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Acid-Catalyzed Nitration

The general Friedel-Crafts acylation principle [36] can be applied to aromatic nitrations involving nitryl halides, dinitrogen pentoxide, and dinitrogen tetroxide (the halides and anhydrides of nitric acid). These should be considered as Friedel-Crafts type reactions, as obviously a very [Pg.152]

Friedel-Crafts type nitration using nitryl chloride had been initially reported by Price and Sears [38] who found AICI3 to be the most suitable catalyst. Deactivated aromatics, however, were nitrated only with difficuhy and the method was, therefore, considered to be of limited value. Investigations of Olah and Kuhn [39] have shown that aromatic compounds, including deactivated ones such as halobenzenes and benzotrifluoridc. can [Pg.153]

Using nitryl chloride as the nitrating agent, which in the laboratory is conveniently prepared by the reaction of nitric acid with chlorosulfuricacid [40], TiCI is found to be the most suitable catalyst. FeCIj, ZrCU. AJCIj Md AlBr3 are also effective but the reactions are more difficult to handle. [Pg.153]

With BCI3, Olah and Kuhn obtained a smaller amount of nitrated product and considerable ring chlorination SbFs is also an active catalyst for the nitryl chloride nitration of aromatics BFj was found to be inactive as a catalyst. The following yields were obtained upon nitration of the aromatics using TiCl4 as catalyst benzene, 88% toluene, 81.5% ethylbenzene, [Pg.153]

There is always a certain amount of ring-chlorinated by-product formed in the nitrations. Reactions carried out either by using an excess of aromatics as solvent (TiCU is miscible with many aromatics) or in carbon tetrachloride solution, always contain chlorinated by-products. The amount of chlorinated by-products can be decreased by using solvents with higher dielectric constants. Tetramethyiene sulfone (sulfolane) was found to be a suitable solvent for the TiCL and also for most of the other Lewis-acid-catalyzed nitrations. It has excellent solvent properties for aromatics and the catalysts as well as for nitryl halides. It is superior to other solvents that can be used, such as nitromethane. As it is completely miscible with water, the work-up of the reaction mixtures after the reactions are completed is very easy. [Pg.153]


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-... [Pg.43]

The reaction (NO + N02 NO+ + NO2 ) is recommended by Ridd (1998) to put in parentheses to imply that it illustrates the stoichiometry of the process, not the mechanism. The mechanism is more complex because the rate of these nitrous acid-catalyzed nitrations greatly exceed the rate of formation of nitronium ions in the solution. [Pg.252]

A kinetic study of nitrous acid-catalyzed nitration of naphthalene with an excess of nitric acid in aqueous mixture of sulfuric and acetic acids (Leis et al. 1988) shows a transition from first-order to second-order kinetics with respect to naphthalene. (At this acidity, the rate of reaction through the nitronium ion is too slow to be significant the amount of nitrous acid is sufficient to make one-electron oxidation of naphthalene as the main reaction path.) The reaction that initially had the first-order in respect to naphthalene becomes the second-order reaction. The electron transfer from naphthalene to NO+ has an equilibrium (reversible) character. In excess of the substrate, the equilibrium shifts to the right. A cause of the shift is the stabilization of cation-radical by uncharged naphthalene. The stabilized cation-radical dimer (NaphH)2 is just involved in nitration ... [Pg.252]

The nitration of phenols can result in anomalous and large differences in product isomer ratios, showing a high dependence on both nitrating agent and reaction medium. Here the situation is complicated by the intervention of an alternative nitration mechanism - that of nitrous acid catalyzed nitration, which proceeds via in situ nitrosation-oxidation (see Section 4.4). [Pg.138]

Olah, G. A., Malhotra, R. and Narang, S. C. Aromatic-substitution. 43. Perfluorinated resinsulfonic acid-catalyzed nitration of aromatics. J. Org. Chem., 1978, 43, 4628-4630. [Pg.119]

Analogous results were obtained for the nitrous acid catalyzed nitration of durene (26). Here, however, CIDNP signals were obtained also in the nitration of durene by N02 +, and their character suggested that durene and N02 were being formed not by the direct transfer of an electron from durene to N02 +, but by the homolysis of an ipso intermediate. Recombination of durene and N02 then led to nitrodurene. [Pg.142]

Nitration with nitric acid in the presence of strong protic acids such as H2SO4, FSO3H, and CF3SO3H or Lewis acids such as boron trifluotide requires subsequent separation of spent acid (due to water formed in the reaction) and neutralization of acid left in the product. One is generally left with a large amount of dilute acid for disposal, which is neutralized in the case of sulfuric-acid-catalyzed nitrations to a mixture of ammonium nitrate and ammonium sulfate. By using a solid acid catalyst most of these environmental problems can be eliminated. The solid acid catalyst is simply separated and recycled for subsequent use. [Pg.146]

Kameo et ai. reported [50] the use of polystyrenesulfonic acid as a catalyst in the nitration of aromatics with HNO3. Nitration of toluene with 90% HNO3 over dried sulfonated polystyrene resin (Rohm and Haas amberlite IR-120) was also reported by Wright et al. at 65-70°C to give an ortho para isomer ratio of only 0.68, much lower than usual ortho-para ratios in acid-catalyzed nitrations [11]. It is considered that the nitroniura ion is strongly ion paired to the resinsulfonic acid. The ion-pair salt thus formed is much bulkier than the free nitronium ion or such nitronium salts as NO2 BF4. [Pg.146]

Both protic- or Lewis-acid-catalyzed nitration of aromatics can be carried out with a/ky/ nitrates (i.e., alkyl esters of nitric acid). Acid catalysts are assumed to form nitronium ion from alkyl nitrates or strongly polarized complexes. [Pg.148]

The sulfuric acid-catalyzed nitration of benzene with ethyl nitrate at 78-80 C gives nitrobenzene in only 12% yield [27], p-Fluoroacetanilide is, however, nitrated under similar conditions at 0°C in 85% yield [28],... [Pg.148]

Studying the acid-catalyzed nitration of alcohols Ingold extended his general scheme of aromatic electrophilic C-nitration to the nitration at oxygen (and nitrogen) centers [101]. [Pg.177]

Hydrogen isotope exchange at the nitrogen atom of A, A -dimethylanilinium ions is catalyzed by acid " and nitrosonium ion. The latter reaction has been studied at acidities for which the subsequent chemical reaction between NO and amines is much slower. The mechanism postulates the formation of a loose complex between NO" and the anilinium ion, followed by proton loss from the nitrogen. This process is related to the direct diazotization of some anilinium ions, and to the nitrous acid-catalyzed nitration and oxidation of the A, A -di-methylanilinium ion. [Pg.73]


See other pages where Acid-Catalyzed Nitration is mentioned: [Pg.250]    [Pg.251]    [Pg.145]    [Pg.583]    [Pg.249]    [Pg.251]    [Pg.252]    [Pg.42]    [Pg.142]    [Pg.15]    [Pg.140]    [Pg.152]    [Pg.191]    [Pg.115]   


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Acidic nitration

Nitrate acid

Nitrating acid

Nitration Lewis-acid catalyzed

Nitration acid

Nitration solid acid catalyzed

Protic-Acid-Catalyzed Nitration

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