Nitrotoluene isomers separation

Naphthali-Sandholm method, 404 dgorithm flowsketch, 411 Nitric acid reactor, 576 Nitrogen fixation, 574,578,588 Nitrotoluene isomers separation, 544 Noncatalytic reactions with solids, 595 Non-Newtonian liquids, 100, 103-109 Bineham. 104.105.107-109 dilatant, 103, 104 laminar flow, 108,109 pressure drop in lines, 106, 109 pseudoplaslic, 103, 104 rheopectic, 104,105 slurries, 71 thixotropic, 104-106 viscoelastic, 105, 106 Notation, 672 NPSH, pumps, 133,146 centrifugal pumps, 146 positive displacement pumps, 134, 135 various pumps, 144 NRTL equation, 475... 

Recently, as the disposal of large volumes of toxic waste waters from the purification of TNT by sulphitation has. become a problem (p. 390), new ways are being sought for the manufacture of TNT free from the unsymmetrical isomers. Apart from the possibility, mentioned above, of the utilization of nitrotoluene obtained by nitrating toluene with a mixture of acetic anhydride and nitric acid, factories TNT are now tending to separate nitrotoluene isomers by methods similar to those applied in the manufacture of dyestuffs intermediates. 

The three nitrotoluene isomers are separated by sequential distillation and crystallization. 2-Nitrotoluene can be recovered as a highly concentrated overhead fraction because of its lower boiling point (221.7 °C). The higher-boiling 3- and 4-nitrotoluenes (232.6 °C and 238.4 °C respectively) are separated industrially by crystallization from the melt, which, with a difference in crystallizing points of 35.3 °C (16.1 °C and 51.4 °C respectively), leads to extremely pure isomers. 

The separation of the isomers is carried out by a combination of fractional distillation and crystallization. In a fractional vacuum distillation step, the distillate, obtained at a head temperature of 96—97°C at 1.6 kPa (12 mm Hg), is fairly pure o-nitrotoluene and can be purified further by crystallization. The meta isomer is distilled from a mixture of m- and -nitrotoluene and can be purified further by additional distillation and crystallization steps. The bottoms product from the distillation steps is cooled in a crystallizer to obtain nitrotoluene. 

While the direct halogenation of toluene gives a mixture of isomers that is difficult to separate into the pure isomers, the isomeric o- and /r-nitrotoluenes 6a and 6b, formed by nitration, are easy to separate from each other. Thus reduction of the single o- or /j-nitrotoluene 6 to the o- or /j-toluidine 7a or 7b respectively, followed by conversion into the corresponding diazonium salt 8 and a subsequent Sandmeyer reaction leads to the pure o- or /j-halotoluene 9. 

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. 

The MEKC separation of explosives was achieved, except that three isomers of nitrotoluenes cannot be resolved [620]. A peak height RSD was 1.7-3.8% for TNB, DNB, TNT, tetryl, 2,4-DNT, 2,6-DNT, and 2-amino-4,6-DNT. But the linear ranges for TNB, DNB, TNT, and tetryl were only 1-5 ppm This narrow linear range, which is caused by the indirect LIF detection based on fluorescent quenching, may be sufficient for screening, but is certainly not useful for quantitation [620]. 

Octakis (2,3,6-tri-0-methyl-gamma-cyclodextrin) was used to separate enantiomers of methyl esters of deltametrinic acid and permetrinic acid the positional isomers of nitrotoluene were also separated on the same column [17,18]. Various alkyl- and dialkyl-benzenes have been separated on beta- and gamma-cyclodextrin [19]. A complete review of the use of cyclodextrins in chromatography has been published by Hinze [20]. Cyclo-dextrins have been analyzed by packed-column gas chromatography as their dimethylsilyl ethers [21]. 

If the pure 2,4-compound is required, mononitration of toluene followed by separation of pure p-nitrotoluene from the ortho isomer, and then further nitration of p-nitrotoluene gives the pure 2,4-dinitro isomer. 

Crude DNT, after it had been separated from acid and washed with water, was sometimes purified by sulphitation. This material partly freed from isomers and derivatives of m-nitrotoluene, was further nitrated. 

Chlorination of o-nitrotoluene gives about two-thirds of the 2,6 isomer and one-third of the 2,4-nitrochlorotoluene. 2,4-Dichlorobenzaldehyde, obtained from the latter isomer, yields no valuable dyes, and it is desirable, therefore, to separate the isomeric nitrochlorotoluenes. The separation can be accomplished by careful fractional distillation under reduced pressure. 

The preparation of aryl halides from diazonium salts is more important than direct halogenation for several reasons. First of all, fluorides and iodides, which can seldom be prepared by direct halogenation, can be obtained from the diazonium salts. Second, where direct halogenation yields a mixture of ortho and para isomers, the ortho isomer, at least, is difficult to obtain pure. On the other hand, the ortho and para isomers of the corresponding nitro compounds, from which the diazonium salts ultimately come, can often be separated by fractional distillation (Sec. 11.7). For example, the o- and />bromotoluenes boil only three degrees apart 182° and 185°. The corresponding o- and -nitrotoluenes, however, boil sixteen degrees apart 222° and 238°. 

Preparation of mononitro toluenes Industrial methods of nitration of toluene Separation of isomers Distillation of crude nUrotx uene Crystallization of p-nitrotoluene Distillation of the mother liquor Continuous vacuum distillation of mononiirotoluene Preparation of pure isomers Dinitrotoluenes Physical properties Thermocbemical properties Chemical properties Toxicity... 

Nitration of Toluene to Dinitrotoluene. The continuous nitration of toluene can be done under milder conditions than are necessary for benzene due to the activating effect of the methyl group. For example, the H20 content of the nitrating acid can be as high as 23%, compared to 10% for the nitration of benzene. The mixture of mononitrated products of toluene consists of the three isomers o-, p- and m-nitrotoluene, whose distribution is influenced only slightly by reaction conditions. A typical composition is 63% o-, 33—34% p-and 4% /w-nitrotoluene. The mixture can be separated by distillation or crystallization. 

The resolution of the mixed isomers of nitrotoluene is done by a series of distillation and crystallization steps. These are very similar to the processes used in the separation of mixed nitrochlorobenzenes (see Fig. 4-15). The pertinent physical properties of the isomers are given in the accompanying table. 

We used the same reaction—the nitration of toKiene—to make both the ortho (10) and pars (for 14) nitrotoluenes. In practice, a mixture is formed and must be separated to give the required isomer. In other circumstances, reactions which give mixtures of products are best avoided but aromatic substitution is so easy to carry out that separation is acceptable, particularly if it is at the first stage in a sequence. The reaction is then carried out on a large scale to get enough of the right isomer and a use sought for the other. 

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