Mechanism Of Aromatic Nitration Research Articles

Is Aromatic Nitration Spin Density Driven?

The mechanism of aromatic nitration is critically reviewed with particular emphasis on the paradox of the high positional selectivity of substitution in spite of low substrate selectivity. Early quantum chemical computations in the gas phase have suggested that the retention of positional selectivity at encounter-limited rates could be ascribed to the formation of a radical pair via an electron transfer step occurring before the formation of the Wheland intermediate, but calculations which account for the effects of solvent polarization and the presence of counterion do not support that point of view. Here we report a brief survey of the available experimental and theoretical data, adding a few more computations for better clarifying the role of electron transfer for regioselectivity.

Cover Picture: Experimental Detection of the H2NO3 Radical (ChemPhysChem 10/2003)

AbstractThe cover pictures shows…︁‥the mass spectrum of nitrogen hydroxide oxide, the H2NO3. radical, which was discovered by neutralization reionization mass spectrometry (NRMS) and characterized as a relatively long‐lived (over 1 μs) metastable species. The discovery required the availability of the appropriate charged precursor that fortunately had previously been prepared by this group (1989) as a result of their sustained interest in gas‐phase ion chemistry of nitrates, nitrites and related molecules. Cacace et al. found that protonation of nitric acid by strong Brønsted acids yields, in addition to the H2ONO2+ ion, smaller amounts of the less stable (HO)2NO+ isomer, namely charged nitrogen hydroxide oxide. This result has allowed the present discovery by NRMS (yellow trace), whereas NRMS of the H2ONO2+ ion does not result in detectable H2NO3. neutral species (green trace). The importance of nitrogen hydroxide oxide stems from its relevance to a variety of research areas, from the reduction of the NO32− anion, to atmospheric chemistry, radiolysis of nuclear‐waste solutions, the charge‐transfer mechanism of aromatic nitration, etc. Find out more in the communication by Cacace et al. on pp. 1128–131.

The mechanism of aromatic nitration in solution: Marcus theory and semiempirical molecular orbital calculations on NO2 + and NO+ as one-electron oxidants

Marcus theory calculations of rates of electron transfer (ET) have been carried out for attack by NO+ and NO2+ on various reactive aromatic substrates including alkylbenzenes and naphthalene. While reasonable agreement between calculation and experiment is obtained for nitrous acid catalysed nitration, the calculated rate of electron transfer in the nitration of naphthalene by nitronium ion is too low by between nine and fifteen orders of magnitude. Possible reasons for this discrepancy are discussed and it is suggested that H2NO3+ may be the ET agent responsible for the previously observed CIDNP effects in this system. Semi-empirical molecular orbital calculations have been carried out on relevant species, including reaction coordinates for the nitration of naphthalene in the 1- and 2-positions. Transition state energies suggest that attack in the 1-position is very much favoured by the ET process.

The mechanism of aromatic nitration by tetranitromethane

Aromatic nitrations by tetranitromethane are shown to be photo-chemically initiated and are believed to proceed via trinitromethyl nitrite.

Mechanism of aromatic nitration

Mechanism of aromatic nitration

203. Kinetics and mechanism of aromatic nitration. Part X. Variation of the rate of aromatic nitration in sulphuric acid media with composition of the solvent

203. Kinetics and mechanism of aromatic nitration. Part X. Variation of the rate of aromatic nitration in sulphuric acid media with composition of the solvent

8. Kinetics and mechanism of aromatic nitration. Part IX. Nitrosating agents in nitrations catalysed by nitrous acid

8. Kinetics and mechanism of aromatic nitration. Part IX. Nitrosating agents in nitrations catalysed by nitrous acid

493. Kinetics and mechanism of aromatic nitration. Part II. Nitration by the nitronium ion, NO2 +, derived from nitric acid

493. Kinetics and mechanism of aromatic nitration. Part II. Nitration by the nitronium ion, NO2 +, derived from nitric acid

512. Kinetics and mechanism of aromatic nitration. Part VI. The nitration of phenols and phenolic ethers: the concomitant dealkylation of phenolic ethers. The role of nitrous acid

512. Kinetics and mechanism of aromatic nitration. Part VI. The nitration of phenols and phenolic ethers: the concomitant dealkylation of phenolic ethers. The role of nitrous acid

495. Kinetics and mechanism of aromatic nitration. Part IV. Nitration by dinitrogen pentoxide in aprotic solvents

495. Kinetics and mechanism of aromatic nitration. Part IV. Nitration by dinitrogen pentoxide in aprotic solvents

496. Kinetics and mechanism of aromatic nitration. Part V. Nitration by acyl nitrates, particularly by benzoyl nitrate

496. Kinetics and mechanism of aromatic nitration. Part V. Nitration by acyl nitrates, particularly by benzoyl nitrate

513. Kinetics and mechanism of aromatic nitration. Part VII. Products of nitration of aniline derivatives, especially of dimethylaniline. The concomitant dealkylation of dialkylanilines

513. Kinetics and mechanism of aromatic nitration. Part VII. Products of nitration of aniline derivatives, especially of dimethylaniline. The concomitant dealkylation of dialkylanilines

494. Kinetics and mechanism of aromatic nitration. Part III. Nitration in acidified aqueous nitric acid

494. Kinetics and mechanism of aromatic nitration. Part III. Nitration in acidified aqueous nitric acid

Kinetics and Mechanism of Aromatic Nitration

IN an earlier note1 it was shown how the study of the kinetics of nitration, particularly the study of reaction order, established (a) the formation of the nitronium ion, and (b) its effectiveness as the entity which attacks the aromatic molecule. Further kinetic investigation, particularly of salt and solvent effects, has given information on two other general features of the reaction. They relate to (c) the reaction stages by which the nitronium ion is formed, and (d) those by which it becomes a nitro-group in the aromatic compound.