The Chemistry Shack
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Ethyl acetate from Ethanol and Piranha Solution? Possibly?
So when I was preparing Piranha solution (1/3 volume ratio of 30% H2O2 to 98% H2SO4) to clean some glassware, I decided to add it to a crucible full
of ethanol, expecting it to burst into flames. Much to my surprise, there was no fire, but the mixture did get quite hot and I also observed a fruity
smell (like peaches, if I remember correctly).
What I think happened, although I'm not entirely sure, is that the Piranha solution oxidized the ethanol to ethanoic (acetic) acid. The ethanoic acid
then reacted with more ethanol, catalyzed by the remaining H2SO4, in a Fischer esterification to make ethyl ethanoate (ethyl acetate).
I'm not entirely sure if this is what happened, but it seems like a pretty logical explanation. There was also some IPA and MIBK in the ethanol as
denaturants, so I may have formed some acetone via oxidation of the IPA, but I couldn't smell any acetone over the fruity smell. Also, I am unaware of
any oxidation reactions of ketones, so I don't know if the MIBK reacted.
It is also possible that some acetaldehyde formed, but I think this is unlikely because, despite the mixture reaching well over 100 C, I didn't notice
any boiling, and the acetaldehyde would have boiled out at those temperatures.
If you think I may have it wrong or have missed something, let me know!
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gdflp
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That's quite possible, a similar reaction using hexavalent chromium as the oxidant is described here http://www.orgsyn.org/demo.aspx?prep=CV1P0138
What you did is quite irresponsible however. Piranha solution is extremely reactive, and explosions have occurred when it came into contact with
residual organic solvent clinging to glass. Pouring it directly into ethanol is an extreme explosion hazard. Here is an example of such an incident
http://cenblog.org/the-safety-zone/2015/01/piranha-solution-...
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The Chemistry Shack
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I appreciate the concern over my safety, but I can assure you I performed the reaction very safely and treated the mixture as a high explosive, even
though it may not be evident from my original post. Fully expecting the crucible to shatter, I placed it in a pile of sand on top of aluminum foil (to
make the sand easier to dispose of). I used a small amount, only about 2 mL of ethanol, and added Piranha solution using a 2-foot long pipet, wearing
a face shield, lab coat, long pants, and close-toed shoes the entire time. Furthermore, after adding the solution, I waited 30 minutes before
disposing of the mixture in 2 L of NaHCO3 solution.
Also, the incidents you described did involve 1:1 Piranha solution, which is considerably more dangerous than the stuff I prepared (not to say the one
I made isn't dangerous, but still).
Also, the incident at Berkeley used a glass reaction vessel, and I make sure to never do explosive reactions in glass containers.
[Edited on 5-8-2015 by The Chemistry Shack]
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byko3y
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http://pubs.acs.org/doi/abs/10.1021/jo01270a082
"Oxidation of aldehyde in alcoholic media with the Caro acid"
The oxidation of alcohol to aldehyde can be explained by traces of chlorides
http://dx.doi.org/10.1021/ol300853z
"Direct and Selective Benzylic Oxidation of Alkylarenes via C–H Abstraction Using Alkali Metal Bromides"
However, this article is about free radical halogenation, and I'm not sure whether chlorine radical is capable of oxidizing the alcohol.
But there's an article actually describing the case of alcohol oxidation to aldehyde using chlorine radicals in gas phase
http://www.sciencedirect.com/science/article/pii/S1540748914... doi:10.1016/j.proci.2014.05.004
"Chlorine atom-initiated low-temperature oxidation of prenol and isoprenol: The effect of C=C double bonds on the peroxy radical chemistry in alcohol
oxidation"
I'm not sure how this corresponds with alcohol oxidation using HOCl + NaCl, but AFAIK molecular chlorine cannot oxidize alcohols in neutral-acidic
environment, despite the fact the following article states the Cl2 is an actual oxidant.
http://www.sciencedirect.com/science/article/pii/S0040403900... doi:10.1016/S0040-4039(00)00296-3
"Mechanism of the oxidation of para-substituted 1-phenylethanols with sodium hypochlorite in acetic acid"
http://link.springer.com/article/10.1007%2FBF02074151
http://link.springer.com/article/10.1007%2FBF02077027
and so on.
upd: another possibility for alcohol oxidation is ferric ions http://pubs.acs.org/doi/abs/10.1021/jo00158a024
[Edited on 5-8-2015 by byko3y]
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deltaH
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Your reaction mixture probably contains a mixture of many compounds. Also consider
ethyl hydrogen sulfate ('sulfovinic acid')
1,1-diethoxyethane ('acetal')
...
[Edited on 5-8-2015 by deltaH]
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kecskesajt
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The fruity smell could be because of acetaldehyde.
Organic solvents+piranha acid=Not good.few drop of acetone into piranha acid(dropped remotely) is explodes for me 10/7 times.
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deltaH
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If acetadehyde had formed, I would expect it to react further with the alcohol under the strongly acidic conditions and elevated temperature to form
1,1-diethoxyethane ('acetal'), itself strongly scented. The acetal is vulnerable to radical formation and certainly with Caro's acid about, it's not
going to neatly stop there, hence the ... in my list.
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clearly_not_atara
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Acetalization is not very favorable and acetaldehyde is much more volatile than ethyl acetate. It's not like all of a reactant reacts at once. He
probably smelled a mixture of acetaldehyde, ethyl ether, ethyl acetate, and various other products, like 2-butenal, two points for whoever figures out
how that'd form. Peracetic acid should also form.
[Edited on 6-8-2015 by clearly_not_atara]
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