This is a quick video showing how to make diethyl oxalate, an ester which we're planning to use in an upcoming reaction.

We're starting here with 100 grams of oxalic acid dihydrate.

To get a good yield we'll first need to convert this to anhydrous oxalic acid.

Pour it into a Pyrex baking tray and bake in the oven at 140 degrees for 2 hours.

Break up the solid occasionally and then at the end weigh the white powder which remains.

After 2 hours in the oven the crystals look slightly different and the weight has decreased to 70 grams.

This is good enough.

Place the relatively anhydrous oxalic acid into a 500 ml flask.

Now prepare 200 ml of absolute ethanol.

It's important that this is water free for a good yield.

Add this to the flask.

The esterification reaction is catalyzed by acid and oxalic is strong enough to act as its own catalyst.

You can add the milk of concentrated sulfuric acid to the mixture but we found it makes little difference.

Give the mixture a stir and you'll see that most of the acid goes into solution in the ethanol.

But there's no reaction as yet.

Now attach a condenser and set up for reflux.

Get a good strong reflux going in the flask and keep this going for 2 hours.

Over this time you won't see much visible change in the reaction mixture.

Here we are after 2 hours of refluxing.

There's hardly any visible change but the mixture has a pleasant and definite slightly sweet smell of rum.

This is due to small amounts of an impurity which makes it hard to see.

We'll remove it.

Our next step is to remove excess ethanol.

So allow the flask to cool slightly and then set up for simple distillation.

We allowed the flask to cool down to room temperature first to see if any oxalic acid crystallized out.

None did as you can see here.

Set up for distillation.

We used a thermometer to track the different fractions coming off the liquid.

First off is excess ethanol.

Around 80 degrees C.

There is probably some water in here as well as the azeotrope.

But we collected around 120 ml.

Then the temperature of the vapors rose to 100 degrees and we collected pure water.

Then the temperature rose still further to around 160 degrees and we started to collect the colorless liquid.

The temperature of the vapors then rises slowly until around 175 degrees C at the end of the distillation.

During the distillation you'll see some smoke-like fumes appearing in the apparatus.

This is almost certainly excess oxalic acid decomposing.

This means that there may be a small amount of water carried over into our product.

But it also means that there are potentially some fumes of carbon monoxide.

This is highly toxic so be careful and use adequate ventilation as it is colorless and odorless and won't give you any warning.

At the end of the distillation a small amount of char remains in the flask, but nothing else.

Here's our distillate starting from 160 degrees C.

It is fairly pure but does contain a small quantity of water and decomposition process.

So prepare 40 ml of a saturated solution of sodium chloride in water.

Add the crude product to a separating funnel.

And then add the saturated sodium chloride solution.

This should sink to the bottom.

Shake the mixture well and then allow the layers to separate.

Our product is the top layer.

Separate off the bottom brine layer which should now contain any residual alcohol, formic acid, and any other water-soluble impurities.

And we're left with our product.

Separate this off into a storage container.

You can also dry it using anhydrous calcium chloride if you want to.

And here's our product 70 grams of diethyl oxalate.

It has a 10% yield on the starting oxalic acid dihydrate.

For information the weight difference between the distillate collected and the final product was only 2 grams.

The product has a slightly oily consistency and an unusual fresh and fruity aroma, a bit like grape juice.

It dissolves very slightly in water and easily forms a bottom later.

Thanks for watching and stay tuned for more reactions.

We'll see you next time.