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how reaction actually happens[how reaction actually happenshow I expect the reaction to happenquestion image

I wonder is it possible for aniline to undergo Reimer-Tiemann reaction just like phenol? What is the problem in that? How to compare rates of carbylamine reaction and RTF?

user55119
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Ritil
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    Alternatively, how might dichlorocarbene react with the nitrogen of aniline? – user55119 Jun 26 '22 at 14:38
  • Yes, how will dichlorocarbene react with aniline – Ritil Jun 27 '22 at 07:19
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    As a recent member of ChemSE, you should be aware that you are expected to make some effort to solve the problem before you can expect to have help. Show me what your thoughts are in the next two days and then I'll post an answer. On homework questions. – user55119 Jun 27 '22 at 14:37
  • https://chemistry.stackexchange.com/questions/98188/in-reimer-tiemann-reaction-why-does-phenol-attack-the-carbene-from-ortho-positio/98197#98197. Also see this. They say that carbon is less electronegative than oxygen (and also nitrogen) thus it is more nucleophilic than them. Also consider that stable intermediate formation – Ritil Jun 28 '22 at 19:35
  • Related paper: https://www.sciencedirect.com/science/article/abs/pii/S0040402001970966 – Nilay Ghosh Jul 07 '22 at 05:02
  • I can't access it for free – Ritil Jul 07 '22 at 05:18

1 Answers1

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The reaction of aniline with chloroform and base (Hofmann isonitrile synthesis, 1867)[1] predates the Reimer-Tiemann reaction (1876)[2] with phenol by 9 years. Strong base reacts with chloroform (1) to form dichlorocarbene (3). The sequence 3 $\rightarrow$ 9 leads to phenylisonitrile (IUPAC: isocyanobenzene). The electron pair on nitrogen in structure 6 can also, and likely preferably, be used to eliminate chloride leading to chloroimine 7.


The course of this reaction is notably different from the Reimer-Tiemann reaction. While the mechanism explains the results, it does not answer why reaction doesn't occur on the aromatic ring. Consider the reaction of phenoxide (10) with dichlorocarbene (3) using a similar mechanism to afford phenylformate (15). This ester is particularly labile to base with the irreversible formation of phenoxide. This process is a dead end; eventual reaction on the ring occurs irreversibly.

One might ask why a similar course of events doesn't occur with base and chloroimine 7 leading to N-phenylformamide (16). N-Phenylformamide is less labile toward base than phenylformate but, if N-phenylformamide is formed, it would be capable of being dehydrated by dichlorocarbene to form the protonated phenylisonitrile 8 just as reagents such as $\ce{POCl3}$ do. I leave it to the reader to write a mechanism for the reaction in the red box.

In summary, both aniline and phenoxide may react kinetically on their respective heteroatoms, except that in the case of oxygen, the reaction is non-productive providing an opportunity for an irreversible reaction on carbon.

user55119
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  • Thanks for the explanation. I think there should not be a hydrogen bonded to the oxygen atom in product number 11 – Ritil Jul 03 '22 at 17:45
  • What do you mean by red box? I can't see any place to fill anything – Ritil Jul 03 '22 at 18:03
  • I have completely understood your explanation but the question is why does not Ortho formyl aniline forms? Like we say that carbon is less electronegative than oxygen and nitrogen and thus more nucleophilic, then why does not it attack? – Ritil Jul 03 '22 at 18:40
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    Ritil: I corrected the error in structure 11. As to your question as to why ortho-C-formylation does not occur, my Answer may not be THE answer but it is AN answer. – user55119 Jul 06 '22 at 00:12