in a previous video we prepared nitro urea today we're going to take this

another step and see if we can reduce the nitro urea and convert it into a

called semicarbazide semicarbazide has a pretty weird and wonderful structure as

you can see it's a hydrazine derivative and you can see the relationship back to

nitro urea we're effectively reducing a nitro group into an amine so let's try

it here's our nitro urea this is as we

prepared in the previous video and it a fairly dry very slightly clumpy white

powder we're going to use 10 grams of this we

recommend trying to make this using your own piss although we did try this in a

previous video start with pure urea crystals now for our reducing agent here

we've got 25 grams of powdered zinc metal we've broken up any lumps and made

it into a very fine flowing powder as you can see 25 grams is a four to one

molar ratio of zinc to nitro urea so we'll see if this works for the zinc to

go into need to use strongly acidic conditions so here's 75 mils of

concentrated 36 percent hydrochloric acid so before we attempt to do the

reaction let's have a small test and see what we're up against here's a very

small spatula full of nitro urea in the bottom of a small beaker let's add some

concentrated hydrochloric acid to this

so now we'll add a small amount of zinc powder to the mixture

as you might expect the zinc is primarily reacting with the acid

producing lots of hydrogen gas it's pretty vigorous the temperature of the

mixture is now probably close to boiling point

and here's the catch apparently intermediates in the reduction process

are unstable if the temperature of the reaction rises above zero degrees C the

product is not semi carboside but decomposition products with that in mind

let's set up first we're going to prepare our nitro urea and

hydrochloric acid mixture we've got a 200 mil beaker set up with stirring for

this we'll add the 75 mils of concentrated hydrochloric acid some wrap

to help control the HCL fumes and now we'll add the 10 grams of nitro urea

we'll start slowly just to see if any of it does actually dissolve in the acid it

doesn't look like it okay so all in now well as we said the reaction is going to

require everything to be kept super cold so what we're going to do now is cover

this up and get it chilled down in the fridge to as cool as we can let's set up

for the reaction since it's exothermic and we've got to try to keep it below

zero we're going to need some serious cooling so we've got a large metal bowl

set up and we'll add lots of ice

and now lots of salt this should get the temperature down but let's see if it

will be enough to make the reaction work so let's prepare our reaction vessel

we're going to use a large 500 mil beaker with lots of surface area to try

to keep the contents cool we've got a thermometer in here in order to try to

measure the temperature and we've placed about 30

grams of salt in here and now we're going to add a little bit of salt to the

beaker we've added about 20 grams of crushed ice into the bottom of the beaker

to begin with now we've added lots more ice into the metal bowl around the beaker

to keep it in place and to keep it cool here's our powdered zinc we pre chilled

this in the freezer to get it down to below zero degrees C we're going to add

this to the crushed ice in the beaker this seems like a weird way to do things

but another requirement for the reaction is to keep the reducing agent from

in order to prevent decomposition of the intermediates. Let's stir around a bit

and get the ice coated in the zinc. Temperature is looking good at about

minus 5 degrees C. So let's get the show on the road. Here's our suspension of

nitro urea in hydrochloric acid which we chilled down to zero. We'll swirl this up

and then use a pipette to slowly add this to the zinc and ice in the reaction

we're trying to drip it onto the zinc coating the ice but it's difficult to

aim. We're starting off very slowly so after adding about one mil of the

suspension we stir the mixture up again.

And then we keep adding slowly.

There's no really vigorous reaction or gas evolution happening which must be a

good sign. Once the temperature rises to zero we allow the mixture to cool down

again before resuming the slow addition.

A gray color soon starts to appear in the mixture presumably the zink metal

being oxidized. This is the boring part complete addition whilst trying to keep

the temperature under control takes two hours. So what's going on? The zinc metal

and hydrochloric acid are generating hydrogen gas. As the vostatin saddles into the mixture it is going to be little planned for that.

As it's produced, it's thought that the hydrogen is temporarily chemically adsorbed

to the zinc metal and in this form can act as a powerful reducing agent.

The nitrouria is first reduced to an intermediate nitrosamine compound.

And it's easy to see why this would be unstable, NH2NO can form water and nitrogen gas very

easily.

But with excess reducing agent and low temperature, this can in turn be reduced further to the

hydrazine derivative as you can see.

And that's semicarbazide, our intended product.

We're well into the addition now, but we're finding it hard to keep the temperature much

below zero.

And towards the end even though we added more ice and salt to the bowl and drained off excess

water, the reaction mixture temperature rose to about 5 degrees C.

So here we are on complete addition.

You can see there's a small amount of gray solid floating on top of the mixture, but

most of the zinc has actually dissolved at this point.

Temperature is slowly now warming back up again.

In order to help separate our product, we're going to saturate this cool reaction mixture

with salt.

This will help force the product out into crystals later on.

Here's 35 grams of sodium chloride salt.

We'll add this to the mixture and stir in order.

To get as much into solution as possible.

Here we go.

While the mixture is cool we're now going to filter off any solids and excess salt.

Filtration was slow, possibly due to fine solids in the mixture.

But here's the filtrate.

About 140 mls in total.

In theory this contains our semi-carbazide product.

But this is very difficult to separate as it is.

So instead what we're going to do is add an organic ketone compound and see if it will

form an adduct.

Here's 9 grams of cyclohexanone.

Let's add to the filtrate.

And there we go.

You can see that cyclohexanone isn't normally miscible or soluble in aqueous solutions.

Now let's stir this up.

And interestingly, that separate layer has gone.

The cyclohexanone has now dissolved.

Again, it's a good sign.

So let's cover this up and chill down in the fridge for 24 hours to see if we can get anything

to crystallize out.

Here we go.

24 hours later we've definitely got a small amount of solid that's

crystallized out overnight it's hopeful but there's not much of it let's filter

this off

okay here's what we've got just over two grams of off white colored crystals it's

certainly not sodium chloride and the flakiness suggests it's organic so what

could it be well if we formed cyclohexanone

semicarbazone this apparently also forms an addition compound with the zinc

chloride that was left in the filtrate from the reaction and it's this addition

compound which crystallizes out apparently by mixing

this with aqueous ammonia we can remove the zinc chloride part of the compound

and get our semicarbazone compound as an insoluble product

so let's give this a go here's our suspected addition compound and here's

20% aqueous ammonia solution about 10 mils in there now let's stir well and

break up all of this and we're ready to go

all the solids carefully the solid

becomes very fine and a whiter color

okay now let's filter this off

and wash with water to get rid of ammonia

and here we go a dry fine white crystallized powder just under a gram

the ammonia reaction definitely did do something

well we suspect that what we've got here is crude cyclohexanone semicarbazone if

so then this is only a 6% yield of crude products starting from our nitro urea and

Although this seems like a convenient reaction pathway, starting from urea and ending up

with an interesting semicarbazone, in practice it's incredibly difficult to get the conditions

right for reduction, especially the cooling.

But we do have a small amount of suspected product, which is nice.

So let's do a final test and set up our makeshift melting point apparatus in order to see what

temperature this product melts at.

It's just a test tube with a small amount of product in the bottom and a thermometer

inserted.

We'll use the hot plate to slowly heat the mixture.

If anything this will underestimate the temperature slightly because the thermometer bulb isn't

totally immersed in the hot material, but let's try.

Heating on.

Temperature slowly rising.

No sign of melting so far.

Just coming up to 100 degrees C.

And now letting the temperature rise a little bit slower.

Just over 140 degrees.

And soon we've got our first sign of the material starting to melt.

On the right side we've got some liquid forming.

Temperature is 151 degrees C.

So now we'll keep going until it's all melted in order to reduce the temperature.

And it looks like we're there.

Everything has melted in the bottom of the test tube.

Temperature now is 154 degrees C.

Well according to literature the melting point of cyclohexanone-semicarbazone is around 165

degrees.

So 151 to 154 is a bit on the low side.

But our equipment is ready to go.

It's in the right ballpark, but it suggests that we've got an impure sample possible still

with some salts in there.

We'd have to recrystallize and retest to be sure.

But this was an interesting reaction, with lots of interesting chemistry involved.

Stay tuned for more reactions.