Make Hydrazine Sulfate by the Hypochlorite-Ketazine Process - The Complete Guide


Uploaded by NurdRage on 11.11.2010

Transcript:
Greetings fellow nerds.
In this video we're going to make hydrazine sulfate.
A useful salt of hydrazine that's safer and easier to handle than the pure liquid hydrazine itself.
We're going to use the hypochlorite ketazine process.
Although the yield is not as high as some other methods,
I prefer it because it's fairly easy, robust, and very reliable.
First, we start with 250mL of concentrated ammonia solution.
I'm using a 30% solution but this will also work with lower concentrations at the cost of some yield.
Now add directly to it 100mL of methyl ethyl ketone.
This is available in hardware stores as a cleaning solvent.
Stir the ammonia and ketone vigorously for about ten minutes to thoroughly mix them.
Now while it's still stirring add in a quarter mole equivalent of sodium hypochlorite solution,
also known as chlorine bleach.
I'm using a 10% solution so I'm adding in 186 grams.
This reaction also works very well with 6 percent household bleach
but you'll need to use more, around 300 grams.
Add the bleach slowly as it's going to produce a lot of gases,
mostly nitrogen and ammonia and some traces of chloramines and hydrazine
so this must be performed in fumehood or outside.
Occasionally cover it and let it react and then add bleach again when it stops bubbling.
Now it might seem insane that we're purposely mixing together bleach and ammonia,
two chemicals that we all know should never be mixed.
But as long as we add the bleach to the ammonia slowly, use a massive excess of ammonia,
and avoid inhaling the gases by performing this in a fume hood, we can be fairly safe.
What's happening is that sodium hypochlorite bleach is reacting with the ammonia and methyl ethyl ketone
to form sodium chloride salt and methyl ethyl ketazine.
This actually goes in a multi-step process but I'm just simplifying it here.
Once all of the bleach is added, continue to vigorously stir the mixture until it stops bubbling.
This takes about ten minutes or so.
The cloudiness is actually really small droplets
of methyl ethyl ketazine along with some methyl ethyl ketone.
Stop stirring and let the mixture separate into two layers.
This is very slow since the droplets are so small, so I’ve time-lapse it over two hours.
Don't start the next step until both layers are completely clear.
Here we are. You can see the layer of methyl ethyl ketazine floating at the top like oil.
I'm using a separatory funnel to separate the two layers as the ketazine is all we want.
If you don't have one of these you'll have to improvise or very carefully decant the ketazine.
Okay, here is the ketazine, now we convert to hydrazine sulfate.
First start with 100mL of water and a stir bar.
Then, with stirring, add in 20mL of concentrated 98% sulfuric acid.
The solution will heat up a lot.
Now get the methyl ethyl ketazine
and pour the sulfuric acid solution directly into it while it's still hot.
Stir it to dissolve the ketazine as it's very soluble and reactive with the acid.
What's happening is the hot acidic solution hydrolyzes the ketazine
and converts it into hydrazine sulfate and methyl ethyl ketone again.
You can see the solution get cloudy; this is hydrazine sulfate crystallizing out.
Keep stirring until the solution cools down to room temperature on its own.
This takes about an hour or so.
Vacuum filter out the hydrazine sulfate
and pull air through it for about an hour to dry on the frit.
Transfer the hydrazine sulfate to a container and there you have it:
Pure hydrazine sulfate.
To test it, put equal quantities of silver nitrate and hydrazine sulfate in separate vials.
Then add just enough ammonia solution to completely dissolve both of them.
Mix them together and after about ten minutes a silver mirror will form on the inside of the vial.
You can also perform a redox titration with iodine for purity.
I found my hydrazine sulfate to be better than 95% pure.
And that is how you make hydrazine sulfate by the hypochlorite ketazine process.
Thanks for watching please subscribe, like and comment.
Now for some additional notes.
What I showed you was the crude method that gave me a yield of about 40% based on hypochlorite.
For you advanced chemists there are a few improvements
to squeeze out an extra ten to twenty percent yield.
First, 200mg of unflavored gelatin could be added to the ammonia at the beginning and stirred in.
Second, was to do the reaction while chilled in ice
and third was to add the bleach very slowly drop wise from an addition funnel.
These three things helped to reduce side reactions and increase yield.
The drawback is that things happen so much slower
and the separation of the layers takes overnight.
Once that's all done, after adding in the sulfuric acid solution to the ketazine,
another improvement was to gently heat the solution up to 85 degrees Celsius.
This caused the methyl ethyl ketone by-product to boil off as an azeotrope with water
and drive the reversible reaction to completion due to the loss of one product from one side.
After about an hour of heating
another improvement was to directly chill the solution with ice to zero Celsius.
The colder temperature helped to squeeze more crystals out of the solution.
Then after filtration, the filtrate itself still had a bit of ketazine in it
so it could be reheated to further hydrolyze it.
This was chilled and filtered again.
The process was repeated until no more hydrazine sulfate could be produced.
Overall I could get up to sixty percent yield based on hypochlorite.
But considering all that hassle,
I preferred the crude approach and just use more of the cheap chemicals.
Now on a completely different note with the reagents,
I know that Methyl Ethyl ketone is not universally available.
Acetone could be used instead,
but the problem is that the acetone azine produced is completely soluble in water.
It doesn't cleanly phase separate like methyl ethyl ketazine.
So to get it out, a fractional distillation has to be done
as acetone azine forms a low boiling azeotrope with water at 95 Celsius.
50mL of acetone is used initially,
and so 150mL of liquid needs to be distilled to ensure all the acetone azine is collected.
Hydrolysis is done this time with an additional 30mL of water and 20mL of sulfuric acid.
Hydrolysis of acetone azine is very slow and repeated heating, cooling and filtration is needed.
Once again keep repeating until no more crystals come out.
The total yield was in the 40% to 50% range.
Instead of distillation I also tried extraction using toluene and absorption into the acid.
But repeated extractions, about five, were necessary to get comparable yields.
Overall I think the acetone method was too much work
and methyl ethyl ketone was worth going the extra mile to get some,
even if you have to order it online.
A lot of people have asked me about pure liquid hydrazine.
It can be made from hydrazine sulfate
by mixing it with a stoichiometric amount of base and distilling off the hydrazine.
Additional drying might be necessary.
Now all this must be done under inert atmosphere conditions
because pure hydrazine is quite dangerous and highly flammable.
I won't be doing this because I don't need pure hydrazine.
Only attempt this yourself if you have the proper equipment
and some experience in inert atmosphere distillations.
As for other methods of making hydrazine,
another major one is a peroxide ketazine process where hydrogen peroxide is used instead of bleach.
It needs a catalyst or two to get it to work.
Since good hydrogen peroxide is harder to get than bleach for the amateur chemist
I don't think I’ll be trying it.
This video took over a month to produce because originally
I was all ready to go with another method involving the Hoffman rearrangement on urea
and had filmed thirty hours worth of video on it.
The idea is to react urea with bleach and sodium hydroxide
and then perform a workup with hydrochloric and sulfuric acids to obtain hydrazine sulfate.
A modification to the process involved the direct use of chlorine gas instead of bleach.
In any case, the overall process took a number of steps and I’ll be honest,
I never got a very good yield and the reproducibility was a big issue.
Nonetheless I have to thank the original posters of the Hoffman rearrangement process
on a message board called sciencemadness.org.
By the way they are a great science board with high-level discussions in all kinds of chemistry topics.
Just note that this is definitely higher-level chemistry done by experienced and seasoned chemists,
many of which have professional ties.
If you think I’m good they're much better.
They probably look down on me, ah well.
I'll post a link to their board and the specific thread on hydrazine in my video description.
The claim their method is the best and easiest for amateurs.
So you can check it out for yourself.