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From literature, it was described that fluorene can react with NCS and conc. HCl to produce the 2,7-diCl derivative. Please help me understand the mechanism.

  • 1
    $\begingroup$ I'd always suggest checking the original paper, rather than relying on the one-liner summary from SciFinder / Reaxys. Since you're on SciFinder, it shouldn't be too many extra clicks. $\endgroup$ Jul 6, 2020 at 11:52
  • $\begingroup$ The source of the reaction conditions presented by the OP is: thieme-connect.de/products/ejournals/abstract/10.1055/…, which predates the link provided by Waylander. $\endgroup$
    – user55119
    Dec 3, 2020 at 17:01

1 Answer 1


According to this paper here

it has been described recently that at very low pH ($\mathrm{pH < 3}$) $\ce{Cl2}$ functions as an active chlorinating agent

In the authors' view the system works by $\ce{NCS}$ oxidising chloride to chlorine which then provides $\ce{Cl+}$ as the chlorinating agent.


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