Today, we're going to prepare nitromethane via a classic reaction starting from chloroacetic
acid.
First, we measured out 45 grams of solid sodium hydroxide into a beaker.
And now we've measured out 120 mils of cold water.
We're going to add the water to the sodium hydroxide and stir to form a solution.
The mixture will get hot, so caution.
Once dissolved, we need to get this chilled down to fridge temperature, so we placed into
a storage bottle.
Let it sit in the fridge for two hours to cool.
OK here we go.
Here's our starting material, 100 grams of chloroacetic acid.
Do know that this is not a very efficient reaction and to make nitromethane from chloroacetic
acid, which is quite hard to obtain, is not a very practical way to synthesize nitromethane
on any sort of scale.
Be careful with chloroacetic acid.
Has it's toxic?
Has it absorbed through the skin?
Wear gloves when handling, but you should be wearing them anyway, right?
We're going to mix the chloroacetic acid with 50 mils of water.
First we've got the chloroacetic acid in a large 600 mil beaker, and with a magnetic
stir bar.
And here's the water.
We place this in a larger container on top of a magnetic stirrer.
And now we've got about 120 grams of ice cubes.
And we add these to the chloroacetic acid in order to chill it right down.
We've also set up an ice bath in a container around the beaker using ice and cold water.
It's getting pretty chilly in there.
What we need to do now is use our cold sodium hydroxide solution we prepared to neutralize
the chloroacetic acid.
Doing this will release heat, but it's important we don't let the temperature rise too high.
Here's our chilled sodium hydroxide solution.
We add a small amount to the stirred chloroacetic acid.
The temperature increases slightly but quickly drops again.
So we add a bit more.
And there we go.
Now we're up to about 10 degrees C and most of the ice in the beaker has dissolved.
This is where we need to slow down with the addition.
It's important not to allow the mixture to go above about 20 to 25 degrees.
Towards the end of the addition we start to measure the pH of the mixture.
This is still on the acid side.
So we'll add more sodium hydroxide.
Let's see.
Let's check again.
Not strongly alkaline, but about pH 9.
This is where we want to be.
Here's our slightly alkaline sodium chloroacetate solution.
Let's get set up for the reaction.
We're going to use a liter flask.
The reaction produces some bubbles.
And if it gets too hot, they'll cause a flake.
There's a risk it will foam, so we want a flask with plenty of headroom just in case.
We've got a stopper in one of the outlets and a thermometer adapter and thermometer
in the other.
We add the sodium chloroacetate solution.
Now for our other reactant.
Reactions of sodium nitrite.
You will note that in contact with even weak acids, sodium nitrite reacts forming nitrous
acid, which is very unstable and rapidly decomposes to nitrogen oxides.
Chloroacetic acid will decompose the nitrite, hence the need to neutralize it before the
reaction using sodium hydroxide.
We're going to dissolve this in 70 ml of warm water.
.
As the salt dissolves, it will cool down, so dissolving takes a bit of stirring.
We're pretty much there.
First we've got our apparatus set up with the flask on a hot plate, and set up for simple
distillation without using the thermometer to measure the vapor temperature.
We've got a regular receiver and flask.
We're stirring the mixture slightly to get it to the right temperature.
a small stir bar and we've got a thermometer measuring the liquid
temperature in the flask. This is important as temperature control is
critical. We removed the stopper and placed a funnel in the flask neck and
now we add the sodium nitride solution.
There's no obvious change or change in temperature at this point. We left the
mixture stirring for a few minutes to react. What's happening now is the
formation of our intermediate nitroacetate compound in the solution.
Then after a few minutes we switched off the stirring and started to strongly
heat the bottom of the flask.
The procedure calls for a naked flame but
we're not too happy about flames and nitro-methane so we're using the hot
plate. The idea is to get the solution at the bottom of the flask hot. Once the
reaction kicks off, it's exothermic and should be self-sustaining but we don't
want this to get out of control. We're watching the temperature closely.
First thing we notice is a slight darkening of the solution.
To a yellow and then to an orange color and at around 55 degrees C we can see
the first tiny bubbles forming from the bottom of the flask. This is carbon
dioxide being produced as our nitroacetate decomposes. The mixture
turns more orange in color and at around 65 degrees C we can see more bubbles
forming throughout the solution.
Now at about 70 degrees and we've got some water condensing in the flask and at
about 80 degrees the bubbling increases rapidly to this point. We removed the hot
plate at this point to see if this would be self-sustaining. The reaction
increased slightly in intensity but felt very smooth with the temperature only
rising slowly.
After about 10 minutes the temperature was around 90 degrees C and we started to
get some distal bait coming over. To begin with this was slow but picked up
after a while.
The natural temperature reached a peak of about 95 degrees C at which point the
reaction mixture looked like this. We started to get two layers forming in the
receiving flask.
A slightly oily cloudy bottom layer with a faint yellow color. Once the reaction
appeared to die down slightly after about 40 minutes we bought a hot plate
back and applied gentle heat using an air gap. This got things back off to a
start and the reaction bubbled away vigorously but again without getting out
of control.
After another
16 minutes or so of gentle heating we put the flask back on the hot plate
directly and heated so that the temperature was around 100 degrees C. This
kept the mixture boiling. We dropped a sheet of indicator paper into the
reaction mixture to have a look at the pH. A byproduct of the reaction is sodium
bicarbonate and with the heat this decomposes into sodium carbonate which
is strongly alkaline.
This is supposedly the reason for the low yields encountered in this reaction as
the alkaline byproduct can decompose both the nitroacetate reactant and the
nitro marathane product. Interesting the mixture appears to be neutral or just
slightly acidic. After a few hours of distillation the layers are now much
more apparent. We kept this slow distillation going for a total of two and
half hours.
Once we collected around 150 mils of distillate we transferred this to a
separate container and then continued to distill. We collected about another 40
mils of distillate but there was no apparent oil coming off as a separate
layer so we stopped heating at this point. We did a final test of the pH of the
Here's the distillate.
About 180 ml in total with a pale yellow bottom layer.
We poured this into a separating funnel.
Then we added about 20 grams of sodium chloride salt in order to saturate the aqueous layer
and try to drive out any dissolved nitromethane.
After lots of shaking the layers separated, but the nitromethane is around the same density
as brine, so it took a while and a bit of tapping the funnel.
We then separated the bottom layer as best we could.
And then added some anhydrous calcium chloride granules.
.
We removed the bottom layer of saturated water using a pipette.
And then dried the liquid using some more calcium chloride.
Here's our product.
22 grams of nitromethane.
We could distill this for greater purity but it seems relatively pure as it is.
So we'll see how we get on with some subsequent reactions.
We'll see how we get on with some subsequent reactions.
This is a 34% yield on starting chloroacetic acid, which isn't really that bad and is about
the same as the larger scale morgescent reference that we used for the reaction.
Let's do a test to prove it's nitromethane, and combine this with a precautionary note.
Here's some solid sodium hydroxide.
Nitromethane has a special property in that it reacts extremely violently with strong
alkalis.
That was three drops.
So please don't get this anywhere near solid alkali or attempt this on a larger scale.
It could explode.
That's it.
Stay tuned to see what reactions we've got planned next.
Thank you for watching.