In our previous video we prepared benzyl via the reaction from benzoin, which in

turn was prepared from benzaldehyde which we prepared before in a few different videos.

Now we're going to continue this reaction sequence and use the benzyl we prepared to

synthesize benzylic acid.

Benzylic acid is somewhat notorious because some of its esters were found to be extremely

powerful military grade incapacitating agents.

3-Quinucleonylbenzylate otherwise known as BZ is the most well known, and gives you an

energetic bad trip lasting 4 days.

Some bad stuff.

But don't worry, we're not going to go anywhere near anything like this.

Here's our setup for the reaction.

We've got a 100ml flask set up on a hot plate with magnetic stirrin, and a smallie big condenser

set up on top.

Let's get some water flowing.

Okay here's our solvent for the reaction.

Measured out 20ml of methanol.

We read a few different procedures and it looks like you can also use ethanol for this,

and possibly also isopropanol as well.

We chose methanol though because it has a lower boiling point and so there's less chance

of us overheating the reaction mixture which can lead to impurities.

We've removed the condenser temporarily.

Let's get the solvent in.

Okay here we go.

Now for our starting material.

4.8 grams of benzyl.

We now add this to the flask.

Here we are.

All out.

When the solvent has been started and with the condenser reattached, at this temperature

the solid isn't particularly soluble.

So we now start to heat the mixture gently and get it up to almost refluxing.

While it's heating we can prepare our other reactant.

Here's 1.9 grams of solid potassium hydroxide.

This is a 1.5 molar amount compared to the benzyl.

Still, we're going to dissolve this in 5 ml of water.

We love the sounds potassium hydroxide makes as it dissolves.

Here we go, a nice clear solution.

Put a pipette in this so it's ready for the reaction.

OK, back to our mixture.

After a few minutes of heating the solid starts to dissolve.

And now we've got a nice clear solution.

So we're ready to do the reaction.

Now we're going to add the potassium hydroxide solution dropwise through the top of the condenser.

OK.

As the first few drops go in the reaction mixture turns brown.

Then a very dark color.

At the end of the addition the color is extremely

light purple tint to it.

Now we just need to continue heating the mixture with the methanol gently refluxing for about

30 minutes.

Okay let's take a look at the reaction.

The hydroxide acts as a nucleophile, and attacks one of the carbonyl groups in our starting

benzyl.

But what then happens is a rearrangement.

The phenyl group attached to that carbon hops over to the adjacent one, creating the carboxyl

acylic acid group.

In order to do this you can imagine an intermediate species which contains the three-membered

cyclic ring as the electron orbitals rearrange themselves.

It doesn't seem likely when you look at it in theory, but it happens.

The mixture is now starting to reflux gently.

So we'll leave this now for 25 minutes more in order to react completely.

Here we are on completion.

You may not be able to see on the video, but the purple tint of the mixture is gone and

the meniscus of the reaction mixture appears brown.

So we remove the heat and allow to cool for a few minutes.

And now we pour the reaction mixture whilst still warm into a beaker.

Okay, we've covered this up and we're going to chill down now in order to see if we can

crystallize out the potassium benzylate salt which should be present.

This takes a few hours, so be patient.

During this time you can see crystals growing in the mixture.

Here we are after a few hours.

Amen.

We've got a mass of yellow crystals, so we set up two filtered these, and got them nice

and dry.

Here's our potassium benzylate.

It looks a bit like brown sugar.

However, there's only about 2 grams here.

And we were expecting a bit more than this from the reaction.

So we decided to process the filtrate that we collected to see if we could get more product.

Okay here it is.

We evaporated this down on a hot plate to remove the methanol.

As we did so, strange patterns and apparitions formed in the dish.

As if a portal to a new world.

had opened up before us.

Pretty soon this evaporated off and on, cooling the contents crystallized.

So we've got some more crystals here. We filtered these and washed them with

about 10 mils of ice cold methadone.

Here's our second batch. Another 1.7 grams of crystals.

This is our second batch. Another 1.7 grams of crystals.

This time the methanol wash has removed the color, but we do notice that the crystals

are slightly different to the first batch and more flaky in appearance.

So we don't know how pure they are.

Okay here's our potassium benzylate.

Now we're going to dissolve this in hot water and then convert into the carboxylic acid.

We're starting off with 50 mils of water, and we've got this in the beaker on a hot

plate.

Let's add our potassium benzylate, first batch, and the second batch.

Now we're going to heat and see if we can get this to dissolve.

We covered the top of the beaker.

We covered the top of the beaker with plastic wrap in order to insulate a little bit.

Well it's pretty hot and there's a lot of solid undissolved so we're going to add some

more water.

Getting hot again.

And still we've got some solid undissolved, so we add a bit more water to make up to about

100 mils in volume.

It looks like there's some fluffy brown material which just won't dissolve.

So we decided to use a spatula.

To remove this from the surface.

Okay most of it has gone now.

So we're ready to do the conversion.

Here's 10 mils of concentrated hydrochloric acid, which should be more than enough to

convert all our product into the carboxylic acid.

We add this to the hot mixture.

Okay.

Let's check the pH.

Strongly acidic.

We removed any remaining brown fluff from the surface so the mixture was nice and clean.

We're not too sure what this is.

Perhaps it's simply excess potassium benzylate and we were overcautious with the recrystallization.

Or perhaps it's a byproduct.

We'll have to do some research.

To find out exactly.

Here's our hot solution.

We're going to let this cool down slowly.

And then chill it down in order to crystallize the benzylic acid in the solution.

As it cools, sparkling white crystals appear in the mixture.

We let this chill out for a while and then set up for filtration one last time.

And here we go.

Our final product, benzylic acid and silvery flaky crystal.

It looks a little bit like phenylacetic acid, only it has a very slightly faintly sweet

sugar aroma.

The final dry weight was 1.3 grams and this corresponds to a 25% yield on our starting

benzyl.

This isn't a great yield, so perhaps we added too much potassium hydroxide, or perhaps

we boiled the mixture for too long.

But it seems very pure and we're pretty happy to have isolated a nice pure

product.

We're not sure where we can go with this now, but we'll have a think and let you

know if we find an interesting use for it.

But please don't ask us to make busy.

Thanks for watching, and stay tuned for more reactions.