Elimination of Nitrite Esters (in EtNO2 synthesis)
Hello all. I've come to you with concerns over the elimination of alkyl nitrite esters that are formed during the synthesis of nitroalkanes.
More specifically, I am interested in the reaction detailed in the 1944 article "Preparation of Nitroethane" by McCombie, Saunders, and Wild in the
Journal of the Chemical Society. I have attached the paper (as a PDF).
Here is the experimental writeup-
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Initial run - Into a stoppered bottle was placed a mixture of diethyl sulfate (120g) and sodium nitrite solution (120g in 160ml of water.) The bottle
was shaken mechanically for 20 hours, the pressure being released at intervals. The contents were then poured into a separating funnel, and the upper
layer separated, dried over calcium chloride. and distilled at 14 mmHg, the distillate up to 60°C being collected (the residue, ca. 230g., consisted
of ethyl sulphate and was used again). The distillate was fractionated at atmospheric pressure, and the fraction of bp 114-116°C collected. This was
shaken with water, dried over calcium chloride, run through charcoal, and redistilled; bp 114-115.5°C. Yield, 17.7g. (31%, or allowing for recovered
ethyl sulfate, 43.5%).
Routine Run - A second experiment was then carried out using the same quantity of ethyl sulfate as above. The recovered nitrite solution (lower layer)
from the first run was concentrated by adding approximately 16 g. of sodium nitrite per 160ml of solution. Yield 26.4g (46%, or allowing for recovered
ethyl sulphate, 65%). For each additional subsequent run approximately 16 g. of nitrite per 160 ml of solution were added, although this represents a
rather diminishing concentration in view of the increased yield of nitroethane.
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Posts by Rosco Bodine describe the same process (I think, except he adds the use of a sulfanilic surfactant catalyst) where he describes a pyrophoric
byproduct created by distillation of the ethyl nitrite and nitroethane mixture. He recommends doing the vacuum distillation under inert conditions and
only releasing the vac to inert atmosphere after cooldown. Described in this post (http://www.sciencemadness.org/talk/viewthread.php?tid=4711#p...) and subsequent posts of his in the same thread.
He said the alkyl nitrite esters and nitrogen oxides form a pyrophoric byproduct that can result in explosion, etc.
Rosco may have been following a different procedure, because he used a surfactant catalyst and obtained a single phase in the end. McCombie's
procedure calls for removal of the aqueous NaNO2 soln. (lower layer) and then vacuum distillation of the upper layer.
Still, the nitrite esters are a definite byproduct of the reaction (with the nitrite ion being the slutty reactant it is).
Now, in this OrgSyn writeup (http://www.orgsyn.org/orgsyn/prep.asp?prep=cv4p0724) on nitroalkane preparation, there is the following notation-
| Quote: | | 6. It is more difficult to remove an alcohol from the corresponding nitroalkane than it is to separate the nitrite ester and the nitroalkane. Minimal
exposure to a moist atmosphere is, therefore, desirable since anhydrous ether is hygroscopic and nitrite esters hydrolyze readily, especially if a
little acid is present. |
In their case, they didn't want the nitrite ester to decompose because the 1-octanol (hydrolysis product of octyl nitrite) was harder to separate from
the 1-nitrooctane than the octyl nitrite ester was.
Now, this leads one to believe that acidic H2O will decompose the nitrite esters.
So- if one was following McCombie's procedure...when you separate the lower aq. NaNO2 soln. from the organic layer (diethyl sulfate/nitroethane/ethyl
nitrite) and proceed to distill the organic layer...could you wash the organic layer with aqueous acid to hydrolyze the ethyl nitrite(prior to
distillation)? I am hoping this will help eliminate the nitrite ester distillation issue.
Sure you would likely get some diethyl sulfate hydrolysis (I think, considering monoethyl sulfate undergoes hydrolysis)- but shouldn't a decent wash
with dilute aq. acid help to hydrolyze the majority of the ethyl nitrite?
Any insight into this possible work-up is greatly appreciated. Thanks for your time and help.
-teragon
Attachment: McCombie-EtNO2 from Et2SO4.pdf (150kB)
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