Of mononitrotoluenes

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). 

Table 12. Isomer Ratio of Mononitrotoluenes with Different Catalysts...

Analytical and Test Methods. o-Nitrotoluene can be analyzed for purity and isomer content by infrared spectroscopy with an accuracy of about 1%. -Nitrotoluene content can be estimated by the decomposition of the isomeric toluene diazonium chlorides because the ortho and meta isomers decompose more readily than the para isomer. A colorimetric method for determining the content of the various isomers is based on the color which forms when the mononitrotoluenes are dissolved in sulfuric acid (45). From the absorption of the sulfuric acid solution at 436 and 305 nm, the ortho and para isomer content can be deterrnined, and the meta isomer can be obtained by difference. However, this and other colorimetric methods are subject to possible interferences from other aromatic nitro compounds. A titrimetric method, based on the reduction of the nitro group with titanium(III) sulfate or chloride, can be used to determine mononitrotoluenes (32). Chromatographic methods, eg, gas chromatography or high pressure Hquid chromatography, are well suited for the deterrnination of mononitrotoluenes as well as its individual isomers. Freezing points are used commonly as indicators of purity of the various isomers. 

Because of Us high polarity and low nucleophilicity, a trifluoroacetic acid medium is usually used for the investigation of such carbocationic processes as solvolysis, protonation of alkenes, skeletal rearrangements, and hydride shifts [22-24] It also has been used for several synthetically useful reachons, such as electrophilic aromatic substitution [25], reductions [26, 27], and oxidations [28] Trifluoroacetic acid is a good medium for the nitration of aromatic compounds Nitration of benzene or toluene with sodium nitrate in trifluoroacetic acid is almost quantitative after 4 h at room temperature [25] Under these conditions, toluene gives the usual mixture of mononitrotoluenes in an o m p ratio of 61 6 2 6 35 8 A trifluoroacetic acid medium can be used for the reduction of acids, ketones, and alcohols with sodium borohydnde [26] or triethylsilane [27] Diary Iketones are smoothly reduced by sodium borohydnde in trifluoroacetic acid to diarylmethanes (equation 13)... 

HPA amount/g Regioselectivity ortho/% meta/% para/% para/ortho Total yield of mononitrotoluene/%... 

Smith and coworkers have screened the solid catalysts for aromatic nitration, and found that zeolite (3 gives the best result. Simple aromatic compounds such as benzene, alkylbenzenes, halogenobenzenes, and certain disubstituted benzenes are nitrated in excellent yields with high regioselectivity under mild conditions using zeolite (3 as a catalyst and a stoichiometric quantity of nitric acid and acetic anhydride.11 For example, nitration of toluene gives a quantitative yield of mononitrotoluenes, of which 79% is 4-nitrotoluene. Nitration of fluorobenzene under the same conditions gives p-fluoronitrobenzene exclusively (Eqs. 2.1 and 2.2)... 

The 60 still base was a 45.5 m3 horizontal, cylindrical, mild steel tank 7.9 m long and 2.7 m diameter. The still was used to separate a mixture of the isomers of mononitrotoluene (MNT), two of which (o-nitrotoluene and m-nitrotoluene) are liquids at room temperature and third (p-nitrotoluene) a solid. Other byproducts were also present, principally dinitrotoluene and nitrocresols. It is well known in the industry that these nitro compounds can be explosive in the presence of strong alkali or strong acid, but in addition explosions can be triggered if they are heated to high temperatures or held at moderate temperatures for a long period. 

Rickert DE et al Hepatic macromolecular covalent binding of mononitrotoluenes in Fischer-344 rats. Chem Biol Interact 52 131-139, 1984... 

The conventional nitration process,[2,5] that involves a mixture of nitric and sulfuric acids (mixed acids method) has remained unchallenged, in the commercial area, for the last 150 years owing to the very favourable economics. However, the method is notoriously unselective for nitration of substituted aromatic compounds and the disposal of waste products and spent acids is a serious environmental issue. For instance, nitration of toluene for production of mononitrotoluenes (MNTs) is conducted using a nitrating mixture usually composed of 52-56 % (w/w) H2SO4, 28-32% (w/w) HNO3 and 12-20% (w/w) H20. The reaction performed at temperatures between 25 and 40°C, yields ca. 96 % MNTs, which are composed of a mixture of ca. 60 % (w/w) o-nitrotoluene, ca. 37 % (w/w) p-nitrotoluene and... 

Three isomers of mononitrotoluene, ortho-, meta-, and para-, are known. 

Gamer and Abemethy [3] give the following thermochemical data for the isomers of mononitrotoluene ... 

HEATS OF COMBUSTION AND HEATS OFFORMATION OF MONONITROTOLUENE ISOMERS... 

The composition of the nitrating mixture also has an influence on the composition of mononitrotoluene. The proportion of m- nitrotoluene is reduced by an... 

The sepMation of the production unit of mononitrotoluene from the next stages of nitration is desirable so as to provide the mononitration unit with a unit for removing m-nitrotoluene by distillation. A mixture of o and p- nitrotoluene or o- nitrotoluene alone is then used for further nitration. In the latter case p- nitrotoluene is utilized for the preparation of dyes (from p- toluidine, derivatives of stilbene, etc.) and pharmaceuticals (p- aminobenzoic acid.)... 

During World War II a method of preparing mixtures of nitro compounds (e.g. TNT and TNX, or TNT and tetryl, see Vol. IV) was developed by the Germans. It consisted in the nitration of the corresponding lower nitrated compounds, namely a mixture of mononitrotoluenes plus mononitroxylenes was nitrated in two stages to form trinitro compounds. In this way a product containing 20% of TNX and 80% of TNT was obtained. 

Houle et al, Development of Mononitrotoluene and Methyl Nitrate Monitors for Army Ammunition Plants , DPG-TR-C985P (1975) 28) P. 

The history of the discovery and preparation of mononitrotoluene runs parallel with that of toluene, since it was by the preparation of the former that tol-... 

Beilstein and Kuhlberg prepared two dinitrotol-uenes, but give the melting-point of but one of the two. This was the same as that of Deville. The work of Beilstein and Kuhlberg seems to have been mostly on the mononitro-compounds of toluene, and the acidic and basic compounds of mononitrotoluene. 

Considering, then, the mixture of mononitrotoluenes to consist of, approximately, 38 per cent para, 4 per cent meta, and 58 per cent ortho nitrotoluene the reactions which occur on nitrating to dinitrotoluene will be investigated. 

A modification of the sulphuric acid process has been patented (1) when applied to a mixture of mono-nitrotoluenes and paraffin hydrocarbons. The nitration of the toluene is carried on carefuUy so as to take it only as far as the mononitrotoluene. The mono-nitrotoluene is dissolved in sulphuric acid, but any paraflShs that may be present will not dissolve, and will form a separate layer. A separation of these two layers and the subsequent nitration of the sulphuric acid solution of mononitrotoluene yields a very high grade TNT. Thus a toluene containing a comparatively large percentage of paraffins may be utilized in the manufacture of TNT. 

Preparation. The alpha dinitrotoluene is obtained usually by the nitration of mononitrotoluene. It may also be prepared by eliminating the amiao group from nitrotoluidin, first diazotizmg, then forming the hydrochloride and saponifying. 

Nitration of toluene for production of mononitrotoluenes (MNT) is conducted either batch-wise or in continuous operation under somewhat milder conditions than those used for benzene nitration because of the activating effect of the methyl group. The nitrating acid usually has the composition 52-56% (w/w) H2SO4,... 

Several substances were evaluated as coatings for the detection of mononitrotoluene (MNT), which can serve as a reliable indicator for the presence of trinitrotoluene (TNT) (49). A crystal coated with carbowax 1000, was found to be the most sensitive at optimum conditions of 30 ml/min flow rate, SO C exposure chamber temperature, and 30 (jg of coating applied to the crystal. The... 

Further testing of the model clearly demanded a knowledge of the values of 0 emd D under the conditions of the nitration experiments. The distribution coefficients of toluene between organic phases with varying concentrations of mononitrotoluene and aqueous phases of different compositions have been mectsured (23). These show 0 to be a function of both toluene conversion and nitric acid concentration for a fixed sulphuric acid concentration. Values of the molecular diffusion coefficient for toluene as a function of the acid phase composition have also been measured using a laminar-jet technique( ). These show some dependence on composition but not to a great extent. 

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