MadSci Network: Chemistry

Re: Advantages of the Fenton reagent?

Date: Wed Sep 8 14:54:51 1999
Posted By: Jeremy Starr, Grad student, Organic Chemistry
Area of science: Chemistry
ID: 936667123.Ch

Hello Lee,

The Fenton reagent is a mixture of Fe(II) and hydrogen peroxide. The Fe(II) 
reacts with the peroxide to form Fe(III), a hydroxyl radical, and a 
hydroxide anion. If the hydroxyl radical is not trapped by a species that 
can react with it, another Fe(II) will react with it to form another 
Fe(III) and another hydroxide anion. This is eqivalent to what is shown 
schematically below _inside_ the dashed border. 

The Haber-Weiss cycle is inclusive of the Fenton reaction but regenerates 
the Fe(II) by oxidation with a peroxyl radical (or dioxygen radical anion 
if the peroxyl radical first loses a proton) to give oxygen gas as the 

Whether or not a Fenton reaction becomes a Haber-Weiss cycle depends on 
stoichiometries of the reactants. Qualitatively, if there is a lot of 
hydrogen peroxide and little Fe(II) then the Haber-Weiss cycle is more 
likely to take place, whereas, if there is very little hydrogen peroxide 
and lots of Fe(II) then the Fenton reaction alone takes place. The acidity 
of the reaction mixture is important as well and should be kept well below 
7 (therefore acidic). In fact, "available hydroxyl radical" can be 
calculated based on the pH of the reaction. 

The advantage of the Fe(III) process is that it _must_ go through the 
Haber-Weiss cycle and therefore must be catalytic in iron. For any process 
that requires a heavy metal it is best (for toxicity, waste disposal and 
cost reasons) if the heavy metal can be present in as little quantity as 
possible thus making the catalytic method better. 

I hope this info was helpful

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