除草剂2-甲基-4-氯苯氧乙酸(MCPA)与~·OH自由基的气相化学反应

采用长光程气体池结合傅里叶变换红外光谱仪测得了除草剂2-甲基-4-氯苯氧乙酸(MCPA)与.OH自由基在23℃时的反应速率常数为2.67×10-11cm3/(s.mol),以此估算了在大气中.OH自由基浓度为7×105mol/cm3时,MCPA与.OH自由基反应导致的大气寿命为14.9 h.结果表明,在大气环境中MCPA较容易降解,不会通过大气输送对环境造成广泛和持久性污染.     

脉冲辐解研究吩噻嗪与CCl3OO·、·OH的反应

采用纳秒级脉冲辐解技术研究了吩噻嗪与CCl₃OO^·、^·OH的反应, 提出了相应的反应机理, 得到了相关的反应速率常数. 研究结果表明: 吩噻嗪与CCl₃OO^·、^·OH反应得到的瞬态产物的最大吸收峰都位于380 nm左右, 该吸收峰归属于CCl₃OO^·、^·OH夺取吩噻嗪氮原子上的氢而产生的吩噻嗪氮自由基. 吩噻嗪与CCl₃OO^·、^·OH反应的速率常数分别为1.1×10⁹和4.0×10⁹ L·mol^-1·s^-1. 这些结果将为进一步研究吩噻嗪的抗氧化活性提供理论基础.     

Fenton反应考察抗坏血酸清除羟基自由基能力及动力学

自由基的清除对维持正常的生理活动和抗衰老具有重要意义。 抗坏血酸(V_C)是常用的天然抗氧化剂之一, 为了有效合理利用V_C的抗氧化性, 实验利用水杨酸捕捉Fenton反应产生的羟基自由基(·OH), 加入V_C考察与水杨酸竞争清除·OH的能力, 选择出最佳清除条件;并根据双底物反应特征, 拟合出Alberty方程, 得到了清除·OH的规律。 结果表明, 当V_C用量为4.54 mmol/L、温度为47 ℃条件下、反应90 min时, V_C对·OH的清除率达到最大, 为46.23%;拟合出的反应动力学参数最大反应速率为0.11 mmol/(L·min), 水杨酸和V_C 的特征常数分别为30.2和1.2×10^-3 mmol/L。 比较实验结果和拟合方程得到的数据, 二者非常接近, 相对误差在1.66%~5.40% 之间, 从而为合理利用抗坏血酸清除羟基自由基提供理论依据。     

CS2与亚硝酸水溶液复相体系的激光闪光光解

利用激光光解-瞬态吸收技术研究了氮气饱和条件下CS2与亚硝酸水溶液复相体系的355nm光解机理.瞬态吸收光谱分析结果表明:CS2与·OH自由基快反应生成CS2OH,产生的CS2OH继续与HONO反应生成CS2OH-HONO加合物,其吸收峰分别为285,305,475,490和980nm,反应CS2OH+HONOCS2OH-HONO的二级速率常数为(2.79±0.05)×108L/(mol·s);230nm处的吸收峰归属为CS2NO+,其一级衰减速率常数为1.28×105s-1.     

脉冲辐解研究喹啉和异喹啉与瞬态粒子的反应

通过合理控制反应条件, 使体系在电子束脉冲作用后只剩下所需要的一种瞬态粒子, 用脉冲辐解研究了喹啉、异喹啉分别与水合电子、羟基自由基、氢自由基等几种典型的氧化还原瞬态粒子的反应过程, 研究了各种瞬态产物的吸收光谱及其变化规律, 测定了相关反应的速率常数. 喹啉、异喹啉与水合电子的反应速率常数分别为7.1×10⁹和3.4×10⁹ mol^-1·L·s^-1, 与羟基自由基的反应速率常数分别为7.2×10⁹和3.4×10⁹ mol^-1·L·s^-1, 与氢自由基的反应速率常数分别为5.7×10⁹和3.6×10⁹ mol^-1·L·s^-1. 这一结果表明, 喹啉、异喹啉均能够非常迅速地与水合电子、羟基自由基、氢自由基发生反应, 喹啉比异喹啉的反应速率更快. 运用电子理论分析了瞬态反应产物结构的稳定性差异, 结果表明, 喹啉的反应产物比异喹啉的稳定, 从而揭示了喹啉比异喹啉反应速率快的原因.     

一种可能形成POPs途径的初探-气相苯的氯化反应

用串联质谱碰撞室模拟大气环境研究了持久性有机污染物(POPs)形成过程,实验发现,经离子-分子反应可以生成氯苯类化合物。 以中性苯与酰氯为反应物在离子源进行反应,在苯含量为4×10^-3Pa、酰氯含量为4×10^-4Pa时,氯苯的生成量为5×10^-8Pa,远远高于背底浓度5×10^-9Pa。对氯苯类化合物的形成,大气环境明显优于质谱环境,实验结果表明,在大气中经离子分子反应形成POPs是可能的。     

Meso-2,3-二氰基-2,3-二苯基丁二酸二乙酯熔融相热异构化反应动力学及中间体EPR测定

测定了2,3-二氰基-2,β-二苯基丁二酸二乙酯meso-异构体熔融相的热异构化反应动力学及苯环对位为X(X=OCH₃,CH₃,H,Cl,NO₂)的相应二乙酯反应中间体自由基的EPR谱,自由基的结构由计算机模拟确定.结果表明,在实验温度范围内,平衡常数随温度的升高而降低.热力学数据为:ΔH_dl-meao= - 18.02 kJ/mol, ΔS_dl-meao= - 26.51 J/mol·K, ΔH^≠ = 151.78 kJ/mol, ΔS^≠ = 71.64 J/mol·K.反应机理是内消旋体的中心碳-碳键发生均裂,生成α-氰基-α-乙氧甲酰基-P-X取代苄基自由基,再重新结合时发生异构化,生成dl-异构体.     

氯化钴/吡嗪-2-羧酸钾体系催化苄基氯双羰化合成β-苄基-α-苯丙酮酸

 将新型氯化钴/吡嗪-2-羧酸钾催化体系用于苄基氯双羰化反应,并对反应条件进行了优化. 结果表明,最佳反应条件为: 氯化钴浓度0.03 mol/L,吡嗪-2-羧酸(Pzca)浓度0.156 mol/L,n(Pzca)/n(KOH)=1,n(Ca(OH)2)/n(苄基氯)=2.7,V(1,4-二氧六环)/V(H2O)=5,反应温度70 ℃,CO压力2.0 MPa,反应时间10 h,此时β-苄基-α-苯丙酮酸的产率为77.3%,双羰化选择性为99.6%. 该催化体系能有效地抑制单羰化反应,双羰化反应的选择性和苄基氯转化率都较高. 同时对该体系的催化活性体进行了初步解释,并用红外光谱和质谱对产物结构进行了表征.     

新型显色剂Meso-四(4-羟基-3-乙氧基苯基)卟啉的合成及其应用

合成了四(4-羟基-3-乙氧基苯基)卟啉, 用元素分析、质谱、紫外-可见光谱、红外光谱及核磁共振氢谱进行了表征, 研究了该卟啉与铅离子的显色反应条件. 结果表明, 当pH=11.0时, 在十二烷基磺酸钠存在下, 沸水浴加热5 min反应完全, 在473 nm处测得配合物的表观摩尔吸光系数为2.08×105 L/(mol·cm), 铅量在0~12 μg/25 mL范围内符合比尔定律, 用此法成功地测定人发标准物质中的微量元素铅的含量.     

紫外光-热双固化聚苯胺防腐涂料

以酸性磷酸酯为掺杂剂对本征态聚苯胺(EB)进行掺杂,制备了可在聚氨酯和聚氨酯丙烯酸酯中进行纳米分散的导电聚苯胺(ES),其粒径分布在80~750 nm之间可控。 在此基础上,制备了不含重金属的紫外光-热双固化聚苯胺防腐涂料。 该防腐涂料先后经过3~5 s紫外光固化和80 ℃下1~3 min的热固化,即可完成紫外光-热双固化过程。 由于ES与聚氨酯或聚氨酯丙烯酸酯之间是不相容体系,因此随着ES质量分数的增大,会导致ES的团聚,分散粒径增大。 当ES质量分数从1.0%增大到5.0%时,ES的粒径从80~119 nm增加到500~750 nm。 ES的分散粒径增大会导致防腐涂层的致密性变差,降低防腐效果。 与普通紫外光固化聚苯胺防腐涂层相比,当ES为1.0%时,紫外光-热双固化防腐涂层在质量分数为3.5%的NaCl水溶液中浸泡2160 h后,其0.1 Hz下的绝对阻抗值(|Z|_{0.1 Hz})仍高于1.0×10⁸ Ω·cm²,优于普通紫外光固化聚苯胺防腐涂层的|Z|_{0.1 Hz}(1.0×10⁷ Ω·cm²),表明紫外光-热双固化涂层的防腐效果有了显著改善。 经过500 h划叉中性盐雾试验后,普通紫外光固化防腐涂层的板面出现了锈蚀宽度小于1 mm的锈蚀,而紫外光-热双固化防腐涂层经过500 h划叉中性盐雾试验,板面没有出现生锈、起泡的现象,表明紫外光-热双固化路线对提高涂层的防腐性能具有较大的价值。     

Photocatalytic oxidation of the herbicide (4-chloro-2-methylphenoxy)acetic acid (MCPA) over TiO2

The photocatalytic decomposition of the herbicide (4-chloro-2-methylphenoxy)acetic acid (MCPA), C₉H₉ClO₃, in aqueous suspensions containing TiO₂ was investigated by following the formation of intermediates via recording proton NMR spectra. One of theoretically possible intermediates, 4-chloro-2-methylphenolmethanoate, was synthesized by a modified esterification procedure. Based on the data obtained a possible reaction mechanism was proposed. The rate of MCPA aromatic ring decomposition was followed by pH changes during illumination. As a result, apparent reaction rate constant was found to be 7.0×10⁻⁶ mol dm⁻³ min⁻¹. The complete mineralization was attained after about 15 h of illumination.     

Rate constant of the reaction of NO3 with CH2I2 measured with use of cavity ring-down spectroscopy

We have applied cavity ring-down spectroscopy to a kinetic study of the reaction of NO₃ with CH₂I₂ in 25–100 Torr of N₂ diluent at 298 K. The rate constant of reaction of NO₃ + CH₂I₂ is determined to be (4.0 ± 1.2) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹ in 100 Torr of N₂ diluent at 298 K. The rate constant increases with increasing pressure of buffer gas below 100 Torr. The reaction of CH₂I₂ with NO₃ has the potential importance at nighttime in the atmosphere.     

Catalytic effect of zinc oxide on the reduction of barium sulfate by methane

Reduction of barium sulfate by methane was investigated in this work. The thermogravimetric method was used to obtain kinetic parameters of the reaction in the temperature range of 900–975 °C at atmospheric pressure. The kinetics of the reaction has been studied both in the absence and presence of zinc oxide as a catalyst. The conversion–time data have been interpreted by using the grain model, and the effect of catalyst on the kinetic parameters has been elucidated. It was found that zinc oxide acted as fairly strong catalyst for the reaction, especially at higher temperatures. At about 975 °C the reaction rate constant was increased more than 7 times by using 2% of zinc oxide. This enhancement in the rate constant is valuable for industries.     

Determination of the rate constants of the reactions of NO3 radical with CF3I and I(2P3/2)

The rate constant of the reaction of NO₃ radical with CF₃I was determined by a relative rate method using a Fourier transform infrared (FTIR) spectrometer smog chamber with a long path length gas cell. As a result, the upper limit of the rate constant was determined to be <2.2 × 10^?18 cm³ molecule^?1 s^?1 in 100 Torr of total pressure at 298 K, which suggests that CF₃I emitted into the atmosphere accumulates during night. The rate constant of the reaction of NO₃ with I(²P_3/2) was also measured using time‐resolved cavity ring‐down spectroscopy. The rate constant showed no pressure dependence in the range of 100–500 Torr of total pressure at 298 K and was determined to be (3.9 ± 1.0) × 10^?11 cm³ molecule^?1 s^?1. The present result is different from the previous ones and is about half of that reported most recently. From this rate constant, it is likely that the reaction of NO₃ radical with I(²P_3/2) does not have a much influence on the loss of I(²P_3/2) and the formation cycle of IO radical in the atmosphere. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 649–660, 2012     

Radiolytic degradation of pesticide 4-chloro-2-methylphenoxyacetic acid (MCPA)—Experimental data and kinetic modelling

The aqueous solutions of MCPA have been γ-irradiated in different conditions, where particular active radical species from water radiolysis predominate. The obtained data confirmed that largest yield of radiolytic decomposition is obtained in oxidation processes, where oxidation is carried out with hydroxyl radicals. The obtained data have been compared with kinetic modelling. A fair agreement was obtained for degradation of MCPA in different experimental conditions, including also irradiation in the presence of hydrogen peroxide, that in optimised conditions can be used to enhance the yield of decomposition. The obtained data have also shown a strong effect of the presence of large amount of chloride on yield of MCPA decomposition, which can be attributed to strong oxidation properties of chlorine radicals formed. It is also shown that MCPA can be completely decomposed in industrial wastes from various stages of MCPA production, although this is not accompanied by satisfactory reduction of toxicity of examined wastes.     

Kinetic method for the determination of traces of thyroxine by its catalytic effect on the Mn(III) metaphosphate-As(III) reaction

A new, highly sensitive and simple kinetic method for the determination of thyroxine was proposed. The method was based on the catalytic effect of thyroxine on the oxidation of As(III) by Mn(III) metaphosphate. The kinetics of the reaction was studied in the presence of orthophosphoric acid. The reaction rate was followed spectrophotometrically at 516 nm. It was established that orthophosphoric acid increased the reaction rate and that the extent of the non-catalytic reaction was extremely small. A kinetic equation was postulated and the apparent rate constant was calculated. The dependence of the reaction rate on temperature was investigated and the energy of activation and other kinetic parameters were determined.

Thyroxine was determined under the optimal experimental conditions in the range 7.0 × 10⁻⁹ to 3.0 × 10⁻⁸ mol L⁻¹ with a relative standard deviation up to 6.7% and a detection limit of 2.7 × 10⁻⁹ mol L⁻¹. In the presence of 0.08 mol L⁻¹ chloride, the detection limit decreased to 6.6 × 10⁻¹⁰ mol L⁻¹. The proposed method was applied for the determination of thyroxine in tablets. The accuracy of the method was evaluated by comparison with the HPLC method.     

Electrolytic preparation of a reduced ninhydrin reagent for amino acid analysis

Summary A flow-through electrolysis using a column electrode was applied to the preparation of a reduced ninhydrin reagent suitable for a highly reproducible and sensitive determination of amino acids. Non-reduced ninhydrin solution, which could be stably stored for long duration even in contact with atmospheric oxygen, was fed at a constant flow rate of 0.25 ml min^–1 into the flow-through electrolysis cell, whereby ninhydrin was reduced to hydrindantin. The hydrindantin content in the reagent (presumably 1.61 mol%) was sufficiently constant for the subsequent quantitative reaction of the amino acids being eluted from the HPLC system. The electrolytically prepared reagent was practically identical with those prepared by chemical reduction.

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Elektrolytische Herstellung von reduziertem Ninhydrinreagens für die AminosÄureanalyse

     

Rate coefficients for the gas-phase reaction of hydroxyl radicals with 2-methoxyphenol (guaiacol) and related compounds

2-Methoxyphenol (guaiacol) and its derivatives are potential marker compounds for wood smoke emissions in the atmosphere. To investigate the atmospheric reactivity of this type of compounds, rate coefficients for their reactions with hydroxyl (OH) radicals have been determined at 294 ± 2 K and 1 atm using the relative rate method with gas chromatography for chemical analysis. The rate coefficients (in units of cm3 molecule?1 s?1) are: 2-methoxyphenol, (7.53 ± 0.41) × 10?11; 3-methoxyphenol, (9.80 ± 0.46) × 10?11; 4-methoxyphenol, (9.50 ± 0.55) × 10?11; 2-methoxy-4-methylphenol, (9.45 ± 0.59) × 10?11; and methoxybenzene, (2.20 ± 0.15) × 10?11. The estimated atmospheric lifetime for 2-methoxyphenol is ~2 h, indicating that it is too reactive to be used as a tracer for wood smoke emissions. The reactivity of the methoxyphenols is compared with other substituted aromatics and interpreted in relation to the type, number, and positions of the different substituents on the aromatic ring. The atmospheric implications of the reactions are also discussed.     

A flow tube study of methyl iodine uptake on soot surface

The black carbon aerosols are now recognized for their potential impact on climate and the halogenated compounds are thought to be very important in atmospheric chemistry. However, there are very few studies on the interactions between soot aerosols and halogenated compounds. We report the measurement of the uptake of CH₃I on soot. The measured uptake coefficient is 0.0103 ± 0.0015 at a total pressure of 2–4 Torr and 298 K. The results suggest that the uptake of CH₃I occurs efficiently on soot particles. The present work suggests that heterogeneous loss of CH₃I on soot may influence the concentration of CH₃I throughout the atmosphere.     

Application fo pressure DTA (DSC) to thermal hazard evaluation

Any hazard evaluation program should necessarily include assessment of the thermal hazards of a material. To this end, differential thermal methods (DTA and DSC) are commonly employed. The utility of these methods in thermal hazard evaluation can be significantly extended if pressurized atmospheres are also employed. The characterization of volatile chemicals as much as 100°C beyond their atmospheric boiling temperature may be achieved with pressures under 1654 kPa (225 p.s.i.g.). The effective oxygen reactivity is enhanced with a pressurized air atmosphere. Also the confined conditions in a pressurized DTA (DSC) atmosphere produce results which can be used in many instances for the semi-quantative assessment of the pressure—temperature change to be expected in more time-consuming “heating under confinements tests”.