How to Prepare Hydrazine Sulfate from Household Bleach

By viewer request in this video we're going to prepare hydrazine sulfate starting from household bleach.

There are a few other good videos out there which show how to make hydrazine, but none which show this method using urea, and this one does a bit more OTC, although the yields aren't as good.

We're starting with 500 ml of 5.25% sodium hypochlorite bleach. Get the cheap watery stuff with no thickening agents or detergents in.

We placed our bottle of bleach in the fridge for a few hours to get it nice and cold,

and then we repeat the process.

And now we've transferred it to a large 1-liter beaker with a large magnetic stir bar in.

If this is the first time you're doing this reaction we recommend starting off with

a smaller quantity and using the very large beaker.

We'll explain why later.

Temperature is at about 7 degrees C, so nice and cool.

We've weighed out 32 grams of solid sodium hydroxide.

This is around the 2.2 molar excess to the sodium hypochlorite we're starting with.

The reaction itself requires two moles, however it's very important to keep the reaction mixture

strongly alkaline, so we use a bit extra in order to make sure it stays this way.

With the temperature nice and cool and the stirrin' going strong, we now add half of

the sodium hydroxide to the bleach in the beaker.

As the sodium hydroxide dissolves, it's going to release heat.

Too much heat and the bleach will decompose and disproportionate, reducing our yield.

But below 20 degrees is pretty safe and we got up to about 18 here.

Let the mixture stir until you've got a nice clear solution.

Now we're going to chill down the bleach mixture again until it's back down to about 7 degrees.

Cover up the beakers, and make sure that the rest of the sodium hydroxide isn't exposed

to the atmosphere otherwise it will absorb water rapidly.

While we're waiting for this to cool down we can prepare our other reagents.

We've weighed out 0.75 grams of powdered gelatin.

This is regular baking grade gelatin, the same gelatin that we used in our cake recipes

before.

Exactly what it does is not completely known, but it's thought to chelate any tiny amounts

of metal ions such as iron which might exist in the reagents.

Metal ions catalyze the decomposition of the hydrazine and so this helps to prevent this.

Apparently using calcium hydroxide also works, but we've not tried it.

Okay, here we've got the beaker of distilled water which we've warmed up.

It's very important to use distilled water.

Tapped water will ruin your yield due to the metal ion content.

The trick now is to use the minimum amount of water possible.

Our product is water soluble so we want to keep the liquid volume to a minimum.

First we dissolve the gelatin in about 15 mils of the hot water.

It takes a bit of stirring to get a clear solution.

Here we go.

Now we're going to add the gelatin.

Now for our next reagent.

Here we've weighed out 22 grams of urea crystals.

This is a very slight stoichiometric excess to the sodium hypochlorite we are using.

We're not 100% sure about the concentration of the bleach so using a slight excess makes

sure all the hypochlorite reacts.

In theory you can also use ammonia for this reaction, but in practice the liquid volume

becomes too great.

Now we're going to use the warm.

Not distilled water to dissolve the urea.

We want to make up a saturated solution using as little water as possible.

As the urea dissolves it cools, but with a little warming we got everything to dissolve

making up about 40 mils of liquid.

If the mixture cools too much and the urea won't dissolve then put the beaker in a microwave

for 10 seconds.

Okay here's our urea solution and our gelatin solution.

Now we're going to add the gelatin.

Add the gelatin to the urea and stir to form a homogenous mixture.

And now reserve this at room temperature ready for the reaction.

Here's our bleach and sodium hypoxide mixture chilled down again.

The temperature is around seven degrees C, so we're ready now to add the rest of the

sodium hypoxide to this.

Make sure the mixture is cushioned.

is stirred well so no local hot spots develop. Temperature rises to about 17

degrees again. Perfect!

We're now ready to do the reaction. As we said before, if you are a hydrazine

virgin, or if you are using reagents of unknown purity, we recommend doing this

that can hold at least three times the volume of your bleach mixture. If

anything goes wrong or you have impurities present, side reactions are

going to produce a lot of nitrogen gas and this is going to cause the mixture

to foam enormously. How much foam you get is directly proportional to the quality

of your reagents and how much the hydrazine respects you as a chemist. But

then your bleach is probably old and useless. Dial up the stirrer to as high as you

can for the reaction. And now in one go, add the urea and gelatin solution. The

mixture turns white as tiny bubbles of nitrogen gas are generated in the

mixture. Note that the foaming can be delayed, so don't get too cocky just yet.

We've got some gentle foaming, but not too much which is great. The reaction has

caused a slight temperature increase up to about 25 degrees C. Soon the gas

production dies down and we obtain a clear solution again. This contains an

intermediate compound, which we now need to decompose in order to get our

hydrazine.

So we switch on the hot plate and heat the mixture quite strongly. The

decomposition occurs above about 70 degrees C, but you get best results if you

heat to above 85. Temperature increasing. It's a smart idea to cover the top of

the beaker with plastic wrap. Hydrazine is quite volatile and you don't want it

escaping as it is formed as you will get a lower yield. In addition, it is highly

toxic and known to be carcinogenic. So you really don't want to be breathing

this in. For the technically minded, here's a simplified reaction schema. Very

similar to the Hoffman rearrangement. As the temperature increases the mixture

starts to foam again due to some product decomposition. Hold the mixture above 80

degrees C for five minutes, then remove and allow to cool down.

Keep the plastic wrap on and chill the mixture down to close to zero degrees C.

As the beaker cools right down you may notice some small white crystals forming on the wrap

and on the sides of the top of the beaker. These rapidly melt when taken out of the freezer.

This is actually pure hydrazine which has evaporated and frozen. Don't try to isolate

this or distill it off because it's very toxic and can be dangerously unstable.

Here's our reaction mixture chilled down to just a few degrees C.

For the next step, we're going to need lots of 50% sulfuric acid in water!

That's 50% concentrated by volume. So make up the batch of about 100 mls using 50 mils

of water and carefully adding simply 50 mils of concentrated sulfuric acid.

The temperature will go above 100 degrees C. So take care!

And then chill the mixture.

liquid in the freezer until it's at zero degrees C you'll need about 60 mils of

acid for this first step get the chilled reaction mixture stirring well and now

slowly add the chilled 50% sulfuric acid to it to begin with the acid is going to

neutralize the excess sodium hydroxide that was present in the mixture so

there's not much effervescence but once this is complete the acid will start to

react with the sodium carbonate that was formed as a reaction product and lots of

co2 is produced so go slowly so you don't risk creating the fountain

towards the end of neutralization the effervescence lasts a while so allow the

mixture to stir and get rid of the co2 gas after about 60 mils you will get to a

point where acid addition no longer generates effervescence in the mixture

at this point measure out an additional 40 mils of 50% sulfuric acid this is

enough to convert all the theoretical yield of hydrazine into its sulfate salt

note that this is only the first step in the process of making the solution.

this is the hydrogen sulfate salt so it's a one-to-one molar ratio let's get

stirring on and we'll add this to our mixture

the mixture turns cloudy and little tiny snowflake like crystals start to appear

in the mixture

enjoy!

watching the crystals form and settle this is our product hydrazine sulfate the

temperature now is around 30 degrees C so we'll now cover the beaker and chill

it down in the fridge in order to maximize our precipitate just be careful

not to go below about 10 degrees C otherwise sodium sulfate can start to

precipitate out at about 15 degrees the precipitation is largely complete so we

don't have to worry about that here we go our final product this is 22.6 grams

of hydrazine sulfate as pure white dry fluffy crystals

this is a yield of 49% on the starting hypochlorite assuming the solution was

at the strength written on the label this is not bad at all and the

alternative kinezine process typically gives about the same sort of yield but

do know that the reaction we've shown you here is not forgiving when it comes to hydrogen sulfate.

to purity of reagents

well we really wanted to claim a yield of over 50% for this method and 49

doesn't quite cut it but we do have a final trick up our sleeve

here's the filtrate leftover from that final filtration of the product this

still contains some hydrazine sulfate dissolved in it

we've weighed out 20 grams of phosphorus sulfate here it's a white color because

the anhydrous salt, and we've got about 80 ml of water.

Let's add the copper sulfate to the water and stir to form a saturated solution.

Looking good.

Now add this to the filtrate.

You can see a turquoise-blue color forming in the mixture.

Cover and leave this for an hour to react.

You'll see a fine light blue powder forming and settling in the beaker.

This is a compound which is an adduct of copper sulfate and hydrazine sulfate.

So we filter this.

Okay.

Okay.

And get it really dry until it forms a fine powder.

And here it is.

An extra 6.9 grams of the copper sulfate and hydrazine sulfate adduct.

This is an extra 24 mmol of hydrazine, which takes our total hydrazine recovery and yield

from this reaction up to 56%.

Not bad for household bleach, urea, sodium hydroxide and sulfuric acid.

All cheap ingredients.

Thanks for watching, and I'll see you in the next video.

Bye-bye.