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Is there a way simple way to turn iron(III) acetate into iron(II) acetate or vice versa?

Edit (as per answer below): an oxidiser like hydrogen peroxide will turn iron(II) acetate into iron(III) acetate. A reducer (not sure what household product) will do the reverse.

Some background: my partner soaks scrap cast iron in white vinegar for several weeks and then uses the resulting liquid as a mordant for dyeing. According to wikipedia's page on iron acetate, soaking iron in vinegar creates a mix of iron(II) acetate and iron(III) acetate. As I understand it, the oxidation state of the iron used as a mordant effects the colour of the dye on the fabric. As such, it would be nice to be able to experiment with just iron(II) or just iron(III). Is this possible to achieve using household chemicals?

Even more background: The dyeing process is soak fabric in mordant water. Dry fabric. Wrap fabric with leaves and place in boiling water. Unwrap and admire beautiful prints :)

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  • $\begingroup$ Did you use hydrogen peroxide in the synthesis or just iron + vinegar? $\endgroup$
    – airhuff
    Jan 22, 2017 at 3:24
  • $\begingroup$ Just iron and vinegar. I think that iron(III) predominates because the water is a red-brown. Would h2o2 force the mixture to iron (III) and a reducing agent (not sure what) force it to Iron(II)? Or am I misunderstanding the chemistry? $\endgroup$
    – vorpal
    Jan 22, 2017 at 9:52
  • $\begingroup$ No, you're not misunderstanding anything, that is exactly my line of thought. I think introducing hydrogen peroxide at the right time in the right conditions will push the oxidation to iron(III). It's probably something you can just experiment with, carefully. I'd say boil the solution in peroxide but I don't know if you have a fume hood, etc. The tougher one is the reduction. Anything that burns in air is being oxidized, and thus is a reductant to some degree. I don't know if sawdust or something like that would be a strong enough reductant, I seriously doubt it. I'll think on it some more. $\endgroup$
    – airhuff
    Jan 22, 2017 at 20:25

1 Answer 1

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You need a reducing agent that will reduce iron(III) back to iron(II). Actually finely distrubuted iron could be the best reagent to do this, as it will not introduce any contaminants. The reaction taking place is 2 Fe(III) + Fe = 3 Fe(II).

Of course the iron used should not be rusty. I am not sure that you can easily get hold of fine iron powder, but I would give a try boiling the vinegary solution with fresh iron shavings or steel wool and as little contact with air as possible. The color change should be visible to greenish from the red-brown of the iron(III) acetate.

Actually, during dissolution of Fe in acetic acid you should get iron(II) acetate predominantly until the Fe runs out, but usually scrap iron is covered by iron(III) oxides/hydroxides, and these also dissolve in the vinegar. When the iron(II) solution is in contact with oxygen in air, it oxidises rather quickly. It is a good idea to start with a batch that was not left standing for weeks.

Other reducing agents work quicker than iron (e.g. tin(II) salts or zinc powder), but these introduce other products that would interfere with your dyeing.

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