In this video we'll prepare pyridine and oxide.

Unlike benzene or toluene, pyridine itself is extremely unreactive towards

electrophiles. By making the N-oxide we're hoping that this will be more

reactive and allow us to explore the chemistry of pyridines a bit easier.

This is our third attempt at this reaction and we've been playing with

conditions and the setup a bit because we couldn't get much out of the

literature. We've set up a 250 ml flask with stirrin and this is sat in

an oil bath. We've got the thermometer in the oil bath. So now for our main

reactant. This is 20 grams of liquid pyridine. It doesn't seem to matter if

it's not completely dry, but we're using reagent grade here. Place the pyridine

into the flask

and heat the flask.

Now pour the flask on the oil bath until the temperature in the oil bath is

between 90 and 95 degrees C.

Now for our oxidizing agent. Literature references suggest using

paracetic acid for this reaction, but given that this is dangerous and

explosive, we're going to use our baryohydrogen peroxide duct that we

prepared in a previous video. We've weighed out 24 grams, which is a

stoichromatic amount to the pyridine.

in order to see how this works the paradigm is heating up and we've added

the thermometer into the flask as well so we can record the temperature of the

liquid inside directly as well wait a few minutes and allow the temperature in

the flask and the water bath to equalize above 90 degrees C this is one of those

reactions where the temperature has to be over a certain amount to react but

temperature can result in an out-of-control reaction so you need to

be careful so now we start to slowly add a small amount of baryoproxide the duct

to the flask

as the solid hits the hot liquid it seems to melt and dissolve and starts to

fit with some decomposition at first the fizzing quickly dies down

you

and it seems as though the addition of the solid cools the mixture slightly so

wait a few minutes for temperature to rise again

and then at some more of the solid that's some point about a quarter of the

way through addition we notice that the fizzing continues when the solid is

added and at some point this seems to trigger off the reaction in the liquid

the temperature starts to rise at this point you see a little bit of pyridine

refluxing it's not hot enough to boil but the high vapor pressure is enough to

cause this watch the temperature closely if it goes over 100 degrees C then we

found that simply removing the flask from the oil bath and leaving the minute

caused the temperature to start to drop again

you notice a yellow color forming in the mixture he pond an ingredient rock

side and try to keep this reaction going but without allowing the temperature to

rise uncontrollably if it does rise to high then at around 115 degrees the

pyridine will boil towards the end of addition the reaction is really in

underway how much of this is simply the hydrogen peroxide decomposing however

we're not sure we'll find out now we've finished addition we left the flask

stirring in the oil bath for an hour during this time the fizzing dies down

substantially and then we allowed the mixture to cool to room temperature it's

now at about 40 degrees C and the color has changed to a dark orange so we

chilled down to zero degrees C in the freezer

and as you can see we've got a large amount of crystalline solid forming and

we filtered this off we count fine much on the solubility of our product except

that it's extremely polar and hence very water soluble we suspect that the

crystals are still in the water and the crystals are still in the water and the

crystals here are in fact urea as a side product of the reaction so we measured

out 20 mils of di-fluoromethane

and washed the crystals in the flask with this hoping that the product would

be somewhat soluble in it with urea not being

so here are the needle-like crystals 10 grams of an unknown substance which

now it's just over 100 degrees C we strongly suspect that this is urea as a

byproduct of the reaction

we placed a small amount in a beaker and then added a drop of a suspension of

manganese dioxide in water so it's definitely not our starting period the

rockside compound

the filtrate contained two layers one apparently aqueous and one dichloromethane

this also has a strong aroma of unreacted pyridine we figured we'd boil

and evaporate this down to see what was in it, but first we did a safety check.

We placed a small amount of the liquid on some starch iodide paper.

No dark blue color means no peroxide.

So we're safe to boil this down.

We boiled down the mixture using strong ventilation in order to avoid dichloromethane and pyridine

fumes.

Eventually the temperature rose to 130 degrees C and only a liquid remained with no further

boiling.

We poured this into a small beaker.

And soon it started to solidify.

This is a good sign because the literature value for the melting point of pyridine n

oxide is 65 degrees C.

Thanks for watching.

Here's our crude product.

8.5 grams of a brown colored amorphous waxy solid.

On exposure to air it seems to slowly absorb moisture and becomes a water solution.

It's not pure but from its properties we're confident this contains a lot of pyridine

n oxide and with a maximum yield of 35%.

We did a few tests to establish its solubility.

It is extremely soluble in water.

And a pyridine n oxide.

It appears to be not at all soluble in toluene.

Very slightly soluble in dichloromethane.

And slightly soluble in ethanol.

It is very slightly soluble in acetone.

But acetone was the only solvent we found which removed some of the yellow color, leaving

the solid.

So we used cold acetone to macerate the solid and crush up the lumps.

And then we filtered this and quickly dried on the pump.

See you next time.

This gave us a tan colored powder.

We'll experiment and use this directly in a follow up reaction to see if this works

okay as it is.

So our conclusions from this reaction.

Urea peroxide works as an oxidizing agent but a lot of it decomposes in the process

and so a large excess is required.

We think probably 2 to 2.5 molar excess.

Due to the polarity of the product, it's hard to separate it from inorganic salts,

and it's hard to get the orange color out.

It's also hygroscopic so you need to handle it carefully or it will just form a puddle.

Stay tuned and see if we manage to use our pyridine endoxide in a follow up reaction.

Subtitles by the Amara.org community