Welcome back to Kemplier.

As part of our research plan for 2016 we want to test out some different ways of performing Riedel-Crafts reactions.

So today we're starting off this project with a few experiments to see if different catalysts can be used for the traditional isolation reaction.

We did lots of reading and so we've got a few possibilities we want to try out.

We're going to use a dry 100 ml flask for the experiments.

We've got an adapter and hose attached to this, leading to a calcium chloride drying tube so that atmospheric moisture can't get into the flask.

As our aromatic compound and solvent we're going to use toluene in all the reactions.

The reason for this is that it's much more reactive toward electrophiles than benzene and so it should allow us to tell more easily which variations have the potential to work.

It's also a lot of work.

It's important given that we're going to be doing things on a small and quick scale.

Okay time for our first reaction.

First let's get the toluene into the flask.

That's stirring gently in there.

Our first catalyst test is based on a viewer's suggestion.

Could zinc chloride be used instead of aluminium chloride?

Let's find out.

Here's 7.5 grams of anhydrous zinc chloride.

We've got it covered up with plastic wrap because it's extremely hydroscopic and absorbs water rapidly.

Let's get this into the flask.

Okay all in.

And we've closed the apparatus up again.

Now for our acetyl chloride.

We're going to start with acetyl chloride because it's normally pretty reactive in these brittle cracks reactions.

Check out some of our other videos for details of how to make this.

It fumes quite strongly in air as you can see.

Okay let's get this into the flask.

We're going to let this sit here now first of all at room temperature to see if anything happens.

We'll keep the mixture well stirred and we'll be keeping our eye on the drying tube.

If any reaction occurs then hydrogen chloride gas should be generated and we will see this as clouds escaping from the tube.

Let's do a recap on what happens in Friedel-Kraft's acylation reactions.

The reaction involves an aromatic substrate such as benzene or toluene.

The aromatic ring in these compounds is electron rich and so it can be attacked by electrophilic species.

When an acyl chloride such as acetyl chloride is mixed with the Friedel-Kraft's catalyst, usually an hydrothaluminium chloride, an addition compound first forms,

which then forms an equilibrium with the species in which the carbon of the acyl compound has been formed.

This has a positive charge.

This positively charged carbon acyl species is highly electrophilic and able to react with the aromatic ring, forming the product which is the aromatic ketone.

What normally also happens is that the catalyst also reacts with the product forming an intermediate compound.

At the end of the reaction this is then quenched using water to give the ketone product again.

Okay here we are an hour later.

No sign of any reaction in the flask.

And looking at the drying tube there's no sign of any HCl gas coming off at all.

So we start to gently heat the flask to see if this makes a difference.

We can't heat too much though because acetyl chloride boils at around 60 degrees C.

An hour later and still no sign of any reaction.

A dark color is generated by the formation of the intermediate compounds.

But in this case nothing, and no HCl gas.

So we have to conclude that zinc chloride is not a viable catalyst.

We decanted off the liquid and saved it for more trial experiments.

One of the trials we did involved exactly the same reaction using zinc chloride, but with propionyl chloride instead.

The result was the same.

No reaction with zinc chloride as the catalyst.

So it was a nice idea and worked the try.

But unfortunately it doesn't work.

Let's try something else now.

Well we were reading a few interesting articles about zinc powder and microwaves as a Friedel-Crafts catalyst.

We weren't so sure about the microwave bit so we first of all decided to try just plain old finely powdered zinc to see what happened.

So here's another dry 100 ml flask.

This time we're not using a stir bar.

We add 25 ml of toluene as our aromatic compound and solvent.

And we're going to try this first of all using propionyl chloride.

We're using about 4.5 ml.

It's slightly cloudy looking but otherwise it's pretty pure.

Let's get this in the flask.

And here's our zinc metal powder.

This is 7.5 grams, which should be an excess on what we need in theory to do the reaction.

Let's get this in as well.

Well very interestingly, within a minute of us putting the zinc in we're got a color change in the reaction mixture and a slight brown color forming.

The bottom of the flask is also warming up.

And these exhalation reactions are normally quite exothermic.

So this is a good sign.

So we get this set up again with a drying tube.

This time it's a bit more makeshift than in the previous experiment, but it should work okay.

We gently heated the flask to the point at which we could see some bubbles forming in the mixture.

And held it there for an hour.

We also occasionally detached the drying tube and gave the mixture a stir with a metal rod.

Okay, here we are an hour later.

We allowed the flask to cool down and then prepared 25 ml. of cold water to quench the reaction mixture.

What's kind of exciting here is that color change from a dark blue to a light blue.

A slight brown color to the yellow.

This looks really similar to the quenching process with the aluminum chloride catalyst.

Let's work up a bit and see what we've got.

First we decanted the liquid into a separating funnel.

Then we washed the solids in the flask with another 10 ml or so of toluene.

And then decanted this into the separating funnel.

First we'll drain off the bottom aqueous layer.

If you were doing this properly you would probably also want to wash and extract the aqueous layer with a bit more toluene.

But we skipped on doing this.

Here's our toluene layer remaining in the funnel.

We want to make sure we've got rid of any propionic acid that might be in here.

So we made up a solution of sodium bicarbonate in water.

And added this to the toluene layer in the funnel.

A good shake and now anything acid should have formed the sodium salt and be in the aqueous layer.

So we separate off the bottom aqueous layer.

It's cloudy probably because of a small amount of zinc left behind which is now converted into the insoluble carbonate.

And now for our organic toluene.

We've put this into a 100 ml flask again.

Again if you were doing this properly you would probably dry the liquid using anhydrous magnesium sulfate at this point.

But we decided to distill it as it is in order to remove the excess toluene.

This process will also remove any water present as well.

So let's see what we've got in here apart from toluene.

We've got the still head insulated with aluminium foil to improve efficiency.

Here we go.

And controlling the heating we find that there's a small amount of liquid remaining in the flask which doesn't boil even when the temperature is increased to 150 degrees C.

So we've got our toluene back again and we can dry this and recycle it.

And here's the non-volatile remainder in the boiling flask.

There are a few crystals as well, presumably due to some inorganic salts remaining because we didn't dry the liquid properly before distilling.

It's quite fluid.

And there's probably a small amount of toluene remaining in here.

But there's a definite aromatic ketone aroma as well.

So here we go.

3.2 grams of a very crude acylation product.

If this was pure methyl propiophenone then it would represent a 42% yield on starting propionyl chloride.

But we suspect it contains a bit less than this.

Although we'd need to do a lot more work to confirm that this contains the right product,

it's certainly good evidence that zinc metal can be used in some cases as a Friedel-Crafts acylation product.

So we'll work on this in the background and see if it can be turned into an actual procedure.

We'll also try it on benzene to see what the result is.

One final note.

We actually did two more test-scale experiments using other metal powders to see if they could also be used.

We tried an acylation reaction using magnesium powder,

and another using fine-valuminium powder.

But the result in both cases was negative.

No reaction.

So zinc has some special powers that other metals don't here.

We'll be exploring more experimental Friedel-Crafts soon, so stay tuned.

Thanks for watching.