Symmetrical Ketones from Aldehyde Trimethylsilyl Enol Ethers on Storage: A Cautionary Note

The widespread use of trialkylsilyl enol ethers has dramatically increased the utility of enolate anion chemistry.¹ These enol ethers are readily prepared, reactive, and in many instances are stable enough to be commercially available. We have been using trimethylsilyl enol ethers as aldehyde enolate precursors and wish to report some observations regarding storage of these 1-alkyl-2-trimethylsilyloxyethenes. We have noted that after 2–3 months in sealed glass ampuoles these trimethylsilyl enol ethers contained significant amounts of symmetrical ketones.     

在酸性条件下合成氧化亚铜纳米立方体(英)

在微酸性(pH：4～6)的水热体系中130 ℃反应18 h合成了氧化亚铜纳米粒子，粒径约为100 nm，呈立方体外形。乙二胺和十六烷基胺在反应体系中充当缓冲试剂，调节反应液的pH值并控制体系中游离Cu²⁺的浓度，使得Cu²⁺不会被迅速还原成单质铜。所合成的纳米立方体的能带宽度约为2.51 eV，比氧化亚铜体材料和氧化亚铜纳米线蓝移了0.51 eV和0.17 eV，它有利于把太阳光谱中能量高的可见光转化成其他形式的能量。     

不同类型探针对免疫层析方法的分析灵敏度影响研究

为研究不同类型探针对免疫层析方法的分析灵敏度影响,该研究以17β-雌二醇(17f3-E2)为检测对象,采用磁性纳米材料标记7 μg/mL的17β-E2单克隆抗体(检测抗体)制备了传统探针,采用磁性纳米材料分别标记5 μg/mL的17P-E2单克隆抗体和5 μg/mL的羊抗鼠IgG多克隆抗体(第二抗体)制备了配对探针,采...     

基于传感器探究酸性条件下铁的吸氧腐蚀

人教版《化学反应原理》中介绍了金属的电化学腐蚀，主要是钢铁的吸氧腐蚀和析氢腐蚀。结合教材分析铁的腐蚀原理，得出铁的析氢腐蚀会导致体系压强增大，吸氧腐蚀会导致体系溶解氧减小。据此利用压强传感器和溶解氧传感器探究酸性条件下铁的吸氧腐蚀，并设计正交实验寻找发生吸氧腐蚀的最佳条件，帮助学生进一步理解铁的吸氧腐蚀。     

不同酸对介孔二氧化硅球表面形貌和介相结构的影响

在室温、不同酸性条件下合成出微米级球形介孔二氧化硅材料，通过XRD、SEM以及氮气吸附等手段对介孔二氧化硅材料进行了表征。用TEM跟踪不同反应时间介孔二氧化硅球的形成，对这些球颗粒的合成机理进行了讨论，同时探讨了不同酸性条件下介孔二氧化硅表面形貌和介相结构的变化。     

Generation and Use of Glycosyl Radicals under Acidic Conditions: Glycosyl Sulfinates as Precursors

We herein report a method that enables the generation of glycosyl radicals under highly acidic conditions. Key to the success is the design and use of glycosyl sulfinates as radical precursors, which are bench-stable solids and can be readily prepared from commercial starting materials. This development allows the installation of glycosyl units onto pyridine rings directly by the Minisci reaction. We further demonstrate the utility of this method in the late-stage modification of complex drug molecules, including the anticancer agent camptothecin. Experimental studies provide insight into the reaction mechanism.     

不同裂解条件对天冬酰胺主要裂解产物的影响

采用在线裂解气相色谱-质谱联用技术(Py/GC-MS)对不同条件下天冬酰胺的主要裂解产物进行分析,并通过裂解同位素标记样品,计算主要含氮裂解产物中的同位素比例,推测其形成途径,研究裂解条件对主要裂解产物形成的影响。结果表明:温度对天冬酰胺裂解影响较大,主要裂解产物在低温和高温下生成量变化较大。300℃时,马来酰亚胺和琥珀酰亚胺为主要的裂解产物,300～600℃时生成量显著增加,600～900℃时马来酰亚胺生成量缓慢增加而琥珀酰亚胺逐渐降低;随着温度升高,酸类和酰胺类物质生成量持续增加;腈类和吡咯类物质在高温下生成量明显增加。此外,温度对含氮裂解产物的形成途径也有较大影响。马来酰亚胺、乙酰胺在低温下N主要来源于标记的酰胺N,而在高温下主要来源于未标记的氨基N。氢氰酸、乙腈和丙烯腈中的N原子均主要由未标记的氨基转变而来,且随着温度升高,这种生成途径所占比例越高。而裂解气氛和裂解时间对天冬酰胺主要裂解产物的生成量及途径影响较小。     

Mechanisms of a Cyclobutane-Fused Lactone Hydrolysis in Alkaline and Acidic Conditions

Searching for functional polyesters with stability and degradability is important due to their potential applications in biomedical supplies, biomass fuel, and environmental protection. Recently, a cyclobutane-fused lactone (CBL) polymer was experimentally found to have superior stability and controllable degradability through hydrolysis reactions after activation by mechanical force. In order to provide a theoretical basis for developing new functional degradable polyesters, in this work, we performed a detailed quantum chemical study of the alkaline and acidic hydrolysis of CBL using dispersion-corrected density functional theory (DFT-D3) and mixed implicit/explicit solvent models. Various possible hydrolysis mechanisms were found: B_AC2 and B_AL2 in the alkaline condition and A_AC2, A_AL2, and A_AL1 in the acidic condition. Our calculations indicated that CBL favors the B_AC2 and A_AC2 mechanisms in alkaline and acidic conditions, respectively. In addition, we found that incorporating explicit water solvent molecules is highly necessary because of their strong hydrogen-bonding with reactant/intermediate/product molecules.     

A Simple Method for Synthesizing Highly Active Amorphous Iridium Oxide for Oxygen Evolution under Acidic Conditions

Water splitting for hydrogen production has been recognized as a promising approach to store sustainable energy. The performance of this method is limited by the oxygen-evolution reaction. Herein, an approach for synthesizing a highly active oxygen-evolving catalyst by a one-step, low-cost, environmentally friendly, and easy-to-perform method is presented, which works by using iridium metal as the anode at a relatively high potential. The obtained IrO_x/Ir interface showed an overpotential of 250 mV at 10 mA cm⁻² in 0.1 m HClO₄ and remained stable under electrochemical conditions. The IrO_x that was mechanically separated from the surface of IrO_x/Ir metal after operation showed a threefold increase in activity compared to the current benchmark IrO₂ catalyst. Various characterization analyses were used to identify the structure and morphology of the catalyst, which suggested nanosized, porous, and amorphous IrO_x on the surface of metallic Ir. This synthetic approach can inspire a variety of opportunities to design and synthesize efficient metal oxide-based electrocatalysts for sustainable energy conversion and utilization.     

SAPO-34催化剂上反应条件对乙烯转化制丙烯的影响

系统研究了反应条件对SAPO-34上乙烯转化制丙烯的影响.结果表明,提高空速或加大He/C2H4稀释比有利于抑制丙烯二次反应的发生,提高丙烯的选择性.升高温度导致乙烯转化率下降,甲烷和乙烷的选择性增加;在相同转化率下,丙烯选择性随温度上升而下降.乙烯在SAPO-34上的转化反应表现出明显的诱导期,且反应条件对诱导期的长短有较大影响.     

Structure‐Dependent Demetalation Kinetics of Chlorophyll a Analogs under Acidic Conditions

Demetalation of chlorophyll (Chl) a and its analogs is an important reaction in oxygenic photosynthetic organisms, which produces the primary electron acceptors in photosystem II reaction centers and is crucial in the Chl degradation. From these viewpoints, demetalation reactions of four Chl a analogs, 3,8‐divinyl‐Chl a (DV‐Chl a), 3‐devinyl‐3‐ethyl‐Chl a (mesoChl a), 13²‐demethoxycarbonyl‐Chl a (pyroChl a) and protochlorophyll a (PChl a), were kinetically analyzed under weakly acidic conditions, and were compared with that of Chl a. DV‐Chl a exhibited slower demetalation kinetics than did Chl a, whereas demetalation of mesoChl a was faster than that of Chl a. The difference in demetalation kinetics of the three chlorophyllous pigments originates from the electron‐withdrawing ability of the vinyl group as the peripheral substituent compared with the ethyl group. Removal of the electron‐withdrawing and homoconjugating 13²‐methoxycarbonyl group in Chl a (Chl a → pyroChl a) accelerated demetalation kinetics by two‐fold. PChl a possessing the porphyrin‐type skeleton exhibited slower demetalation kinetics than Chl a. The structure‐dependent demetalation properties of Chl a analogs will be useful for understanding in vivo Chl demetalation reactions in oxygenic photosynthetic organisms.     

Preparation of 1,3-Dithiol-2-ones from 1,2-Bis-triisopropylsilanylsulfanyl Alkenes Under Mild Acidic Conditions

1,2-Bis-triisopropylsilanylsulfanyl alkenes are readily converted to 1,3-dithiol-2-ones with phosgene under very mild acidic conditions at room temperature.     

On the Mechanism of the Reactivity of 1,3‐Dialkylimidazolium Salts under Basic to Acidic Conditions: A Combined Kinetic and Computational Study

Comprehensive spectroscopic kinetic studies illustrate an alternative mechanism for the traditional free‐carbene intermediated H/D exchange reaction of 1,3‐dialkylimidazolium salts under neutral (D₂O) and acidic conditions (DCl/D₂O 35 wt % solution). The deuteration of high purity [bmim]Cl in D₂O is studied at different temperatures, in absence of catalyst or impurities, to yield an activation energy. DFT transition‐state modelling, of a small water cluster and [bmim] cation, also yields an activation energy which strongly supports the proposed mechanism. The presence of basic impurities are shown to significantly enhance the exchange reaction, which brings into question the need for further analysis of technical purities of ionic liquids and the implications for a wide range of chemical reactions in such media.     

Synthesis of Azinylvinylpyridazines: A General Note on the Isomerization of Hetaryldienamines

Azinyldienamines underwent Diels Alder reaction of inverse electron demand with 1,2,4,5-tetrazine diester to give azinylvinylpyridazines. Comparison of the products obtained from mono-, di-, and triazinyldienamines revealed that, in some cases, isomerization of the olefinic side chain occurred which can be rationalized by the tautomeric conditions of the intermediates bearing these azine moieties. These experimental findings supported also by semiempirical calculations suggest the importance of the influence of the hetaryl group in such isomerizations.     

Note High Yield Synthesis of Low Molecular Weight Poly(Vinyl Acetate) in Aqueous Acidic Media

Polymerization of vinyl acetate continues to interest workers in the field as evidenced by recent publications [1–3]. However, little information is available concerning the synthesis of low molecular weight poly(vinyl acetate) (PVAc) despite its industrial importance.