SunriseSunset
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Can't find a Peroxy acid mechanism of formation
This question is killin' me. I don't know why, but I cannot find an example of the mechanism to form ANY peroxy acid from ANY said carboxylic acid and
hydrogen peroxide... Am I being dumb or something, is the answer to this question really so simple that there are no mechanisms needed for examples
-___-
.. could really use some enlightenment thx
[Edited on 30-10-2015 by SunriseSunset]
Why do chemists call helium, curium and barium the medical elements?
because if you cant helium or curium, you barium! - Heimerdinger
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SunriseSunset
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IS there not a mechanism? is it a redox reaction?
Why do chemists call helium, curium and barium the medical elements?
because if you cant helium or curium, you barium! - Heimerdinger
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IrC
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Did you search? https://en.wikipedia.org/wiki/Peroxy_acid
"Several organic peroxyacids are commercially useful. They can be prepared in several ways. Most commonly, peracids are generated by treating the
corresponding carboxylic acid with hydrogen peroxide:
RCO2H + H2O2 <> RCO3H + H2O"
"Science is the belief in the ignorance of the experts" Richard Feynman
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SunriseSunset
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Yes of course lol but that doesn't say what's going on there. It's just a balanced equation, not a mechanism or the type of reaction it is. It just
says "treated" .. But what is really going on? o.O
I want to know if (aq)H2O2 dissociates to +H3O and -O2H in solution.
^ scratch this, H2O2 is too weak of an acid
I basically want to know if any of the conjugate species play a role as an intermediate species to form the final peroxy acid. such as the formate
anion?
I don't know the actual steps for the mechanism. It would be great to have this cleared up!!!!!
[Edited on 30-10-2015 by SunriseSunset]
Why do chemists call helium, curium and barium the medical elements?
because if you cant helium or curium, you barium! - Heimerdinger
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SunriseSunset
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Yes, it does at least tell me water is produced as a side product. But it doesn't say how the peroxy acid is formed. What I'm trying to say, is there
are no descriptive layouts to teach the formation of peroxy acids online. No mechanism information or steps involved.
Everything you search for just brings up the action of peroxy acid on alkenes to form epoxides, it's rather stressful
I can't figure out what is the electrophile or nucleophile
Maybe I'm making this more complicated than it needs to be. Could someone please help me
[Edited on 30-10-2015 by SunriseSunset]
Why do chemists call helium, curium and barium the medical elements?
because if you cant helium or curium, you barium! - Heimerdinger
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AJKOER
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Here are some brief comments and sources I cited on a recent thread, that you may find helpful:
Some specifics:
2 SO2 + 2 H2O = 2 H2SO3 = 2 HSO3- + 2 H+
HSO3- + •OH → •SO3- + H2O
•SO3- + O2 → •SO5-
•SO5- + HSO3- → •HSO5- + •SO3-
1/2 •SO3- + 1/2 •SO3- → 1/2 S2O6(2-)
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Net: 2 SO2 + H2O + •OH + O2 → 2 H+ + •HSO5- + 1/2 S2O6(2-)
[Edit] There is also possible a second reaction occurring for the 4th reaction above, but per the reaction constant found in Table 2 on page 135 of
"Heterogeneous and Liquid Phase Processes: Laboratory Studies Related to ...", edited by Peter Warneck, link:
https://books.google.com/books?id=vVvrCAAAQBAJ&pg=PA138&... ,it occurs only 4% of the time (.36/(.36+8.6)) given by:
•SO5- + HSO3- → SO4(2-) + •SO4- + H+
Note, the required hydroxyl radical employed above, can be provided either by the action of either sunlight or pulse radiation on N2O in the presence
of water, for example, as I have documented previously on SM. Also, hydroxyl radicals can be generated from the photolysis of aqueous nitrate or
nitrite per the reactions:
NO3-(aq) + hv → •NO2 + •OH (see http://pubs.acs.org/doi/abs/10.1021/ja073609 )
Or, NO2-(aq) + hv → NO + •OH
[Edited on 31-10-2015 by AJKOER]
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Darkstar
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I haven't studied this reaction at all, but my guess is that the H2O2 first disassociates into two hydroxyl radicals:
HOOH → HO• + •OH
Then one hydroxyl radical reacts with the carboxylic acid and removes its acidic proton, cleaving the oxygen-hydrogen bond homolytically and producing
a resonance-stabilized carboxyl radical and a water molecule:
RCOOH + •OH → RCOO• + H2O
Finally, the second hydroxyl radical combines with the carboxyl radical to form the peroxy acid:
RCOO• + •OH → RCO3H
Another possible route I thought of could be something like the carbonyl oxygen on the carboxylic acid getting protonated followed by a nucleophilic
attack on carbon by H2O2. The intermediate then undergoes a proton shift to convert one of the hydroxyl groups to an oxonium
group, which then leaves as water as a double bond forms between carbon and the other hydroxyl group oxygen. The charged carbonyl oxygen is then
deprotonated to give the peroxy acid.
If it helps you visualize what I mean, this is a post that I made recently in another thread showing the mechanism for Fischer esterifications. Just replace the ethanol in that
reaction with H2O2.
[Edited on 10-31-2015 by Darkstar]
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SunriseSunset
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| Quote: |
I haven't studied this reaction at all, but my guess is that the H2O2 first disassociates into two hydroxyl radicals:HOOH → HO• + •OH
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What could cause this to happen?
For how reactive the radical is, I would think it would take a lot to split that sigma bond
[Edited on 31-10-2015 by SunriseSunset]
Why do chemists call helium, curium and barium the medical elements?
because if you cant helium or curium, you barium! - Heimerdinger
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Darkstar
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Light, heat, harsh language . . . pretty much any input of energy can potentially cause the bond to cleave homolytically. The oxygen-oxygen single
bond in peroxides is extremely weak for the same reason the bonds in diatomic halogens are weak. The similar electronegativity between the two oxygen
atoms makes the sigma bond between them easily breakable. Why do you think organic peroxides are so unstable? Some of them seem to detonate if you so
much as even look at them the wrong way.
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SunriseSunset
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Ok.. That clears up a ton.. Thank you!! btw
Why do chemists call helium, curium and barium the medical elements?
because if you cant helium or curium, you barium! - Heimerdinger
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UC235
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I'm pretty sure that there is no radical mechanism at play here. Sulfuric acid is a commonly used catalyst (and would have no effect on a radical
mechanism). Probably the carboxylic acid is protonated, attacked at the carbonyl by peroxide's oxygen lone pair, followed by proton transfer and
elimination of water. The entire thing is reversible and mechanistically looks a lot like Fischer Esterification but with hydrogen peroxide in place
of an alcohol.
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Darkstar
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Quote: Originally posted by UC235  | | I'm pretty sure that there is no radical mechanism at play here. Sulfuric acid is a commonly used catalyst (and would have no effect on a radical
mechanism). Probably the carboxylic acid is protonated, attacked at the carbonyl by peroxide's oxygen lone pair, followed by proton transfer and
elimination of water. The entire thing is reversible and mechanistically looks a lot like Fischer Esterification but with hydrogen peroxide in place
of an alcohol. |
The Fischer esterification-esque route was the second mechanism I proposed. I do tend to agree that protonation followed by nucleophilic attack will
likely dominate in acidic media; however, I'm not entirely sure I'd completely discount the possibility of at least some kind of competing radical
mechanism. And it's just as reversible via a radical mechanism as it is a reverse Fischer esterification. (peroxy acid disassociates back into a
carboxyl radical and a hydroxyl radical. the carboxyl radical grabs a proton from water to give back the carboxylic acid and create a second hydroxyl
radical, and then two hydroxyl radicals recombine to give back H2O2)
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SunriseSunset
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Could this b about right?
Why do chemists call helium, curium and barium the medical elements?
because if you cant helium or curium, you barium! - Heimerdinger
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Darkstar
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Yes, that very likely could be the mechanism.
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SunriseSunset
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It's interesting though, with a strong enough carboxylic acid such as Formic acid, you don't need an acid catalyst. So formic acid would be the source
for Hydronium to kick this reaction off.
Why do chemists call helium, curium and barium the medical elements?
because if you cant helium or curium, you barium! - Heimerdinger
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