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According to The Pearson Guide To Organic Chemistry For The IIT JEE by Atul Singhal, the reaction between $\ce{NOCl}$ and $\ce{CH3CH2-NH2}$ is as follows:

$$\ce{CH3CH2-NH2 + NOCl -> CH3CH2Cl + N2 + H2O}$$

But how exactly does the reaction proceed?

The first step (what I think) could be that $\ce{NOCl}$ dissociates into $\ce{NO+}$ and $\ce{Cl-}$ ions and then the $\ce{Cl-}$ ion attacks the amine group and replaces it by $\mathrm{S_N2}$ mechanism.

But according to paperplane.io (via the Internet Archive), a diazonium product is produced. Even though a diazo product is formed, how does it produce an alkyl halide according to my textbook?

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    $\begingroup$ If you know how to form a diazonium salt with NOCl (or HONO/HCl) then you are an SN2 reaction away from the answer. $\endgroup$ – user55119 Nov 27 '19 at 16:30
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    $\begingroup$ Please cite the textbook (as in 'according to my textbook'), or leave out that statement if it is not relevant. Always cite the sources you are using. $\endgroup$ – Martin - マーチン Nov 28 '19 at 16:17
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Why would the chloride ion attack the electron rich amine? The amine is the better nucleophile in the system, and will attack the $\ce{NO+}$. This gives a $\ce{RNH-NO}$ nitroso species which is then protonated on oxygen, loses water, and gives the diazonium cation. The resultant diazonium cation loses nitrogen rapidly and get attacked by chloride to give the primary alkyl chloride.

More can be read about this process here (which is where I sourced the reaction scheme) or by searching the term "nitrosation of primary amine"

Nitrosation of primary amine

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  • $\begingroup$ I don't understand how amine is a better nucleophile than chloride ion. $\endgroup$ – user85683 Nov 26 '19 at 11:29
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    $\begingroup$ @praig_ Well, what you don't understand? You have some serious misunderstandings there. Probably wanted to get too much while not knowing necessary facts. This is such fact. You can get amine from halide and ammonia, not otherwise (unless it's silyl amine) $\endgroup$ – Mithoron Nov 26 '19 at 23:58
  • $\begingroup$ @user85683: You may need to read this to start. $\endgroup$ – Mathew Mahindaratne Jun 1 at 21:12

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