which is able to convert an aromatic aldehyde into a nitrile, using a

combination of iodine and aqueous ammonia as the reactants. Sounds too good

to be true, right? There's a catch. Before we try out the reaction, let's first do a

little experiment with iodine and ammonia and find out about that catch. So

here's about 20 mls of about 20% aqueous ammonia solution. The fumes are pretty

stinky and choking, so use ventilation if you need to.

And here's a very small amount of solid iodine in the bottom of this beaker.

Certainly way less than a gram. Notice that it's recycled from reactions

and finely powdered, not the usual pellets of iodine you see us sometimes

use. This is important. And here's a small beaker with a stir

bar so that we can do the reaction. So we'll set this up on a magnetic stirrer

and first we'll add the iodine.

Last of all we'll add the ammonia solution to the beaker. Washing up is

meditation. Let's get it stirring. And we'll add the solid iodine. It looks

pretty uneventful at this point. You might think that the iodine would

dissolve in the alkali solution like it would in sodium hydroxide,

but it doesn't. You can see a slight brown tint in the mixture. When solid

iodine meets strong aqueous ammonia, it reacts forming a rather unusual compound.

A black solid, which used to be called nitrogen triiodide, but in reality it's

actually an addition compound of nitrogen triiodide and ammonia, which

looks like this.

The reaction doesn't take long to complete,

switch off the stirring we've got a fine dark brown to black colored precipitate

in here it looks like the iodine hasn't actually reacted but we'll soon find out

so let's filter this off we're going to use a old-fashioned paper filter in a

glass funnel as you can see there's a good reason for this as you'll find out

we don't want the solid drying out too fast and fluted filters are cool and

making them is very relaxing it's also good practice because once you get good

you can make other things as well you can even attract a non-chemistry minded

mate by demonstrating your artistic prowess and convincing them that

there's a softer side to your character

let's filter

it takes some time for the majority of the

residuals to dry out so let's filter this off and let's see how it turns out

okay this is looking good first we'll take the damp filter paper out and place

it onto a sheet of paper towel to dry excess liquid a bit and we've separated

the wet black product into two piles and whilst still wet onto two sheets of

clean filter paper we put a bit of distance between them okay you're asking

well the catch is that this sheet of paper and this bit of product here

spontaneously turned into this with a very large bang we didn't even touch it

this is why you do this in two batches let's use a hot metal spatula to see how

bad it is now that was a big bang the microphone really doesn't do just it was

we don't normally mess with anything explosive but this is a bit of an old

student classic the trouble is that in larger quantities and especially

confined and with glass around it something like this happening could be

incredibly dangerous so that's the catch on this reaction we will therefore

proceed with some caution so let's do this the paper says that

this works with phenolic aldehydes as well so we're going to use our favorite

aerosol and we're going to use our favorite aerosol and we're going to use

aromatic aldehyde as a test so here's five grams of vanillin crystals in case

you've forgotten the structure of vanillin here it is as a reminder we use

vanillin a lot because it's easy to obtain and a great chemical for many

different types of reactions next here's our iodine we're using 4.5 grams which

is a slight excess in theory to what is required stoichiometrically but not a

long time ago

large excess we don't want to blow ourselves up and here's the 20% ammonia

solution we're going to use 50 mils of this to start with and more later if we

need to in order to get a solution so we'll start off and get this into a nice

sized beaker stirring on and first up we'll add the vanillin crystals

you

these start to dissolve and form a yellow colored solution typical of the

water-soluble vanillin phenolate the original procedure calls for tetra

hydra furon as a co solvent but we're going to experiment and try using a

little ethanol as we know vanillin is very soluble in it so here's 15 mils of

absolute ethanol we'll wash out the vanillin beaker and add this

and add this

it definitely helps solubility and there's only a few crystals in

suspension now so we'll top the mixture up with 20% aqueous ammonia now and see

if we can get everything dissolved

and after about another 20 mils of ammonia we're there a pale yellow

solution

you

there's quite a lot of ammonia fumes so we've switched on ventilation.

so now for the iodine.

we'll start off slowly and cautiously and add just a little bit to see what

happens.

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though most of it has dissolved. Just some black specks remaining.

So we keep the addition going and add the iodine in portions, making sure that it's

mostly dissolved before adding the next one.

Addition takes about

15 minutes, and towards the end the mixture gets dark and there's some buildup of the

black solid.

We're worried for a moment that this is nitrogen triiodide, but soon we notice that it's also

dissolving and disappearing into the mixture.

And after about 5 more minutes of stirring we notice a white deposit on the bottom of

the beaker, and some precipitate forming.

We let the mixture stir for another 15 minutes, so a total reaction time of about 40 minutes,

and then we let the mixture settle.

Then we cover it up and place it in the fridge for an hour to chill it down.

The thinking here was to see if we could maximize the precipitate.

There's obviously been some sort of reaction, so we'll start with the precipitate and try

to separate this.

So here we are.

Here we are an hour later.

Nice and chilled.

Not much more precipitate has come off though.

So let's filter.

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with ice water a number of times until there was no more ammonia aroma

it takes a lot of drying and even after an hour on the pump we still had a paste

it does have a faint vanillin aroma but that could just be due to some residual

vanillin it's a pale tan color to get this dry we made up a makeshift

desiccator and placed the beaker into this over phosphorus pentoxide for a few

days and this did the job while we were

waiting though we did a quick qualitative test to give us a clue as to

what this is we made up a saturated solution of sodium hydrogen sulfide

in a little bit of water we know that vanillin and many of its derivatives are

aldehydes and as a result for a ducts with sodium bisulfite unlike with

benzaldehyde these are highly soluble in water so let's add some of the tan

colored paste if it's an aldehyde then it should dissolve if it's a nitrile

then it's unlikely to

to begin with it doesn't dissolve easily but after a bit of stirring

most of the tan solid does dissolve in the solution forming a slightly yellow

colored solution so this isn't looking good for a successful reaction at least

for the precipitate we obtained okay let's go back and look at the

filtrate now we'll go through the process quickly

we first tried extracting the amber colored filtrate using diethyl ether as

recommended by the original prep after shaking well we've got a slightly orange

colored ether layer and we're ready to go to the next step which is to extract the

layer so we separated this off and then evaporated it down to see if it

contained anything on evaporating we've got a flaky cream colored solid but only

a tiny amount and it smells a bit like creosol which we made in a previous

video by reducing vanillin there's not enough here to analyze so this might be

our elusive vanillyl nitrile but if it is then the yield is tiny so we decided

to take the aqueous ammonia layer and add a little bit of aqueous ammonia to the

layer and acidify this firstly using citric acid crystals and then using

sulfuric acid until strongly acid the heat generated by neutralization caused

some residual ether to boil off we're getting a white emulsion produced as the

sulfuric acid neutralizes that last of the ammonia and then some red colored

oil which floats to the surface and dances around in interesting patterns so

So we extracted this mixture, again using diethyl ether.

And now the red color has extracted completely into the ether layer.

We evaporated the solvent to see what remains.

Once the ether had evaporated we were left with a oily red residue.

Probably a couple of mils in total.

But this had a very strong aroma of vanillin.

Washing with sodium thiosulfate also didn't remove the brown color,

so our guess is that this is just vanillin with some impurities in as well.

So now back to our original precipitate.

It's dried a fair amount after a few days, although still a little clumpy.

So what could it be?

Well we weighed it and it's pretty dense.

There's just over 4 grams here.

And although it's not totally dry this is a surprisingly high weight.

The only explanation we can come up with is that this is a product which has chemically absorbed some of the iodine,

hence leading to a large weight increase.

The previous test we did suggests it's an aldehyde so our guess is that this is 5-io-dovanillin.

The same product that we made in a previous video.

It looks the same, it's just as hard to dry, it's about the same density.

So this is interesting.

Perhaps it was the conditions we used which varied slightly from the procedure.

But our suspicion is that in reality vanillin is just too reactive towards electrophilic attack by the iodine,

especially with a base like ammonia around to absorb the H I produced for this reaction to work successfully with it.

We might come back to this in the future when we have a less reactive aldehyde to try.

But at least we got an excuse to blow up some nitrogen triodide.

Stay tuned.