2
$\begingroup$

Can anyone explain why the acylation of ferrocene produces the following results:

Ferrocene + acetic anhydride + AlCl3 ==> mono-acylated ferrocene

but:

Ferrocene + acetyl chloride + AlCl3 ==> di-acylated ferrocene (an acyl group on each ring).

I have seen various statements confirming this, but not a single explanation for it! My current thoughts are that it must be something to do with the carboxylic acid produced from the reaction with the anhydride somehow hydrogen bonding/blocking the second site, but not really sure how it would work.

Any explanations greatly appreciated!

$\endgroup$
  • $\begingroup$ Could it also maybe be that the HCl produced by the first acetyl chloride-catalyzed acylation is a stronger acid than the HOAc produced by the acetic anhydride acylation, and that the resulting acid could promote the 2nd acylation? (Honestly not sure, just a thought...) $\endgroup$ – Curt F. Feb 14 at 2:02
1
$\begingroup$

One factor: since ferrocene is covalently bonded, the rings "communicate" with each other via the molecular orbitals passing through the iron atom. Thus the acetyl group placed on one ring not only deactivates that ring, but to some extent deactivates the second ring as well. The second ring would still be attacked preferentially in the second stage but may require a stronger electrophile, which acetyl chloride is compared with acetic anhydride.

|improve this answer|||||
$\endgroup$
  • 1
    $\begingroup$ Thank you - this seems to make sense! $\endgroup$ – gd99 Feb 14 at 11:28

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.