killswitch
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Unconventional aromatic nitrations
So I've learned from personal experience that phosphorus pentoxide and sodium nitrate in 98% sulfuric acid works as an admirable substitute for
oleum/99% HNO3 in aromatic nitrations.
However, P2O5 is expensive as hell.
So here are some thoughts I've had for alternate methods of electrophilic aromatic substitution with nitronium on partially deactivated rings, and am
looking for advice and feedback on what would work and what wouldn't.
Na2S2O7: The manufacture of SO3 usually goes by heating sodium bisulfate until it decomposes, first to
sodium pyrosulfate and finally to sodium sulfate and sulfur trioxide. However, the complete decomposition requires temperatures beyond what
borosilicate glass can take, and SO3 can undergo something called an alpha explosion if not handled just so.
So, does the addition of sodium pyrosulfate to sulfuric acid result in dehydration? Not necessarily of the acid itself to its anhydride, but by
drawing in the water from the substitution and reverting to 2 moles of bisulfate? This might not be thermodynamically plausible; my physical chemistry
is very rusty. Alternatively, could sodium pyrophosphate serve the same purpose?
Methylene chloride: Toluene and many nitrarenes dissolve in nonpolar solvents like DCM. The addition of DCM to mixed acid results in the extraction of
the nitric acid into the DCM layer. This effect is exploited in one method of creating anhydrous HNO3.
Now, from what I can gather, nitric acid only extracts into DCM in appreciable amounts when sulfuric acid is present, suggesting that protonation of
the nitric acid is involved in the phase transfer.
Since DCM is completely immiscible with water, the sideproduct of substitution should be expelled immediately, resulting in a consistent mixture of
nitric acid and aromatic substrate in an anhydrous environment.
However, the exact mechanism of what's going on in the DCM/mixed acid/substrate system is unclear to me, since I can't find any sources.
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franklyn
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Mind you I am not a chemist thus what seems doable to me , can have results unforeseen by me. The last few posts
here I addressed dry salt melt as a possible approach. C6Cl6 + 6 NaNO2 => 6 NaCl + C6(NO2)6
www.sciencemadness.org/talk/viewthread.php?tid=1226#pid17906...
The last post of this particular thread refers a patent.
Another Idea I mentioned once briefly : SO3 gas introduced steadily at some pressure into a closed vessel , dissolves into a chilled mixture of fuming
nitric acid and the organic substance to be attached with NO2 radicals. As the water is abstracted by the SO3 from the HNO3 it will be consumed and
replaced entirely with H2SO4 mixed with the end product
C6H6 + 6 HNO3 + 6 SO3 => 6 H2SO4 + C6(NO2)6
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