Sciencemadness Discussion Board

N2O Synthesis Problems

MattEx - 11-9-2005 at 14:52

I tried this a few days ago, and didn't get the results I desired at all.

I used the NH4NO3 + Heat method.

The AN was put in a boiling tube, and a rubebr stopper with glass-quartz tube put in the top of it, which then led to a makeshift condenser, and then to a rubber hose, to a balloon on the end of it. I tried using a neutralising solution (to remove any NO or NO2 formed) , but backpressure forced the solution back into the boiling tube, quenching the molten AN instantly, and I feared the the tube might sustain damage, so I didn't use that anymore.

The gas given off smelled like wax for some reason.
To eliminate the chance my AN was coated with wax, I disolved some in water - nothing left in it, all dissolved nicely. Mmm, instant cold :) !

So, any ideas on why? And, how could I set up a system so that the neutralising solution does not get sucked back? I need the N2O to pressurize the balloon, this creates problems.

The_Davster - 11-9-2005 at 17:56

Hmm...first time I posed this my post did not appear?

Well, anyway, the method you are using to produce N2O produces impurities as well. Here is a method of producing much purer N2O and as for your suckback problem, prevention of suckback is discussed here.

neutrino - 11-9-2005 at 19:21

It sounds as if you may have some wax contamination in your AN. Try recrystalizing it from boiling water.

woelen - 11-9-2005 at 22:37

Another source of the wax-like smell may be your stoppers and tubing. My experience with new rubber stoppers is that they frequently are covered with some white stuff, which can be quite smelly. When you rub your hands with it, it smells like you rubbed your hand with candles.

Btw, what solution did you use to remove NO and NO2. Keep in mind that NO does not dissolve easily in water, unless some complexing agent is present (e.g. ferrous ions). NO2 quickly dissolves in alkaline solution.

garage chemist - 12-9-2005 at 01:26

I succesfully made very pure N2O from technical grade AN.

Now, even ultrapure AN will yield toxic and smelly contaminants in the crude N2O.
Technical AN does so even more.

The problem is not the production of the gas (heat until a gentle production is established and it doesn't get violent- use a round- bottom flask! Doing the preparation in a distillation setup is very convenient, as this will condense the water vapor in the condenser and cool down the gas), it's the purification.

To remove the NO2 and NO, first wash the gas with NaOH solution (about 10% strength) and then with 10% ferrous sulfate solution.
The ferrous sulfate should be obtained from a chemical supplier since the OTC stuff is way too dirty to be of use here.
This is one of the rare instances where the purity of a chemical is really important!
Don't hesitate to call up a chemical supplier or go to the pharmacy and try to convince them to order the stuff for you.

The design of the washing flasks is also very important. A simple tube dipped 30cm into the liquid won't remove the contaminants!
You need a washing bottle with a bubble distributor which forms very small bubbles. An aquarium bubbler is useful here.

MattEx - 13-9-2005 at 21:33

Oh ok, thanks for the responses!

I'll be sure to give them a try :).