The rate constant for the reaction or NH3 + OH → NH2 + H2O has been measured in a high temperature fast flow reactor over the range 294–1075 K k = (5.41 ± 0.86) × 10-12 exp[?(2120 ± 143) cal mole?1/RT cm3 molecule?1 s?1. This result is compared with literature values and discussed. 相似文献
The absolute rate constant of the reaction of NH2 with NO2 has been measured using a flash-photolysis laser resonance-fluorescence technique. The value obtained at room temperature is k1 = 2.3 (± 0.2) × 10?11 cm3 molecule ?1 s?1. A negative temperature coefficient has been found between 298 and 505 K for this reaction, k1 = 3.8 × 10?8 × T?1.30 cm3 molecule?1 s?1. It is thought that this is the major reaction of NH2 in the troposphere. 相似文献
The rate constant for the reaction NH3 + OH → NH2 + H2O was determined by the comparison of the calculated induction period data with experiments by the shock tube technique in the range 1360–1840 K, for NH3-H2-O2-Ar mixtures. The rate constants can be represented by the expression k = 1012.49±0.04exp[(?1.95±0.15) kcal/,RT] cm3 mol?1 s?1. 相似文献
The absolute rate constant of the reaction between NH2 and ozone has been measured using a flash photolysis-laser resonance technique and found to be k4 = 6.3 (=1.0) × 10?14 cm3 molecule? s?1 at room temperature. The Arrhenius expression, determined from measurements in the temperature range 298–380 K is k4 = 4.2 × 10?12 exp(?2.5 = 0.5/RT) (E in kcal mole ?1. The possibility of formation or elimination of nitrogen oxides from the reactions of NH2 in the atmosphere is examined. 相似文献
Although the reaction products are unstable at the reaction temperatures, at a heating rate of 2 deg·min?1 ammonium peroxo vanadate, (NH4)4V2O11, decomposes to (NH4)[VO (O2)2 (NH3)] (above 93°C); this in turn decomposes to (NH4) [VO3 (NH3)] (above 106°C) and then to ammonium metavanadate (above 145°C). On further heating vanadium pentoxide is formed above 320°C. The first decomposition reaction occurs in a single step and the Avrami-Erofeev equation withn=2 fits the decomposition data best. An activation energy of 148.8 kJ·mol?1 and a ln(A) value of 42.2 are calculated for this reaction by the isothermal analysis method. An average value of 144 kJ·mol?1 is calculated for the first decomposition reaction using the dynamic heating data and the transformation-degree dependence of temperature at different heating rates. 相似文献
An electroanalytical method, based on derivative chronopotentiometry of the iron complex with 2-(5′-bromo-2′- pyridylazo)-5-diethylaminophenol (5-Br-PADAP) accumulated adsorptively on the surface of a hanging mercury drop electrode, for determining trace iron in food has been developed. The dependences of the peak height on the dt/dE vs. E curve on the preconcentration time, preconcentration potential and electrode area are discussed. Optimum experimental conditions include 0.005 mol 1?1 NH3NH4Cl, 2 × 10?7 mol 1?1 5-Br-PADAP and a preconcentration potential of ?0.40 V (vs. SCE). Under these conditions, the detection limit and the linear range are 2 × 10?9 and 6.7 × 10?9?1.7 × 10?7 mol 1?1, respectively. The relative standard error of the method is 1.5% for 6.7 × 10?8 mol 1?1 Fe(III). The method was applied to samples of microwave digested food. 相似文献
The kinetics of the reaction NH2 + NO → N2 + H2O were studied, using a conventional flash photolysis system. A value of k1 = (1.1 ± 0.2) × 1010 & mole?1 s?1 was obtained at room temperature and in the pressure range 2–700 torr in the presence of nitrogen. A slight negative temperature coefficient was observed between 300 and 500 K, equivalent to a negative activation energy of 1.05 ± 0.2 kcal mole?1. 相似文献
The mechanism of NH3 pyrolysis was investigated over a wide range of conditions behind reflected shock waves. Quantitative time-history measurements of the species NH and NH2 were made using narrow-linewidth laser absorption. These records were used to establish an improved model mechanism for ammonia pyrolysis. The risetime and peak concentrations of NH and NH2 in this experimental database have also been summarized graphically. Rate coefficients for several reactions which influence the NH and NH2 profiles were fitted in the temperature range 2200 K to 2800 K. The reaction and the corresponding best fit rate coefficients are as follows: with a rate coefficient of 4.0 × 1013 exp(?3650/RT) cm3 mol?1 s?1, with a rate coefficient of 1.5 × 1015T?0.5 cm3 mol?1 s?1 and with a rate coefficient of 5.0 × 1013 exp(?10000/RT) cm3 mol?1 s?1. The uncertainty in rate coefficient magnitude in each case is estimated to be ±50%. The temperature dependences of these rate coefficients are based on previous estimates. The experimental data from four earlier measurements of the dissociation reaction were reanalyzed in light of recent data for the rate of NH3 + H → NH21 + H2, and an improved rate coefficient of 2.2 × 1016 exp(?93470/RT) cm3 mol?1 s?1 in the temperature range 1740 to 3300 K was obtained. The uncertainty in the rate coefficient magnitude is estimated to be ± 15%. 相似文献
The reaction of O2(1Δg) with HO2(X?) was studied in an isothermal flow reactor in the pressure range 7?p? 10.7 mbar at temperatures between 299?T? 423 K. H-atom production was observed in the reaction O2(1Δg) + HO2(Ã2A′) - H(2S)+ 2O2 (3Σg?). The rate of this reaction (k1) is estimated to be k1 = (1 ± 0.5) × 1014 CM3 Mol?1 s?1. The implications of this reaction to recent determinations of the rate of the reaction H + O2(1Δg) are discussed. 相似文献
Fourier transform ion cyclotron resonance mass spectrometry has been used to measure the reaction rates for ions derived from methylamine with dimethylamine or trimethylamine. The use of the selective ion ejection technique greatly simplifies the elucidation of the ion-molecule reaction channels. The rate constants for proton transfer from protonated metwlamine, CH3NH3+ (m/z 32), to dimethylamine and trimethylamine are 16.1 ± 1.6 × 10?10 and 9.3 ± 0.9 × 10?10 cm3 molec?1s?1, respectively. The rate constants for charge transfer from methylamine molecular ion, CH3NH2+ (m/z 31), to dimethylamine and trimethylamine are 9.3 ± 1.8 x 10?10 and 15.0 ± 5 × 10?10 cm3molec?1s?1, respectively. 相似文献
The decay of NH2 radicals, from 193 nm photolysis of NH3, was monitored by 597.7 nm laser-induced fluorescence. Room-temperature rate constants of (1.21 ± 0.14) × 10?10, (1.81 ± 0.12) × 10?11, and (2.11 ± 0.18) × 10?11 cm3 molecule?1 s?1 were obtained for the reactions of NH2 with N, NO and NO2, respectively. The production of NH in the reaction of NH2 with N was observed by laser-induced fluorescence at 336.1 nm. 相似文献
The structure of ammonium hexafluoroarsenate, NH4AsF6, has been determined by X‐ray diffraction using a single crystal grown from saturated solution in anhydrous HF. NH4AsF6 crystallizes rhombohedral with the KOsF6 structure type, with a = 7.459(3) Å, c = 7.543(3) Å (at 200 K), Z = 3, space group (No. 148). No phase transition was observed in the 100 K–296 K temperature range. The structure is dominated by regular AsF6 octahedra and disordered NH4+ cations. Raman spectrum of a single crystal of NH4AsF6 shows the bands at 372 cm?1, 572 cm?1, 687 cm?1 (AsF6?) and at 3240 cm?1 and 3360 cm?1 (NH4+). 相似文献
First, the direct and indirect electrochemical oxidation of ammonia has been studied by cyclic voltammetry at glassy carbon electrodes in propylene carbonate. In the case of the indirect oxidation of ammonia, its analytical utility of indirect for ammonia sensing was examined in the range from 10 and 100 ppm by measuring the peak current of new wave resulting from reaction between ammonia and hydroquinone, as function of ammonia concentration, giving a sensitivity 1.29×10?7 A ppm?1 (r2=0.999) and limit‐of‐detection 5 ppm ammonia. Further, the direct oxidation of ammonia has been investigated in several room temperature ionic liquids (RTILs), namely 1‐butyl‐3‐methylimidazolium tetrafluoroborate ([C4mim] [BF4]), 1‐butyl‐3‐methylimidazolium trifluoromethylsulfonate ([C4mim] [OTf]), 1‐Ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2mim] [NTf2]), 1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ([C4mim] [NTf2]) and 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([C4mim] [PF6]) on a 10 μm diameter Pt microdisk electrode. In four of the RTILs studied, the cyclic voltammetric analysis suggests that ammonia is initially oxidized to nitrogen, N2, and protons, which are transferred to an ammonia molecule, forming NH via the protonation of the anion(s) (A?). However, in [C4mim] [PF6], the protonated anion was formed first, followed by NH . In all five RTILs, both HA and NH are reduced at the electrode surface, forming hydrogen gas, which is then oxidized. The analytical ability of this work has also been explored further, giving a limit‐of‐detection close to 50 ppm in [C2mim] [NTf2], [C4mim] [OTf], [C4mim] [BF4], with a sensitivity of ca. 6×10?7 A ppm?1 (r2=0.999) for all three ionic liquids, showing that the limit of detection was ca. ten times larger than that in propylene carbonate since ammonia in propylene carbonate might be more soluble in comparison with RTILs when considering the higher viscosity of RTILs. 相似文献
The rate of the reaction has been investigated at 40–65°C with [HClO4] varying from 0.04 to 0.6 M (μ = 0.6 M, NaClO4). The observed rate law has the form: -d[Cr(NH3)5(NCO)2+]/dt = kobs[Cr(NH3)5(NCO)2+] where kobs = a[H+]2{1 + b[H+]2} and ?1 at 55.0°C, a = 0.36 M?1 s?2 and b = 6.9 × 10?3 M?1 s?1. The rate of loss of Cr(NH3)5(NCO)2+ increases with increasing acidity to a limiting value (at [H+] ~ 0.5 M) but the yield of Cr(NH3)63+ decreases with increasing [H+] and increases with increasing temperature. In the kinetic studies the maximum yield of Cr(NH3)63+ was 35% but a synthetic procedure has been developed to give a 60% yield. 相似文献
The effect of the concentrations of propylene oxide and the catalyst (salen)CoDNP/[PPN]Cl ((salen)CoDNP: [PPN]Cl = 1: 1, mol/mol) on the kinetics of the copolymerization of CO2 and propylene oxide at 0.5 MPa and 20°C has been studied. The reaction proceeds at a constant rate after an induction period, and the value of this period varies with the reagent concentrations. The steady-state reaction rate increases linearly with the propylene oxide concentration in the range 5.0–14.3 mol/L. At high catalyst concentrations, such as (5.2–7.3) × 10?3 mol/L, the reaction rate is first order in the catalyst; at concentrations below 5 × 10?3 mol/L, the reaction rate is second order in the catalyst. Molecular mass increases in proportion to the propylene oxide conversion, that is consistent with a living polymerization process. A regioregular copolymer with 96% head-to-tail (HT) connectivity of propylene oxide has been obtained. 相似文献
The gas-phase reactions of negative ions (O-., NH2?, C2H5NH?, (CH3)2N?, C6H5t-, and CH3SCH2?) with fluorobenzene and 1,4-difluorobenzene have been studied with Fourier transform ion cyclotron resonance mass spectrometry. The O?. ion reacts predominantly by (1) proton abstraction, (2) formal H2+. abstraction, and (3) attack on an unsubstituted carbon atom. In addition to these processes, attack on a fluorine bearing carbon atom yielding F? and C6H4FO? ions occurs with 1,4-difluorobenzene. Site-specific deuterium labeling reveals the occurrence of competing 1,2-, 1,3-, and 1,4-H2+. abstractions in the reaction of O?. with fluorobenzene. Attack of the O?. ion on the 3- and 4-positions in fluorobenzene with formation of the 3- and 4-fluorophenoxide ions, respectively, is preferred to reaction at the 2-position, as indicated by the relative extent of loss of a hydrogen and a deuterium atom in the reactions with labeled fluorobenzenes. The NH2?, C2H5NH?, (CH3)2N?, C6H5?, and CH3SCH2? anions react with fluoroberuene and 1,4-difluorobenzene only by proton abstraction. The relative importance of H+ and D+ abstraction in the reaction of these anions with labeled fluorobenzenes indicates that the 2-position in fluorobenzene is more acidic than the 3- and 4-positions, suggesting that the literature value of the gas-phase acidity of this compound (ΔHacido = 1620 ± 8 kJ mol?1) refers to the former site. Based on the occurrence of reversible proton transfer between the CH3O? ion and 1,4-difluorobenzene, the ΔHacido of this compound is redetermined to be 1592 ± 8 kJ mol?1. 相似文献
Studies of the stoichiometry and kinetics of the reaction between hydroxylamine and iodine, previously studied in media below pH 3, have been extended to pH 5.5. The stoichiometry over the pH range 3.4–5.5 is 2NH2OH + 2I2 = N2O + 4I? + H2O + 4H+. Since the reaction is first-order in [I2] + [I3?], the specific rate law, k0, is k0 = (k1 + k2/[H+]) {[NH3OH+]0/(1 + Kp[H+])} {1/(1 + KI[I?])}, where [NH3OH+]0 is total initial hydroxylamine concentration, and k1, k2, Kp, and KI are (6.5 ± 0.6) × 105 M?1 s?1, (5.0 ± 0.5) s?1, 1 × 106 M?1, and 725 M?1, respectively. A mechanism taking into account unprotonated hydroxylamine (NH2OH) and molecular iodine (I2) as reactive species, with intermediates NH2OI2?, HNO, NH2O, and I2?, is proposed. 相似文献