Mesitylene, nitration

N 16.47%, OB to C02 —103.4%, triclinic needles (from ale). prisms (from acet), mp 238.2°, bp expl at 415°, d 1.48g/cc. Insol in w, si sol in hot ale eth, misc in hot acet benz. Can be prepd by treating mesitylene with a mixt of. nitric sulfuric acids in the cold (Refs 2 3). Blanksma (Ref 4) prepd it by dissolving mesitylene in sulfuric acid, partial sulfonation taking place, and then adding the soln to nitric acid, with the pptn of trinitio-mesitylene. Kholevo (Ref 6) nitrated mesitylene with nitric acid 27, sulfuric acid 69, water 4% to yield white crysts. The expl power of trinitro-mesitylene is less than PA (Ref 9), and it develops a bomb press 84% that of TNT (Ref 8), Its impact sensitivity is 52% that of TNT (Ref 7), and it expls at 415° (Ref 5)... 

When the concentration of 2-phenylethanesulphonate anion was >0-5 mol 1, or when 2-mesitylethanesulphonate anion (v), " mesitylene-a-sulphonate anion, or iso-durene-a -sulphonate anion were nitrated, the initial part of the reaction deviated from a first-order dependence on the concentration of the aromatic towards a zeroth-order dependence. 

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. 

Rates of nitration in perchloric acid of mesitylene, luphthalene and phenol (57 I-6i-i %), and benzene (57 i-64 4%) have been deter-mined. The activated compounds are considered below ( 2.5). A plot of the logarithms of the second-order rate coefficients for the nitration of benzene against — ( f + log over the range of acidity... 

The rates of nitration, under a variety of conditions (56-80% sulphuric acid, 57-62% perchloric acid), of mesitylene and benzene... 

For nitration carried out in sulpholan ([HNO3] = 4-91 mol 1" ), zeroth-order nitration was observed with mesitylene. With toluene and benzene the kinetics were of mixed-order and first-order, respectively. ... 

Compound nitrated Zeroth order Benzene and homologues Toluene (benzene) Mesitylene... 

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. 

The observation of nitration nitrosation for mesitylene is important, for it shows that this reaction depends on the reactivity of the aromatic nucleus rather than on any special properties of phenols or anilines. 

Nitration at the encounter rate and nitrosation As has been seen ( 3.3), the rate of nitration by solutions of nitric acid in nitromethane or sulpholan reaches a limit for activated compounds which is about 300 times the rate for benzene imder the same conditions. Under the conditions of first-order nitration (7-5 % aqueous sulpholan) mesitylene reacts at this limiting rate, and its nitration is not subject to catalysis by nitrous acid thus, mesitylene is nitrated by nitronium ions at the encounter rate, and under these conditions is not subject to nitration via nitrosation. The significance of nitration at the encounter rate for mechanistic studies has been discussed ( 2.5). 

Under the conditions mentioned, i-methylnaphthalene was nitrated appreciably faster than was mesitylene, and the nitration was strongly catalysed by nitrous acid. The mere fact of reaction at a rate greater than the encounter rate demonstrates the incursion of a new mechanism of nitration, and its characteristics identify it as nitration via nitrosation. 

The data of table 4.1, column [a), do not suggest that nitration of the alkylbenzenes with nitronium tetrafluoroborate in sulpholan occurs upon encoimter mesitylene might be so reacting ( 3.3) but comparison with a more inherently reactive substance would be necessary before this possibility could be considered. 

Zeroth-order nitrations. The rates of nitration at 25 °C in solutions of acetyl nitrate (6xio —0-22 mol 1 ) in acetic anhydride of 0- and jw-xylene, and anisole and mesitylene were independent of the concentration and nature of the aromatic compound provided that... 

Fig. 5.1. Zeroth-order rates of nitration with acetyl nitrate compared with those for other systems, (a) HNOa/ sulpholan, (i) HNO3/CCI4, (c) AcONOj/AcjO/O % AcOH, (d) AcONOj/AcaO/O % AcOH/[mesitylene] = o-8 mol l-i,n (e) AcONOj/AcaO/ [AcOH] = 2-2moll-i,ii >(/)AcONOa/AcaO/[AcOH] = 1-96 mol l-i and (g) AcONOa/ AcaO/[AcOH] 3 9i mol l-i/[mesitylene] = o-8 mol 1-i H.

Nitrations of the zeroth order are maintained with much greater difficulty in solutions of acetyl nitrate in acetic anhydride than in solutions of nitric acid in inert organic solvents, as has already been mentioned. Thus, in the former solutions, the rates of nitration of mesi-tylene deviated towards a dependence on the first power of its concentration when this was < c. o-05-o-i mol 1 , whereas in nitration with nitric acid in sulpholan, zeroth-order kinetics could be observed in solutions containing as little as 10 mol 1 of mesitylene ( 3.2.1). 

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. 

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

The evidence outlined strongly suggests that nitration via nitrosation accompanies the general mechanism of nitration in these media in the reactions of very reactive compounds.i Proof that phenol, even in solutions prepared from pure nitric acid, underwent nitration by a special mechanism came from examining rates of reaction of phenol and mesi-tylene under zeroth-order conditions. The variation in the initial rates with the concentration of aromatic (fig. 5.2) shows that mesitylene (o-2-0 4 mol 1 ) reacts at the zeroth-order rate, whereas phenol is nitrated considerably faster by a process which is first order in the concentration of aromatic. It is noteworthy that in these solutions the concentration of nitrous acid was below the level of detection (< c. 5 X mol... 

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... 

Nitrations can be performed in homogeneous media, using tetramethylene sulfone or nitromethane (nitroethane) as solvent. A large variety of aromatic compounds have been nitrated with nitronium salts in excellent yields in nonaqueous media. Sensitive compounds, otherwise easily hydroly2ed or oxidized by nitric acid, can be nitrated without secondary effects. Nitration of aromatic compounds is considered an irreversible reaction. However, the reversibihty of the reaction has been demonstrated in some cases, eg, 9-nitroanthracene, as well as pentamethylnitrobenzene transnitrate benzene, toluene, and mesitylene in the presence of superacids (158) (see Nitration). 

Mesitylene is converted to a dye iatermediate, 2,4,6-trimethyl aniline [88-05-1] (mesidine), via nitration to l,3,5-trimethyl-2-nittobenzene [603-71-4] followed by reduction, eg, catalytic hydrogenation (38). Trinitromesitylene has been prepared for use ia high temperature tolerant explosives (39). The use of mesitylene to scavenge contaminant NO from an effluent gas stream has been patented (40). 

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. ... 

Nitrated Solvent Naphtha (N.S.N.). As nitration of crude solvent naphtha by the usual one-stage method results in yields that are too low, because of oxidation, E. Blecher et al (Ref 3) proposed nitrating only the refined material, and in two stages. The two-stage method is described in Colver, pp 255 686—87 (Ref 4). The product consists chiefly of 2,4,6-Trinitro-mesitylene (see under Mesitylene and Deriva- tives in this Vol), and 3,5,6-trinitropseudocumene, with small quantities of the nitrated products of xylene, ethylbenzene, etc... 

Analogies for such a mechanism in diazotization are found in the nitrous acid-catalyzed nitration of A,A-dimethylaniline, mesitylene, 4-nitrophenol, and some related compounds, which were investigated by 15N NMR spectroscopy in Ridd s group (Ridd and Sandall, 1981 Ridd et al., 1992 Clemens et al., 1984a, 1984b, 1985 Johnston et al., 1991 review Ridd, 1991). Ridd and coworkers were able to demonstrate clearly that not only the nitration proper, but also the preceding C-nitrosation, is accompanied by a marked 15N nuclear polarization. This was at-... 

An alternative to the above mechanism is that acetoxylation is an addition-elimination process involving N02 and OAc , leading to nitro and acetoxy products77, and it follows that this process would be less likely to occur, for example, with mesitylene and significantly perhaps, experiments seeking acetoxylation in mesitylene have failed78 on the other hand, mesitylene is a very reactive substrate so it could be that an alternative nitrating species is involved here. 

Mesitylene was studied using the range 5-7 M nitric acid, and when the nitrous acid concentration is small (< 0.014 M) nitronium ion nitration appears to occur, giving zeroth-order kinetics weakly retarded by nitrous acid. At rather higher nitrous acid concentrations the reaction is catalysed by nitrous acid and the kinetics go over to first-order (at constant nitrous acid concentration). 

The simultaneous annihilation of the aromatic cation radical by its triad partners N02 and pyridine, as presented in Scheme 12, is most apparent in the nature of the aromatic product (i.e., stoichiometry) from mesitylene, among all the other aromatic (benzenoid) donors. Thus, the direct incorporation of N02 and pyridine into the aromatic nucleus is shown by the concomitant ring nitration and pyridination of mesitylene (Kim et al., 1993),... 

Since the latter conditions pertain to aromatic nitration solely via the homolytic annihilation of the cation radical in Scheme 16, it follows from the isomeric distributions in (81) that the electrophilic nitrations of the less reactive aromatic donors (toluene, mesitylene, anisole, etc.) also proceed via Scheme 19. If so, why do the electrophilic and charge-transfer pathways diverge when the less reactive aromatic donors are treated with other /V-nitropyridinium reagents, particularly those derived from the electron-rich MeOPy and MePy The conundrum is cleanly resolved in Fig. 17, which shows the rate of homolytic annihilation of aromatic cation radicals by NO, (k2) to be singularly insensitive to cation-radical stability, as evaluated by x. By contrast, the rate of nucleophilic annihilation of ArH+- by pyridine (k2) shows a distinctive downward trend decreasing monotonically from toluene cation radical to anthracene cation radical. Indeed, the... 

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