Nitration, mechanism

With very few exceptions, the final step in the nitration mechanism, the deprotonation of the ff-complex, is fast and therefore has no effect on the observed kinetics. The fast deprotonation can be confirmed by the absence of an isotope effect when deuterium or... 

The term nitrolysis is usually applied to a nitrating mechanism in which both the rupture of the C-N bond and the formation of a nitramine occur simultaneously with the formation of an alcohol which subsequently undergoes esterification (1) ... 

Titov and co-workers, although conceding the validity of the ionic nitration mechanism for liq phase nitrations with coned acids, believe that many nitrations occur via a free-radical mechanism involving the free radicals (at any rate molecules having an unpaired electron) N02, N03, and NO. For vapor phase nitration of hydrocarbons, nitration of side chains of aromatic compds in... 

We shall discuss ionic nitration mechanisms in terms of nitration by pure nitric acid and where appropriate comment on effects of such additives as sulfuric acid, water, nitrous acid etc. The nitration scheme now generally ac-... 

Amongst these are the studies of Lowen et al (Ref 37), Urbanski et al (Ref 58) and Brennecke Kobe (Ref 46), and in particular those of Titov (Refs 28 65). These studies suggest the necessity for a non-nitronium nitration mechanism and such a mechanism will be examined in the next subsection Free Radical Nitration... 

In recent years there has appeared a considerable volume of literature dealing with nitrations. The expl-oriented publications on nitrations can be divided, albeit somewhat arbitrarily, into three general headings nitration mechanisms TNT production and miscellaneous nitrations, ie, production and prepn of expls other than TNT. Studies of nitration mechanisms were summarized in the preceding section. Recent investigations on expl production and prepn via nitration will be presented below in chronological order TNT Production... 

Examples of mnltiplicity of nitration mechanisms that depend on IPs of substrates are the nitration of naphthalene (NaphFI + N02 system) and perylene (PerH -I- N02 system) (Scheme 4.40). 

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). 

Don t try to memorize a nitration mechanism as a sepcirate mechanism from halogenations or sulfonation. Let your understanding of one mechanism reinforce your understanding of other mechanisms. 

J. Persoz said that nitrous oxide reacts with moist potassium hydroxide, forming nitric acid and ammonia, or ammonium nitrate, but later considered that these substances were derived from some ammonium nitrate mechanically mixed with the gas prepared from that salt. M. Berthelot could find no trace of ammonia... 

The remaining steps in the mechanism are identical with those in the bromination and nitration mechanisms The charge around the ring is delocalized, and then the loss of a proton reestablishes the aromaticity of the ring. 

HMordenite, HFaujasite-780, HFaujasite 720 and Na-Faujasite zeolites. Among the different catalysts, HFaujasite-720 was the most active and selective catalyst towards 2,4-dinitrotoluene, achieving a yield of dinitrotoluenes of 92 % with a ratio of 2,4- to 2,6- isomers of 4.3 1 in 3 min reaction time. Using this zeolite, l-chloro-2-nitrobenzene and pyrazole were also nitrated regioselectively to obtain l-chloro-2,4-dinitrobenzene in a l-chloro-2,4-dinitro l-chloro-2,6-dinitro ratio of 30 1, and 1,4-dinitropyrazole in 80% yield, respectively. The authors proposed a nitration mechanism in which the protons in the zeolite are replaced by nitronium ions derived from N2Os in a fast pre-equilibrium process. This produces active sites for transfer of nitronium ion from faujasite to aromatic in the rate-controlling step. 

L. Eberson, M. P. Hartshorn, F. Radner, Ingold s Nitration Mechanism Lives , Acta Chem. Scand. 1994, 48, 937-950. 

A similar nitration mechanism was suggested by Vorozhtsov [21], He also assumed the formation of an addition product of the hydrocarbon with HN03 and H2S04, followed by splitting off H2S04 and H20. 

A nitration mechanism formula of this type was suggested by Ingold [28] in 1935. 

Ingold and his co-workers [33] and Bennett and co-workers [34-36] believed that the reaction rate depends on the concentration of the nitronium ions, N02+. They suggested the following summarized nitration mechanism ... 

Another nitration mechanism has been offered by Perrin for arenes oxidized more easily than toluene [17], In his opinion, a one-electron transfer from the aromatic substrate to the nitronium cation takes place (Scheme 4). 

Without going into further discussion on the role of one-electron transfer in the mechanism of nitration of aromatic compounds, it should be noted that the nitration mechanism, which seemed to be strictly proved and clear after Ingold s studies [2], now again attracts steadfast attention. The research in this direction is worth further development. 

With regard to the nitration of alcohols attention should be drawn to the work of Eremenko [140) who pointed out the role of undissociated nitric acid in the 0 nitration mechanism. 

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