Boobzilla
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Registered: 11-9-2006
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Large Scale Production of 2,6-dimethylnitrobenzene
Does anyone know how 2,6-dimethylnitrobenzene is produced on an industrial scale? I know of small scale syntheses that can be done, but it doesn't
seem cost effective on the large scale. I haven't been able to find any patents about this, plus the search engine turned up nothing. I have been
considering ways to get to it from chemicals that are abundant, specifically m-xylene, but nitration would seem to much prefer not to add to the
position between both methyl groups. Thanks for the help.
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Sauron
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Ullmann's in their Nitro Aromatics -> Nitroxylenes section says:
"All three xylenes can be nitrated readily, with o- and m-xylene giving mixtures of products. Even under simple conditions with mixed acid, isomer
ratios can be changed significantly by varying the reaction conditions."
and illustrates the case for m-xylene nitration with a 75-85% 4-nitro-m-xylene versus 16-25% 2-nitro-m-xylene. Maddeningly no references are given nor
are experimental conditions.
Federoff in PATR 2700 vol 10 p X-25 says that according to another US Army document that I don't have, PATM 1728 (1966) by M.Warman*, "Preparation of
Trinitro-meta-Xylene" describes a pilot-plant process for the nitration of m-xylene in two stages. The first stage is nitration to your target
2-nitro-m-xylene with mixed acid (sulfuric 59/nitric 25/water 16 weight-%) at 35-50 C.
No mention of other isomers, so it sounds like your target is main or even exclusive product.
Second stage is also with mixed acids sulfuric 79/nitric 17.7/water 3.5 weight-% at 85 to 102 C.
Yield up to 94% on m-xylene basis.
If this is true (and Picatinny Arsenal usually is) then your target compound is available in one step from m-xylene in high yield and at low cost.
*Maurice Warman of the Explosives Research Branch, Picatinny Arsenal
PATR 2700 = Picatinny Arsenal Technical Report 2700 Vols 1-10 edited by Basil Federoff and also knows as Federoff's Encyclopeadia of Explosives.
Almost 10,000 pages of well referenced information on materials of interest to military ordnance personnel. Well worth obtaining if you are being
tasked as process engineer for aromatic nitrations like this.
Davis in The Chemistry of Powder & Explosives agrees that TNX can be had with mixed acids only, no fuming nitric acid needed. However he gives no
details. TNX is a weak and often incompletely detonable explosive mostly used in low melting mixtures with TNT.
Other explosives references I have fail to discuss nitrated xylenes at all. Hoggett's excellent "Nitration and Aromatic Reactivity" discusses studies
of conc nitric acid in acetic acid as nitration agent but that was for kinetic studies and predicted predominance of the 4-nitro isomer. Many many
contemporary papers with various exotic nitrating systems either give the 4-isomer exclusively (like bismuth subnitrate/thionyl chloride) or favor the
4-isomer in 85:15 ratio over the 2-isomer. If you want the 4-nitro-m-xylene then the lanthanide triflate catalyzed nitration under mild conditions
gives a high conversion rate at 85% selectivity and the catalyst is very recyclable.
A little physical data
2-nitro-m xylene mp 14-16 C bp 225 C
4-nitro-m-xylene mp 5-7 C bp 244 C
Both commercially available, the 2-isomer 1/3 the price of the 4-isomer. 250 ml to 500 g packaging easy to find. Cost in such quantities about 10 US
cents a gram for the 2-isomer.
The sole industrial use for these is reduction to corresponding xilidines as intermediates for dyes and agro chemicals.
[Edited on 30-4-2007 by Sauron]
Attachment: Pages from Encyclopedia of Explosives and Reated Items 10 by B. Fedoroff.pdf (271kB)
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