I have a solution of potassium dichromate ($\ce{K2Cr2O7}$) and I want to convert it to a less toxic solution. What would be the best way to do this?

I was thinking of using the dissolved potassium dichromate as an oxidizer in the oxidation of alcohols to organic acids, to eventually produce the chromium(+III) ion (what is less toxic)

Or are there any other, easier methods?

  • 2
    $\begingroup$ >Or are there any other, easier methods? The cheapest and safest one is probably to use ethyl alcohol and some acid (acetic acid should work). $\endgroup$ – permeakra Mar 2 '14 at 15:39
  • $\begingroup$ Ethyl and any other alkohol is a bad idea. Reaction of chromate with alcohols is slow. Try FeII as Kwak recommends. $\endgroup$ – Georg Mar 3 '14 at 19:30

That looks like one way to reduce the dichromate ion which is known to be toxic. MSDS sheets indicate that potassium dichromate has category 1B carcinogenicity.

Another way I believe is to just start from an aldehyde and convert it into a carboxylic acid:

$$\ce{3RCHO + 2Cr_2O_7^- + BH^+ -> 3RCOOH + 2Cr^{3+} + 4H_2O} $$

Alternatively, one can put dichromate in acidic solution with iron:

$$\ce{Cr2O7^{2-} + 6Fe^{2+} + 14 H^+ -> 2 Cr^{3+} + 6 Fe^{3+} + 7H_2O }$$

Dichromate oxidizes $ \ce{Fe^{2+}}$ ions and produces $\ce{Cr^{3+}}$ and $\ce{Fe^{3+}}$ ions.

  • $\begingroup$ thanks! I'll use the iron oxidation method, however : would an acid such as acetic acid be sufficient for this redox reaction? $\endgroup$ – user2117 Mar 3 '14 at 7:33
  • $\begingroup$ @LievenB Hi, I believe so. As long as you have enough acetic acid to form a ratio of moles of 14:6:1, that would be sufficient for this redox reaction. $\endgroup$ – Jun-Goo Kwak Mar 3 '14 at 12:40

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