syldaril
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Picric acid to 2,4-Dinitrophenol
How does one convert picric acid (2,4,6-trinitrophenol) to 2,4-dinitrophenol?
It seems like a pretty easy conversion in theory: we're just talking about removing a nitro group (one of the nitro goups next to the OH).
Syldaril.
PS: where is a good source to buy reagents in general and 2,4-dinitrophenol in particular? thanks the info 
[Edited on 8-2-2006 by syldaril]
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sparkgap
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"...it seems like a pretty easy conversion in theory..."
Actually, no.  This is for the simple reason that how exactly will nitro group
removing reagent X distinguish between the two nitros flanking the hydroxy group, and the lone nitro at the other end?
For making 2,4-dinitrophenol, search around here; I do remember one of the threads discussing the possible synthesis routes.
sparky (~_~)
"What's UTFSE? I keep hearing about it, but I can't be arsed to search for the answer..."
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garage chemist
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Chlorobenzene is nitrated to 2,4-dinitrochlorobenzene (same reaction conditions as for nitrating benzene to dinitrobenzene) and then boiled with NaOH
solution to hydrolyse the chlorine. On acidification of the sodium dinitrophenolate solution, 2,4-dinitrophenol is obtained.
This is the first part of a new picric acid production process, since the 2,4-dinitrophenol can be easily further nitrated to picric acid.
No sulfonation is needed, since chlorobenzene is resistant against oxidation. Danger of runaway is also practically eliminated.
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syldaril
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...very interesting! 
"...(same reaction conditions as for nitrating benzene to dinitrobenzene)..."
what is the pocess used to achieve this? How do you nitrate chlorobenzene to dinitrobenzene.
And upon this, do you exclusively obtain 2,4-dinitroclhlorobenzene or fo you also obtain 2,6-dinitroclhlorobenzene as well, and in what proportions?
Thanks
Syldaril.
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unionised
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IIRC dinitro chlorobenzene is one of the more potent sensitisers- not very nice to work with.
OTOH It is widely available as a fine chemical so it must be reasonably easy to make.
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garage chemist
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Fuming HNO3 (ca. 95%) and conc. H2SO4 have to be used, and be present in excess (don't worry, it won't nitrate to trinitrochlorobenzene). I don't know
reaction conditions, but it will most likely have to be heated.
The 2,6 isomer will also be formed, though in small amounts. The 2,4-isomer will be the main product.
They must be separated, e.g. by using fractional crystallisation.
Purity has to be controlled, for example by DC chromatography.
I don't have a procedure for this synthesis, you'll have to look for one. I think that patents describing this do exist, you should look for "picric
acid manufacture" or something like that and look if you can find the process starting from chlorobenzene.
The process will include both the purification of the 2,4-dinitrochlorobenzene and its hydrolysis to dinitrophenol, as 2,4-dinitrophenol is an
intermediate in the synthesis and required in pure form.
Or alternatively you could just search for 2,4-dnp production, it's an important intermediate for several other things if I remember correctly.
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syldaril
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Thank you guys.
Your input is much appreciated
Syldaril.
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garage chemist
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I found a synthesis for 2,4-dinitrochlorobenzene in Gattermann from 1982. Go get that book, it's good.
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