Dinitrotoluenes

Further nitration of the 2- and 4- isomers yields 2,4-dinitrotoluene, yellow crystals, m.p. 71 "C. This material is reduced to 2,4-di-aminotoluene and treated with phosgene to give 2,4-diisocyanatotoluene, a precursor of polyurethanes. 

Toluene, Proceed as for Benzene but use 0-5 ml. of toluene and a mixture of 3 ml. of concentrated sulphuric acid and 2 ml. of fuming nitric acid. Gently warm the mixture over a free flame for 1-2 minutes, cool, and pour into 20 ml. of ice water. Recrystalhse the product from dilute alcohol. 2 4-Dinitrotoluene, m.p. 71°, is obtained. 

Nitrotoluene is similarly converted largely into 2 4-dinitrotoluene ... 

Place 18 g. (12 ml.) of fuming nitric acid, sp. gr. 1 5, and 30 g. (16-5 ml.) of concentrated sulphuric acid and a few fragments of broken glass in a 250 or 500 ml. round-bottomed flask. Add gradually, in small portions, 14 g. of p-nitrotoluene do not allow the temperature to rise above 50 and cool the flask, if necessary, by immersion in cold water. Place a small funnel in the mouth of the flask and heat on a water bath at 90-95° for 30 minutes. Allow to cool almost to the laboratory temperature and pour the reaction mixture slowly into about 500 ml. of ice water containing a few small pieces of ice. Filter the crude dinitrotoluene through a Buchner funnel at the pump, wash it thoroughly with cold water, and drain as completely as possible. RecrystalUse from the minimum volume of hot methyl alcohol (flask, reflux condenser, and water bath experimental details as in Section IV,12). The yield of pure 2 4-dinitrotoluene, m.p. 71°, is 12 -5 g. 

Formic acid is a good reducing agent in the presence of Pd on carbon as a catalyst. Aromatic nitro compounds are reduced to aniline with formic acid[100]. Selective reduction of one nitro group in 2,4-dinitrotoluene (112) with triethylammonium formate is possible[101]. o-Nitroacetophenone (113) is first reduced to o-aminoacetophenone, then to o-ethylaniline when an excess of formate is used[102]. Ammonium and potassium formate are also used for the reduction of aliphatic and aromatic nitro compounds. Pd on carbon is a good catalyst[103,104]. NaBH4 is also used for the Pd-catalyzed reduction of nitro compounds 105]. However, the ,/)-unsaturated nitroalkene 114 is partially reduced to the oxime 115 with ammonium formate[106]... 

Attempts have been made to develop methods for the production of aromatic isocyanates without the use of phosgene. None of these processes is currently in commercial use. Processes based on the reaction of carbon monoxide with aromatic nitro compounds have been examined extensively (23,27,76). The reductive carbonylation of 2,4-dinitrotoluene [121 -14-2] to toluene 2,4-diaLkylcarbamates is reported to occur in high yield at reaction temperatures of 140—180°C under 6900 kPa (1000 psi) of carbon monoxide. The resultant carbamate product distribution is noted to be a strong function of the alcohol used. Mitsui-Toatsu and Arco have disclosed a two-step reductive carbonylation process based on a cost effective selenium catalyst (22,23). 

Mixtures of HNO, H2SO4, and SO also result in high concentrations of NO/, and toluene can be readily nitrated at —40 to — 10°C as a result (6). At these low temperatures, the formation of the meta-isomer of mononitrotoluene (MNT) is greatiy reduced. Such a reduction is highly desired in the production both of dinitrotoluenes (DNTs) employed to produce intermediates for polyurethane production and of trinitrotoluene (TNT), which is a high explosive. > -MNT results in the production of undesired DNT and TNT isomers (see Nitrobenzene and nitrotoluenes). 

Organic Reactions. Nitric acid is used extensively ia iadustry to nitrate aHphatic and aromatic compounds (21). In many iastances nitration requires the use of sulfuric acid as a dehydrating agent or catalyst the extent of nitration achieved depends on the concentration of nitric and sulfuric acids used. This is of iadustrial importance ia the manufacture of nitrobenzene and dinitrotoluene, which are iatermediates ia the manufacture of polyurethanes. Trinitrotoluene (TNT) is an explosive. Various isomers of mononitrotoluene are used to make optical brighteners, herbicides (qv), and iasecticides. Such nitrations are generally attributed to the presence of the nitronium ion, NO2, the concentration of which iacreases with acid strength (see Nitration). 

Environmental aspects, as well as the requirement of efficient mixing in the mixed acid process, have led to the development of single-phase nitrations. These can be divided into Hquid- and vapor-phase nitrations. One Hquid-phase technique involves the use of > 98% by weight nitric acid, with temperatures of 20—60°C and atmospheric pressure (21). The molar ratios of nitric acid benzene are 2 1 to 4 1. After the reaction is complete, excess nitric acid is vacuum distilled and recycled. An analogous process is used to simultaneously produce a nitrobenzene and dinitrotoluene mixture (22). A conversion of 100% is obtained without the formation of nitrophenols or nitrocresols. The nitrobenzene and dinitrotoluene are separated by distillation. 

Manufacture and Processing. Mononitrotoluenes are produced by the nitration of toluene in a manner similar to that described for nitrobenzene. The presence of the methyl group on the aromatic ring faciUtates the nitration of toluene, as compared to that of benzene, and increases the ease of oxidation which results in undesirable by-products. Thus the nitration of toluene generally is carried out at lower temperatures than the nitration of benzene to minimize oxidative side reactions. Because toluene nitrates at a faster rate than benzene, the milder conditions also reduce the formation of dinitrotoluenes. Toluene is less soluble than benzene in the acid phase, thus vigorous agitation of the reaction mixture is necessary to maximize the interfacial area of the two phases and the mass transfer of the reactants. The rate of a typical industrial nitration can be modeled in terms of a fast reaction taking place in a zone in the aqueous phase adjacent to the interface where the reaction is diffusion controlled. 

If pure isomers are required, the ortho and meta compounds can be prepared by indirect methods. o-Nitrotoluene can be obtained by treating 2,4-dinitrotoluene with ammonium sulfide followed by diazotization and boiling with ethanol. / -Nitrotoluene can be prepared from -toluidine by acetylation, nitration deacetylation, diazotization, and boiling with ethanol. A fairly pure -nitrotoluene, which has been isolated from the isomeric mixture, can be purified further by repeated crystallization. 

Dinitration of toluene results in the formation of a number of isomeric products, and with a typical sulfuric—nitric acid nitrating mixture the following mixture ofisomers is obtained 75 wt % 2,4-dinitrotoluene [121-14-2] 19 wt % 2,6-dinitrotoluene [606-20-2], 2.5 wt % 3,4-dinitrotoluene [610-39-9], 1 wt %... 

Dinitrotoluene crystallizes in yellow needles from carbon disulfide and is soluble in a number of organic solvents. It is only slightly soluble in water, 0.03 g/100 g of water at 22°C. Its physical properties are Hsted in Table 13. 

Dinitrotoluene can be prepared by the nitration of -nitrotoluene with yields of ca 96% or it can be obtained from the direct nitration of toluene. 

Dinitrotoluene is oxidized to 2,4-dinitrobenzoic acid [610-30-0] by potassium permanganate or chromic acid, and is reduced to 2,4-diaminotoluene by iron and acetic acid. It is reduced partially by zinc chloride and hydrochloric acid to 2-amino-4-nitrotoluene [99-55-8] and by ammonium sulfide to 4-amino-2-nitrotoluene [119-32-4],... 

Dinitrotoluenes can be catalytically hydrogenated to toluenediamines under a wide variety of temperatures, pressures, and solvents the catalyst can be supported noble metal, eg, Pd/C or nickel, either supported or Raney type. The reduction requires six moles of hydrogen per mole of DNT and produces four moles of water. 

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