Esterification of butyric acid with n-butanol: Kinetic study using experimental data and modeling

Present study involves the investigation of the esterification kinetics between butyric acid and n-butanol. This reaction was conducted in a batch reactor, utilizing homogeneous methanesulfonic acid (MSA) catalyst. Response surface methodology (RSM) was conducted prior to the kinetic study using “Design Expert; version-11.0” for finding the causal factors influencing the conversion of butyric acid. Most important factors identified with their limits against conversions (during optimization of the process using RSM) were taken up to critically analyze the effect of them on butyric acid conversion. Concentration and activity-based model of the process were proposed assuming second order reversible reaction scheme using homogeneous MSA catalyst. During the study of non-ideal behavior of the system, UNIFAC model was adapted for assessing the activity coefficients of species present in equilibrated liquid phase. Experimental data were used to evaluate kinetic and thermodynamic parameters such as rate constants, activation energy, enthalpy, and entropy of the system. The endothermic nature of esterification was confirmed by positive value of enthalpy obtained. The effect of various levels of causal variables like temperature (60–90°C), catalyst concentration (0.5–1.5 wt.%), and molar ratio of n-butanol to butyric acid (1–3) on conversion kinetics of butyric acid was investigated during transient and equilibrium phase of the reaction. It has been observed that molar ratio of butanol to butyric acid has the highest influence on the conversion. The rate equation derived offered a kinetic and thermodynamic framework to the generated data. It also exhibits a notable degree of conformity of predicted data to the experimental ones and effectively characterizes the system across different reaction temperatures, reactant molar ratio, and catalyst concentration.     

Anilinolysis of O‐butyl phenyl phosphonochloridothioate in acetonitrile: Synthesis,characterization, kinetic study,and reaction mechanism

This paper describes a simple optimized method for the synthesis of O‐butyl phenyl phosphonochloridothioate ( 4 ) under mild conditions. The target compounds were characterized by ¹H‐nuclear magnetic resonance (NMR), ¹³C‐NMR, and ³¹P‐NMR spectroscopy, as well as mass spectroscopy. The apparent structure of 4 was confirmed by optimization using the B3LYP/6‐311 + G(d,p) level in the Gaussian 09 program in acetonitrile. The nucleophilic substitution reactions of 4 with X‐anilines (XC₆H₄NH₂) and deuterated X‐anilines (XC₆H₄ND₂) were investigated kinetically in acetonitrile at 55.0°C. The free energy relationship with X in the anilines looked biphasic concave upwards with a break region between X = H and X = 3‐MeO, giving large negative ρ_X and small positive β_X values. The deuterium kinetic isotope effects were secondary inverse (k_H/k_D < 1: 0.789‐0.995) and the magnitudes, (k_H/k_D), increased when the nucleophiles were changed from weakly basic to strongly basic anilines. A concerted S_N2 mechanism is proposed on the basis of the selectivity parameters and the variation trend of the deuterium kinetic isotope effects with X.     

L-AlaC4NTf2手性离子液体作为新型气相色谱固定相的性能研究

合成了一种手性离子液体L-丙氨酸叔丁酯双三氟甲烷磺酰亚胺(L-AlaC4NTf2), 将其作为新型气相色谱固定相, 并与OV-1701按不同比例混合, 考察了它们的色谱性能. 研究结果表明, 该离子液体作为手性固定相的热稳定性高于175 ℃; 平均McReynolds常数为665; 在容量因子为1.02时, 理论塔板数可达每米1095块; 其对烷烃、醇类、酮类、芳香族化合物、位置异构体以及一些手性化合物具有良好的分离效果.     

Applications of polymethacrylate-based monoliths in high-performance liquid chromatography

Monolithic columns were introduced in the early 1990s and have become increasingly popular as efficient stationary phases for most of the important chromatographic separation modes. Monoliths are functionally distinct from porous particle-based media in their reliance on convective mass transport. This makes resolution and capacity independent of flow rate. Monoliths also lack a void volume. This eliminates eddy dispersion and permits high-resolution separations with extremely short flow paths. The analytical value of these features is the subject of recent reviews. Nowadays, among other types of rigid macroporous monoliths, the polymethacrylate-based materials are the largest and most examined class of these sorbents. In this review, the applications of polymethacrylate-based monolithic columns are summarized for the separation, purification and analysis of low and high molecular mass compounds in the different HPLC formats, including micro- and large-scale HPLC modes.     

A rapid and sensitive liquid chromatography/positive ion tandem mass spectrometry method for the determination of cimetropium in human plasma by liquid-liquid extraction

We have developed and validated a simple detection system with high-performance liquid chromatography (HPLC) with positive ion electrospray ionization tandem mass spectrometry (ESI-MS/MS) for determining cimetropium levels in human plasma using scopolamine butyl bromide as an internal standard (I.S.). The acquisition was performed in the multiple reaction monitoring (MRM) mode, by monitoring the transitions: m/z 357.9 > 103.1 for cimetropium and m/z 359.9 > 103.1 for butyl-scopolamine. The method involves a simple single-step liquid-liquid extraction with dichloromethane. The analyte was chromatographed on an YMC C18 reversed-phase chromatographic column by isocratic elution with 10 mM ammonium formate buffer-methanol (19:81, v/v; adjusted to pH 4.0 with formic acid). The results were linear over the studied range (0.2-100 ng ml(-1)), with r2 = 1.0000, and the total analysis time for each run was 2 min. Intra- and interassay precisions were 0.70-8.54% and 1.08-4.85%, respectively, and intra- and interassay accuracies were 97.56-108.23% and 97.48-103.91%, respectively. The lower limit of quantification (LLOQ) was 0.2 ng ml(-1). At this concentration, mean intra- and interassay precisions were 8.54% and 4.85%, respectively, and mean intra- and interassay accuracies were 97.56% and 98.91%, respectively. The mean recovery ranged from 62.71 +/- 4.06 to 64.23 +/- 2.32%. Cimetropium was found to be stable in plasma samples under typical storage and processing conditions. The devised assay was successfully applied to a pharmacokinetic study of cimetropium bromide administered as a single oral dose (150 mg) to healthy volunteers.     

Rapid separation and determination of aconitine alkaloids in traditional Chinese herbs by capillary electrophoresis using 1-butyl-3-methylimidazoium-based ionic liquid as running electrolyte

A novel and very simple capillary electrophoretic method for analyzing aconitine components in Aconitum plants was developed using 1-butyl-3-methylimidazoium tetrafluoroborate (1B-3MI-TFB)-based ionic liquid as running electrolyte solution for the first time. The optimum conditions were 35 mM 1B-3MI-TFB solution (pH 8.50) and 15 kV applied voltage. The detection was performed at 254 nm. Aconitine, meaconitine and hypaconitine in Aconitum plants were separated and identified within 5 min. The recoveries were 91.0-103.0% for hypaconitine, 92.8-96.2% for aconitine and 96.0-106.6% for mesaconitine, respectively. Compared with other methods, the analytical time was decreased 4-8-fold and the effect of Joule heating was weaker because the current was smaller.     

氢及其同位素在溴化丁基橡胶中渗透的分子模拟

使用分子动力学(MD)和巨正则蒙特卡罗(GCMC)的方法,对H_2,D_2,T_2在溴化丁基橡胶(BIIR)中的扩散和溶解行为进行了计算模拟,运用自由体积理论探讨了气体分子在聚合物内的扩散机理,并得出气体的运动轨迹。结果表明:对氢及其同位素而言,质量越小,运动速度越快,扩散系数越大,溶解度系数比较接近,渗透系数的模拟值与实验值基本吻合,为提高材料的阻隔性能提供了一定理论基础,同时预测出硫化溴化丁基橡胶对氚水也有较好的阻隔性能。     

Self‐assembly of p‐tert‐butyl thiacalix[4]arenes and metal cations into nanoscale three‐dimensional particles

The shape of supramolecular aggregates based on stereoisomers of p‐tert‐butyl thiacalix[4]arenes functionalized with secondary, tertiary amide and hydrazide groups at the lower rim in cone, partial cone and 1,3‐alternate conformations with several metal cations were investigated by atomic force microscopy. The examined p‐tert‐butyl thiacalix[4]arenes form host–guest complexes; dimers, spherics ellipsoids and elongated nanoscale particles depending on the conformation of macrocycles, the nature of the binding centers and the nature of the metal cation. Only associates formed by p‐tert‐butyl thiacalix[4]arenes with morpholide groups at the lower rim in cone conformation with silver cations exhibited a higher antimicrobial activity. Copyright © 2012 John Wiley & Sons, Ltd.     

Review of recent advances in the preparation of organic polymer monoliths for liquid chromatography of large molecules

In recent years the use of monolithic polymers in separation science has greatly increased due to the advantages these materials present over particle-based stationary phases, such as their relative ease of preparation and good permeability. For these reasons, these materials present high potential as stationary phases for the separation and purification of large molecules such as proteins, peptides, nucleic acids and cells. An example of this is the wide range of commercial available polymer-based monolithic columns now present in the market.