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question about Nitroethane-synths

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hest:
Hey Karel, I would love to hear some more info on your nitroethane synth.

karel:
The procedure in Org. Synth., Coll. Vol. 4, 724 (http://www.orgsyn.org/orgsyn/prep.asp?prep=cv4p0724) was followed with 2 mol EtBr and 2 mol AgNO2. Distillation of the reaction mixture at atmospheric pressure gave ether contamined with EtONO and NOx as a forerun and then 75-80 % yield of EtNO2 boiling at 108-112 C.

Ether containing EtONO was attempted to purify by shaking with dilute HCl and water. Drying with NaOH and then with metallic Na led to reduction of leftovers of nitrogen impurities to ammonia, which was precipitated with concd H2SO4. Ether was after drying with NaOH and then with Na suitable for using in the reaction.
I assume that low-boiling petroleum ether could be good substute for ether, but I didn't try it.

The AgBr precipitate*, which was filtered from the reaction mixture, was allowed to dry in air and suspended in 1000 ml hot water. Diluted H2SO4 was added to destroy nonreacted AgNO2 and NOx were allowed to escape. The addition of H2SO4 was repeated at times to maintain the solution acidic. To slightly acidic hot solution was then added zinc wire** of diameter 3-5 mm. It is advantageous to use this wire as a stirring rod. Immediately after the wire reached the AgBr precipitate, the reduction of black Ag occured at the point of contact. After several hours the reaction was finished; it was necessary to keep solution acidic by occasional addition of H2SO4. Reduced Ag formed characteristic light gray precipitate, which was dried in air.
This Ag was dissoved in cca 20 % HNO3, solution was shortly boiled to remove NOx and excess acid was carefully neutralized with diluted NaOH. The neutral solution was suitable for production of next batch of AgNO2 (see Org. Synth. procedure).

* The mother liquor and washing liquors from AgNO2 preparation were collected and excess of NaCl solution was added to them. Precipitated AgCl was then added to AgBr, so the overall lost of Ag at this 2 molar scale was lower than 1 g.

** Zinc wire was used in excess. It was found to be much better than zinc powder. If slight contamination of Ag with carbon doesn't matter, the steel wire could be also used, but I didn't try it.

SpicyBrown:
Holy shit karl, this seems to be a very promising procedure you've just tossed into the mix... Will have to get some AgNO3 and get started on the inorganic side of things..

Why does this work so much better? Is silver nitrite more reactive than sodium nitrite? Something to do with the rather insoluble AgBr formed as a product (as a driving force)? Anybody?

The shitty thing is, I spent hours one day scouring OrgSyn looking for stuff on making nitroalkanes, and managed to miss this entry entirely...

Thanks karl!

-SpicyBrown

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