Today we're going to try out an experimental procedure which claims to be able to nitrate toluene selectively in the ortho position.

The reagent is nitric acid dissolved in dichloromethane.

It is apparently possible to obtain nitric acid in DCM using the 68% concentrated acid.

But we wanted to keep water out of the way so we decided to prepare this ourselves starting with a nitrate salt.

We started with a 250 ml conical flask equipped with a large magnetic stir bar.

We measured out 25 ml of 98% concentrated sulfuric acid.

And we added this to the conical flask.

And we got this stirring in a bowl of ice and water to keep it cool.

We then weighed out 40 grams of potassium nitrate.

We had prepared this by first of all taking the commercial crystalline solid and then heating it.

We put it in an oven to dry it.

Then crushing up to a very fine powder with a consistency of icing sugar.

It's important to get this crushed up finely otherwise the acid extraction is very low yielding.

We then started adding the potassium nitrate powder to the stirred chilled sulfuric acid in the flask.

This dissolved at first, then started to form a thick gel with the acid.

Fumes of nitric acid were apparent coming out of the flask.

On complete addition we covered up the top of the flask and let the mixture stir for a while slowly.

You can see the thick gel that resulted.

With the potassium nitrate being dry, there wasn't actually much heat produced on addition to the sulfuric acid.

So we took the flask out of the cooling bath.

We allowed it to stir gently for 30 minutes.

Now we're going to try to dissolve the free nitric acid present in the mixture without using around 90 ml of dichloromethane.

We added this to the flask.

The result was this, a pale yellow DCM layer with a gelatinous solid which was difficult initially to stir.

We used a spatula to break up all the lumps of solid in the flask carefully and to try to create a more homogenous mixture.

With the lumps broken up we found that the result was able to be stirred quite well magnetically.

The resulting DCM solution fumed very strongly when exposed to air, so it seems to have a lot of nitric acid dissolving into it.

After stirring the mixture for one hour we decanted off the top DCM layer from the solids.

As you can see the liquid fumes in air very strongly indeed.

Here we go.

About 75 ml of very pale yellow liquid.

We decided not to do a further extraction of the solids, and just use this as is.

We wanted to check the reactivity of this nitric acid in DCM solution, so we did some tests.

Here's a piece of aluminium foil.

The liquid fumes, but there's no reaction with the metal foil.

This is possibly due to there being no water present.

Now with some sugar.

Again no sign of a reaction.

Not even the yellow color.

Here's a piece of foil heated to 300 degrees C on a very hot plate.

There's some latent frost effect with the liquid dancing around, but no reaction, even when the liquid touches the plate.

So let's try using this to nitrate some toluene.

We placed the beaker of DCM and nitric acid solution high in an ice bath.

We set up some magnetic stirrin.

And we used a thermometer to keeps track of the temperature.

Starting from about 6 degrees C.

Here's 25 ml of toluene.

Based on some previous attempts we made the assumption that about 60% of the nitrate had made it through to the DCM solution.

So we used 60% of the molar equivalent of toluene.

With the mixture chilled and stirred let's add a little to start with.

There's an immediate orange color produced in the mixture as you can see.

Only a slight temperature increase.

So we added a little more.

After about 10 ml of toluene are added the temperature is around 11 degrees C.

After a few minutes this started to drop again.

So we added the remainder of the toluene.

A slightly stronger orange color now.

The maximum temperature was 18 degrees C.

This is interesting because the regular nitration using mixed acid is highly exothermic.

But in this case it appears not.

We let the mixture stir in the ice bath for one hour.

Then we removed it and let it warm up to room temperature with stirrers.

We let this stir for a further hour and we noticed that the color of the liquid changed to a more golden yellow tint.

We noticed something unusual about the mixture.

Which we can't explain.

Here's the liquid at about 35 degrees.

Near to the boiling point of the DCM.

Let's put this in ice.

On cooling the color darkens.

And as the mixture get close to 0 degrees C it becomes quite a red color.

On warming again it turns orange and then yellow.

Very unusual.

Here's the mixture after an hour stirring.

And at room temperature.

We first added 80 ml of water to dissolve any excess nitric acid present.

We gave this a good stir.

The result was this.

A milky yellow colored bottomed organic layer.

We transferred this into a separating funnel.

And then separated the bottomed organic layer.

The aqueous dilute acid layer we discarded.

We transferred the organic layer back into the funnel again.

And then prepared 50 ml of a saturated sodium bicarbonate solution to wash this with.

As with the regular nitration workup process.

Unshaking the bicarbonate solution absorbed a lot of the orange color from the mixture.

We allowed this to settle and then separated off the bottomed organic layer.

The top bicarbonate layer we discarded.

But it would be interesting to know what it is causing the red orange color.

Finally, we transferred the organic layer back to the funnel.

And washed with 50 ml of water.

Unshaking and allowing to separate this seemed to remove the further small amount of yellow color.

We then transferred the bottomed organic layer containing our product into a 250 ml round bottomed flask.

Here we go.

This has the characteristic strong sweet almond and varnish aroma of nitro toluene.

There's obviously deacetam in here.

And probably some unreacted toluene as well.

We set up for distillation with the idea being to distill off anything lower boiling than our product.

Including all solvents.

We used an oil bath so we had careful control of the flask.

Temperature.

And a thermometer in the oil.

Pretty soon after heating we started to get dichloromethane coming off.

Then with more heating up to about 120 degrees C we got toluene and a very small amount of water.

The last bit of toluene was hard to get out.

So we used a vacuum pump attached to get this out.

The maximum temperature was around 140 degrees C.

Once all the toluene has come off we allowed the flask to cool down.

In the receiving flask, the mixture of DCM and toluene.

We'll retain this and see if we can use in another reaction run.

Here's the crude product of the reaction with the solvent removed.

9.5 grams of a yellow liquid.

With a strong sweet almond and flora polish aroma of nitro toluene.

This product looks almost identical to the orthoisomeric product from our previous mixed acid nitration reaction.

Purified by freezing.

With a 29% yield on the toluene we used.

Which isn't great but it's possible that the reaction needs a lot longer to complete than the 2 hours we gave it.

To do a test to see if this contains the pyroisomer we chilled the product down to negative 12 degrees C.

As you can see the liquid remained as is.

With no crystal or turbidity present at all.

This isn't a conclusive test.

But it's a good sign.

According to the paper this should be almost pure ortho nitro toluene.

But we'd have to do a lot more complex testing to be sure.

So if you need the pure orthoisomer.

Then this might be a good reaction to try out.

We recommend maybe giving the reaction 12 hours at T for working up to see if this improves the yield.

Thanks for watching and stay tuned.

We'll see you next time.