In the first ever KimpleHeater video we showed you how to make mixed nitrotol

toluenes, and how pyrro nitro toluene could be frozen out of the mixture as a crystalline

solid.

In this video we're going to oxidize this to pyrro nitro benzoic acid.

This is very similar to the preparation of benzoic acid by oxidizing toluene.

We're starting with 8.5 grams of pyrro nitro toluene here.

Here's what it looked like when we separated it from the frozen mixed nitro toluene.

Next, our oxidizing agent.

You can use the manganate for this reaction but it's quite a strong agent so today we're

going to use potassium dichromate which may be slightly cleaner.

Here we've got 28 grams, which is a 1.5 molar ratio compared to the nitrotol toluene.

We've got the 250 ml flask set up.

And this has our favorite lucky ethyl chloroacetate infused and dyed magnetic stir bar.

We add the dichromate to the flask.

Next we've measured out 45 ml of water which will be our solvent.

This won't initially dissolve all the dichromate, but you'll see how this works later.

So let's get this into the flask.

Okay.

And now we're going to add our starting material, the pyrro nitro toluene.

So this is now all in the flask and floating around.

We're going to switch on stirring now.

To start with, it's a bit difficult, but it will soon start working.

On top of the flask we've set up a pressure equalized addition funnel.

You can use a regular addition funnel but it does need to be ground glass, and in addition

you will also need some wafer steam to come off the reaction and condense.

It's going to get very hot in there.

Next we've measured out 40 mils of concentrated 98% sulfuric acid.

Double-check that the tap on the funnel is off, and we pour the acid into the addition funnel.

Here we go, we're all set for lift off.

And we now adjust the tap so we've got a slow and steady stream of acid dripping into the

stirred reaction mixture.

As the acid drips in you can see what's inside.

see some wisps of smoke in the flask, and the heat causes the nitrotoluene to turn into

a liquid. Keep the addition slow and steady and the

heat in the flask will slowly rise. You'll also see the red color of chromic acid forming

in the flask. Soon this color turns a dark brown and at

about this point the crunching sound of dichromate crystals being stirred disappears as they

all go into solution. All easy so far. As you can see we're about

halfway through acid addition now. And as the mixture heats to boiling point,

things start to get hairier. The mixture boils and refluxes in the flask

quite strongly as you can see.

The milky color of the liquid is due to nitrotoluene being steamed distilled along with the water.

This is why the apparatus must be contained. You can't do this in an open vessel.

Oh dichromate. Dichromate. What thou art my petty hate? More timid than permanganate.

And next to persulfate thou art flaccid. Except f with my ribonucleic acid.

Dichromate does get a bad name but it's beautiful really and even inspires us to poetry.

But pretty soon it's turning mean. We've flowed down the acid addition now because

each drop is almost a small explosion and it hits the reaction mixture.

And we've got a bit of an internal reflux going on in the apparatus. This is okay, but

to do this on a larger scale we recommend using a separate reflux condenser.

Again you can see the milky color of the distillate due to unreacted nitrotoluene.

We're getting towards the end of addition now.

And now all the acid is added.

At this point we now need to heat the flask gently and keep a little bit of reflux going

for the next 20 minutes or so.

We're just going to leave the apparatus as it is because we're lazy, but you could also

replace the funnel with a reflux condenser.

On a small scale this works okay.

After about 20 minutes of gentle refluxing the mixture has turned what appears to be

a dark green color.

And no more milky.

Dizziness can be seen in the condensing steam.

So the reaction is complete at this point.

So we removed the stirring and heating and allowed the reaction mixture to cool down

until it was just warm.

And then we prepared 120 grams of ice in a large beaker.

And poured in the reaction mixture.

This chills down the solution, dissolves the chromium salts, and allows the product to

precipitate from the cold solution.

You can see it solid separating out.

So we set up to filter this off.

There we are.

We washed out the beaker with 100 ml of cold water and then used it to wash the precipitate as thoroughly as we could.

As you can see there's still a lot of green chromium salts being washed out.

After this wash though the solid was more brown in color than green, and the filtrate was nearly colorless, so we allowed the solid to dry well on the pump.

Here's what we got.

Around 12 grams of a crude product which is brown and green in color.

It's still slightly damp and contains a lot of chromium still.

So this is going to need some purification.

We read that it is possible to recrystallize from benzene but we really didn't like the safety of doing this.

So we're going to try something different.

Here's 4.5 grams of solid sodium hydroxide we've weighed out.

And we're going to get this into solution in about 100 ml of water.

Here we go.

Now we add the crude product to this vigorously stirred solution.

The idea is to make the product water-soluble as its corresponding sodium salt, and to precipitate out the chromium as insoluble chromium hydroxide.

We left the mixture stirring for a good 30 minutes so as to ensure that the reaction with the solid and soluble product,

could complete.

After 30 minutes we had a green colored mixture like this which appeared to contain a very fine blue precipitate.

So we set out for filtration and filtered the mixture.

Due to the fineness of the precipitate this took about 40 minutes to complete.

We washed the blue colored solid with a further 20 ml of water.

And here's our clear dark green colored filtrate.

Obviously this still has a lot of un-precipitated chromium in it.

But adding this to sodium hydroxide or sodium carbonate solutions didn't produce any more precipitate.

Perhaps it's in solution as a complex of some sort.

To get our product back we now measured out 10 ml of concentrated hydrochloric acid.

And then added this to the filtrate.

As you can see we've got a thick green colored precipitate.

We gave the mixture a good stir and then chilled it down.

And now our final filtration.

We washed the beaker out with about 50 ml of cold water.

And used this to wash the precipitate.

We then dried it thoroughly on the pump.

And then placed in the oven at 100 degrees C to dry completely for about an hour.

Here's our final product.

8.8 grams of pyronitrile benzoic acid.

Which is an 85% yield on our starting nitrotoluene.

It's a yellow color and we're not sure if it's supposed to be or not.

But it seems pretty pure and although it still probably is some chromium salts in it.

It's only a tiny amount and so this is good enough for subsequent reactions.

Overall a very nice reaction.

But please be very careful if you plan to scale up.

Thanks for watching.

Stay tuned.