Nitration of mesitylene

The rates of nitration of mesitylene-a-sulphonate anion (iii) and iso-durene-a -sulphonate anion (iv) in mixtures of aqueous nitric and perchloric acid followed a zeroth-order rate law. Although the rate of exchange of oxygen could not be measured because of the presence of perchloric acid, these results again show that, under conditions most amenable to its existence and involvement, the nitric acidium ion is ineffective in nitration. 

In experiments on the nitration of benzene in acetic acid, to which urea was added to remove nitrous acid (which anticatalyses nitration 4.3.1), the rate was found to be further depressed. The effect was ascribed to nitrate ions arising from the formation of urea nitrate. In the same way, urea depressed the rate of the zeroth-order nitration of mesitylene in sulpholan. ... 

The effect of nitrous acid on the nitration of mesitylene in acetic acid was also investigated. In solutions containing 5-7 mol 1 of nitric acid and < c. 0-014 mol of nitrous acid, the rate was independent of the concentration of the aromatic. As the concentration of nitrous acid was increased, the catalysed reaction intervened, and superimposed a first-order reaction on the zeroth-order one. The catalysed reaction could not be made sufficiently dominant to impose a truly first-order rate. Because the kinetic order was intermediate the importance of the catalysed reaction was gauged by following initial rates, and it was shown that in a solution containing 5-7 mol 1 of nitric acid and 0-5 mol 1 of nitrous acid, the catalysed reaction was initially twice as important as the general nitronium ion mechanism. 

Similarly, acetic acid catalysed the zeroth-order nitration of mesitylene without affecting the kinetic form... 

Fig. 5.2. Initial rates of nitration of mesitylene and phenol under zeroth-order conditions. Temperature 25 °C. [AcONOo] = r. 7 x io mol 1 . [HNO ] < 10" mol 1. ...

The kinetics of the nitration of benzene, toluene and mesitylene in mixtures prepared from nitric acid and acetic anhydride have been studied by Hartshorn and Thompson. Under zeroth order conditions, the dependence of the rate of nitration of mesitylene on the stoichiometric concentrations of nitric acid, acetic acid and lithium nitrate were found to be as described in section 5.3.5. When the conditions were such that the rate depended upon the first power of the concentration of the aromatic substrate, the first order rate constant was found to vary with the stoichiometric concentration of nitric acid as shown on the graph below. An approximately third order dependence on this quantity was found with mesitylene and toluene, but with benzene, increasing the stoichiometric concentration of nitric acid caused a change to an approximately second order dependence. Relative reactivities, however, were found to be insensitive... 

Nitromesitylene has been prepared by the direct nitration of mesitylene with concentrated nitric acid/ and by the action of benzoyl nitrate on mesitylene in carbon tetrachloride at low temperature. ... 

One test of this approach is to calculate the rate coefficient under the limiting conditions in terms of the concentrations of the aromatic substrate and the nitronium ion as in (26). The concentration of nitronium ions in the reaction medium cannot be measured directly, but an indirect estimation is possible from the fact that nitric acid is entirely converted to nitronium bisulphate in 90% sulphuric acid and the assumption that the change in reaction rate with the concentration of sulphuric acid comes essentially from the change in the position of the nitric acid-nitronium ion equilibrium. Then, from the rate coefficient for the nitration of mesitylene in 68.3% sulphuric acid (2.1 mol-1 s 1 dm3) (Coombes et al., 1968), the rate coefficient for the nitration of the phenyltrimethylammonium ion in 90.1% sulphuric acid (3.5 x 10 2 mol-1 s dm3) (Gillespie and Norton, 1953), and the relative reactivity of mesitylene and the phenyltrimethylammonium ion (a factor of 1.0 x 109) (Table 6 see also Gastaminza et al., 1969) it is possible to calculate that the concentration of nitronium ions in 68.3% sulphuric acid is less than the stoichiometric concentration of nitric acid by a factor of ca. 6 x 10 8. The value of the rate coefficient for mesitylene in (26) then becomes 3.5 X 107 mol-1 s dm3. This is... 

A further test of this interpretation is provided by the activation energies of the reactions that occur at the limiting rate. The observed activation energies for the nitration of mesitylene and naphthalene in 67.1% sulphuric acid are 75.3 and 64.8 kJ mol"1 respectively (Coombes et al., 1968). On the interpretation in terms of reaction on encounter the activation energy should be the sum of the AH° term for the formation of the nitronium ion (43 kJ mol"1 in 68.3% sulphuric acid) (Hartshorn et al., 1972), and the term derived from the temperature dependence of the viscosity of the solvent (24 kJ mol"1 see (8) and Table 2). Thus, the expected activation energy is ca. 67 kJ mol-1, a value in reasonable agreement with the experimental results. 

Nitration of mesitylene to di- and tri-nitromesitylenes proceeds with great... 

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