Kinetic study of BH3 reduction of benzaldehydes: identification of effective reducing species

A kinetic study was carried out for the reaction of benzaldehyde and borane (BH₃) in tetrahydrofuran. The effect of BH₃ concentration on the rate constant showed that the reaction order with respect to BH₃ was 1.6. Substituent effects gave a linear Hammett plot with a ρ value of ?0.51. It was concluded that the reaction proceeds through a rate‐determining hydride‐transfer transition state with two BH₃ molecules, in which one molecule of BH₃ acts as a reducing agent and the other serves as a catalyst. Copyright © 2011 John Wiley & Sons, Ltd.     

Speciation of Arsenic in Rice by High-Performance Liquid Chromatography–Hydride Generation-Atomic Fluorescence Spectrometry with Microwave-Assisted Extraction

Arsenic speciation in paddy rice is of considerable interest due to its impact on the food safety and human health. In this study, a simple methodology was developed to simultaneously extract and analyze As species in rice from China. Arsenic species, including arsenite (As(III)), arsenate (As(V)), dimethylarsinic acid (DMA), and monomethylarsonic acid (MMA), were extracted by methanol-water (50:50, v/v) containing 0.02 mol L^?1 nitric acid with a microwave-assisted procedure, and then determined by high performance liquid chromatography–hydride generation-atomic fluorescence spectrometry (HPLC–HG-AFS). The results showed that the method has good efficiency (>90%) for rice, indicating that there were no significant losses or transformations of arsenic during sample treatment and analysis. The limits of quantification (LOQ) of the method were 8.0, 20, 12, and 12 ng g^?1 for As(III), As(V), DMA, and MMA, respectively. When this method was applied to the analysis of rice, As(III) had the highest concentration, followed by DMA, As(V), and MMA. The estimated weekly intake of inorganic As from rice by Chinese people accounted for 11.83% of the provisional tolerable weekly intake. The As speciation results in this study suggest that the risk associated with As in rice to human health may be negligible.     

Study of the Effectiveness of Arsenic Hydride Generation from Various Arsenic Species with the Use of Some Borane Reducing Agents by Inductively Coupled Plasma Atomic Emission Spectrometry

Abstract

The application of H₃B–NH(CH₃)_2,H₃B–NH₂C(CH₃)₃ and NaBH₄ as derivatizing reagents in hydride generation from As(III), As(V), and As(V)-dimethyl forms was investigated. The effects of hydrochloric, acetic, and citric acids on the As responses were studied by using inductively coupled plasma optical emission spectrometry. Intensities of As, B, and H lines, and the pH of the reaction mixture were recorded. The effectiveness of the hydride generation depended on the arsenic form and changed with reductant type as well as with kind and concentration of the acids. The H line intensities were different from those expected from stechiometric reactions between the reductants and acids.     

由扩散阻抗过渡区求金属氢化物电极中氢扩散系数的不确定性(英文)

本文参照文献[1] 报导的利用扩散阻抗过渡区求金属氢化物电极中氢扩散系数的方法测定了MlNi3.75Co0 .6 5Mn0 .4 Al0 .2 电极中氢的扩散系数 .结果发现 :运算过程中由于所用到的一些函数具有周期性 ,使计算结果变为多解 ,而且这些解之间存在着数量级上的差别 ;对同一组实验数据 ,过渡区内依据不同频率点求得的扩散系数也很不同 .总之 ,该方法尚不成熟 ,有待于进一步完善     

纳米LiH的热稳定性与催化加氢反应活性

考察了纳米LiH在不同温度热处理后比表面积的变化及其与Cp2TiCl2组成催化剂的加氢反应活性之间的关系,300度热处理后LiH比表面积已呈较大幅度的下降,但催化剂的加氢反应活性反而更高,说明比表面积是克杨纳米LiH高活性的一个主要原因,但不是唯一 的因素。     

Investigation on the mechanism and applications of the reaction Cl2+2HBr=2HCl+Br2

The mechanism of reaction Cl₂+2HBr=2HCl+Br₂ has been carefully investigated with density functional theory (DFT) at B3LYP/6-311G^** level. A series of three-centred and four-centred transition states have been obtained. The activation energy (138.96 and 147.24 kJ/mol, respectively) of two bimolecular elementary reactions Cl₂+HBr→HCl+BrCl and BrCl+HBr→HCl+Br₂ is smaller than the dissociation energy of Cl₂, HBr and BrCl, indicating that it is favorable for the title reaction occurring in the bimolecular form. The reaction has been applied to the chemical engineering process of recycling Br₂ from HBr. Gaseous Cl₂ directly reacts with HBr gas, which produces gaseous mixtures containing Br₂, and liquid Br₂ and HCl are obtained by cooling the mixtures and further separated by absorption with CCl₄. The recovery percentage of Br₂ is more than 96%, and the Cl₂ remaining in liquid Br₂ is less than 3.0%. The paper provides a good example of solving the difficult problem in chemical engineering with basic theory.     

Iridium Cluster Chemistry: The Synthesis and the Solid State Structures of [HIr5(CO)12]2− and [HIr4(CO)10PPh3]−

The cluster [HIr₅(CO)₁₂]^2- (1) was prepared by condensation of [HIr₄(CO)₁₁]^- and [Ir(CO)₄]^- (molar ratio 1:1) in refluxing THF, with almost quantitative yields. Its solid state structure was determined by X-ray diffraction at low temperature on the salt [PPh₃CH₂Ph]₂[HIr₅(CO)₁₂]. The metal atoms define a trigonal bipyramidal arrangement. The hydride ligand was located indirectly as a bridge between apical and equatorial metal atoms. The phosphine-substituted cluster [HIr₄(CO)₁₀PPh₃]^- (2) was synthetized by CO displacement on [HIr₄(CO)₁₁]^-, in THF at room temperature. This reaction is selective, with no traces of polysubstitution products. In the solid state, the hydride and the triphenylphosphine are axially bound on basal iridium atoms; the terminal hydrogen atom was directly located by X-ray analysis at a Ir–H distance of 1.57(9) Å. On the contrary, two isomers are present in THF solution, and they interconvert rapidly at room temperature, as shown by¹H and ³¹P NMR spectra.     

串接反应色谱法对甲醇催化脱水产物的一次性分析

提出一种用微反应色谱法来研究甲醇气相脱水制备二甲磨灭 的色谱分析流程,可以一次性分析得到气相和液相组份的定量数据,实现在线化实时分析,避免通常必须对液相组份进行冷凝然后单独对液相组份进行化学分析,流程的安排是：首先用一个色谱柱将甲醇脱水产物中的水、甲醇、乙醇完全分离并与其他组份分开,在氢化钙转化反应器中,将已经分离的水、甲醇、乙醇集资转化成氢,用热导检测器测定,在吕接的第二个色谱柱中实现其它组份的     

Asymmetric reduction of ketones with sodium aluminum hydride modified by various chiral diols

New stereoselective reducing reagents were preparedin situ by modification of NaAlH₄ with various chiral diols. The efficiency of 1,4- and 1,3-diols as chiral auxiliaries in the reactions of alkyl aryl ketones with modified NaAlH₄ was considerably higher than that of 1,2-diols. The effect of the nature of the achiral ligand additionally introduced into the chiral hydride reagent on the enantioselectivity of ketone reduction was studied. It was proposed that the sodium cation does not necessarily participate at the stage governing the reaction stereochemistry. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp 459–464, March, 2000.