Studies in aromatic nitration. 2. Nitrogen-14 NMR study of the nitric acid/nitronium ion equilibrium in aqueous sulfuric acid

Ross, David S.; Kuhlmann, Karl; Malhotra, Ripudaman

doi:10.1021/ja00351a030

Cited by 43 publications

(23 citation statements)

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“…The equilibria of Eqs. (17) and (18) have been experimentally studied using various spectroscopic techniques, amongst others Raman and UV spectroscopy [29-311 and r4N NMR [32] in a wide acidity range from 1 to 98 Table 1 Frequency factor and activation energy for the reaction rate constant k;…”

Section: Hno Ti H + + Nomentioning

confidence: 99%

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Aromatic nitrations by mixed acid. Slow liquid-liquid reaction regime

Zaldı́var

Molga

Alós

et al. 1995

Chemical Engineering and Processing: Process Intensification

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Aromatic nitrations by mixed acid have been selected as a specific case of a heterogeneous liquid-liquid reaction. An extensive experimental programme has been followed using adiabatic and heat-flow calorimetry and pilot reactor experiments, supported by chemical analysis. A series of nitration experiments has been carried out to study the influences of different initial and operating conditions such as temperature, stirring speed and sulphuric acid concentration. In parallel, a mathematical model to predict the overall conversion rate has been developed. In this paper the mathematical modelling and the implementation and experimental validation for benzene, toluene and chlorobenzene mononitration in the kinetic control regime (slow liquid-liquid reaction) are presented and discussed.

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Section: Hno Ti H + + Nomentioning

confidence: 99%

“…(c) The equilibrium constants KNot and KHNo3 as a function of temperature. It has been assumed for the nitric acid dissociation that KHN03= eXp( -*) (32) where AGHNo, was calculated from data at 298.2 K. Ross et al [22], using 14N NMR, studied the equilibrium Eq. (18) k; for each aromatic compound.…”

Section: No-j+mentioning

confidence: 99%

Aromatic nitrations by mixed acid. Slow liquid-liquid reaction regime

Zaldı́var

Molga

Alós

et al. 1995

Chemical Engineering and Processing: Process Intensification

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“…3 Raman spectra of NO 2 þ have been observed in solution 4 as well as in the solid state. 5 Using 14 N NMR, Ross et al 6 have examined the nitric acid/nitronium ion equilibrium in aqueous sulfuric acid. Dimeric nitric acid, (HNO 3 ) 2 or (DNO 3 ) 2 , was detected by FTIR in HNO 3 or DNO 3 :H 2 O:Ar matrices.…”

mentioning

confidence: 99%

Great Enhancement in the Oxidation Ability of Dilute Nitric Acid in Nanoscale Water-Droplets of Reverse Micelle Systems

Hojo¹,

Ueda²,

Daike³

et al. 2006

Bulletin of the Chemical Society of Japan

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In reverse micelle systems, a large enhancement of the oxidation ability of dilute nitric acid was discovered, and its oxidation mechanism was explored. The Br À ion in the surfactant, CTAB, was oxidized to Br 2 (or Br 3 À ) in the CHCl 3 / CTAB/H 2 O reverse micelle system with W ¼ 1:0{4:0 by diluted nitric acid (0.25-2.5 mol dm À3 in 1.0 vol % H 2 O portion) at 15-40 C where CTAB stands for cetyltrimethylammonium bromide, and the W value is the ratio of [. At higher concentrations of nitric acid and temperatures, faster reactions occurred. Otherwise, long reaction times were needed, e.g., 10 h for 1.0 mol dm À3 HNO 3 at 25 C. Light or ambient oxygen did not appear to affect the reaction. The ratio of produced Br 2 or (Br 3 À ) to the initial amount of HNO 3 indicated the following reaction scheme:The nitroyl ion (or nitronium ion), NO 2 þ , was proposed as the intermediate active species. The addition of HClO 4 as a proton source caused the complete reduction of N(V) as follows: The nitrate ion has high chemical stability, especially at low concentrations. Standard redox potentials indicate that it should serve as an excellent oxidizing agent, but in order to react with suitable reactants to form elemental nitrogen or ammonia, special conditions are required, such as the presence of catalysts and high temperature and pressure.1 Concentrated nitric acid has strong oxidation ability, although dilute nitric acid in aqueous solution at room temperature exhibits no apparent oxidation trend. Cotton and Wilkinson have described that nitric acid with a concentration of less than 2 mol dm À3 has almost no oxidation ability.2 Mixtures of concentrated nitric acid and sulfuric acid (''mixed acid'') are used for nitration of organic compounds, and the nitroyl ion (or nitronium ion) NO 2 þ is regarded as the active intermediate. 3 Raman spectra of NO 2 þ have been observed in solution 4 as well as in the solid state.5 Using 14 N NMR, Ross et al. 6 have examined the nitric acid/nitronium ion equilibrium in aqueous sulfuric acid. Dimeric nitric acid, (HNO 3 ) 2 or (DNO 3 ) 2 , was detected by FTIR in HNO 3 or DNO 3 :H 2 O:Ar matrices. 7 We have been studying the structure of water in nanoscale water-droplets of reverse micelles, stabilized by surfactants in organic solvents. 8 The size of the ''water-pool'' or ''water-droplet'' may vary from 1 to %100 8 It is well known that the properties of water localized in the interior of reverse micelles differ from those of bulk water, and the difference becomes progressively smaller as the amount of water in the micelle system increases.10

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“…245,448 It has also been shown by 14 N NMR spectroscopy that a mixture of nitric acid in 88% sulfuric acid contains both nitronium ion and free nitric acid. 522 At 95% H 2 SO 4 only the NO 2 þ ion was detected (a single peak at d 14 N 251 relative to external liquid NH 3 ). Prakash, Heiliger, and Olah 523 have recently arrived at similar conclusions through 15 N NMR studies of the nitric acidnitronium ion system.…”

Section: -Brmentioning

confidence: 98%