White Yeti
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Radical chemistry.
I recently looked up how photochemical smog was produced, and one set of equations caught my attention:
'OH+ CO-->H+ CO2
H+O2-->HO2
HO2+ NO-->'OH+ NO2
So in a sense, the hydroxyl radical catalyses the formation of NO2 from NO and O2. But in real life, how are hydroxyl radicals formed/ made?
Are they as short lived as the OH- ions and H3O+ ions that form when water self dissociates? If so, how do they have time to react?
Also, if I where to make these radicals on purpose just to demonstrate the phenomenon, how would I go about doing that?
Thanks.
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DJF90
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You might expect photolysis of hydrogen peroxide to yield hydroxyl radicals. In the atmosphere, it could be formed by hydrogen abstraction from water
molecules by another radical. Radicals are generally very short lived - they are reactive intermediates like carbenes and arynes. However there are
some very persistant radicals, that are stabilised electronically (as in Fremy's salt) and/or sterically (as in TEMPO). You can form hydroxy radicals
in the lab using Fenton chemistry - Ferric chloride dissolved in 3% hydrogen peroxide will chew up organics due to the formed hydroxy radicals.
An interesting point is that the oxidation of nitric oxide by molecular oxygen is a reaction that follows third order kinetics.
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bfesser
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Radicals will travel farther in gas phase than in solution without reactive collision. In the upper atmosphere UV is likely more intense.
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White Yeti
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Ok. Thank you very much.
I have a few more questions.
In order to make an HO2 radical, is it possible to take a solution of 'OH radicals and O2 and irradiate it with UV rays? Would the free oxygen that
results from the photolysis of O2 react with 'OH to yield HO2?
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