Nitration of m-xylene

Nitration of m xylene is directed ortho to one methyl group and para to the other... 

The presence of two methyl groups in m-xylene makes it a more reactive substrate than toluene, but as a consequence, this substrate is more susceptible to oxidation. Therefore, the nitration of m-xylene requires lower temperatures and the use of less concentrated mixed acid. In fact, the nitration of either 2,4- or 2,6-dinitro-m-xylenes to 2,4,6-trinitroxylene (TNX) can be achieved with mixed acid containing up to 10 % water. TNX is a less powerful explosive than TNT and has a poor oxygen balance (—78.4 %). 

M. Warman, Preparation of Trinitro-Meta-Xylene (TNX) , PATM 1728 (1966) [Reported is a procedure for the pilot plant prepn of TNX from m-xylene. The nitration of m-xylene is carried out in two stages 1) The conversion of m-xylene to 2-nitro-m-xylene using mixed add (sulfuric 59/nitric 25/w 16%) at 35 to 50°, and 2) The trinitration of 2-nitro-m-xylene to trinitro-m-xylene, again using mixed add (sulfuric 79/nitric 17.5/w 3.5%), at 95 to 102°. The author states that the overall yield of TNX from m-xylene is as high as 94%. One crystn of the crude product from acet is sufficient to raise the mp to the 182-83° value reported in the literature]... 

In m-xylene the two methyl groups agree in activating the same positions, and this is the only one of the three isomeric xylenes which can be nitrated satisfactorily to yield a trinitro derivative. Since the three isomers occur in the same fraction of coal tar and cannot readily be separated by distillation, it is necessary to separate them by chemical means. When the mixed xylenes are treated with about their own weight of 93 per cent sulfuric acid for 5 hours at 50°, the o-xylene (b.p. 144°) and the m-xylene (b.p. 138.8°) are converted into water-soluble sulfonic acids, while the p-xylene (b.p. 138.5°) is unaffected. The aqueous phase is removed, diluted with water to about 52 per cent acidity calculated as sulfuric acid, and then heated in an autoclave at 130° for 4 hours. The m-xylene sulfonic acid is converted to m-xylene, which is removed. The o-xylene sulfonic acid, which remains in solution, may be converted into o-xylene by autoclaving at a higher temperature. The nitration of m-xylene is conveniently carried out in three steps. The effect of the two methyl... 

The extension of the interfacial area by emulsification explains Miyagawa s [95] observation that the nitration rate can be considerably increased by the action of ultrasonics on a reacting system. For example, nitration of m- xylene to trinitro-m- xylene, which generally takes 2 hr, takes only 30 min when ultrasonics are used. There is no evidence as yet whether and how ultrasonic waves effect group orientations. 

Preparation from m- xylene. Giua [15] suggested sym-trinitrobenzene might be prepared by the nitration of m- xylene to the trinitro derivative, followed by oxidation and decarboxylation ... 

The 2,4,6- isomer is the principal component of the products of nitration of m- xylene. It constitutes the largest part of the purified commercial product. The 4,5,6- isomer is formed only in an insignificant quantity. 

The two-stage preparation of TNX consists in the nitration of m- xylene in two stages. 

The nitration of m-xylene produces a mixture of isomers of nitroxylene, which consists of 80 to 85% 2,4-dimethylnitrobenzene and 15 to 20% 2,6-dimethylnitro-benzene the proportion of 3,5-dimethylnitrobenzene is minor. Separation of this mixture of isomers is effected by distillation and melt crystallization. The corresponding xylidines are produced by reduction of the nitro compounds with Raney nickel. 

C12H15N3O6, Mr 291.21, mp 114°C, does not occur in nature. It forms yellow crystals with a persistent musk odor. Musk xylol is prepared by alkylation of m-xylene with isobutene and subsequent nitration with a sulfuric acid nitric acid... 

Relative rate coefficients from (25) are listed in Table 6, taking that for benzene as unity. The most interesting feature of these results is the apparent limiting reaction rate at about forty times the reactivity of benzene. This limit is quite inconsistent with the predictions of the additivity principle. Thus, from the additivity principle and the partial rate factors for the nitration of toluene, the reactivities of m-xylene and mesitylene would be expected to exceed that of benzene by factors of 400 and 16 000 respectively (Coombes et al., 1968). 

Recently Milczak et al.[57] have reported the nitration of o-xylene using 100% nitric acid over silica supported metal oxide solid acid catalysts with high yields (up to 90 %) but low selectivity to 4-o-NX (40-57 %). Choudary et a/. 5X 591 performed the nitration of o-xylene and other aromatic hydrocarbons by azeotropic removal of water over modified clay catalysts achieving low yields of 4-o-NX and a selectivity of 52%. Better results were obtained when HBeta zeolite was used as catalyst, performing the reaction in dichloromethane at reflux temperature.[60] Conversions of 40 % and maximum selectivity 68 % of 4-o-NX were obtained. Similar conversions and higher selectivities for 4-o-NX (65-75 %) were reported by Rao et al M 1 using a nanocrystaUine HBeta sample and working at 90 °C in the absence of solvent. 

Patil, P. T., Malshe, K. M., Dagade, S. P. and Dongare, M. K. Regioselective nitration of o-xylene to 4-nitro-o-xylene using nitric acid over solid acid catalysts. Catal. Commun., 2003, 4, 429-434. 

According to Kholevo and Eitington [130] the nitratiton of m- xylene leads to formation of 4-nitro-3-methylbenzoic acid. Here the mercuric nitrate also enhances the oxidation of the methyl group. 

Recent German specifications for nitration grade xylene require determination of the freezing point of m- xylene, which should not be lower than -52°C. 100% of the xylene should distil within 1-2°C. 

For one part of m- xylene, 2.5 pMts of nitrating mixture of the composition ... 

The nitration temperature should not exceed 35°C. From 100 parts of m- xylene, 130-135 parts of MNX are obtained, i.e. the yield is 90-94% of the theoretical. Further procedure (separation of the nitro compound from the spent acid) is similar to that used in other nitration processes. 

Reactions specific to sym-trinitrobenzene Addition compounds Preparation of sym-trinitrobenzene Direct nitration of m-dinitrobenzene Preparation from a-trinitrotoluenc Preparation from picryl chloride Preparation from benzyl chloride Preparation from m-xylene Other preparatory reactions... 

Moreover, studies of products formed during the smog-chamber oxidations of multialkyl benzenes invariably indicate the presence of ring decomposition reactions (leading, for example, to the production of per-oxyacetyl nitrate from m-xylene or mesitylene). Chemical reactivity of aromatic hydrocarbons is enhanced by an increasing number of alkyl groups, especially those in meta positions on the benzene ring. 

The nitration reactions also exhibit high selectivity when the reactions proceed at the encounter controlled diffusion limit. To Illustrate, the nitration of anisole yields little meta product the ortho and para isomers are produced almost exclusively. Similarly, the substitution products of m-xylene... 

Unlike o-xylene and p-xylene, the application of m-xylene is limited to the production of isophthalic acid, nitrated xylenes and m-xylylenediamine. Production of 3,5-dimethylphenol, which was carried out in earlier times by alkali fusion, has now been replaced by gas-phase aromatization of isophorone (see Chapter 53.4.3.2). 

Xylidine can be produced by the reduction of 2,6-dimethylnitrobenzene, which is formed during nitration of m- and p-xylenes, and also by ammonolysis of 2,6-xylenol. It is used in the production of plant protection agents such as the fungicide metalaxyl Ciba Geigy) (see page 171) and the herbicide metazachlor (BASF),... 

Because of the inefficiency of the nitrodeiodination reaction and the faster rate of nitration of o-xylene relative to 4-iodo-o-xylene, I2 cannot be used as a catalyst to alter the substitution pattern in the nitration of o-xylene. ° Mononitration of m-xylene with HNO3 in a liquid mixture of m-benzenedisulphonic acid and phosphoric acid gives excellent yields and a 4-nitro-isomer content higher than that obtained by the usual method. In a typical experiment, the yield was 96% and the 4- to 2-isomer ratio ca. 7.5. A white product obtained during the nitration of toluene has been identified as (46). The catalytic para-nitration of substituted benzenes, especially toluene, has been reviewed, but in Japanese. 

Acetoxylation and nitration. It has already been mentioned that 0- and m-xylene are acetoxylated as well as nitrated by solutions of acetyl nitrate in acetic anhydride. This occurs with some other homologues of benzene, and with methyl phenethyl ether,ii but not with anisole, mesitylene or naphthalene. Results are given in table 5.4. 

Nitration of 1 4 dimethylbenzene (p-xylene) gives a single prod uct having the molecular formula C8H9NO2 m high yield What is this product... 

Tnflic acid is an excellent catalyst for the nitration of aromatic compounds [.S7]. In a mixture with nitnc acid, it forms the highly electrophilic nitronium inflate, which can be isolated as a white crystalline solid Nitronium inflate is a powerful nitrating reagent in inert organie solvents and in tnflic acid or sulfuric acid. It nitrates benzene, toluene, chlorobenzene, nitrobenzene, m-xylene, and benzotn-fluoride quantitatively in the temperature range of-110 to 30 °C with exeeptionally high positional selectivity [87],... 

Acetoxylation has been found to accompany the nitration of o- and m-xylene... 

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