A new synthetic route to nitromethane
Quite a long time ago (about two years ago), I noticed some interesting reactions involving acetic acid. At the time, I had a rather fanciful idea of
attempting low-temperature nitrosation of acetic acid, even though I knew that the carboxyl group of acetic acid is not sufficient to activate its
α-hydrogen for attack by a relatively weak electrophile such as the nitrosonium ion. However, when I added acetic acid to sodium nitrite, I still
observed a pale blue coloration, which is a very characteristic feature of nitro–nitroso compounds. When I subsequently added 45% nitric acid, the
color became extremely intense—a very deep blue, even deeper than that of the tetraamminecopper(II) ion—which further convinced me that a
nitro–nitroso compound had indeed formed.
However, its behavior differed from what is typically reported in the literature. First, upon addition of a strong base, instead of forming the
nitroximide salt I had expected—usually accompanied by a distinct red coloration—the color faded almost immediately, as if the reaction had never
occurred. I suspect that after the nitroximide salt formed, it rapidly eliminated nitrite to give fulminic acid or some other product. Unfortunately,
I currently lack the proper analytical tools to verify this (having an IR spectrometer would have been ideal).
Later, I also tried omitting nitric acid and instead using hydrogen peroxide as the oxidant, in order to prevent further nitration. After the
reaction, the solution again lost its color, and a very thin oily layer formed. This layer was indeed flammable, which made me suspect that it might
be nitromethane. The flame, however, was slightly yellow, likely due to the presence of sodium ions.
Unfortunately, two years have passed and I have lost the video recordings from that time, so I am unable to share footage of the combustion.
Nevertheless, I still consider this to be a very important reaction, especially because of its potential to form nitroximic acid. If an additional
oxidant such as peracetic acid were added to the deep blue solution, it might indeed form a dinitro compound, although the stability of such a species
would be poor and it might be difficult to observe directly.
If I have time, I may try to reproduce this reaction later this month or next month, although I might have overloaded myself with too many tasks this
month and end up postponing it again. You are also welcome to attempt reproducing this reaction yourself—but of course, I take no responsibility for
it
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