Contribution to the Design and Construction of Thermic Flow Detectors for Liquids

Thermic detectors are seldom used in analytical laboratories, in spite of their advantageous properties. Their theoretical basis provides simple relations and useful equations for the design and construction of thermic liquid analyzers. In this paper a home-made detector system was used for the continuous determination of hydrochloric acid. The results were in accordance with the theoretical considerations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Non-Covalent Interaction-Controlled Site-Selective C−H Transformations

Site-selective C−H transformations are important to obtain desired compounds as single products in a highly efficient manner. However, it is generally difficult to achieve such transformations because organic substrates contain many C−H bonds with similar reactivities. Therefore, the development of practical and efficient methods for controlling site selectivity is highly desirable. The most frequently used strategy is “directing group method”. Although this method is highly effective and promotes site-selective reactions, it has several limitations. Our group recently reported other methods to achieve site-selective C−H transformations using non-covalent interactions between a substrate and a reagent or a catalyst and a substrate (non-covalent method). In this personal account, the background of site-selective C−H transformations, our reaction design to achieve site-selective C−H transformations, and recently reported reactions are explained.     

广义酸碱体系电极电势的设计和应用

根据路易斯酸碱理论,把任何广义的酸碱反应,设计出一定形式的可逆电池,计算电池电动势,可以判断酸碱加合反应的方向,生成的加合物的稳定性,以及广义酸碱的酸碱性强弱等性质。     

软硬酸碱理论与元素的存在形式

在无机化学元素部分教学中,元素的存在形式既是该元素化学性质的重要组成部分,又决定了元素单质和化合物的制备与合成方法。运用离子的电子结构知识及化学基本原理分析元素在自然界中的存在形式,既可以加深学生对化学基本知识和基本原理的理解,又可以将元素知识形成知识链以减少记忆量。本文利用软硬酸碱理论和地球环境的基本状况来分析元素在自然界的存在形式,得到了与实际较为符合的结果,表明这是一种简单实用的思路和方法。     

The effect of electrolytes on the reaction rates and acid-base equilibria in ionic micelles

The influence of a number of electrolytes on the micellar effect of cetyltrimethylammoniurn bromide (CTAB) in the hydrolysis ofp-nitrophenyl acetate (1) and bis(p-nitrophenyl) methylphosphonate (2) and in the course of the acid-base dissociation of thep-nitroanilide of bis(chloromethyl)phosphinic acid (3) has been examined. The activity of the salts studied increases in the following order: MeCOOK2CO₃3<p-MeC₆H₄SO₃K. It has been found that in the presence of electrolytes the catalytic effect of CTAB micelles in the hydrolysis reactions of esters1 and2 decreases, and the pK _a value of anilide3 increases. The results obtained are interpreted in terms of the pseudophase model of micellar catalysis. The analysis of the experimental data carried out using logarithmic coordinates revealed a relationship between phase transitions in micellar catalysis and in micellization.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1396–1400, August, 1993.     

In Situ Solid‐State Reactions Monitored by X‐ray Absorption Spectroscopy: Temperature‐Induced Proton Transfer Leads to Chemical Shifts

The dramatic colour and phase alteration with the solid‐state, temperature‐dependent reaction between squaric acid and 4,4′‐bipyridine has been probed in situ with X‐ray absorption spectroscopy. The electronic and chemical sensitivity to the local atomic environment through chemical shifts in the near‐edge X‐ray absorption fine structure (NEXAFS) revealed proton transfer from the acid to the bipyridine base through the change in nitrogen protonation state in the high‐temperature form. Direct detection of proton transfer coupled with structural analysis elucidates the nature of the solid‐state process, with intermolecular proton transfer occurring along an acid‐base chain followed by a domino effect to the subsequent acid‐base chains, leading to the rapid migration along the length of the crystal. NEXAFS thereby conveys the ability to monitor the nature of solid‐state chemical reactions in situ, without the need for a priori information or long‐range order.     

Characterization of the Acid-Base Properties of Humic Substances by Chemometric Analysis of Synchronous Fluorescence and pH Potentiometric Data

Abstract

A procedure for the analysis of the acid-base characteristics of humic substances based on a self-modeling analysis of synchronous fluorescence spectra, collected at varying pH, and on a non-linear least squares adjustment of potentiometic pH data, is described. The data analysis methodology consists of two steps: first, the number of acid-base systems and the corresponding spectra and distribution diagrams are calculated by evolving factor analysis (EFA) with concentration constraints of the spectroscopic data; second, the potentiometric data is analyzed by a standard non-linear least square procedure using as fixed parameters the number of components and their pKas, determined in the first step of the analysis. As an example, for a sample of marine fulvic acids studied at pH between 2 and 11, four acid-base systems were found with average pKas: 3.1, 4.8, 8.0 and 10.0. The concentrations of the corresponding systems were: 2.55(5), 1.95(7), 0.14(4) and 1.8(3) meq/g.     

慢性呼吸性酸碱平衡紊乱时肾调节能力的量化研究

在慢性呼吸性酸碱平衡紊乱研究中,引入一新的概念,即顺应性C=Δ[HCO_3^-]/ΔPaCO_2,它的变化范围大小能够描述肾调节能力的大小.为了将肾调节能力进行了量化,以X=PaCO_2为自变量,Y=C=Δ[HCO_3-]/ΔPaCO_2,它的变化范围大小能够描述肾调节能力的大小.为了将肾调节能力进行了量化,以X=PaCO_2为自变量,Y=C=Δ[HCO_3^-]/ΔPaCO_2为因变量,分别绘制出顺应性C=Δ[HCO_3-]/ΔPaCO_2为因变量,分别绘制出顺应性C=Δ[HCO_3^-]/ΔPaCO_2范围中左端点和右端点的散点图,并求出其拟合曲线方程及其变化率,这种定量方法为进一步深入研究肾的调节能力提供依据.     

Acid-base properties of alumina prepared from a hydrated product of centrifugal thermal activation of hydrargillite (cta-product)

Summary Acid-base properties of aluminas prepared by thermal treatment of a hydrated CTA-product at 600°C were studied. The CTA-oxides, representing γ-Al₂O₃, were shown to contain terminal and bridged OH-groups. The concentration of the terminal OH-groups in the CTA-oxides was found to exceed their concentration in γ-Al₂O₃ prepared by dehydration of the “precipitated” pseudoboehmite, whereas the concentration of the bridged OH-groups in the CTA-oxides was lower than that in γ-Al₂O₃ prepared from pseudoboehmite. The total concentration of the surface Lewis acid sites in CTA-oxides varies within the limits of 2.80-4.14 mmol/m² and is essentially above that in g-Al₂O₃ (2.25 mmol/m²). The distinctive feature of the CTA-oxides is that their surface contains strong Lewis acid sites with n_CO = 2220 and 2238 cm^-1. The total concentration of basic sites in the CTA-oxides is lower than that in g-Al₂O₃, however, in contrast to g-Al₂O₃,they contain strong basic sites with n_CDCl3 = 2200 cm^-1.