I want to determine rate of Fenton reaction with different concentration of $\ce{Fe^2+}$. These are some questions that I have encountered:

  1. How long does it usually take for the reaction to complete?

  2. What concentration of $\ce{Fe^2+}$ is usually used for the reaction?

  3. I am planning to use titration of $\ce{H2O2}$ with $\ce{KMnO4}$ to determine the rate of reaction. Is it possible to quench to reaction mixture by adding an excess of EDTA solution and would it affect the titration?


How can I determine the rate of Fenton reaction? I proposed to titrate $\ce{H2O2}$ with $\ce{KMnO4}$ to determine change in $\ce{H2O2}$ as a mean of determining rate of reaction. However, I realised that $\ce{KMnO4}$ would also react with $\ce{Fe2+}$, so I need to either find another way to measure the reaction rate or find a way to remove all $\ce{Fe2+}$. Also, I am not sure if there would be any reaction between $\ce{KMnO4}$ and the hydroxyl radicals.

I am also wondering about adding in some wastewater and determine the before and after COD to determine the rate of reaction. However, I am wondering if the water that don't really have high COD (as opposed to the industrial wastes used in other papers) would result in a very slow reaction rate. Also, it seems like the part involving oxidizing by hydroxyl radicals is very exothermic. If I don't want to add $\ce{H2O2}$ bit by bit to control rate of reaction, is it OK?

Do I have to add acid to $\ce{Fe2+}$ and $\ce{H2O2}$ for the reaction to occur?

Is it necessary to add $\ce{H2O2}$ bit by bit, if so how much should I add at each turn?


This is only a partial answer:

I am not sure about which step you're looking for or the substrate of your reaction, but the Fenton-based chemistry I work with is extremely fast. I use it to (supposedly) form a methyl radical from DMSO which then reacts with an α-iodoester to form another radical.

Literature suggests I add brine immediately after I've completed the hydrogen peroxide addition and work it up from there. Truth be told, I usually give it a few minutes, but the reaction is certainly quite fast. The whole process takes me less than 5 minutes, and if I wasn't using DMSO and skatole (so smelly), it would be my favorite reaction of the ones I do.

I use iron(II) sulfate heptahydrate as my catalyst, and I use 0.5 equiv. relative to the iodide. It ends up being about 0.1 g per milliliter of solvent.

As for the peroxide titration, I use a decent excess, so I've never needed to titrate it. That is why I said this was a partial answer. I will say this: don't quench large amounts of hydrogen peroxide with sodium thiosulfate at room temperature. You end up forming sulfuric acid in aqueous solution. Very exothermic (like the water in the flask can start boiling in your hand).

  • 1
    $\begingroup$ For quenching part, I suggest ethanol, cheap and really effective. I always used Fe2SO4.7H2O and 30%~ peroxide and a couple ml of ethanol generally helped to cease reaction less than one minute, though after vigorous part ended. $\endgroup$ – Güray Hatipoğlu Apr 14 '18 at 18:42

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