Nitrogen isotope exchange between nitric oxide and nitric acid

The rate of nitrogen isotope exchange between NO and HNO₃ has been measured as a function of nitric acid concentration of 1.5–4M·1^–1. The exchange rate law is shown to beR=k[HNO₃]²[N₂O₃] and the measured activation energy isE=67.78kJ ·M^–1 (16.2 kcal·M^–1). It is concluded that N₂O₃ participates in¹⁵N/¹⁴N exchange between NO and HNO₃ at nitric acid concentrations higher than 1.5M·1^–1.     

The kinetics of plutonium oxide dissolution in nitric/hydrofluoric acid mixtures

The dissolution rate of plutonium oxide powder in nitric/hydrofluoric acid mixtures is controlled by a chemical reaction at the PuO₂ surface rather than by diffusion. The reaction is first order with respect to both the surface area (S) of PuO₂ and the concentration of free (non-complexed) hydrofluoric acid ([HF]_ƒ) in solution. As the dissolution progresses, the surface area decreases and free HF is consumed by complexation with dissolved Pu(IV) to form PuF_x^(4−x)+ complexes. This results in a rapid decrease of the dissolution rate with time. The initial rate is not affected by HNO₃ concentration in the range of 4–12 M. However, at longer reaction times the rate increases with increasing HNO₃ concentration. At higher HNO₃ concentrations more free HF is available for reaction since plutonium fluoride complexes are less stable. Rate equations which describe changes in S and [HF]_ƒ during dissolution are derived and rate constants are given for dissolution of PuO₂ obtained by burning the metal. The second order rate constant is 3.0 × 10⁻⁶l/sec-m² at 35°C for dissolution of this oxide.     

Vibration–vibration energy exchange between 15N14NO and CO

The temperature dependence of the vibration–vibration energy transfer between the v₃ mode of ¹⁵N¹⁴NO and the first vibrational level of CO was determined over a range of 680 to 1300°K using a shock tube. Several mixtures of ¹⁵N¹⁴NO? CO were tested, diluted in 95% Ar. The resulting exothermic transfer probabilities for the reaction, are compared to previous work on N₂O—CO. The results for ¹⁵N¹⁴NO? CO exhibit a more pronounced direct temperature dependence than for N₂O—CO even though the process has a closer resonance (ΔE = 59 cm^?1 for ¹⁵N¹⁴NO? CO and ΔE = 81 cm^?1 for N₂O? CO).     

The kinetics of the 15NO exchange with transition metal nitrosyls

The kinetics of the ¹⁵NO exchange with M(NO)₂IL [M = Fe or Co, L = P(C₆H₅)₃ or As(C₆H₅)₃] in toluene have been studied, and the activation parameters evaluated. The effects of the ligands, L, on the rate constants indicate that the nitrosyl group behaves in much the same way as the CO group of carbonylic complexes.     

The kinetics of the chlorine isotopic exchange between chloride ion at O,O-diarylphosphorochloridates or O,O-diarylphosphorochloridothionates

The kinetics of the chlorine isotopic exchange reaction between tetraethylammonium chloride-³⁶Cl and O,O-diarylphosphorochloridates (p-RC₆H₄O)₂POCl or O,O-diarylphosphorochloridothionates (p-RC₆H₄O)₂PSCl has been studied in acetonitrile solution. Good Hammett's correlations of the rate constants with Taft's σ⁰ constants were obtained. The values of the reaction constants ρ were found identical for phosphoryl and thiophosphoryl compounds. In comparison with oxygen in the phosphoryl group, the sulfur atom exhibits an electron-donating effect (Δσ⁰ ～ 0.80). No correlation has been found for the enthalpy and entropy of activation. The effect of the substituents aryloxy groups, oxygen, or sulfur atoms in the phosphoryl group on the kinetics of the S_N2-P reaction is discussed. The reactivity of the investigated compounds is determined by the extent of the positive charge localized on the phosphorus atom. The positive charge is formed by the direct interactions of the substituents with the reaction center and the indirect–intramolecular interactions revealed in the structure of the compound.     

The crystallization kinetics and morphology of nitric acid trihydrate

Crystallization kinetics of stable and metastable nitric acid trihydrate (NAT) were investigated by time dependent X-ray powder diffraction (XRD) measurements. Kinetic conversion curves were evaluated adopting the Avrami model. The growth and morphology of the respective crystallites were monitored in situ on the cryo-stage of an environmental scanning electron microscope (ESEM) under a partial pressure of nitrogen gas (0.3 Torr, 40 Pa). The results show a close relationship between the presence of ice in the sample and the crystallization mechanism of NAT, which results in different shapes and sizes of NAT crystal particles.     

The kinetics of Ogawa band chemiluminescence in the nitric oxide afterglow

Nitric oxide Ogawa band chemiluminescences emanating from NO(b⁴Σ⁻) υ′ = 4, 3 and 2, associated with combining N(⁴S) and O(³P) atoms in a discharge flow system, have been detected photoelectrically. In N₂ carrier the intensities (Iυ′) followed relationships Iυ′ = kυ′ [N][O] with kυ′ independent of [N₂] in the range (4 - 15) X 10⁻⁵ mol/dm³ at both 195 K and 298 K. The temperature coefficients of kυ′, expressed as T^-nv′, were n₃ = 1.8±0.4, n₂ = 1.5±0.8 and n₃ - n₄ = 0.62±0.20. Addition of Ar (⩽76%) had no effect upon kυ′ but distinct quenching of k₃ and k₂ occurred when N₂ was partly replaced with CO₂, N₂O and H₂O (⩽46%). On the simplest basis CO₂ was about twice, N₂O about four times and H₂O about six times as effective as N₂ in removing NO(b⁴Σ−) υ′ = 2, 3. Only with H₂O was any quenching detected for k₄ and that ∼3 times less than for k₃.The results for υ′ = 4 were interpreted in terms of the lowest rotational level being within 5 to 10 kJ/mol of the first dissociation limit of NO, so that preassociation/predissociation operates in the mechanism.Absolute intensity measurements gave 1/photons dm⁻³ s⁻¹ = 1.4 X 10³ ([N][O]/mol²/dm⁶) for the bands observed between 700 and 1000 nm. A lower radiative lifetime limit of 6 X 10⁻⁶ s is deduced for υ′ = 3 on the basis of a mechanism where depopulation is dominated by collisional removal and quenching in mixed carriers.     

The kinetics of zinc dissolution in nitric acid

The dissolution of zinc in 0.48–1.49M HNO₃ was studied at 15–25°C, by following simultaneously the concentration changes of the reactants (Zn and HNO₃), intermediate (HNO₂) and product (Zn²⁺) with time. Explicit mechanisms were suggested for the dissolution of zinc in nitric acid. The kinetics of the dissolution process show that it is of the first-order with respect to [Zn] and [HNO₂]. The data obtained show that the dissolution process is diffusion-controlled. The mechanism of zinc dissolution is compared with the mechanism of copper dissolution.

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Die Kinetik der Auflösung von Zink in Salpetersäure

Zusammenfassung Die Auflösung von Zink in 0.48–1.49M HNO₃ wurde bei 15–25°C mittels gleichzeitiger Verfolgung der Konzentrationsänderungen der Reaktanden (Zn und HNO₃), des intermediären HNO₂ und des Produkts Zn²⁺ untersucht. Es wird ein Mechanismus vorgeschlagen. Die Kinetik der Auflösung ist erster Ordnung bezüglich [Zn] und [HNO₂]. Die Daten zeigen, daß der Auflösungsvorgang diffusionskontrolliert ist. Der Mechanismus der Auflösung von Zink wird mit dem der Kupferauflösung verglichen.

     

New direction of the reaction between N,N′-disubstituted hydrazine and nitric acid

Conclusions The action of conc. HNO₃ on N,N-bis-(2,2-dinitropropyl)hydrazine and azo-(2,2-dinitro)propane at low temperatures was investigated, and it has been shown that in both cases 2,2-dinitropropionylhydrazone of 2,2-dinitropropionaldehyde is formed.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1202–1203, May, 1970.     

Chemical and thermodynamic characteristics of the isotopic exchange reaction between radioiodine and iodohippuric acid isomers.

The parameters affecting the absolute radiochemical yield of the isotopic exchange reaction between radioiodine (125I-) and iodohippuric acid isomers on molten ammonium acetate as a medium exchange at 120 degrees C without any carrier added (radioiodine, 125I-) was determined. The isotopic exchange reactions of radioiodine as 125I- for iodine-127 of o- and p-iodohippuric acid isomers occur more rapidly than m-iodohippuric acid isomer. These reactions proceed by nucleophilic second order substitution reaction. The kinetics and thermodynamic parameters of these isotopic exchange reactions were determined. The absolute radiochemical yield and radio pharmaceutical purity were determined by HPLC and TLC techniques.     

Substitution kinetics of chelate complexes as studied by isotopic exchange

The fact that isotopic exchange reactions take place at chemical equilibirum makes this type of reaction useful for kinetic studies. In the case of chelate complexes [M(chel)_n] isotopic exchange reactions can be classified as metal exchange reactions. [M(chel)_n]+^*M⇆[^*M(chel)_n]+M and ligand exchange reactions [M(chel)_n]+^*chel⇆[M(chel)_n−1 ^*chel]+chel The literature on type (a) and type (b) reactions of mainly transition metal complexes is reviewed with respect to the kinetic information obtained. The value and the limitations of isotopic exchange studies as a kinetic technique are discussed.     

H/D isotopic exchange between water molecules at ice surfaces

H/D isotopic exchange between H(2)O and D(2)O molecules was studied at the surface of ice films at 90-140 K by the technique of Cs(+) reactive ion scattering. Ice films were deposited on a Ru(0001) substrate in different compositions of H(2)O and D(2)O and in various structures to study the kinetics of isotopic exchange. H/D exchange was very slow on an ice film at 95-100 K, even when H(2)O and D(2)O were uniformly mixed in the film. At 140 K, H/D exchange occurred in a time scale of several minutes on the uniform mixture film. Kinetic measurement gave the rate coefficient for the exchange reaction, k(140 K)=1.6(+/-0.3) x 10(-19) cm(2) molecule(-1) s(-1) and k(100 K)< or =5.7(+/-0.5) x 10(-21) cm(2) molecule(-1) s(-1) and the Arrhenius activation energy, E(a)> or =9.8 kJ mol(-1). Addition of HCl on the film to provide excess protons greatly accelerated the isotopic exchange reaction such that it went to completion very quickly at the surface. The rapid reaction, however, was confined within the first bilayer (BL) of the surface and did not readily propagate to the underlying sublayer. The isotopic exchange in the vertical direction was almost completely blocked at 95 K, and it slowly occurred only to a depth of 3 BLs from the surface at 140 K. Thus, the proton transfer was highly directional. The lateral proton transfer at the surface was attributed to the increased mobility of protonic defects at the molecularly disordered and activated surface. The slow, vertical proton transfer was probably assisted by self-diffusion of water molecules.     

Determination of the 15N/14N, 17O/16O, and 18O/16O ratios of nitrous oxide by using continuous-flow isotope-ratio mass spectrometry

We developed a rapid, sensitive, and automated analytical system to determine the delta15N, delta18O, and Delta17O values of nitrous oxide (N2O) simultaneously in nanomolar quantities for a single batch of samples by continuous-flow isotope-ratio mass spectrometry (CF-IRMS) without any cumbersome and time-consuming pretreatments. The analytical system consisted of a vacuum line to extract and purify N2O, a gas chromatograph for further purification of N2O, an optional thermal furnace to decompose N2O to O2, and a CF-IRMS system. We also used pneumatic valves and pneumatic actuators in the system so that we could operate it automatically with timing software on a personal computer. The analytical precision was better than 0.12 per thousand for delta15N with >4 nmol N2O injections, 0.25 per thousand for delta18O with >4 nmol N2O injections, and 0.20 per thousand for Delta17O with >20 nmol N2O injections for a single measurement. We were also easily able to improve the precision (standard errors) to better than 0.05 per thousand for delta15N, 0.10 per thousand for delta18O, and 0.10 per thousand for Delta17O through multiple analyses with more than four repetitions with 190 nmol samples using the automated analytical system. Using the system, the delta15N, delta18O, and Delta17O values of N2O can be quantified not only for atmospheric samples, but also for other gas or liquid samples with low N2O content, such as soil gas or natural water. Here, we showed the first ever Delta17O measurements of soil N2O.     

Oxygen surface exchange kinetics of erbia-stabilized bismuth oxide

The surface oxygen exchange kinetics of bismuth oxide stabilized with 25 mol% erbia (BE25) has been studied in the temperature and pO₂ ranges 773–1,023 K and 0.1–0.95 atm, respectively, using pulse-response ¹⁸O–¹⁶O isotope exchange measurements. The results indicate that BE25 exhibits a comparatively high exchange rate, which is rate determined by the dissociative adsorption of oxygen. Defect chemical considerations and the observed pO₂^1/2 p{{hbox{O}}_2}^{1/2} dependence of the rate of dissociative oxygen adsorption suggest electron transfer to intermediate superoxide ions as the rate determining step in surface oxygen exchange on BE25.     

Kinetics of isotopic exchange between chloramine-B and radioactive chloride

The kinetics of chlorine isotope exchange between chloramine-B /CAB/ and chloride has been studied using ion-exchange separation and tracer technique. McKay's plot are linear. The exchange reaction is fast in acidic medium, very slow in neutral medium and does not take place in alkaline medium. In the acidic range the exchange is maximum at pH 3.3. The rate of exchange decreases at pH >3.3 and <3.3. The order with respect to CAB and chloride is unity. The order with respect to [H⁺] is unity at pH>5. Addition of neutral salt or parent compound has no effect on the rate of exchange. Activation energy and activation entropy for this exchange reaction have been calculated.     

Nitrosoruthenium nitrite-nitrate complexes in aqueous and nitric acid solutions as probed by 15N NMR

Aqueous and nitric acid solutions of Na₂[Ru¹⁵NO(¹⁵NO₂)₄OH] in the concentration range $c_{H^{15} NO_3 }$ = 0–3.3 mol/L have been studied by ¹⁵N NMR, dominating complex species have been identified, and the equilibrium constants for the nitrate ion incorporation into the inner coordination sphere of nitrosoruthenium have been estimated. The equilibration time for such equilibria is no more than 2 h at room temperature. In addition to the nitro complexes, isomeric nitritonitronitrosoruthenium compounds have been identified in solutions. In weak acidic solutions at $c_{HNO_3 }$ < 0.25 mol/L, nitro and nitritonitro complexes containing four and three coordinated nitrite ions predominate. At the HNO₃ concentration 0.4–1.7 mol/L, the vast majority of ruthenium presents in solution as fac-dinitronitrosoruthenium complexes containing coordinated water molecules and nitrate ions. In solutions with $c_{HNO_3 }$ > 1.5 mol/L, the fractions of dinitro- and mononitronitrosoruthenium complexes are comparable. In strong nitric acid solutions ( $c_{H^{15} NO_3 }$ = 10 mol/L) kept for three years in contact with air, nitro complexes are absent, and mononitrato- and dinitratoaquanitrosoruthenium complexes are dominating.     

Ultrahigh-resolution capillary electrophoretic separation with indirect ultraviolet detection: isotopic separation of [14N]- and [15N]ammonium.

Separation of isotopically labeled [14N]/[15N] ammonium was performed with capillary electrophoresis. This ultrahigh-resolution separation was based on mobility counterbalance with precise control of the anodic electroosmotic flow. Mixtures of zwitterionic surfactant (Rewoteric AM CAS U) and cationic surfactant (cetyltrimethylammonium bromide) were used as buffer additives to modify the electroosmotic mobility. Indirect ultraviolet detection was used with benzyltributylammonium as the buffer coion. Baseline-resolved peaks of [14N]- and [15N]ammonium were obtained within 11 min. The detection limit was 0.01 mM for both [14N]-and [15N]ammonium. Linear calibration in concentration was observed up to 1.0 mM for [15N]ammonium and 2.0 mM for [14N]ammonium. Calibration of the isotopic ratio, [15N]ammonium concentration to total ([14N] and [15N])ammonium, was valid from 5 to 95%.