Keras
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Acetanilide nitrosation
Folks,
In the wake of Apoptosis’s (™) video on acetanilide nitration, I was wondering if nitrosation instead of nitration was possible. The aim is to
convert the nitroso- product (a priori 4-nitrosoacetanilide) to 4-aminoacetanilide using sodium hydrosulfite as reductant.
Problem: contrarily to phenol, whose benzene ring is readily activated by the lone oxygen pair, the amide group is only mildly activating. As a
result, when dissolved in glacial acetic acid, with addition of methanesulphonic acid and cooled down to below 0°C, the reaction with sodium nitrite
is almost inexistent. The solution slightly turns yellow with the very first drops, then gradually changes to greenish, which I attribute to the
formation of free, bluish nitrous acid, then… the mixture froths up. Bubbles inside the frothing are full of nitric oxide, when they burst in the
air they immediately release nitrogen dioxide. The gas must be produced by the slow decomposition of the nitrous acid, probably unreactive towards
acetanilide at that temperature.
As a result, after dealing painfully with the froth, and letting the erlenmeyer warm up to room temperature, I ended up with a yellow mixture, but no
crystals. I decided to go ahead and add sodium hydrosulfite directly, and – pleasantly enough – the yellow tinge disappeared and a characteristic
smell of aromatic amine at once escaped. With the mixture set in the freezer, I got a precipitate of flaky white crystals, which I hope are
4-aminoacetanilide. But the yield is poor at best.
Question is: how to conduct the nitrosation to get a better yield of the nitroso- product? Would cooling to ~ 10 °C be enough (instead of below 0
°C). Wouldn't nitrous acid be too short lived to work properly at that temperature?
Or, is it simply impossible to do, and nitration should be attempted in all cases instead?
Thanks!
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clearly_not_atara
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IIRC nitrosation of this substrate goes to the N-nitrosoamide using N2O3 or similarly powerful nitrosation reagents.
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Keras
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You mean that instead of obtaining NO-Φ-CONH₂, the nitrosation proceeds to yield Φ-CONH(NO)? [EDIT: And then after reduction, to
phenylacethydrazide Φ-CONHNH₂?]
That’s a possibility I didn't account for, clearly.
[Edited on 7-10-2025 by Keras]
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clearly_not_atara
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I have heard of the generation of AcN(NO)Ph this way, yes. However, IIRC I looked into this specifically in hopes of finding a prep of phenylhydrazine
and it seems that virtually all reduction conditions return the acetanilide with no detectable hydrazine. This is why I inverted the question and
ended up learning about the prep of indole from nitrosobenzene:
https://www.sciencemadness.org/whisper/viewthread.php?tid=16...
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Keras
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Phenylhydrazine normally is made by diazoting aniline, right? And reducing the diazonium salt with hydrosulfite.
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kmno4
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Just a handful of informations from 1876 (in German) year 
Attachment: nnitroso.pdf (70kB)
This file has been downloaded 82 times
Слава Україні !
Героям слава !
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Keras
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Thanks!
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