SO_4~(●-)氨酸反应中的溶剂效应(英文)

研究了水-乙腈混合溶液中SO~●_4-自由基氧化酪氨酸的反应.实验结果表明,SO~●_4-自由基氧化酪氨酸的反应机制不因乙腈的加入而改变,但所产生的瞬态粒子的动力学行为受到较大影响.随介质中乙腈体积分数的增加,SO~●_4-的衰变速率减慢而酪氨酸中性自由基(TyrO●)的衰变速率加快.我们认为这两种自由基所呈现出来的相反的溶剂效应是由于其所带电荷的不同.随介质中乙腈体积分数的增加,SO~●_4-氧化酪氨酸的反应速率减慢.这一实验结果意味着,在有机溶剂存在的情况下TyrO●/TyrOH的氧化还原电势可能发生了变化,从而旁证了关于TyrO●/TyrOH的氧化还原电势因酪氨酸从游离状态变到肽或蛋白质中而发生变化的推测.     

微波辐照下（Bi_2O_3）_（0．8）（La_2O_3）_（0．2）固熔体对甲

微波辐照下（Ｂｉ_２Ｏ_３）_（０．８）（Ｌａ_２Ｏ_３）_（０．２）固熔体对甲烷氧化偶联的催化行为陈长林,洪品杰,戴树珊,阚家德（云南大学化学系,昆明,６５００９１）关键词微波,甲烷氧化偶联,（Ｂｉ_２Ｏ_３）_（０．８）（Ｌａ_２Ｏ_３）_（０．２）甲烷氧化...     

3-乙氧基-4-羟基苯乙醇酸在聚邻甲苯胺-Cu~(2+)膜电极上的电氧化

采用循环伏安法制备了聚邻甲苯胺(POT)膜电极,再以浸泡吸附法在此膜中嵌入Cu2+,制成POT-Cu2+膜电极.研究了POT-Cu2+膜电极对3-乙氧基-4-羟基苯乙醇酸的电氧化行为,并讨论了影响电氧化活性的主要因素.结果表明,50℃下,在含有0.5mol.L-13-乙氧基-4-羟基苯乙醇酸的1.5mol.L-1氢氧化钠溶液中,POT-Cu2+膜电极具有高的电氧化活性和良好的稳定性.将该电极用于3-乙氧基-4-羟基苯乙醇酸电解氧化脱羧制备乙基香兰素,在0.55V(vsSCE)下恒电位电解1h,乙基香兰素的产率可达89%以上,电流效率达97%以上.     

取代芳烃电解氧化产物的GC-MS分析(Ⅱ)

采用GC-MS方法,分析了3种取代芳烃直接电解氧化的产物;从甲苯电解氧化产物中鉴定出7种主要成分,从对甲基苯甲醚电解氧化产物中鉴定出6种主要成分,从对叔丁基甲苯电解氧化产物中鉴定出6种主要成分;根据成分鉴定和含量测定结果,解释了以获取目标产物苯甲醛、对甲氧基苯甲醛和对叔丁基苯甲醛为目的的电解氧化反应要求。     

取代芳烃电解氧化产物的GC-MS分析(Ⅰ)

采用 GC- MS方法分析了两种取代芳烃直接电解氧化的产物; 从对伞花烃电解氧化产物中鉴定出 10种主要成分, 从对二甲苯电解氧化产物中鉴定出 8种主要成分; 根据成分鉴定和含量测定结果, 提出了以获取目标产物枯茗醛和对甲基苯甲醛为目的的电解氧化反应要求.     

11α-羟基-17, 17α-环氧黄体酮的间接电解氧化

本文研究了以Ag^+/Ag^26+及Gr^3^+/Cr~2O~7^+为双媒质, 对甾体药物中间体, 11α-羟基-16,17α-环氧黄体酮进行双媒介电解氧化, 产物为11-酮基-16,17α-环氧黄体酮。其化学收率>95%, 电流效率达到70%以上。说法与用铬酐在醋酸中进行氧化的化学法比较, 既大大降低原料的单耗, 又可消除Gr^3^+对环境的污染。本文还探讨双媒介电解氧化的机理。     

化学沉积镍-铁-磷合金和它的伏安行为(英文)

在以次亚磷酸钠为还原剂 ,硼酸为缓冲剂和柠檬酸钠为络合剂的碱性介质中 ,研究了镍_铁_磷合金化学沉积条件 (pH值 ,温度及 [Fe2 + ]/([Ni2 + ]+[Fe2 + ])物质的量比 )对沉积速率和镀层组成的影响 ;并由此建立镀液稳定的最佳沉积工艺 .实验表明 ,镀液中硫酸亚铁对沉积镍_铁_磷合金有阻碍作用 (降低了化学沉积速率 ) ,造成镀层中铁含量不高 (小于 2 0 % ) ,使用循环伏安技术研究了镍_铁_磷合金的电沉积机理 .结果发现铁对次亚磷酸钠的氧化不起催化作用 ,提高镀液温度和pH值有增加沉积速率之效     

间接电氧化2-丁酮制备α-羟基缩酮的研究

在板框式循环电解槽中,以KOH为电解质,KI为催化剂,石墨电极分别为阳极和阴极,研究电化学间接氧化2-丁酮合成乙偶姻中间体α-羟基缩酮,讨论电流密度、极板间电解液流速、电解液中2-丁酮浓度、电解温度以及通电量等电解条件对中间体收率和电流效率的影响,经优选工艺条件为：电流密度40 mA·cm^-2,流速6.4 cm·s^-1,2-丁酮浓度1.75 mol·L^-1,电解温度30℃,通电量为1.5 F·moL^-1时,中间体收率可达78.9%,电流效率40.1%. 循环伏安测试结果表明,电解时碘离子在阳极氧化生成碘单质,甲醇在阴极还原生成甲氧基负离子,原料2-丁酮与电解产物反应,并最终生成乙偶姻中间体.     

若干μ_3-氧桥三核锰(Ⅲ)Schiff碱配合物的研究

用元素分析、电导率、磁化率、热分析、红外光谱和电子光谱等方法对新合成的7种μ_3-氧桥三核锰(Ⅲ)Schiff碱配合物:Mn_3O(bzaea)_2(C_2H_3O_2)_3、Mn_3O(bzaea)_2(C_2H_3O_2)_2(NCS)、Mn_3O(bzaea)_3ClO_4·2H_2O、Mn_3O(bzaea)_2(C_2H_3O_2)_2Br、Mn_3O(bzaea)_3I·2H_2O、Mn_3O(bzaea)_2(C_2H_3O_2)_2NO_3和Mn_3O(bzaea)_2(C_2H_3O_2)_2BPh_4·3H_2O(其中bzaea~(2-)是三齿Schiff碱2-(β-羟基乙基-亚胺)-4-苯基-丁酮(4)的负二价阴离子)进行了研究,并提出了配合物的可能构型。     

含有金属-金属键的双核原子簇离子体系[Mo~2Sn]^2-(n=6~9)的电子结构与电子光谱

使用SCF-CI方法研究了含有Mo—Mo单键的原子簇离子体系[Mo_2Sn]~(2-)(n=6～9)的电子结构及电子光谱。讨论了随n增加,配体S,S_2,S_4对Mo—Mo键序、原子电荷的影响及其变化规律。分析了原子簇离子中的d-d相互作用能级次序及Mo—Mo,Mo—S′_t等键的性质,CI计算得到的谱带波数及强度次序与实验符合。指认分析表明,谱带的跃迁性质是有趣的,如第一吸收带为成键轨道之间的跃迁σ_(x~2-y~2)→π_(xz)(n=6～8),同时,对电子跃迁的性质进行了分类,对谱带的电荷转移性质也进行了讨论。     

Investigation of the electro-oxidation and oxidation of catechol in the presence of sulfanilic acid

The electrochemical oxidation of catechol (1) in the presence of sulfanilic acid (2) was investigated. Some electrochemical (EC) techniques such as cyclic voltammetry and controlled-potential coulometry were used. The oxidation reaction of catechol (1) with periodate in the presence of sulfanilic acid (2) was also investigated spectrophotometrically. The results indicate that the o-quinone derived from catechol participate in Michael addition reaction with sulfanilic acid (2). In addition, according to the ECE mechanism, the observed homogeneous rate constant (k_obs) for the reaction of o-quinone derived from catechol (1) with sulfanilic acid (2) has been estimated by digital simulation of cyclic voltammograms.     

乙醇在Ni-Mo合金电极上氧化的动力学模型

利用循环伏安以及稳态极化曲线等方法研究了在１ｍｏｌ．Ｌ＾－１ＫＯＨ溶液中,乙醇在电沉积Ｎｉ－Ｍｏ合金电极上氧化的电化学特性,提出了一个数学模型来预计乙醇在电沉积Ｎｉ－Ｍｏ合金电极上的电化学行为,在碱性溶液中,Ｎｉ（ＯＨ）２／ＮｉＯＯＨ电对的氧化还原过程是乙醇氧化的前期步骤,Ｎｉ（ＯＨ）２／ＮｉＯＯＨ）电对相应的速度常数（即ｋ１和ｋ－１）是电极电位的函数,乙醇氧化是通过一个速度常数为ｋｃ１的化学反应来完成,推导出了各个动力学方程并将实验数据与方程进行比较而获得各个动力学参数,电化学速度常数ｋ１（Ｅ）＝１．４１＊１０＾７ｅｘｐ（０．５ＦＥ／ＲＴ）ｍｍｏｌ．ｃｍ＾－２．ｓ＾－１以及ｋ－１（Ｅ）＝０．７１１ｅｘｐ（０．５ＦＥ／ＲＴ）ｍｍｏｌ．ｃｍ＾－２．ｓ＾－１,Ｅ是相对饱和甘汞电极（ＳＣＥ）的电极电位,而化学反应的速     

Kinetic determinations of accurate relative oxidation potentials of amines with reactive radical cations

Accurate oxidation potentials for organic compounds are critical for the evaluation of thermodynamic and kinetic properties of their radical cations. Except when using a specialized apparatus, electrochemical oxidation of molecules with reactive radical cations is usually an irreversible process, providing peak potentials, E(p), rather than thermodynamically meaningful oxidation potentials, E(ox). In a previous study on amines with radical cations that underwent rapid decarboxylation, we estimated E(ox) by correcting the E(p) from cyclic voltammetry with rate constants for decarboxylation obtained using laser flash photolysis. Here we use redox equilibration experiments to determine accurate relative oxidation potentials for the same amines. We also describe an extension of these experiments to show how relative oxidation potentials can be obtained in the absence of equilibrium, from a complete kinetic analysis of the reversible redox kinetics. The results provide support for the previous cyclic voltammetry/laser flash photolysis method for determining oxidation potentials.     

Investigation into phenoxonium cations produced during the electrochemical oxidation of chroman-6-ol and dihydrobenzofuran-5-ol substituted compounds

A series of chroman-6-ol and dihydrobenzofuran-5-ol based compounds with structures similar to vitamin E were examined by cyclic voltammetry and controlled potential electrolysis. The compounds displayed characteristic voltammetric features that enabled their electrochemical behavior to be interpreted in relation to the oxidation mechanism for vitamin E. The electrochemical experiments indicated the presence of several oxidized species: cation radicals, phenoxyl radicals, phenoxonium ions, hemiketals, and p-quinones, whose lifetimes varied depending on the extent of methylation of the aromatic ring (R(1), R(2), R(3)) and the nature of substituents R(4) and R(5).     

An Electrochemical Cinnamyl C—H Amination Reaction Using Carbonyl Sulfamate

An electrochemical cinnamyl C—H amination reaction in the absence of transition metal catalyst and oxidant was reported. The choice of carbonyl sulfamate as nitrogen source is the key to achieve desired chemoselectivity. A series of terminal amine derivatives are prepared using this protocol and the sulfonyl group can be removed with basic hydrolysis. The reaction is suggested to proceed via a continuous anodic oxidation, deprotonation, anodic oxidation, and intermolecular nucleophilic addition pathway, demonstrating the first example of electrochemical cinnamyl C—H amination.     

The electrochemical reaction mechanism of selenocystine on selenium-gold film modified glassy carbon electrode

A simple and selective voltammetric method based on selenium-gold film modified glassy carbon electrode has been developed for investigating electrochemical reaction mechanism of selenocystine. With N₂ saturated, redox reactions between selenocystine (SeC) and selenocysteine (SeCys) were judged to be two simple electron-transfer processes. With air saturated, the reduction reaction was diagnosed to be EC catalytic reaction (the chemical oxidation reaction of the SeCys by O₂ (C) following the electron-transfer reaction (E)) and oxidation reaction is a simple electron-transfer process. With pure O₂ saturated, only reduction peak was observed and the reaction was judged to be EC catalytic reaction. The electron-transfer numbers of redox reaction were calculated to be 2 by chronocoulometry and rotating disk electrode.     

Synthesis and Properties of Aza‐ullazines

A range of aza‐ullazines, which represent a new heterocyclic core structure, were synthesized through a scalable four‐step reaction, including a Sonogashira reaction and metal‐free cyclization promoted by p‐toluenesulfonic acid. The optical and electrochemical properties of selected derivatives were investigated, they were found to have similar absorption and emission spectra but a higher oxidation potential than the parent ullazine core.     

Total synthesis of (-)-heptemerone B and (-)-guanacastepene E

A concise, stereoselective, and convergent total synthesis of the unnatural enantiomer of the neodolastane diterpenoid heptemerone B has been completed. Saponification of (-)-heptemerone afforded (-)-guanacastepene E. The absolute stereochemistry of (-)-heptemerone B was thus established as 5-(S), the same as (-)-guanacastepene E. The longest linear sequence of the synthesis comprises 17 (18) steps from simple known starting materials. Our general synthetic approach integrates a diverse set of reactions, including an intramolecular Heck reaction to create one quaternary stereocenter and a cuprate conjugate addition for the establishment of the other. The central seven-membered ring was closed with an uncommon electrochemical oxidation, whereas the five-membered ring was formed through ring-closing metathesis. The absolute configuration of the two key building blocks was established through an asymmetric reduction and an asymmetric ene reaction.     

Spectroscopic investigation of the adsorption and oxidation of thiourea on polycrystalline Au and Au(111) in acidic media

In the present paper, a systematic electrochemical investigation on thiourea (TU) electrooxidation was developed on polycrystalline and (111) single-crystal gold electrodes in 0.1 M perchloric acid. The combination of cyclic voltammetry with in situ Fourier transform infrared spectroscopy (FTIRS) and differential electrochemical mass spectrometry techniques have allowed the nature of the species formed during the electroadsorption and electrooxidation of TU to be established. FTIRS experiments were performed in D2O to clean up the region of the H2O bending around 1600 cm(-1). It was concluded that TU adsorbs tilted on the surface in the 0.05-0.40 VRHE potential range. A dual-path reaction mechanism was evidenced in the oxidation process. The first pathway takes place from adsorbed TU at E > 0.40 VRHE and implies the formation of [Au(I)-(TU)2]+, which is oxidized to NH2CN and S0 at E > 0.80 VRHE. In a following oxidation step at E > 1.20 V, N2, CO2, and HSO4-/SO4(2-) were produced. The second parallel reaction occurs from TU in solution at E > 0.50 VRHE to form (TU)2(2+). All these species were characterized from the spectroscopic experiments. Similar results were obtained for both surfaces.     

Electro‐Oxidation of 3,4‐Dihydroxybenzoic Acid in the Presence of 6‐Methyl‐1,2,4‐Triazine‐3‐Thione‐5‐One: Unique Synthesis of 7H‐Thiazolo[3,2‐b]‐1,2,4‐Triazin‐7‐One Derivative in Aqueous Media

The electrochemical oxidation of 3,4‐dihydroxy benzoic acid ( 1 ) has been studied in the presence of 6‐methyl‐1,2,4‐triazine‐3‐thione‐5‐one ( 2 ) in aqueous solution. The oxidation mechanism of 1 and its reaction in the presence of 2 was offered. It was confirmed that 1 is converted to 7H‐thiazolo[3,2‐b]‐1,2,4‐triazin‐7‐one derivative 5 through Michael addition reaction of 2 to anodically generated o‐benzoquinone. The results of the research were used for electrochemical synthesis of 5 in an undivided cell in good yield and purity.