Hyponitrous Acid Research Articles

Stoicheiometry, kinetics, and mechanism of the oxidation of hyponitrous acid by iodine in acetate buffers

The reaction of hyponitrous acid with iodine occurs as (i) in the pH range 4–6 and at [I–] H2N2O2+ I2+⅙H2O → 2HI +½N2O +⅔NO +⅓HNO3(i) < 0.025 mol dm–3. One of the identified intermediates is HNO2 which is the main source of NO. Several reactions involving HNO2, H2N2O2, and iodide may follow. The decomposition of H2N2O2 is very significant at pH < 4 and [I–] > 0.025 mol dm–3, and the stoicheiometry Δ[H2N2O2]/Δ[I2] changes from 1 :1 to 2:1 or even 6:1. The rate law (ii) applies where Kd′ is the first acid-–d[I2]T/dt=KK′d[H2N2O2]T[I2]T/[H+](1 +K[I–])(ii) dissociation constant of H2N2O2 and K is the equilibrium constant for the formation of I3–; k was found to be (2.1 ± 0.1)× 104 dm3 mol–1s–1at 35 °C employing K′d= 6.3 ×10–8 mol dm–3 and K= 549 dm3 mol–1.

ChemInform Abstract: Redox Chemistry of Hyponitrous Acid. Part 4. Stoichiometry, Kinetics and Mechanism of Oxidation by Cerium(IV) in Acid Sulfate Solutions, and Determination of Hyponitrous Acid in Acid Perchlorate Solutions.

AbstractThe mechanism of the reaction outlined in the scheme involves oxidation of H2N2O2 to an intermediate, probably H2N2O3, which decomposes to yield N2O and an isomer of HNO2 that subsequently reacts with one more H2N2O2 to yield N2 and HNO3.

Prediction of Isotope Effects for Anticipated Intermediate Structures in the Course of Bacterial Denitrification

Vibrational-analysis methods have been used to estimate the equilibrium 14N/15N isotope effects to be expected for conversion of nitrite anion to thirteen possible intermediate-state and productstate structures [HONO, NO+ , NO, NO-, FeNO, ON*NO2, O*NNO2, O2NNO2, ONO*N, O*NON, ONNO, *NNO, N*NO] in the reduction of nitrite ion to nitrous oxide denitrifying bacteria. The results, taken in combination with previous experimental isotope-effect and tracer studies of the Pseudomonas stutzeri and related systems, are consistent with a suggestion that a second nitrite anion enters the enzyme-catalytic cycle at the stage of a nitrosyl-ion intermediate but re-emerges after entry of the reducing electrons; the product nitrous oxide is then formed by disproportionation of enzymically generated hyponitrous acid. The calculations are consistent with contributions, under different experimental conditions, of several different transition states to limiting the rate of the enzymic reaction. These transition states (and the corresponding experimental conditions) are the transition states for N -O fission in the generation of a mononitrogen electrophilic species from nitrite anion (high reductant, high nitrite concentrations), for attack of nitrite on this electrophile (high reductant, low nitrite concentrations) and for electron transfer to a dinitrogen-trioxide-like species (low reductant concentration).

ChemInform Abstract: The Aqueous Solution Chemistry of Nitrogen in Low Positive Oxidation States

Abstract Recent developments in the aqueous solution chemistry of nitrogen are described, with particular attention to the low positive oxidation states +1 and +2. The compounds discussed include hyponitrous acid and hyponitrites, nitrosyl hydride (HNO, “nitroxyl”), trioxodinitrate, nitric oxide, and nitroamine. The numerous redox pathways in which these and other nitrogen compounds are participants illustrate the versatility of that element, and bear important relation to current problems in nitrogen cycle research that focus upon the identity and reactivity of nitrogen species in intermediate oxidation states.

Stoicheiometric and nitrogen-15 labelling studies on the hyponitrous acid–nitrous acid reaction

The stoicheiometry of the hyponitrous acid–nitrous acid reaction has been determined over a wide acidity range, up to 8.5 mol dm–3 HClO4. For approximately 1 : 1 reaction conditions, the major reaction pathway gives N2 and HNO3 as products, together with the production of N2O (by self decomposition of hyponitrous acid) and NO (by self decomposition of nitrous acid). In addition, 15NO produced by self decomposition of H15NO2 reacts with H214N2O2 to give some 14NO and N2O of mixed isotopic composition. Reactions under other conditions gave products that may be accounted for by varying contributions from these reactions.

The kinetics and mechanism of the hyponitrous acid–nitrous acid reaction at 0 °C

The kinetics of the reaction between hyponitrous acid and nitrous acid have been examined, mainly at 0 °C, over the acidity range 0.01 to 11.6 mol dme–3 perchloric acid. Values of kobs, the measured first-order rate constant, increase dramatically with [HClO4] from about 4 mol dme–3 HClO4, and then decrease again as [HClO4] increases beyond about 7 mol dm–3. The maximum value of kobs. at 0 °C occurs just above 7 mol dm–3 perchloric acid and is greater than 2.5 × 10–2s–1 at 0.005 mol dm–3 nitrous acid. The reaction may be described by the two-term rate law: rate ={k2′+k3**(K/(K+hr))h0aw}[HNO2][H2N2O2], where k2′= 4.62 × 10–2 dm3 mol–1 s–1 and k3**= 5.41 × 10–3 dm6 mol–2 s–1 at 0 °C, and acidity functions, HR =–log10hR and Ho=–log10ho. The fall in rate at high acidity is attributed to the conversion of nitrous acid to the nitrosonium ion, suggesting that molecular nitrous acid is a kinetically active species. Added bromide ion at 5.56 mol dm–3 perchloric acid results in lowered rates due to the conversion of nitrous acid to nitrosyl bromide.

The Aqueous Solution Chemistry of Nitrogen in Low Positive Oxidation States

Abstract Recent developments in the aqueous solution chemistry of nitrogen are described, with particular attention to the low positive oxidation states +1 and +2. The compounds discussed include hyponitrous acid and hyponitrites, nitrosyl hydride (HNO, “nitroxyl”), trioxodinitrate, nitric oxide, and nitroamine. The numerous redox pathways in which these and other nitrogen compounds are participants illustrate the versatility of that element, and bear important relation to current problems in nitrogen cycle research that focus upon the identity and reactivity of nitrogen species in intermediate oxidation states.

The photoelimination of N-nitroso-N-acetyl-α-amino acids; a new synthesis of 1,2,4-oxadiazoles

The excitation of N-nitroso-N-acetyl-α-amino acids, nitrosopeptide model compounds, under neutral and weakly basic conditions, caused the homolysis of the N–N bond followed by decarboxylation to give hyponitrous acid (HNO) and N-acetylimines which were susceptible to nucleophilic addition. While weak bases caused the carboxylate group to assist intramolecular rearrangement to a small extent, they functioned primarily to provide nucleophilic NO–, which initiated nucleophilic attack leading to the C-nitroso derivatives. These C-nitroso derivatives spontaneously cyclized to 1,2,4-oxadiazoles much more rapidly than tautomerism to the corresponding oximes; the latter oximes failed to cyclize under the basic conditions.

Reaction of nitric oxide with hyponitrous acid: a hydrogen atom abstraction reaction

La reaction a lieu avec et sans inhibiteur de chaine (C 2 H 5 OH). Mesure des rendements en N 2 , N 2 O. Mecanismes

Oxidation of hydroxylamine by nitrous and nitric acids

The kinetics of the reaction of hydroxylamine with nitrous acid and with nitric acid were studied in an acidic nitrate medium. The mechanism of the reaction with nitrous acid in an acidic perchlorate medium, proposed by previous workers, is O-nitrosation of the hydroxylammonium ion; our data are consistent with this mechanism at an ionic strength of 2 M. The data at higher ionic strength (3 and 4 M), when compared to an extended treatment of the proposed mechanism, indicate either a deviation from this mechanism at high acid concentration or a change in one of the principal species in solution. Raman and UV spectroscopies were unable to verify a change in the species. In the reaction of hydroxylamine with nitric acid, we identified HNO/sub 2/, N/sub 2/O, and N/sub 2/ as products. This reaction is autocatalytic in HNO/sub 2/, and the distribution of products is dependent on the initial concentration of HNO/sub 2/, NH/sub 3/OH/sup +/, and HNO/sub 3/. The product N/sub 2/O derives from the nitrosation of NH/sub 3/OH/sup +/. HNO/sub 2/ with hyponitrous acid, which is an intermediate in the nitrosation of NH/sub 3/OH/sup +/. A kinetic model is partially successful in rationalizing the distribution of products.

Thermodynamics of Inorganic Nitrogen Transformations1

Standard free energies of formation for various inorganic N species were selected from the literature and used to calculate equilibrium constants for reactions involving various inorganic N species. These reactions were systematized into stability diagrams and used to discuss possible N transformations that may occur in soils. The developments show that N2(g) is the only stable N species in the redox range of pe + pH of 4 to 18. At lower redox NH4+ is stable, whereas at higher redox NO3- is stable. Stability diagrams were developed on the basis that first N2, then N2O, and finally N3- do not attain equilibrium with other inorganic N species. These diagrams provide insight into possible reaction sequences that may be involved in chemical denitrification. The hypothesis proposed herein is that NO0 (nitric oxide) and possible H2N2O2 (hyponitrous acid) may be rate-limiting intermediates in chemical denitrification. These N species are metastable but reach maximum stability in the narrow redox range of pe + pH 13.5 to 14.0. The possibility that these species may be the kinetically feasible intermediates in chemical denitrification are discussed.

On the electronic structure of NOH (hyponitrous acid monomer) in the ground state

The present MRD CI study confirms an earlier speculation of a paramagnetic NOH (GS). The X 3A″ and 1A′ states are found at +97.1 kJ/mol (23.2 kcal/mol) and +180.8 kJ/mol (43.2 kcal/mol) above the X 1A′ (HNO), respectively. The latter Δ Eisomerization is 60–80% larger than prior SCF results. A D e value of 125.3 ± 4 kJ/mol for NOH ( 3A″) → NO ( 2Π) + H ( 2S) has been estimated.

The mechanism of the barton reaction

Photolysis of 6β-nitroso-oxy-5α-cholestan-3β-yl acetate gave the 19-oxime, 6β,19-oxide, 6-oxo-5α-cholestan-3β-yl apetate, and 6β-hydroxy-5α-cholestan-3β-yl acetate. The 6β.19-oxide was formed from the C-19 nitrosodimer by a novel photochemical reaction involving nitric oxide and with subsequent displacement of the presumed 19-diazonium salt by the 6β-hydroxy-function. The formation of ketone was coupled with the appearance of hyponitrous acid. The alcohol was formed by intermolecular hydrogen atom abstraction by the intermediate C-19 alkyl radical in a reaction not related to ketone formation. Evidence for the intermediacy of peroxynitrites in the formation of nitrate esters by nitrite photolysis under oxygen is presented. Hydroperoxides and nitrosyl chloride gave the derived nitrates. Attention is drawn to the formation of androst-4-ene-3,17-dione (59%) from reaction of trifluoroacetic anhydride and 17α-hydroperoxyprogesterone.

Kinetics and mechanism of oxidation of aliphatic ketoximes by thallium(III) acetate—part I

AbstractThe oxidative cleavage of some aliphatic ketoximes by thallium(III) acetate was studied in the temperature range of 20–40°C. The reactions were followed by determination of the rates of disappearance of thallium(III) acetate for variations in [substrate], [Tl(III)], [H+], ionic strength, temperature, etc. The reactions were found to be totally second order–first order with respect to each reactant. The second‐order rate constants and thermodynamic parameters were evaluated and discussed. The mechanism proposed involves one‐electron oxidation to the iminoxy radical followed by an another one‐electron oxidation to the hydroxynitroso compound which dimerizes and decomposes to give the carbonyl compounds and hyponitrous acid.

Nitrogen nuclear magnetic resonance spectroscopy. Part IV. The azo-compounds and hyponitrite ion

14 N Chemical shifts are reported for azoethane, hexafluoroazomethane, hyponitrous acid, and hyponitrite ion, and are compared with those for azobenzene, the difluorodiazines, and pyridazine. The order of the shifts follows that of the inductive effect of the ligand as it increases the excitation energies (opposed by the inductive effect of the ligand to increase the radius term 〈r–3〉). The azo-compounds in this way resemble the nitroso- and nitro-compounds.The nitrogen shifts show evidence of the splitting of the lone-pair orbitals in the azo-compounds.

Recent developments in the chemistry of nitrogen fixation.

This discussion is concerned mainly with the biological fixation of nitrogen, and I am the only speaker to discuss its purely chemical aspects. I shall consider first the pure chemistry, and outline recent developments which may be relevant to the biological process. Until three years ago chemistry was concerned only with the mapping of possible routes from nitrogen to simple inorganic compounds, such as ammonia or nitric acid, under mild conditions. Intermediates such as di-imine, hydrazine, hydroxylamine, or hyponitrous acid were postulated. These routes were purely speculative with nothing more to commend them than that they were thermodynamically possible. None had been realized experimentally under mild aqueous conditions and no intermediate between nitrogen and ammonia, the primary product of the biological process, has been detected in the natural system. The nitrogen molecule is a very stable entity with a dissociation energy of 224.5 kcal and an ionization potential as high as 15.58 eV. Its unique electronic structure in relation to nitrogen fixation has already been outlined (Chatt &amp; Leigh 1968). The high dissociation energy and low ionization potential precludes any routes involving either dissociation, or oxidation by stable molecules such as oxygen or even fluorine in their ground states at room temperature. Reduction is the third major reaction type; it depends upon the possibility of adding electrons to the nitrogen molecule, which for this reaction must have vacant orbitals of low energy to receive them. The energetically lowest vacant molecular orbitals are two degenerate antibonding π -orbitals at — 7 eV. These are too high in energy to be attacked by any but the strongest reducing agents, such as the more electropositive metals, and indeed very electropositive metals do attack nitrogen at room temperature. This is part of the explanation of the rapid nitriding of lithium wire observed during the formation of lithium reagents from lithium and alkyl halide in pentane under nitrogen. This reaction can be induced to yield considerable quantities of Li 3 N (J. Chatt &amp; G. J. Leigh unpublished). Indeed a clean film of any metal to the left of Group VII in the long form of the Periodic Table, except the heavier alkali metals, is rapidly nitrided on the surface by gaseous nitrogen at room temperature. All of these are very electropositive metals and very strong reducing agents, which equally rapidly react with water or oxygen under the same conditions. It seems unlikely that nitriding in this manner could form the basis of the activation of nitrogen in the aqueous environment of the biological system, although such a possibility certainly cannot be ignored. I personally do not favour such a nitriding route. However, it is receiving attention at the present time, and I shall outline briefly the direction it is taking.

Preparative conversion of oximes to parent carbonyl compounds by cerium(IV) oxidation

Oximes and semicarbazones are oxidized by ceric ammonium nitrate to the parent carbonyl compound in good yield. Suitable solvent systems include aqueous alcohols, acetonitrile, and acetic acid. The reaction is rapid at 0° or below. This procedure for regeneration of aldehydes and ketones from these derivatives may be preferable to the well-known hydrolytic procedures in some cases. The stoichiometry of the reaction was studied by isothermal calorimetry; two equivalents of oxidant are consumed by one mole of oxime evolving approximately 40 kcal/mole. A smaller consumption of oxidant by hexane-2,5-dione dioxime was attributed to stabilization of the monoxime as a nitroso chelate. Gaseous products were studied by infrared spectroscopy and nitrous oxide was identified as the sole product absorbing between 3 and 15 μ. A reaction mechanism is proposed involving one-electron oxidation to the iminoxy radical, oxidized by a second one-electron step to the α-hydroxy nitroso compound. Dimerization and elimination of hyponitrous acid gives the carbonyl compound. Nitrocyclohexane was absent from the oxidation product from cyclohexanone oxime. Carvone oxime was oxidized to carvone without racemization or significant attack of the olefin groups.

Kinetics and mechanism of the reaction between nitrous acid and hydroxylamine. Part III. The formation of hyponitrous acid

The yield of a minor product of the reaction between nitrous acid and hydroxylamine, trans-hyponitrous acid, has been studied over a wide range of conditions. It has been shown that, for nitrosation of free hydroxylamine by four different neutral nitrosyl compounds, the yield varies with the nature of the reagent: ON·Br 27, ON·NCS 12, ON·NO2 6, and ON·Cl 15 %. For nitrosation of the hydroxylammonium ion by the nitrous-acidium ion the yield is 2·0 %. An isotopic study of the reaction shows that a symmetrical intermediate is involved in several cases, probably cis-hyponitrous acid. The results are interpreted as showing that the initial nitrosation is an electrophilic displacement of a proton rather than an addition reaction of the type thought to occur in diazotisation and deamination.

Photochemistry of nitroso compounds in solution. V. Photolysis of N-nitrosodialkylamines

N-Nitrosodialkylamines underwent photolysis in the presence of an acid. From the analysis of the end products, the primary photolysis products were shown to be [NOH] and the corresponding alkylideneimine, which underwent further reaction, e.g. (i) recombination of the two species to give amidoximes, (ii) hyponitrous acid formation, and (iii) hydrolysis or polymerization. A pathway is proposed for the reaction. Evidence is presented to show that the formation of the parent amines was not the result of hydrolysis of nitrosamines.

Inorganic Nitrogen Transformations Through the Oxidation and Reduction of Iron

AbstractIn acid solution nitrate can be reduced by ferrous iron to N2 through such intermediates as nitrogen tetraoxide, nitrous acid, hyponitrous acid and nitrous oxide or through nitrogen tetraoxide, nitrous acid, nitric oxide, and nitrous oxide. These sequences show similarities to those occurring in the denitrification process. In a basic solution the reduction of nitrite to N2 may go through nitric oxide, N2O22‐, and nitrous oxide, or it may be reduced to ammonia through hydroxylamine, and hydrazine. Hydrazine and hydroxylamine are very unstable in the presence of iron in solution. In acid solution both hydrazine and hydroxylamine are oxidized by ferric iron to N2 and N2O. The amount of N2O formed is proportional to the ferric iron concentration.