I’m working on a synthesis problem that requires me to draw the arrow mechanism for the second half of the Sandmeyer reaction. Basically it’s the halogenation of an aryl diazonium compound. Typically it’s done using a copper catalyst, but it can also be done using just potassium or sodium iodide. Problem is, I can’t find any reference showing how this works in an arrow pushing mechanism. Does anyone know where I could find an example to show me how it works?

Conversion of aryl diazonium to aryl iodide

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    $\begingroup$ Well, it's probably SN1 so not much of writing ;) $\endgroup$
    – Mithoron
    Commented May 6, 2018 at 23:15
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    $\begingroup$ I was taught that it's a radical mechanism, and that makes sense because if it was a pure SN1 then this would work with chloride ion too, but you need CuCl (not just NaCl) for that $\endgroup$ Commented May 6, 2018 at 23:22

1 Answer 1


It follows a radical mechanism (SET = Single Electron Transfer) enter image description here

  • $\begingroup$ Your source for this? $\endgroup$
    – Waylander
    Commented May 7, 2018 at 18:33
  • $\begingroup$ I found the image online, but I studied this mechanism on the course of Mechanisms for Organic Reactions. $\endgroup$ Commented May 7, 2018 at 18:48
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    $\begingroup$ Where does the .I2- come from in 1)? $\endgroup$
    – Waylander
    Commented May 7, 2018 at 19:51
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    $\begingroup$ @Andrea can you tell where the image was found so we can trace it? $\endgroup$ Commented Jun 6, 2018 at 22:50
  • $\begingroup$ @Waylander once the mechanism is going then the di-iodine radical anion is generated by Step 3. But yes, we need a startup path. I would guess the cation reacts with iodide ion to generate di-azo and mono-iodine radicals, then the latter adds another iodide ion while the former jumps into Step 2. $\endgroup$ Commented Sep 4, 2018 at 22:51

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