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Author: Subject: Very low yield of nitroethane
nimgoldman
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[*] posted on 16-11-2018 at 10:55
Very low yield of nitroethane


I have recently ran the Victor Meyer reaction with bromoethane and silver nitrite in ether.

I have followed the procedure as presented by ChemPlayer, except I used bromoethane instead of iodoethane.

  • silver nitrite not being pure or dry enough (the powder has been dried in a vacuum desiccator over calcium chloride at 100 mbar for 3 days in darkness, however, the prowder still looked colored, not grayish like in ChemPlayer's video)
  • bromoethane not being pure (unlikely as fractional distillation showed stable vapour temperature)
  • bromoethane could evaporated during reaction (temperature never exceeded 10 °C though; I have not used reflux condenser)
  • reaction must run much longer for bromoethane than for iodoethane (I ran it for 5-6 hours total as it was just a test run)
  • evaporation of ether done at temperature too high (up to 60 °C to drive off all ether, but maybe this could volatilize nitroethane too?)


It seems there should have been much more nitroethane produced judging from the amount of silver bromide.

There should have been over 8 grams of nitroethane produced even at 50% yield.

I am trying to find where I made a mistake.

Unfortunately, my magnetic stirrer is too weak to stir a suspension of silver salt, so I had to use JJ-1 overhead stirrer with Teflon paddle. The stirrer has a sealed guide, but when used, the paddle falls off after a short while. The stirrer is of typical chinese quality standard unfortunately.

So I could not use mag. stirring or stirrer guide, hence the flask had to be open and using reflux condenser would not make sense. Maybe this was the issue, but the reaction temperature was cold.

I forgot to continue reaction for further hour in an ice bath so maybe this was the time where bromoethane evaporated. Still does not explain the amount of silver bromide though... maybe bromoethane it turned preferentially into ethyl nitrite and evaporated?

IMG_20181116_061356.jpg - 42kB
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Tsjerk
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[*] posted on 16-11-2018 at 11:57


Did your reaction heat up during addition of the ethyl bromide?

If not, start by running it for a couple of days. I don't see why this reaction should stay cold, you can let it come up to RT after addition. as long as the reaction is sealed, RT sounds fine for this reaction. It has to be stirred though.

Edit: I just saw Chemplayers video, I would use acetone, not ethanol to dry the silver nitrite, acetone comes anhydrous from the hardware store. Also aceton is not hygroscopic by itself, any salt will be dry in minutes if it was washed with acetone. As silver nitrite is not hygroscopic the desiccator seems unnecessary.

[Edited on 16-11-2018 by Tsjerk]
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[*] posted on 16-11-2018 at 12:13


If nitroethane forms an azeotrope with ether I could have partially gone with it
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nimgoldman
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[*] posted on 16-11-2018 at 12:14


Quote: Originally posted by Tsjerk  
Start by running it for a couple of days. I don't see why this reaction should be cold, as long as the reaction is sealed, RT sounds fine for this reaction. It has to be stirred though.


I see. I will try the silver nitrate test for reaction completion (adding sample of reaction mixture into a dilute solution of silver nitrate - clouding would indicate incomplete reaction).

Sealing would be a problem with the cheapo stirrer. I will maybe look for a stronger magnetic stirrer and report the results back in the thread.
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Tsjerk
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[*] posted on 16-11-2018 at 12:20


Sorry, I heavily edited my post... It changed a bit, but essentially it is the same.
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nimgoldman
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[*] posted on 16-11-2018 at 15:56


I found my ethanol is only 98%, it still should have drying capability but I am not sure if the little water could have been left in it and caused problems.

Using dry acetone seem to be a better choice. It's more accessible to me than the abs. ethanol and it's safer as presence of residual silver fulminate in the precipitate has been reported to cause explosion (Armarego, Wilfred LF. Purification of laboratory chemicals. Butterworth-Heinemann, 2017)

There are possible azeotropes of nitroethane (e.g. with water, ethanol), but neither below the temperature used for distillation (source: Nitroethane, ANGUS Chemical Company Technical Data Sheet)

Slight heatup occured when adding bromoethane, but since I used saline bath, it never went above 5 °C. The whole addition took about 50 minutes. None should have evaporated, but since the stirring was strong, it might evaporated through the necks of the flask.

ChemPlayer removed the ether with simple water bath and I used distillation with thermostat-controlled waterbath (going slowly from 35 °C to 60 °C). The nitroethane residue made gluey bubbles and looked like evaporating - not sure if it will eventually evaporate even at 60 °C. Is nitroethane so volatile?

Maybe adding fractionating column would be a good idea.

Plummer and Drake ("An Improved Procedure for Preparing Primary Nitroalkanes by the Victor Meyer Reaction." Journal of the American Chemical Society 76.10 (1954): 2720-2722.) used petroleum ether as the solvent, which might be more convenient than diethyl ether due to higher boiling point.

So the improvements:

- seal the necks
- use reflux condenser
- dry silver nitrite with anhydrous acetone
- try pet ether as solvent
- run the reaction for considerably longer time, test for completeness
- use fractionating column when distilling off ether, check for vapour temperature for possible mixed fractions
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[*] posted on 16-11-2018 at 18:03


IMHO the ideal solvent would be ethyl iodide. The 1954 JACS articles with OK yield of nitrobutane display a conspicuous absence of lower bromides. Meyer tried and failed 80 years earlier.



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nimgoldman
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[*] posted on 16-11-2018 at 18:33


Quote: Originally posted by S.C. Wack  
IMHO the ideal solvent would be ethyl iodide. The 1954 JACS articles with OK yield of nitrobutane display a conspicuous absence of lower bromides. Meyer tried and failed 80 years earlier.


The reason I have not followed this method is because it produces 50:50 nitroethane and ethyl nitrite. Unfortunately, I have absolutely no use for ethyl nitrite.

Rhodium's nitroethane syntheses colllection mentions 80% yield (when using the DMF modification) and the only difference with iodoethane being shorter reaction time. This made me think the yield of Victor Meyer will be similar or same with bromoethane and iodoethane, the reaction time being the only difference.

ChemPlayer's yield with Victor Meyer and iodoethane is 57% (some can reach up to 80%) which is still at leat 7% better than 50% with using iodoethane directly. That 7% can be a difference of 10 or 20 milliliters (after reasonably scaling up the reaction), which is a lot for such a precious solvent (at least for me as an amateur).

Finally, iodine is much harder for me to get than bromide salts (and more expensive, too). The good thing is that it can be quite easily recycled.

It seems I will have to ditch the "bromine path" to nitroethane and switch to iodine.

I don't know why so many sources treat bromoethane and iodoethane equally and even mention one can be substitued for the other, since this is not really true. Wikipedia in its "Nitroethane" article even mentions chloroethane:

Quote:
Alternatively, nitroethane can be produced by the Victor Meyer reaction with haloethanes like Chloroethane, bromoethane, or iodoethane with silver nitrite in diethyl ether or THF.


I guess this is theoretical stuff. Yes, chloroethane will probably work too, but unfortunately no one mentions reaction times will be unbearable and yields will be next to nothing.

[Edited on 17-11-2018 by nimgoldman]

[Edited on 17-11-2018 by nimgoldman]
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[*] posted on 16-11-2018 at 23:44


Try the a-bromopropionic acid , Sodium Nitrite route to nitroethane.
Its not as much work as the victor meyer synth and yields are ok too.




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[*] posted on 17-11-2018 at 07:55


Quote: Originally posted by nimgoldman  
Quote: Originally posted by S.C. Wack  
IMHO the ideal solvent would be ethyl iodide. The 1954 JACS articles with OK yield of nitrobutane display a conspicuous absence of lower bromides. Meyer tried and failed 80 years earlier.


The reason I have not followed this method is because it produces 50:50 nitroethane and ethyl nitrite. Unfortunately, I have absolutely no use for ethyl nitrite.


[Edited on 17-11-2018 by nimgoldman]

[Edited on 17-11-2018 by nimgoldman]


Why do you feel that ethyl nitrite would not be produced using bromoethane, assuming bromoethane would work with this synth?

Maybe I am just dull in the head but I would have thought the reaction path would have been the same from either the bromoethane or iodoethane.
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[*] posted on 17-11-2018 at 15:18


Quote: Originally posted by Tsjerk  
I just saw Chemplayers video, I would use acetone, not ethanol to dry the silver nitrite, acetone comes anhydrous from the hardware store. Also aceton is not hygroscopic by itself, any salt will be dry in minutes if it was washed with acetone. As silver nitrite is not hygroscopic the desiccator seems unnecessary.


Acetone does evaporate quickly, but its temperature drops fast when it does so. Cakes of acetone washed solids left in open air can get cold as ice, condensing atmospheric moisture and drying slowly. Drying under vacuum is good but you will need active heating or a long amount of time at r.t. to drive off the acetone.

At least this has been my experience.
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[*] posted on 18-11-2018 at 01:40


Quote: Originally posted by happyfooddance  

Acetone does evaporate quickly, but its temperature drops fast when it does so. Cakes of acetone washed solids left in open air can get cold as ice, condensing atmospheric moisture and drying slowly. Drying under vacuum is good but you will need active heating or a long amount of time at r.t. to drive off the acetone.

At least this has been my experience.


Yes, you are right, but when working with small batches, say less than 50 grams, this shouldn't be a problem. Especially when you take of most acetone while vacuum filtering it won't get so cold it condenses water from air.
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[*] posted on 18-11-2018 at 11:52


Quote: Originally posted by morganbw  
Why do you feel that ethyl nitrite would not be produced using bromoethane, assuming bromoethane would work with this synth?

Maybe I am just dull in the head but I would have thought the reaction path would have been the same from either the bromoethane or iodoethane.


It will but not as much as the pure iodoethane approach, since the reported yields are over 50% (at least 57%) while using just iodoethane leads to 50% yield according to literature.

Bromoethane should work just fine too, only having longer reaction time (I hope).

---

nux vomica, capturing the ethyl nitrite to synthesize more nitroethane is a good idea, thanks.
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[*] posted on 18-11-2018 at 17:46


Would the reaction conditions need to be acidic to form ethyl nitrite as the main product, or does it not matter? It seems that the prep that I recall from the top of my head involves adding acid to an alcohol/metal nitrite solution in water to form alkyl nitrite. Was the bromoethane neutralized, or left acidic? Just an idea.

I wonder what would happen if excess ethanol was added directly to chilled liquid N2O3...




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