Formation and stability of a nitric oxide donor: S-nitroso-N-acetylpenicillamine

The formation, reaction dynamics, and detailed kinetics and mechanism of the reaction between nitrous acid and N-acetylpenicillamine (NAP) to produce S-nitroso-N-acetylpenicillamine (SNAP) was studied in acidic medium. The nitrous acid was prepared in situ by the rapid reaction between sodium nitrite and hydrochloric acid. The reaction is first order in nitrite and NAP. It is also first order in acid in pH conditions at or slightly higher than the pK(a) of nitrous acid. In lower pH conditions, the catalytic effect of acid quickly saturates. Higher acid concentrations also induce a faster decomposition rate of the SNAP, thus precluding the quantitative formation of SNAP from HNO2 and NAP. Both HPLC and quadrupole time-of-flight mass spectrometry techniques proved that SNAP was the sole product produced. No nitrosation occurred on the secondary amine center in NAP, and only the thiol group reacted to form the nitrosothiol. Cu(I) ions were found to be effective SNAP-decomposition catalysts. Cu(II) ions had no effect on the stability of SNAP. Ambient oxygen in reaction solutions was found to have no effect on initial rates of formation of SNAP, products obtained, and stability of SNAP. The formation of SNAP occurs through two distinct pathways. One involves the direct reaction of NAP and HNO2 to form SNAP and eliminate water, and the second pathway involved the initial formation of the nitrosyl cation, NO+, which then nitrosates the thiol. The bimolecular rate constant for the reaction of NAP and HNO2 was derived as 2.69 M(-1) s(-1), while that of direct nitrosation by the nitrosyl cation was 3.00 x 10(4) M(-1) s(-1). A simple reaction network made up of four reactions was found to be sufficient in simulating the formation kinetics and acid-induced decomposition of SNAP.     

A thermoanalytical study of the metal nitrate-edta precursors for lead zirconate titanate ceramic powders

Lead zirconate titanate (PZT) ceramic powder has been synthesized from metal nitrate solutions using the EDTA-gel method with different nitric acid/EDTA ratios. It was found that the thermal decomposition of the precursor was strongly affected by the nitric acid/EDTA ratio, the amount of sample, the atmosphere, and the heating rate. Crystallization of the perovskite PZT phase initiated at external temperatures as low as 250°C, as a result of the exothermic decomposition reaction of the nitrate-EDTA complexes. Possible reaction schemes are suggested and discussed to describe the thermal decomposition of PZT-EDTA precursors under different experimental conditions.     

大气中一元酸催化亚硫酸分解反应的从头算及动力学研究

采用从头算的理论计算方法,在CCSD（T）/aug-cc-pVDZ//MP2/aug-cc-pVDZ水平下,对甲酸、乙酸、丙酸和硝酸催化亚硫酸分解成二氧化硫和水的微观反应机理进行了理论研究.结果表明,这4种一元酸均可使亚硫酸分解反应能垒显著降低,降低幅度由大到小的顺序为丙酸 > 乙酸 > 甲酸 > 硝酸.其中,丙酸甚至使反应能垒从裸反应时的99.84 kJ/mol降至27.24 kJ/mol.在此基础上,计算了200~320 K温度范围内4种一元酸催化亚硫酸分解反应的速率常数,并结合它们在大气中的实际浓度计算了有效速率常数.结果表明,在实际大气环境中,乙酸对亚硫酸分解反应的催化效果最为显著.当乙酸存在时,亚硫酸在室温下的大气寿命仅为0.02 s.     

Thermal properties of hydrazine in nitric acid solution

Since some combustible, oxidative and reductive chemicals are used in the extracting process in the nuclear reprocessing plant the process has potential hazards of a fire and explosion due to the undesired reaction. In this study to obtain a better understanding of the thermal properties of hydrazine in nitric acid solution which is used for preventing the oxidation of extracted plutonium, thermal analysis was carried out for the mixtures in various conditions. From the results of DSC it was revealed that the vessel material has an influence on the thermal decomposition of hydrazine. It was also found that hydrazine reacted with nitric acid in an autocatalytic manner, and concentration of nitric acid has a strong influence on the thermal hazard of hydrazine and nitric acid mixtures.     

Influence of urea on initiation and termination of reaction between nitric acid and formic acid

The influence of urea on initiation and termination of the reaction between nitric and formic acids was experimentally examined. The urea injection can terminate the denitration reaction in 2 to 10M salt-free nitric acid solutions and the simulated high level liquid wastes (HLLWs) with a nitric acid concentration of 2 to 6M. An excess of urea can interrupt the initiation of denitration in both simulated HLLW and salt-free nitric acid solutions. The initiation and termination of denitration are in relation with nitrous acid formation and decomposition. Urea reacts with nitrous acid easily in the denitrating solution and decomposes nitrous acid. As the urea concentration increases in the solution, the continuance of denitration become impossible because the decomposition rate of nitrous acid exceeds the generation rate. In addition, the nitrous acid concentration can not be high enough to initiate the denitration in the solution with an excess of urea because nitrous acid is decomposed by urea.     

原位漫反射新方法研究煤中氢键的分解动力学

采用一种新的原位漫反射红外技术研究了干燥脱灰褐煤中氢键的分解动力学,同时介绍并应用了一种防止高温下挥发分冷凝的原位漫反射红外实验方法。基于两条假设,当煤加热至560℃时,单一反应模型可以用于除OH－π键以外氢键分解动力学参数的求解。结果表明,煤中羧酸二聚体、OH－N 和SH－N三种氢键的分解动力学遵循二级反应;OH－OR₂,紧密结合的羟基四聚体和自缔合的羟基多聚体则遵循一级反应。计算所得的几种氢键分解活化能与文献中采用其他 方法所得结果基本一致。在所考察的六种氢键中,羧酸二聚体、OH－N 、SH－N和紧密结合的羟基四聚体的分解可以分为两个阶段（230℃~380℃和 380℃~500℃）,而OH－OR₂和自缔合的羟基多聚体的分解可以按照一段来处理。另外,通过比较自缔合的羟基多聚体的分解活化能和文献中的氢键键能,获得了其分解机理。
     

Zur thermischen Zersetzung der hochkonzentrierten Salpetersäure

The thermal decomposition of highly concentrated nitric acid was observed at atmospheric pressure between 0 and 60 °C for up to 273 d. The decomposition of highly concentrated nitric acid $$2 HNO_3 \rightleftharpoons 2 NO_2 + H_2 O + {1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2} O_2 $$ is a second order reaction in nitric acid. The reversible reaction proceeds to equilibrium. The velocity and equilibrium constants were obtained by kinetic evaluation of the readings for HNO₃ and NO₂. The activation energy for decomposition was — 134 kJ/mol.     

Kinetics and optimisation of process parameters for electrochemical generation of uranous ions in nitric acid–hydrazine media

For the quantitative generation of uranous from uranyl ions in the presence of hydrazine in nitric acid medium, electrochemical reduction was carried out in divided and undivided cells. The influence of process conditions, viz. current density, concentration of nitric acid and hydrazine was studied for 50, 100 and 150 g/l of U(VI) solutions. The performance of the cathodes (titanium and platinum) was evaluated by calculating the conversion efficiencies in the reduction process using these electrodes for the reduction of 100 g/l U(VI) at 6 mA/cm² as the cathodic current density. Batch mode experiments using Ti cathode revealed the reduction reaction of U(VI) to follow zero order kinetics and the simultaneous reduction of nitric acid to follow first order kinetics. From the temperature dependence, the activation energy for the reduction of U(VI) was determined to be 4.05 kJ/mol. The chemical stability of U(IV) in nitric acid–hydrazine medium, under ambient conditions of temperature and pressure was established from the amount of U(VI) produced from U(IV) by aerial oxidation over a period of 16 weeks.     

Thermal hazard analysis of mixed system of hydrazine and nitric acid

In order to obtain a better understanding of the thermal hazard of hydrazine and nitric acid mixtures which are used in plutonium and uranium recovery by extraction (PUREX) process during recycling of spent fuel in nuclear plant, DSC was carried out for the mixed system made by the small scale reaction calorimeter super-CRC in various conditions. It was found that the concentration of the nitric acid has a strong influence on the thermal behavior of the mixed system, and hydrazine nitrate which is formed in the reaction in the mixture was determined by DSC with FTIR analysis.     

The complex reaction kinetics of neptunium including redox and extraction process in 30% TBP—nitric acid system

In order to understand the complex and dynamic neptunium process chemistry in the TBP-HNO₃ system, the kinetics involved reversible redox reaction and extraction mass transfer was investigated. The results indicates that the mass transfer rate of Np(VI) is much faster than the redox reaction in aqueous solution. The concentrations of nitric acid and nitrous acid not only can change the Np(V) oxidation reaction and Np(VI) reduction reaction rate, but also can ultimately determine the distribution of neptunium extraction equilibrium. The variety of temperature can only influence the extraction equilibrium time, but cannot alter the equilibrium state of neptunium.     

Oxidation of cholesterol by a biomimetic oxidant, cetyltrimethylammonium dichromate

The oxidation of cholesterol by cetyltrimethylammonium dichromate (CTADC) in dichloromethane (DCM) yielded 7-dehydrocholesterol, while with addition of acetic acid in DCM the product was found to be 5-cholesten-3-one. The kinetics of oxidation of cholesterol by CTADC in DCM, in the presence of acid, was investigated with change in [acid], [cholesterol], [CTADC], [surfactant], temperature, and solvents. The reaction was found to be first order with acetic acid and fractional order with CTADC and cholesterol. Michaelis-Menten-type kinetics was observed with respect to cholesterol. The solvent isotope effect was found to be k(D2O)/k(H2O) = 0.72. The observed experimental data suggest that the reaction occurs in reversed micellar system, akin to an enzymatic environment, and the reaction path involves the intermediate formation of an ester complex, which undergoes decomposition to give the product.     

Thermal decomposition characteristics of octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide-tri n-butyl phosphate–nitric acid systems

Thermal stability of neat octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (OΦD[IB]CMPO) and TRUEX solvent composition (0.2M OΦD[IB]CMPO-1.2M tri n-butyl phosphate-in n-dodecane) in the presence and absence of nitric acid has been studied in ambient air in a closed vessel, employing an adiabatic calorimeter. Enthalpies and kinetic parameters for the decomposition reaction were derived wherever possible and are reported for the first time. Neat OΦD[IB]CMPO was found to be thermally stable up to 633 K and exhibited an exothermic decomposition later. It decomposed at lower temperatures (376–386 K) depending on the nitric acid concentration. The exothermic rise in temperature and pressure increased exponentially, while activation energies exhibited exponential decrease for the decomposition reactions with increase in nitric acid content. TRUEX solvent was found to be stable up to 661 K in the absence of nitric acid while in the presence of 8 and 4M HNO₃, it decomposed between 387 and 413 K. All these samples on decomposition formed incompressible gases and viscous black liquids. The results also indicate that the neat OΦD[IB]CMPO and the TRUEX solvent are thermally more stable than neat tri n-butyl phosphate (TBP), PUREX solvent (1.1M TBP/n-DD), neat diamyl amyl phosphonate (DAAP) and 1.1M DAAP/n-DD, triisoamyl phosphate (TiAP) and 1.1M TiAP/n-DD.     

Kinetics and Mechanism of Catalytic Reduction of U(VI) with Hydrazine on Platinum Catalysts in Nitric Acid Media

The kinetics of U(IV) produced by hydrazine reduction of U(VI) with platinum as a catalyst in nitric acid media was studied to reveal the reaction mechanism and optimize the reaction process. Electron spin resonance (ESR) was used to determine the influence of nitric acid oxidation. The effects of nitric acid, hydrazine, U(VI) concentration, catalyst dosage and temperature on the reaction rate were also studied. In addition, the simulation of the reaction process was performed using density functional theory. The results show that the influence of oxidation on the main reaction is limited when the concentration of nitric acid is below 0.5 mol/L. The reaction kinetics equation below the concentration of 0.5 mol/L is found as: -dc(UO₂²⁺)/dt)=kc^0.5323(UO₂²⁺)c^0.2074(N₂H₅⁺)c^-0.2009(H⁺). When the temperature is 50 ℃, and the solid/liquid ratio r is 0.0667 g/mL, the reaction kinetics constant is k=0.00199 (mol/L)^0.4712/min. Between 20 ℃ and 80 ℃, the reaction rate gradually increases with the increase of temperature, and changes from chemically controlled to diffusion-controlled. The simulations of density functional theory give further insight into the influence of various factors on the reaction process, with which the reaction mechanisms are determined according to the reaction kinetics and the simulation results.     

Pressurization studies in a sealed autoclave for thermal decomposition of nitrated TBP and TiAP

Study of runaway reaction between tri-n-butyl phosphate (TBP) and nitric acid resulting in red-oil formation (and related problems) in the process evaporators of reprocessing plants has been a major safety concern since last 50 years. Thermal decomposition of nitrated TBP results in rapid pressurization and in close-vent condition it may lead to failure of process vessel and containment. Thermal decomposition of nitrated TBP is reported in the literature but corresponding studies for alternate PUREX/UREX solvent tri-iso-amyl phosphate (TiAP) are not available. In this work, comparative study of the thermal decomposition of nitrated solvents (TBP as well as TiAP) under adiabatic conditions in a sealed autoclave is presented. Experimental results indicate much lesser pressurization in the case of TiAP as compared to TBP.     

Kinetics and mechanism of p-isopropenylphenol synthesis via hydrothermal cleavage of bisphenol A

Although bishydroxyarylalkanes are known to be reactive in high-temperature (T > 200 degrees C) liquid water (HTW), no mechanistic insight has been given to explain the reactivity of methylene bridge-containing diaryls under hydrothermal conditions. We examined the kinetics and mechanism of p-isopropenylphenol (IPP) synthesis via bisphenol A (BPA) cleavage in HTW. The cleavage reaction is first order in BPA. Cleavage of BPA in HTW occurs by specific acid catalysis, by specific base catalysis, and by general water catalysis. Under neutral conditions, the dominant mechanism is general base catalysis with water serving as the proton acceptor. We generated a detailed chemical kinetics model for the decomposition reaction based on a base-catalyzed mechanism in the literature. This three-parameter model fit the experimental data for BPA disappearance and formation of IPP and phenol and accurately predicted the yield of the IPP hydrolysis product acetone. Using acid- and base-catalyzed mechanisms, we explain the reactivity in HTW reported for other diaryl groups linked by methylene bridges and propose criteria for assessing the reactivity of methylene bridges under hydrothermal conditions.     

Kinetics and mechanism of Ru(III)-catalyzed oxidation of aliphatic alcohols by trichloroisocyanuric acid in HClO4 medium

The kinetics and mechanism of Ru(III)-catalyzed oxidation of some aliphatic alcohols by trichloroisocyanuric acid (TCICA) has been studied in aqueous HOAc-HClO₄ medium. The reaction is zero order in [TCICA], fractional order in [alcohol] and first order in [Ru(III)]. The reaction is insensitive towards changes in acid concentration. The rate is not affected by an increase in [Cl⁻]. The polar reaction constant (ρ*) was found to be −1.27 at 308 K. A mechanism involving complex formation between the substrate and catalyst in the fast equilibrium step followed by its decomposition in a slow step is proposed.     

Kinetics and mechanism of the oxidation of lower oxyacids of phosphorus by hexamethylenetetramine bromine

The oxidation of lower oxyacids of phosphorus by hexamethylenetetramine bromine (HABR) in glacial acetic acid resulted in the formation of corresponding oxyacids with phosphorus in a higher oxidation state. The reaction exhibited 2:1 stoichiometry. The reaction is first order with respect to HABR. Michaelis–Menten‐type kinetics were observed with respect to the acids. The formation constant of the phenylphosphinic acid–HABR complex also has been determined spectrophotometrically. The thermodynamic parameters for the complex formation and the activation parameters for their decomposition were calculated. The reaction showed the presence of a substantial kinetic isotope effect. It is proposed that the HABR itself is the reactive oxidizing species. It has been shown that the pentacoordinated tautomer of the phosphorus oxyacid is the reactive reductant. A suitable mechanism has been proposed. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 165–170, 2000     

Effects of modified multi-walled carbon nanotubes on the curing behavior and thermal stability of boron phenolic resin

One kind of boron phenolic resin (BPR) was prepared from the solvent-less reaction of resoles with boric acid. X-ray photoelectron spectroscopy (XPS) showed that the reaction degree of boric acid was 83.8%. Multi-walled carbon nanotubes (MWCNTs) were modified by nitric acid, 4,4′-Diaminodiphenyl methane and boric acid. The effect of modification was determined by Fourier transform infrared (FT-IR), thermogravimetric analysis (TGA) techniques and XPS. The cure kinetics and thermal behavior of BPR and modified multi-walled carbon nanotubes (m-MWCNTs)/BPR were studied. It was found that the curing apparent activation energy (E_a) decreased with the increasing amount of m-MWCNTs. But there was no obvious change in the orders of curing reactions. The results of TGA showed that 1.0 wt% of the m-MWCNTs could increase the thermal decomposition temperature (T_d) and the char yield of m-MWCNTs/BPR nanocomposites by 36.7 °C and 6.2%. These critical enhancements will definitely help to attract more researches on this area.     

过氧亚硝酸盐的化学发光反应与测定

过氧亚硝酸盐是一氧化氮衍生物,由一氧化氮和超氧阴离子反应生成,它是很强的生物氧化剂,具有很高的反应活性和不稳定性。本文详细介绍了ONOO-的化学发光分解、ONOO-与二氧化碳的化学发光反应、ONOO-化学发光测定和应用,并展望了其发展前景。引用参考文献54篇。     

Toluene and benzyl decomposition mechanisms: elementary reactions and kinetic simulations

The high temperature decomposition kinetics of toluene and benzyl were investigated by combining a kinetic analysis with the ab initio/master equation study of new reaction channels. It was found that similarly to toluene, which decomposes to benzyl and phenyl losing atomic hydrogen and methyl, also benzyl decomposition proceeds through two channels with similar products. The first leads to the formation of fulvenallene and hydrogen and has already been investigated in detail in recent publications. In this work it is proposed that benzyl can decompose also through a second decomposition channel to form benzyne and methyl. The channel specific kinetic constants of benzyl decomposition were determined by integrating the RRKM/master equation over the C(7)H(7) potential energy surface. The energies of wells and saddle points were determined at the CCSD(T) level on B3LYP/6-31+G(d,p) structures. A kinetic mechanism was then formulated, which comprises the benzyl and toluene decomposition reactions together with a recently proposed fulvenallene decomposition mechanism, the decomposition kinetics of the fulvenallenyl radical, and some reactions describing the secondary chemistry originated by the decomposition products. The kinetic mechanism so obtained was used to simulate the production of H atoms measured in a wide pressure and temperature range using different experimental setups. The calculated and experimental data are in good agreement. Kinetic constants of the new reaction channels here examined are reported as a function of temperature at different pressures. The mechanism here proposed is not compatible with the assumption often used in literature kinetic mechanisms that benzyl decomposition can be effectively described through a lumped reaction whose products are the cyclopentadienyl radical and acetylene.