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Nicodem
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Quote: Originally posted by amazingchemistry  | | Ah, my understanding was that you had also performed this reaction. Or was it for monitoring purposes only? Perhaps the oxidation can be mitigated by
adding zinc dust, as per Vogel, resulting in a better yield. |
Yes, I did perform the reaction (see above), but as far as I know, only Jor reported a preparative experiment (you asked for isolated yields which
only be given for preparative experiments). For obvious reasons, I was more interested in studying the reaction, rather than preparing acetanilide
(which I had anyway). What I found is that it gives no side products and gives good conversion in mater of hours. You now have all the information
needed to easily develop a high yielding preparative version (both products can easily be separated and isolated).
I don't know exactly what you mean by adding zinc. There is no oxidation going on under proper reaction conditions. Actually, I observed no competing
reaction pathways.
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amazingchemistry
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Well, Jor started out with colorless aniline but reported his reaction mixture turned brown upon heating, and speculated (correctly I think) that this
was due to some amount of aniline being oxidized. Perhaps this is due to his reaction being solventless? In the section concerning acetanilide
preparation, Vogel presents several methods, and a small amount of zinc dust to is added to those that require some amount of reflux. He states that
it serves to both reduce colored impurities and prevent aniline oxidation. If no side reactions are observed with an appropriate solvent however, this
would be redundant. On the topic of the solvent, would acetonitrile or ethyl acetate be better? IIRC, you mentioned that IPA or some other alcohol
could also be used. Would you expect the choice of a polar over a non polar solvent to affect yield much?
Edit: On rereading, I did notice that, as you correctly pointed out, Jor heated his rather too much (above the melting point of the desired product)
could this explain the oxidation he observed?
[Edited on 15-6-2013 by amazingchemistry]
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