We showed you in the previous video how to extract acetylsalicylic acid from

aspirin tablets, but it uses lots of solvent and it's difficult to get a lot of product.

Salicylates are useful compounds and luckily there's another very OTC source of these compounds.

Oil of winter green, which is methyl salicylate, the methyl ester of salicylic acid.

As you know, esters can be hydrolyzed back to their corresponding carboxylic acid and

alcohol.

Either using acid or alkali conditions.

We couldn't find a good video showing you the procedure for alkali ester hydrolysis.

And since we need some salicylic acid for an up and coming reaction, we'll show you

how it works.

Here's 100 mils of methyl salicylate, which is about 120 grams of starting reagent.

It's got a really nice slightly sweet mentheal-like aroma.

To perform the hydrolysis we'll need an aqueous mixture.

So we've measured out 200 mils of water.

Ultimately this reaction involves breaking the ester and adding water back in.

So water is also a reagent.

Next we've weighed out 47 grams of solid sodium hydroxide.

This is an excess of what we need and corresponds to a 1.5 molar ratio to the methyl salicylate.

We're going to use that to prevent the salicylic acid from being absorbed.

Unlike an acid hydrolysis, the product of this reaction isn't the free carboxylic acid,

but the sodium salt.

But this is pretty easy to convert back to the acid as you'll see later on.

Okay let's get our water stirring.

And we'll add the sodium hydroxide.

It dissolves very rapidly, but gives off a lot of heat in the process.

We've got a nice clear solution now.

So we're ready to go.

Let's set up for the reaction.

We've got the 500 ml flask equipped with a magnetic stirred bar, sitting on a hot plate.

First thing we're going to do is add our warm sodium hydroxide solution.

And now our methyl salicylate oil of winter.

Refrigerate.

We call it ethnogenesis

What is very interesting is that as this is added a thick white clump precipitant forms in the flask

This definitely isn't Salicylic acid, and it's very unlikely to be sodium salicylate.

As this is very soluble in water.

Since methyl salicylate has a phenolic hydroxyl group on the aromatic ring, it's quite possible that this is acidic enough to reflect or form the sodium salt.

presently

does so we're guessing that this is what's forming here as an intermediate

we've now set up a reflux condenser on top of the flask and we'll start heating

to reflux temperature remember that methyl is also produced as a product of

the reaction and this is toxic so don't do this in an open beaker or flask

without adequate ventilation and you're dealing with a hot strongly alkaline

solution and nothing is worse for causing ground glass joins to seize up

so use plenty of grease on your apparatus to safeguard against this

okay the mixture is starting to warm up now and the precipitate is becoming

less thick and seems to be dissolving into the mixture we've got a reflux just

starting up

to get a more efficient heating use a cloak of aluminium foil around the flask

which will trap the air at the bottom and enable better heat transfer pretty

soon the remainder of the solid dissolves and there's a yellow colored

reaction mixture to make sure the reaction goes to completion

keep refluxing for the next two hours because the sodium salt of the

carboxylic acid

is produced our product is present in the reaction mixture as the salicylate

ion this isn't able to react again with a molecule of methanol to reform the

ester effectively making our reaction irreversible this is slightly different

to acid ester hydrolysis where the process is an equilibrium after two

hours of refluxing remove the heat and allow the reaction mixture to cool down

even when that fridge temperature there was no sign of any solids separating and

the mixture and no separate layers just one homogenous AHA This video,

you can skip the next step but we decided to do things proper

Lee and see if we could isolate the methanol jarr89 or react manifestation

so we set up for distillation just using the same flask that we had used for the

hydrolysis reaction we've got the thermometer to check the liquid vapor

temperature and we've got nice cool water running through so that our

methyl is all condensed everything's cool to start with so let's start

heating the mixture pretty soon we've got some condensation inside the still

head and the vapor temperature starts to rise and soon after we've got

distillation occurring

we kept this going and the temperature of the vapor slowly rose up towards 100

degrees C

this is interesting because we didn't think that method all forms and I see a

throat with water but the vapor temperature definitely rose slowly as if

a boiling mixture was coming off once the temperature rose above 95 degrees C

we stopped the distillation and allowed the flask to cool down we collected

about 35 melts of liquid up to this point which is mostly

method

although this contains some water as well you would have to dry this if you

wanted to use it in another reaction or as a solvent

it burns with a nice blue flame so it's pretty clean

okay let's focus on our salicylic acid now you'll need a large beaker for the

next step capable of going up to about a liter of liquid we pour in the cooled

remaining and distillation flask this contains sodium salicylate and some

excess sodium hydroxide we've measured out 100 mils of concentrated hydrochloric

acid by our calculations this should be just slightly more than enough to

neutralize all the salicylic acid plus the excess sodium hydroxide we started

with

We've got the mixture stirring, so we start adding the hydrochloric acid slowly.

There's a bit of heat evolution, and to begin with we're just neutralizing the excess sodium

hydroxide.

Then after about 30 ml are added, the color changes like an indicator.

Let's keep adding the acid.

There we go.

Precipitation of salicylic acid.

At this point use some extra water to dilute the mixture enough to stir, and add the remainder

of the hydrochloric acid.

The mixture will become pretty thick again.

Also add water again.

This time up to about 800 ml in total volume.

Now heat the mixture and stir well.

We want to make sure that every bit of sodium salicylate in there has a chance to react.

After about 15 minutes remove from heat and allow the mixture to cool right down to fridge

temperature.

This will ensure that we get as much of the salicylic acid as possible.

utilizing out of the solution as possible.

Here we go.

So now it's filtration time.

There's a lot to filter so we're going to use a filter paper and our book nerd funnel.

We wash with a bit of cold water, and then spend about 30 minutes getting as dry as possible

on the pump.

You'd be forgiven for thinking that Pablo is a genius.

It would be nice to have a little Escobar drop by for a chat, but no, this is our crude

product.

Nice fluffy white salicylic acid.

It tends to hold onto water, so it's difficult to get dry and wave, but we're certainly not

going to complain about the yield.

The quantity speaks for itself.

Let's do a quick test and check we've got salicylic acid.

Here's a small sample of our product in a small beaker.

and some hot water to dissolve it.

It's not very soluble even in hot water as you can see.

Now here's a solution of iron chloride in water.

Let's add it to our product.

An intensely colored solution is formed.

It looks blue in daylight.

An iron-3 salicylate complex has been formed,

which is what creates the color.

Interestingly the resulting solution,

even when diluted right down still has an intense color,

but appears red with our lead lamp behind.

Okay back to our product.

You can recrystallize this if you want a really pure product.

The trick is to use a liquid.

Add boiling water and keep it boiling.

Use some plastic wrap to prevent evaporation and heat loss.

When the temperature of the water gets to over 95 degrees,

you'll start to notice a big difference in the solubility.

Once you've got a nice saturated and clear solution,

remove the beaker and allow to cool.

Pour yourself a well-deserved drink and sit back and watch.

After a nice meditation,

allow the mixture to chill down again.

And set up to filter one last time.

And get them as dry as you can on the pump.

Here's a small sample of the recrystallized product.

Beautiful fluffy tiny needle-like crystals of salicylic acid.

Even simple reactions can be interesting and beautiful.

Thanks for watching and we'll see you again soon for more reactions.

Stay tuned.

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