acid and see what the reaction is.
Lots of CO2 being produced.
Now for our distillate.
We placed this into a separating funnel so that we can easily extract off the dense bottom
layer.
And here it is.
So we'll drain this off into a dry flask.
And here's a crude product.
About 24 mils of clear liquid weighing 36 grams.
And here's a crude product.
It's got the very characteristic aroma of chloroform.
Let's just dry this using a little anhydrous calcium chloride.
And we decant into a dry clean pre-weighed storage bottle.
So here's our product.
It's got the very characteristic aroma of chloroform.
And by the color, aroma, and density we think it's pretty pure.
If we do a yield calculation on this, we find that this is 58% of the possible total yield.
So just over half of the trichloroacetic acid we started with got converted into chloroform.
We're not sure what happened to the rest.
There's probably some left in the boiling flask, and we probably also lost a bit to
evaporation.
But it was an interesting experiment.
And relaxing experiment, and it's not a bad amount of chloroform to recover.
Thanks for watching and stay tuned.