N2O Evolution Research Articles

Abiotic nitrous oxide production from hydroxylamine in soils and their dependence on soil properties

Despite the fact that microbial nitrification and denitrification are considered the major soil N2O emission sources, especially from agricultural soils, several abiotic reactions involving the nitrification intermediate hydroxylamine (NH2OH) have been identified leading to N2O emissions, but are being neglected in most current studies. Here, we studied N2O formation from NH2OH in cropland, grassland, and forest soils in laboratory incubation experiments. Incubations were conducted with and without the addition of NH2OH to non-sterile and sterile soil samples. N2O evolution was quantified with gas chromatography and further analyzed with online laser absorption spectroscopy. Additionally, the isotopic signature of the produced N2O (δ15N, δ18O, and 15N site preference) was analyzed with isotope ratio mass spectrometry. While the forest soil samples showed hardly any N2O evolution upon the addition of NH2OH, immediate and very large formation of N2O was observed in the cropland soil, also in sterilized samples. Correlation analysis revealed soil parameters that might explain the variability of NH2OH-induced N2O production to be: soil pH, C/N ratio, and Mn content. Our results suggest a coupled biotic–abiotic production of N2O during nitrification, e.g. due to leakage of the nitrification intermediate NH2OH with subsequent reaction with the soil matrix.

Changes in greenhouse gas evolution in heavy metal polluted paddy soils with rice straw return: A laboratory incubation study

Heavy metal pollution in rice paddies has been known to alter soil microbial biomass, diversity and, in turn, the processes mediating soil biogenic greenhouse gas evolution. However, there has been poor knowledge of potential changes in greenhouse gas evolution with rice straw return from polluted rice paddies. In this study, a 90-day lab incubation experiment under anaerobic condition was conducted to track changes in CO2, CH4 and N2O evolution from heavy metal polluted paddy soil with polluted rice straw return, compared to from unpolluted soil with unpolluted straw return. Our results showed that the total CO2 and CH4 evolution from polluted soil incorporating polluted straw were decreased by 21% and 79%, respectively compared to unpolluted straw amended in unpolluted soil. Compared to unpolluted straw, the total carbon mineralization of metal polluted straw was reduced by 13% and 34% in unpolluted and polluted soils, respectively and metal pollution changed the proportion of CH4 and CO2 to total straw carbon mineralized. Though there was a generally reduction of N2O evolution with straw amendment, the total N2O evolution was increased by 190% in unpolluted soil and by 352% in polluted soil with polluted straw amendment compared to with unpolluted straw. The overall global warming potential (GWP) increased significantly by 31% and 58% with polluted straw amendment in unpolluted and polluted soils, respectively compared to with unpolluted straw. Therefore, metal pollution both in soil and straw resulted in a slow carbon mineralization but a high N2O evolution, and then enhanced the overall GWP in metal polluted rice paddies with rice straw return. The increased GWP would pose a risk to soil carbon sequestration in metal polluted paddy field.

Selective Nitrite Reduction at Heterobimetallic CoMg Complexes

Heme-containing nitrite reductases bind and activate nitrite by a mechanism that is proposed to involve interactions with Brønsted acidic residues in the secondary coordination sphere. To model this functionality using synthetic platforms that incorporate a Lewis acidic site, heterobimetallic CoMg complexes supported by diimine-dioxime ligands are described. The neutral (μ-NO2)CoMg species 3 is synthesized from the [(μ-OAc)(Br)CoMg](+) complex 1 by a sequence of one-electron reduction and ligand substitution reactions. Data are presented for a redox series of nitrite adducts, featuring a conserved μ-(η(1)-N:η(1)-O)-NO2 motif, derived from this synthon. Conditions are identified for the proton-induced N-O bond heterolysis of bound NO2(-) in the most reduced member of this series, affording the [(NO)(Cl)CoMg(H2O)](+) complex 6. Reduction of this complex followed by protonation leads to the evolution of free N2O. On the basis of these stoichiometric reactivity studies, the competence of complex 1 as a NO2(-) reduction catalyst is evaluated using electrochemical methods. In bulk electrolysis experiments, conducted at -1.2 V vs SCE using Et3NHCl as a proton source, N2O is produced selectively without the competing formation of NH3, NH2OH, or H2.

Cyclic Lean Reduction of NO by CO in Excess H2O on Pt–Rh/Ba/Al2O3: Elucidating Mechanistic Features and Catalyst Performance

This study provides insight into the mechanistic and performance features of the cyclic reduction of NOx by CO in the presence and absence of excess water on a Pt–Rh/Ba/Al2O3 NOx storage and reduction catalyst. At low temperatures (150–200 °C), CO is ineffective in reducing NOx due to self-inhibition while at temperatures exceeding 200 °C, CO effectively reduces NOx to main product N2 (selectivity >70 %) and byproduct N2O. The addition of H2O at these temperatures has a significant promoting effect on NOx conversion while leading to a slight drop in the CO conversion, indicating a more efficient and selective lean reduction process. The appearance of NH3 as a product is attributed either to isocyanate (NCO) hydrolysis and/or reduction of NOx by H2 formed by the water gas shift chemistry. After the switch from the rich to lean phase, second maxima are observed in the N2O and CO2 concentrations versus time, in addition to the maxima observed during the rich phase. These and other product evolution trends provide evidence for the involvement of NCOs as important intermediates, formed during the CO reduction of NO on the precious metal components, followed by their spillover to the storage component. The reversible storage of the NCOs on the Al2O3 and BaO and their reactivity appears to be an important pathway during cyclic operation on Pt–Rh/Ba/Al2O3 catalyst. In the absence of water the NCOs are not completely reacted away during the rich phase, which leads to their reaction with NO and O2 upon switching to the subsequent lean phase, as evidenced by the evolution of N2, N2O and CO2. In contrast, negligible product evolution is observed during the lean phase in the presence of water. This is consistent with a rapid hydrolysis of NCOs to NH3, which results in a deeper regeneration of the catalyst due in part to the reaction of the NH3 with stored NOx. The data reveal more efficient utilization of CO for reducing NOx in the presence of water which further underscores the NCO mechanism. Phenomenological pathways based on the data are proposed that describes the cyclic reduction of NOx by CO under dry and wet conditions.

Characterization and influence of biochars on nitrous oxide emission from agricultural soil

Extensive use of biochar to mitigate N2O emission is limited by the lack of understanding on the exact mechanisms altering N2O emissions from biochar-amended soils. Biochars produced from giant reed were characterized and used to investigate their influence on N2O emission. Responses of N2O emission varied with pyrolysis temperature, and the reduction order of N2O emission by biochar (BC) was: BC200 ≈ BC600 > BC500 ≈ BC300 ≈ BC350 > BC400. The reduced emission was attributed to enhanced N immobilization and decreased denitrification in the biochar-amended soils. The remaining polycyclic aromatic hydrocarbons (PAHs) in low-temperature biochars (300–400 °C) played a major role in reducing N2O emission, but not for high-temperature biochars (500–600 °C). Removal of phenolic compounds from low-temperature (200–400 °C) biochars resulted in a surprising reduction of N2O emission, but the mechanism is still unknown. Overall, adding giant reed biochars could reduce N2O evolution from agricultural soil, thus possibly mitigating global warming.

Mitigation of nitrous oxide emissions from paddy soil under conventional and no-till practices using nitrification inhibitors during the winter wheat-growing season

The net effect of no-till techniques on nitrous oxide (N2O) emissions is inconsistent and poorly quantified in comparison to conventionally tilled farming. This study assesses N2O emissions and yields from paddy fields during the wheat-growing season under conventional and no-till farming, as well as mitigation of N2O evolution using dicyandiamide and chlorinated pyridine (CP) as nitrification inhibitor (NI). Both tillage practices and NIs significantly (P < 0.01) affected cumulative N2O emissions and yields. In comparison to conventional tillage, the cumulative N2O emissions under no-till farming were increased by 8.2–19.3 % and the water-filled pore space was higher on most days. Relative to no-tillage, the conventional tillage averagely increased the wheat yield by 6.0 % and reduced yield-scaled N2O–N emission by 44.5 %. The two NIs averagely increased the wheat yield by 9.7 % and reduced yield-scaled N2O–N emission by 67.7 %. The treatment with CP produced the highest yield with the lowest N2O emissions, thus leading to the lowest yield-scaled N2O–N emission (0.15–0.17 kg N2O–N t−1 grain yield) under both tillage practices.

Gaseous emission during the composting of pig feces from Chinese Ganqinfen system

The Ganqinfen system – a process of manually cleaning animal feces by means of a shovel – is a widely used manure separating method in Chinese pig farms. Ganqinfen pig feces and chopped corn stalks were mixed at the ratio of 7:1, and composted in 1.5m3 rotting boxes for 70d. Evolution of CH4, N2O and NH3 during composting, and the effects of turning and covering, were studied in this research. Results showed that 20–39% and 0.5–4% of total nitrogen were lost in the form of NH3 and N2O respectively, and 0.1–0.9% of initial organic carbon was emitted as CH4. Turning enhanced air exchange in the piles, thus decreasing CH4 emission by 83–93% and shortening the maturing period. When trials were finished, all non-turned piles were separated to three layers by moisture content. This structure caused the N2O losses of non-turning treatments to be 6–12.7times higher than that of turning treatments. Covering materials reduced air exchange at the surface of the pile, thus decreasing the O2 supply and consequently increasing CH4 production by 33–45%. Covering also reduced NH3 emission by 4–34%. For the composting of Ganqinfen pig feces, we suggest that a program of turning twice weekly without covering will result in compost that is sufficiently matured after 6wk with the lowest resultant greenhouse gas emission.

Long-term effects of cropping system on N2O emission potential

The potential for N2O emissions outside the main growing season may be influenced by long-term effects of cropping system. This was investigated by collecting intact soil cores (100 cm3, 0–4 cm depth) under winter wheat in three organic cropping systems and a conventional reference within a long-term crop rotation experiment. Average annual inputs of C in crop residues and manure ranged from 1.7 to 3.3 Mg ha−1. A simulated freeze–thaw cycle resulted in a flush of CO2 during the first 48 h, which could be mainly from microbial sources. Other samples were adjusted to approximately −10, −30 or −100 hPa and amended with excess 15NO3− prior to freezing and thawing. Denitrification was the main source of N2O during a 72-h incubation at 22 °C, as judged from N2O and total 15N evolution. Although the input of C in the conventionally managed cropping system was significantly less than in the organic cropping systems, it showed higher N2O evolution at all three matric potentials. Estimates of relative gas diffusivity (DP/D0) in soil from the four cropping systems indicated that C input affected soil aeration. Soil from the two cropping systems with highest C input showed N2O evolution at DP/D0 in excess of 0.02, which is normally considered a threshold for development of anaerobic sites in the soil, presumably because the oxygen demand was also high. The study shows that cropping system affects both soil gas diffusivity and C availability, and that both characteristics significantly influence the N2O emission potential.

Greenhouse gas emissions and nutrient supply rates in soil amended with biofuel production by-products

Ethanol production results in distiller grain, and biodiesel produces glycerol as by-product. However, there is limited information on effects of their addition on evolution of N2O and CO2 from soils, yet it is important to enable our understanding of impacts of biofuel production on greenhouse gas budgets. The objective of this study was to evaluate the direct effects of adding wet distillers grain (WDG), thin stillage (TS), and glycerol at three rates on greenhouse gas emissions (N2O and CO2) and nutrient supply rates in a cultivated soil from the Canadian prairies. The WDG and TS application rates were: 100, 200, or 400 kg N ha−1, whereas glycerol was applied at: 40, 400, or 4,000 kg C ha−1 applied alone (G − N) or in a combination with 300 kg N ha−1 (G + N). In addition, conventional amendments of urea (UR) and dehydrated alfalfa (DA) were added at the same rates of total N as the by-products for comparative purposes. The production of N2O and CO2 was measured over an incubation period of 10 days in incubation chambers and Plant Root Simulator™ resin membrane probes were used to measure nutrient (NH 4 + -N, NO 3 − -N, and PO 4 −3 -P) supply rates in the soil during incubation. Per unit of N added, urea tended to result in the greatest N2O production, followed by wet distillers grain and thin stillage, with glycerol and dehydrated alfalfa resulting in the lowest N2O production. Cumulative N2O production increased with increasing the rate of N-containing amendments and was the highest at the high rate of UR treatment. Addition of urea with glycerol contributed to a higher rate of N2O emission, especially at the low rate of glycerol. The DA and WDG resulted in the greatest evolution of CO2 from the soil, with the thin stillage resulting in less CO2 evolved per unit of N added. Addition of N fertilizer along with glycerol enhanced microbial activity and decomposition. The amendments had significant impacts on release of available nutrient, with the UR treatments providing the highest NO 3 − -N supply rate. The TS treatments supplied the highest rate of NH 4 + -N, followed by WDG compared to the other amendments. The WDG treatments were able to provide the greatest supply of PO 4 −3 -P supply in comparison to the other amendments. Microbial N immobilization was associated with glycerol treatments applied alone. This study showed that the investigated biofuel by-products can be suitable soil amendments as a result of their ability to supply nutrients and N2O emissions that did not exceed that of the conventional urea fertilizer.

Nitrous oxide evolved from soil covered with plastic mulch film in horticultural field

Soil solarization practice, in which soil is covered with plastic mulch film and exposed to high temperature prior to crop cultivation, is expected to be an effective method for reducing weeds and pathogenic microorganisms without using agricultural chemicals. Although the production of nitrous oxide (N2O), a major greenhouse gas, is enhanced in fertilized soil covered with plastic mulch films, its transport route to the atmosphere has not been sufficiently elucidated to date. In this study, we investigated the N2O evolution from plastic-mulch-film-covered agricultural soil. In a horticultural field where ridge soil was covered with a plastic mulch film after fertilization, we observed significant N2O flux from the soil surface of the unfertilized furrow between the ridges, indicating the horizontal diffusion of N2O from the ridge soil covered with the mulch film to the adjacent furrow soil surface. On the other hand, the measurement of the permeance (permeation coefficient) of the plastic mulch film for gaseous N2O by laboratory experiment revealed that N2O gradually permeated the mulch film; the permeance increased exponentially with an increase in ambient temperature, indicating possible N2O emission by permeation through the mulch film under field conditions. In winter, the amount of N2O emission by permeation through the mulch film was estimated to be lower than that emitted from the furrow soil surface, and it was lower than that in summer. On the other hand, it was estimated to be much higher in summer owing to the higher permeance of the film at high temperatures.

An in-depth in situ IR study of the thermal decomposition of yttrium trifluoroacetate hydrate

The pyrolysis of Y(CF3COO)3·nH2O at temperatures up to 1,000 °C, under flowing pure Ar, O2 and O2 saturated with water vapour, was extensively analysed. The formation of HF is observed directly and the existence of a :CF2 diradical is inferred during a trifluoroacetic acid salt decomposition. High resolution thermogravimetry, differential scanning calorimetry, X-ray diffractometry and scanning electron microscopy indicated that the exothermic one-stage decomposition of the anhydrate salt occurs at 267 °C, forming YF3. Fourier transform infrared spectroscopy identified (CF3CO)2O, CF3COF, COF2, CO2 and CO as the principal volatile species; and revealed the influence of water on the reactions liberating gaseous CF3COOH, CHF3, HF, and SiF4 (from reactions with glass or quartz components). NO2 and N2O evolution suggested that traces of CH3NO2 were present in the starting material. Thermogravimetry and X-ray diffractometry indicated that the slow hydrolysis of the fluoride occurs between 630 and 655 °C, forming a mixture of Y2O3, YOF, Y7O6F9, and YF3. The decomposition and hydrolysis temperatures are significantly lower than previously reported, which has implications for sol–gel processing.

Short term effects of bioenergy by-products on soil C and N dynamics, nutrient availability and biochemical properties

The shift towards a biobased economy will probably trigger the application of bioenergy by-products to the soil as either amendments or fertilizers. However, limited research has been done to determine how this will influence C and N dynamics and soil functioning. The aim of this work was to investigate the effects of different bioenergy by-products on C and N mineralisation, nutrient availability and microbial content and activity of amended soil and compare them to other more commonly used organic amendments.Two agricultural soils were amended (0.5% w/w) with four different bioenergy by-products (anaerobic digestate, rapeseed meal, bioethanol residue, biochar) and three other commonly used organic amendments (sewage sludge and two composts) and incubated at 20°C in the laboratory for 30 days. During incubation, soil CO2 and N2O evolution were measured every 4h by an automatic chromatographic system. After 2, 7 and 30 days of incubation, soil samples were analysed for K2SO4–extractable C, N, NO3−, NH4+ and P, microbial biomass C and three enzymatic activities (β-glucosidase, alkaline phosphatase and leucine aminopeptidase). Soil amendment led to a general increase in soil respiration, available N and P and microbial content and activity, but with remarkably different dynamics and values. Particularly, rapeseed meal and the bioethanol by-product led to N2O emissions and the greatest increases in soil respiration, N availability and enzymatic activity compared with the other amendments. The exception was represented by biochar that did not cause any significant variation with respect to the control, but promoted C accumulation. According to their impact on soil biochemical properties, the materials can be ranked as follows: rapeseed meal, bioethanol residue>anaerobic digestate, sewage sludge>composts>biochar. For each measured parameter, soil properties did not affect the response pattern found for the different treatments, but modified the magnitude of the response. In particular, soil respiration and enzymatic activity were higher in the slightly acidic soil, while greater values of available P were found in the alkaline soil.This study clearly indicates that the impact on GHG emissions and soil functioning of bioenergy by-products needs to be taken into account for a correct life cycle assessment of the bioenergy chain. Moreover, when properly managed, they may represent an effective alternative to usual amendments to improve the quality and nutrient balance of amended soils.

Effects of biochar addition on N2O and CO2 emissions from two paddy soils

Impacts of biochar addition on nitrous oxide (N2O) and carbon dioxide (CO2) emissions from paddy soils are not well documented. Here, we have hypothesized that N2O emissions from paddy soils could be depressed by biochar incorporation during the upland crop season without any effect on CO2 emissions. Therefore, we have carried out the 60-day aerobic incubation experiment to investigate the influences of rice husk biochar incorporation (50 t ha−1) into two typical paddy soils with or without nitrogen (N) fertilizer on N2O and CO2 evolution from soil. Biochar addition significantly decreased N2O emissions during the 60-day period by 73.1% as an average value while the inhibition ranged from 51.4% to 93.5% (P 0.05) in terms of cumulative emissions. Therefore, biochar can be added to paddy fields during the upland crop growing season to mitigate N2O evolution and thus global warming.

Synthesis and Properties of N7O+

The reaction of NOF(2)(+)SbF(6)(-) with an equimolar amount of HN(3) in an anhydrous HF solution at -45 degrees C produces N(3)NOF(+)SbF(6)(-). When an excess of HN(3) is used in this reaction, N(7)O(+)SbF(6)(-) is formed. However, this compound could not be isolated as a solid and rapidly decomposed in a quantitative manner with N(2)O evolution to N(5)(+)SbF(6)(-). This reaction represents a novel and more convenient synthesis for N(5)(+)SbF(6)(-) because NOF(2)(+)SbF(6)(-) is more readily accessible than N(2)F(+)SbF(6)(-) and the N(5)(+) can be labeled in all five positions with (15)N by the simple use of terminally singly labeled N(3)(-). The formation of the N(7)O(+) cation was established by isotopic labeling experiments and theoretical calculations. It is shown that the addition of a second azido ligand to the same central atom allows the attack of the negatively charged Nalpha atom of one ligand by the positively charged Ngamma atom of the second ligand, thereby greatly lowering the activation energy barrier toward decomposition and explaining why geminal diazides are much less stable than either monoazides or vicinal diazides.

Effects of inorganic nitrogen and phosphorus enrichment on the emission of N2O from a freshwater marsh soil in Northeast China

The freshwater marshes in northern China are heavily impacted by anthropogenic disturbances such as cultivation and fertilization and increased levels of nutrients (especially N and P) through atmospheric deposition and agricultural surface runoff. These disturbances have affected the emission of N2O from these systems. This laboratory study was conducted to determine the effects of increased inputs of inorganic N and P on N2O emission from marsh soil in response to different soil moisture conditions. The results showed that the emission of N2O increased with the enhancement of N inputs when the soil was submerged, but that the highest N treatment suppressed the emission of N2O when the soil was at 60% water holding capacity (WHC), which may have occurred due to an inadequate amount of available C. Furthermore, the results of this study indicated that a small amount of N fertilizer induced much more N2O evolution from freshwater wetland soil, while P fertilizer inputs appeared to stimulate the emission of N2O only during the first few days of the experiment. Additionally, soil that was treated with P appeared to absorb N2O when it was at 60% WHC after around 6 weeks of the incubation, which indicates that the input of P fertilizer might serve as a shift of source or N2O sink in wetland soils under non-flooded conditions. When compared to soil at 60% WHC, submerged soil had significantly higher N2O emissions, except when subjected to the medial N treatment. These findings indicate that the soil moisture condition had a significant effect on N2O emissions when the same amount of N or P was applied. Therefore, the effects of N and P fertilization in the northern temperate wetlands cannot be neglected from regional or national emissions of N2O.

Nitrous Oxide Production in an Eastern Corn Belt Soil: Sources and Redox Range

Nitrous oxide derived from soils is a main contributor to the greenhouse gas effect and a precursor to ozone‐depleting substrates; however, the source processes and interacting controls are not well established. This study was conducted to estimate the magnitude and source (nitrification vs. denitrification) of N2O production as affected by the form of N fertilizer, soil water content, and redox potential (Eh). Soils from continuous corn (Zea mays L.) experimental plots with a history of eight consecutive years of either side‐dressed urea–NH4NO3 (UAN) or fall liquid swine manure (FM) were collected and N2O evolution was traced in both aerobic and anaerobic incubations using 15N labeling. Partitioning results were highly variable but suggested that enhanced denitrification occurred after an extreme increase in soil water content (from 45 to 90% water‐filled pore space [WFPS]) while a more coupled nitrification–denitrification process drove N2O evolution at moderate water content (55% WFPS). Manured soils at high water contents registered shorter duration peaks but with higher overall N2O production rates than those observed at moderate water content (7‐d weighted average of 0.61 vs. 0.09 μg N2O kg−1 soil h−1). Under anoxic conditions, manured soils showed higher N2O production rates than UAN soils (up to 336 and 145 μg N2O kg−1 soil h−1, respectively) shortly after flooding, which coincided with a sharp drop in Eh (from 575 to 466 mV). Irrespective of the N source, a narrow, consistent Eh range for N2O production occurred under moderate reducing conditions (420–575 mV). These results indicate that soils receiving repeated manure application that are subject to intensive, recurrent soil rewetting events may be prone to higher N2O emissions.

Fourier Transform Infrared Studies in Hypergolic Ignition of Ionic Liquids

A class of room-temperature ionic liquids (RTILs) that exhibit hypergolic activity toward fuming nitric acid is reported. Fast ignition of dicyanamide ionic liquids when mixed with nitric acid is contrasted with the reactivity of the ionic liquid azides, which show high reactivity with nitric acid, but do not ignite. The reactivity of other potential salt fuels is assessed here. Rapid-scan, Fourier transform infrared (FTIR) spectroscopy of the preignition phase indicates the evolution of N 2O from both the dicyanamide and azide RTILs. Evidence for the evolution of CO 2 and isocyanic acid (HNCO) with similar temporal behavior to N 2O from reaction of the dicyanamide ionic liquids with nitric acid is presented. Evolution of HN 3 is detected from the azides. No evolution of HCN from the dicyanamide reactions was detected. From the FTIR observations, biuret reaction tests, and initial ab initio calculations, a mechanism is proposed for the formation of N 2O, CO 2, and HNCO from the dicyanamide reactions during preignition.

Investigation of dynamical processes in the polar stratospheric vortex during the unusually cold winter 2004/2005

The 2004/2005 Arctic winter was unusually cold with high potential for Polar Stratospheric Clouds formation. We use O3 and N2O assimilated fields from Aura/MLS in order to describe the dynamical processes inside the polar vortex during this winter. The evolution of N2O assimilated field shows that subsidence was the dominant dynamical process between early December and late January. The mixing effect between the polar vortex and midlatitudes has been diagnosed using the effective diffusivity parameter. It shows that from early February to the end of March, mixing was dominant compared to diabatic descent. The vortex‐averaged ozone loss profile from O3 assimilated field shows a maximum of ∼1.5 ppmv at 425 K, which is less pronounced compared to other winters of similar meteorological conditions (e.g., 1999/2000). This is due to the importance of the mixing processes between the polar vortex and midlatitudes which bring in ozone‐rich air to the vortex.

Reversible N−N Coupling of NO Ligands on Dinuclear Ruthenium Complexes and Subsequent N2O Evolution: Relevance to Nitric Oxide Reductase

Unprecedented N−N coupling of two nitrosyl ligands on dinuclear complexes was discovered, which is proposed as a critical step in the bacterial NO reductase (NOR). The N−N coupled complex (TpRu)2(μ-Cl)(μ-pz){μ−κ2-N(O)−N(O)} (2a) (Tp = BH(pyrazol-1-yl)3) was prepared from the reaction of TpRuCl2(NO) (1) with pyrazole in the presence of Et3N. The curious N−N bond distance was X-ray crystallographically determined to be 1.861(3) A for the N−N coupled analogue with a 4-methylpyrazolato bridge, and was confirmed by DFT calculation. The N−N bond of 2a was cleaved by oxidation to give [{TpRu(NO)}2(μ-Cl)(μ-pz)](BF4)2 (4a·(BF4)2), which on reduction reformed 2a. It is interesting to note that the N−N coupled complex 2a was also transformed into the oxo-bridged dinuclear species 5a with the evolution of N2O. These findings would provide valuable information regarding the mechanism of NO reduction to N2O by NOR.

The Interaction between Otto Fuel II and Aqueous Hydroxylammonium Perchlorate (HAP), Part III: Depletion of Components within the Reacting Liquids

AbstractGas chromatography (GC) with a Flame Ionisation Detector (FID) has been used to determine changes in the concentrations of the components of Otto Fuel II (OF) in contact with an 82% aqueous solution of hydroxylammonium perchlorate (HAP) in sealed vials at 31.7 °C during the period leading up to auto‐ignition of the two liquids. The concentration of hydroxylamine in HAP was monitored over the same period using a titration method. It was found that 2‐nitrodiphenylamine (2NDPA), the stabiliser in the OF, is completely consumed after about 65–70 h and that the concentration of hydroxylamine begins to fall at this point. 1,2‐Propanediol dinitrate (propylene glycol dinitrate, PGDN), the energetic component in the OF, is not depleted significantly until after about 90 h. The evolution of nitrous oxide (N2O) between 65 and 90 h is attributed to the reaction of the hydroxylammonium ion with nitrous acids produced by PGDN decomposition at the liquid‐liquid interface. Carbon dioxide (CO2) is evolved after ~ 90 h and is attributed to PGDN decomposition. HAP and PGDN are each thought to contribute to N2O evolution after ~ 90 h.