Toluene, nitration

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. 

Table 14. United States Toluene, Nitration-Grade DCI Historical Prices...

Compare energies fox meta andpara-nitroanilinium ions (intermediates in nitration of aniline). Are these differentiated to a lesser or greater extent than the intermediates in toluene nitration Examine electrostatic potential maps. What do these suggest about the relative electron-donor strengths of methyl and amino groups ... 

Inductive and resonance effects account for the directing effects of substituents as well as for their activating or deactivating effects. Take alkyl groups, for instance, which have an electron-donating inductive effect and are ortho and para directors. The results of toluene nitration are shown in Figure 16.13. 

The effects of reactant feeding methods on toluene nitrations were studied by Yamasue et al (Ref 70) in a 15 liter nitrator with a 500rpm agitator. Production of pu re MNT or DNT was favored by addition of acid to the toluene or MNT, while in the production of TNT the addition of oil to acid is to be preferred, provided sufficient cooling and agitation is available. Purest TNT was produced when the MA contained free S03... 

This reaction cannot be elementary. We can hardly expect three nitric acid molecules to react at all three toluene sites (these are the ortho and para sites meta substitution is not favored) in a glorious, four-body collision. Thus, the fourth-order rate expression 01 = kab is implausible. Instead, the mechanism of the TNT reaction involves at least seven steps (two reactions leading to ortho- or /mra-nitrotoluene, three reactions leading to 2,4- or 2,6-dinitrotoluene, and two reactions leading to 2,4,6-trinitrotoluene). Each step would require only a two-body collision, could be elementary, and could be governed by a second-order rate equation. Chapter 2 shows how the component balance equations can be solved for multiple reactions so that an assumed mechanism can be tested experimentally. For the toluene nitration, even the set of seven series and parallel reactions may not constitute an adequate mechanism since an experimental study found the reaction to be 1.3 order in toluene and 1.2 order in nitric acid for an overall order of 2.5 rather than the expected value of 2. 

Write a plausible reaction mechanism, including appropriate rate expressions, for the toluene nitration example in Section 1.3. 

OS 32] ]R 16a] ]P 23]Toluene nitration rates determined in the capillary-flow reactor were generally higher than benzene nitration rates [31, 97]. This is not surprising, as it stems from the higher reactivity of toluene towards electrophilic substitution owing to its more electron-rich aromatic core. For instance, at a reaction temperature of 60 °C, rates of 6 and 2 min were found for toluene and benzene nitration, respectively. However, care has to be taken when quantitatively comparing these results, since experimental details and tube diameters vary to a certain extent or are not even listed completely. 

OS 32] ]R 16a] ]P 23] On increasing the ratio of flows in favor of the acid content, the toluene nitration reaction rate decreases, especially at low temperature (25 °C ... 

Table 4.1 Influence of reaction temperature and acid-to-organic flow rate on the reaction rate of toluene nitration [31, 97].

Bakke et al. (1982) have shown how montmorillonite catalyses chlorination and nitration of toluene nitration leads to 56 % para and 41 % ortho derivative compared to approximately 40 % para and 60 % ortho derivatives in the absence of the catalyst. Montmorillonite clays have an acidity comparable to nitric acid / sulphuric acid mixtures and the use of iron-exchanged material (Clayfen) gives a remarkable improvement in the para, ortho ratio in the nitration of phenols. The nitration of estrones, which is relevant in making various estrogenic drugs, can be improved in a remarkable way by using molecular engineered layer structures (MELS), while a reduction in the cost by a factor of six has been indicated. With a Clayfen type catalyst, it seems possible to manipulate the para, ortho ratio drastically for a variety of substrates and this should be useful in the manufacture of fine chemicals. In principle, such catalysts may approach biomimetic chemistry our ability to predict selectivity is very limited. 

Moreover, the thermal nitration of various aromatic substrates with different X-PyNO cations shows the strong rate dependence on the acceptor strength of X-PyNO and the aromatic donor strength. This identifies the influence of the HOMO-LUMO gap in the EDA complexes (see Chart 3), and thus provides electron-transfer activation as the viable mechanistic basis for the aromatic nitration. Indeed, the graphic summary in Fig. 18 for toluene nitration depicts the isomeric composition of o-, m- and p-nitrotoluene to be singularly invariant over a wide range of substrate selectivities (k/kQ based on the benzene... 

T. Krasiejko I. Missala, Analysis of Toluene Nitration Products by Gas Chromatography , ChemAnal 18 (5), 1081-83 (1973)... 

Study of Toluene Nitration , Case Western Reserve Univ, Cleveland, Contract DAA-21-72C-0528 (1975) 5) Bretherick (1975), 530-31... 

Nitric Acid and Toluene. Nitration of toluene with mixed concentrated acids must be carefully controlled or an explosion can result.18... 

Smith et a/.[24] have investigated deactivation and shape-selectivity effects in toluene nitration in the vapour phase with N02 as nitrating agent using zeolites, MCM-41 and sulfated zirconia as catalysts. Almost all the catalysts exhibited deactivation over a period of about 5 h on stream, due mainly to coke formation. 

Smith, J. M., Liu, H. and Resasco, D. E. Deactivation and shape selectivity effects in toluene nitration over zeolite catalysts, Stud. Surf. Sci. Catal., 1997, 111, 199-206. 

How reactive are the different sites in toluene Nitration of toluene produces the three possible products in the ratios shown. What would be the ratio of products if all sites were equally reactive What is the actual relative reactivity of the three sites (You could express this as x y. 1 or as a b c where a+fo+c=l00.) Comment on the ratio you deduce. 

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