Sciencemadness Discussion Board

"Food" grade nitrous oxide production and water displacement of the same

Quantum - 19-1-2006 at 17:47

I was reading the old archives and found this post:
Making pure N2O
Quote:

Nitrous oxide having a high purity is produced by reacting urea, nitric acid and sulfuric acid at a temperature of 40 DEG through 100 DEG C., and isolating the resultant nitrous oxide from the reaction gas mixture, without any danger of, for example, explosion during the reaction and without using expensive catalysts and sulfamic acid.



My plan is to trap the resulting gas using water displacement(like in middle school science). The water will be a dilute solution of NaOH to remove the CO2 formed - thus it will be a nice, easy and elegent reaction. Once the gas is trapped it can be stored and used for other reactions that need high grade N2O and of course for some testing on the organism.

I have but a limited suppy of 90%+ H2SO4 and so I was wondering if there was any reason I could not make a standard nitration bath of the sort used for explosives(ie KNO3/H2SO4)? Would that be any less safe? Obviously the gas needed to be very very pure...

prole - 21-1-2006 at 18:52

Recently on an episode of 'Mythbusters', they got a rocket to launch using Civil War technology. They used nitrous oxide as an oxidiser to help launch the thing. The cool part though, was watching them make the nitrous oxide. They censored their lips and voices when talking about the 'ingredients', but showed what appeared to be urea pellets and some acids. These they reacted and collected the resulting gas in large plastic water-filled tubes.

garage chemist - 22-1-2006 at 04:04

Using ammonium nitrate is so much cheaper and easier... I have made N2O in quite large amounts and even pressed it into a gas bottle using a fridge compressor.

The AN is heated in a round- bottom flask so that it is maintained at a vigorous boil (don't use more than 70g at a time, it could get out of control since the reaction is slightly exothermic- with less than 70g the radiative and convective heat loss outweigh the heating from the reaction so that no runaway can occur).

The resulting mix of water vapor and N2O is fed into the top of a dimroth condenser attached to a two- necked flask. The water drips down and the crude N2O is withdrawn at the second neck.
The N2O is first washed with 10% NaOH solution (NO2 removal) and then with 10% FeSO4 solution (NO removal). It is of good purity then.
For compression, the N2O needs to be dried with conc. H2SO4 or CaCl2, otherwise water will condense in the gas bottle and cause corrosion.

This is, in my opinion, the best process for N2O production. the method with decomposition of AN in aqueous HNO3 solution with chloride catalyst has no danger of runaway but the reaction is exceedingly slow.

I have not tried the urea method, however the gas contains CO2 which needs further processing to get it out.
The big disadvantage of the urea method is the use of HNO3 which is not easy to access and not cheap either.

There is a superior method that produces totally pure N2O in one step, I'm going to look it up. However, I remember that NaNO2 is needed (plus some other chemical, I think it was hydroxylamine or sulfamic acid- not sure which).

[Edited on 22-1-2006 by garage chemist]

pyridine - 8-2-2006 at 18:07

Does the urea method produce other nasty byproducts I would not want to consume by accident? I happen to have access to everything needed and would rather give that a try then mess around with trying to filter out NO2 and NO but if need be I can go that route

Thanks

[Edited on 9-2-2006 by pyridine]