[poolloop]

I've read something about "Ferrocene can be dissolved in concentrated sulfuric acid and recovered unchanged" and that make me wonder. Can you explain what is the reaction behind it? and it same for acetylferrocene?

Thanks for you answer 

[billnotgatez]

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[poolloop]

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Thanks Billnotgatez and I apologize for my mistake.
I think iron was oxidized to iron3+ Because sulfuric acid is oxidizing agent and then overall charge is +1 so, it can solute in aqueous solution. But for word "Recovered unchanged", I don't know what does it change. If reduction, what is the reducing agent.
Another possibility is sulfonation reaction but It can't explain solubility and reversibility.

[Borek]

Only thing I can think of is a protonation, simple reversible reaction. Any redox would make recovery difficult (if at all possible).

[opsomath]

This is surprising to me, since I'd expect one at least of the rings to become protonated. I guess that in the extremely non-nucleophilic environment of conc. sulfuric, the cyclopentadiene ligand remains attached to the iron (II) center without anything to displace it. But it surprises me that the alkene ligand does not in turn react by becoming protonated and degrading through that mechanism.