killswitch
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Transesterification
I encountered this phenomenon firsthand when trying to purify picric acid via recrystallization from hot 95% ethanol. There was a distinct smell of
trace NO2, and a milky blob resembling crude nitroglycerin formed and sank to the bottom. I obviously don't have a NMR available at my place of
residence, but would I be correct in assuming that this was ethyl nitrate? I thank Schrodinger that I had not used methanol. I used a very long
plastic pipette to gingerly remove the blob and dilute it with acetone before burning it outside.
Has anyone else had unfortunate encounters with this phenomenon? What steps should be taken to minimize it? And what ratio of 2,4 to 2,6 TNP is likely
in solution?
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Motherload
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I doubt there was enough H2SO4 and HNO3 present in the Picric acid to form ethyl nitrate. Especially if the Picric acid had a couple of cold water
washes.
Ethyl Nitrite might have formed but not in significant quantities.
Was your Picric acid made from pure Phenol ?
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Ral123
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How does your blob behave like? How does your remaining "picric acid"? behave like?
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DraconicAcid
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Quote: Originally posted by killswitch  | I encountered this phenomenon firsthand when trying to purify picric acid via recrystallization from hot 95% ethanol. There was a distinct smell of
trace NO2, and a milky blob resembling crude nitroglycerin formed and sank to the bottom. I obviously don't have a NMR available at my place of
residence, but would I be correct in assuming that this was ethyl nitrate? I thank Schrodinger that I had not used methanol. I used a very long
plastic pipette to gingerly remove the blob and dilute it with acetone before burning it outside.
Has anyone else had unfortunate encounters with this phenomenon? What steps should be taken to minimize it? And what ratio of 2,4 to 2,6 TNP is likely
in solution? |
I'm not an organic chemist, but ethyl nitrate wouldn't have been my first guess. But I suppose it would depend on what exactly was in your picric
acid before you started recrystallizing it.
You can't have 2,4 or 2,6 TNP. Trinitrophenol will be 2,4,6. Dinitrophenol will be mostly 2,4-DNP (I can't find a cite at the moment, but I do
recall an undergraduate lab where we nitrated chlorobenzene to get the pure 2,4-nitro product; any 2,6 was a minor impurity that was not isolated).
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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killswitch
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The blob behaved just like nitroglycerin, only a lot less viscous.
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Ral123
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It ignites a little difficult, burns fast with knida gray color?
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Hennig Brand
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I don't think you are observing transesterification. Picric acid is a nitro aromatic not a nitric ester. Also, I don't think aromatic nitrations are
in most cases considered reversible, unlike the reversible esterification reactions producing nitroglycerine, nitrocellulose or ethyl nitrate for
instance. There are often resinous products that separate out as a blob during a picric acid recrystallization, but these are normally yellow to red
in color, not milky white from my experience and from reading what others have to say. To tell the truth though, I think I have seen resinous blobs
before that were very pale yellow, almost white, during a recrystallization.
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