2甲-基吡啶在丙酮-水混合溶剂中的电氧化

在质子交换膜为隔膜的电解槽内,以2甲-基吡啶为原料,在丙酮/水混合溶剂中,以PbO2为阳极,电氧化合成了2-吡啶甲酸。通过循环伏安、线性扫描伏安和恒电位电解实验,考察了丙酮与水体积比、反应温度、硫酸浓度、反应物2-甲基吡啶浓度和阳极电位对选择性和电流效率的影响。结果表明,V(丙酮)∶V(水)=3∶1,硫酸浓度1.0~1.2 mol/L,2甲-基吡啶浓度0.5 mol/L,温度30℃,阳极电位1.75~1.80 V,生成2吡-啶甲酸的选择性可达88.7%,电流效率达到48.3%。而在纯水作溶剂的溶液中,相同条件下生成2-吡啶甲酸的选择性和电流效率仅分别为67.4%和42.2%。     

Span 60对3-甲基吡啶电氧化的影响

通过循环伏安曲线测定,考察了Span 60(山梨糖醇酐单硬脂酸酯)对3-甲基吡啶电氧化的影响。正交实验确定的最佳反应条件是:n(3-甲基吡啶)/n(硫酸)=0.4,添加高于或接近临界胶束浓度的Span 60,反应温度15℃,阳极电位1.9~2.0 V,电解电量为理论电量的10%;其选择性可达85.46%,电流效率为48.69%,电流密度提高300 mA/cm2,并根据最佳反应条件进行外循环放大实验,其结果与小试基本相同。在选定的实验范围内,Span 60对3-甲基吡啶电氧化有明显的促进作用,有应用前景。     

茴香脑的选择性间接电氧化

研究了以茴香脑为原料,用Ce4 /Ce3 为氧化还原媒质,选择性间接电氧化合成茴香醛.用正交实验和单因素实验研究了Ce3 电解氧化成Ce4 的反应条件,并优化出了最佳电解条件:电解液中Ce3 的浓度为0.3mol·L-1,H2SO4浓度为1 mol·L-1,电流密度为80mA/6cm2,电解温度为30℃,阴阳极面积比为1:6,通电量1.5F·mol-1.     

锌催化电还原脱氯合成2,3,5,6-四氯吡啶:反应机理和工艺优化

采用循环伏安法和恒电位电解法,探讨了含有ZnCl_2的乙睛水混合溶液中五氯吡啶(PCP)在不锈钢阴极表面电还原脱氯生成2,3,5,6-四氯吡啶(2,3,5,6-TCP)的反应机理;采用恒电流电解法对该电还原脱氯过程的各种工艺条件进行了优化。结果表明:该体系中PCP电还原脱氯生成2,3,5,6-TCP主要遵循以Zn/Zn~(2+)为氧化还原媒介的间接电还原机理;优化工艺条件下(阴极液含0.025 mol·L~(-1)HCl+15%(体积分数)水+0.2 mol·L~(-1)苯磺酸钠+0.16 mol·L~(-1) ZnCl_2的乙腈溶液;电流密度为1.25 A·dm~(-2)),0.08 mol·L~(-1) PCP能高选择性地脱氯生成2,3,5,6-TCP,2,3,5,6-TCP的收率和电解电流效率分别可达88.7%和59.1%。     

异烟酸的电化学合成及示波极谱法测定

以钛基二氧化铅电极（Ti/PbO2)为阳极,在硫酸水溶液介质中,电解氧化4－甲基吡啶合成异烟酸。最佳合成条件：硫酸浓度为2.80mol/L,4-甲基吡啶浓度为0.60mol/L,电解电流密度为80mA/cm^2,温度60℃。在此条件下,4－甲基吡啶的转化率为64．6％,电流效率67％。产物纯度为97．7％。     

Ce~(4+)/Ce~(3+)做氧化媒质间接电合成邻氯苯甲醛

用硫酸做介质、Ce4 + Ce3+ 做氧化媒质间接电合成邻氯苯甲醛。通过正交实验和单因素实验确定出最佳工艺条件为 :反应温度 348K ,表面活性剂浓度 1 .4× 1 0 - 3～ 2 .2× 1 0 - 3mol L ,硫酸浓度 7.5mol L。在优化的实验条件下邻氯苯甲醛的产率达 93.1 % ;在相应的电解实验中 ,电流效率为 89.46% ,电解收率为 50 .1 5%。     

“槽内式”间接电氧化法制备2-甲基-1,4-萘醌

以Ti/PbO2为阳极、Pb为阴极、硫酸为支持电解质,采用Cr6+/Cr3+为氧化媒质,四丁基溴化铵为相转移剂,在阳离子交换膜为隔膜的“板框式”电解槽中,进行“槽内式”间接电氧化2-甲基萘(2-MN)合成2-甲基-1,4-萘醌(2-MNQ)的研究。考察了2-MN间接电氧化制备2-MNQ的工艺条件对2-MNQ选择性和电流效率的影响规律。实验结果表明:在2-MN和Cr2O72-浓度分别为0.02 mol/L和0.03 mol/L,硫酸质量分数20%,温度50℃,电流密度110 A/m2,通电量为理论通电量0.2倍的工艺条件下进行电解,2-MNQ的平均选择性为71.9%,平均表观电流效率为69.7%。     

电解氧化4-甲基吡啶合成异烟酸

以Ti基PbO2 为阳极 ,Cu或Ni为阴极 ,在硫酸介质中 ,电解氧化 4 甲基吡啶合成了异烟酸。经过实验确定的最佳合成条件为 :c(硫酸 ) =4 6 0mol/L ,c(4 甲基吡啶 ) =0 6 0mol/L ,电解电流密度i=6 0mA/cm2 ,t=6 0℃。在此条件下 ,异烟酸的收率为 6 4 6 % ,电流效率为 6 7%。同时还研究了电解过程中反应物转化率、电流效率、槽压的变化规律。经示波极谱、红外光谱和熔点测定法证明电合成的物质为异烟酸 ,质量分数为 97 7%。     

羟基新戊酸的电化学合成

在质子交换膜电解槽中,以PbO2 为阳极,以羟基新戊醛为原料,利用直接电氧化方法合成羟基新戊酸。通过四因素三水平正交实验,得到最佳合成条件:pH=1,阳极电位1 65V,反应物浓度0 22mol/L,反应温度15℃。在此条件下,该反应的选择性达到91 6%,电流效率达到56 9%。研究发现,在4个影响因素中,pH对选择性和电流效率的影响最大。通过耗竭性电解实验,得到消耗电量与转化率的关系,可以由消耗电量近似地估算反应物的转化率。     

不同金属氧化物膜电极上苯酚的电催化氧化

分别以自制的金属氧化物膜电极Ti/SnO2+Sb2O3、Ti/SnO2+Sb2O3/PbO2和Ti/SnO2+Sb2O3/RuO2+PbO2为阳极，恒电流电解低浓度苯酚溶液，研究了不同金属氧化物阳极对苯酚电催化氧化过程的影响。实验结果表明：在实验条件下，苯酚溶液在3种金属氧化物膜电极上的电催化氧化过程的宏观动力学符合一级反应动力学规律，但不同金属氧化物阳极上苯酚电催化氧化过程的表观反应速率及电流效率有明显的差异。25℃下苯酚在Ti/SnO2+Sb2O3、Ti/SnO2+Sb2O3/PbO2和Ti/SnO2+Sb2O3/RuO2+PbO2电极上电催化氧化的表观反应速率常数k分别为6.66×10-2min-1、2.49×10-2min-1和9.76×10-3min-1;瞬时电流效率随电解时间的增长而下降，初始电流效率分别为78.7%、38.9%、13.2%。以Ti/SnO2+Sb2O3电极为阳极电解60 min后，苯酚浓度从初始浓度2.13×10-3mol·L-1降至3.27×10-5mol·L-1，苯酚的转化率达98.5%;而在相同的反应条件下，以Ti/SnO2+Sb2O3/PbO2和Ti/SnO2+Sb2O3/RuO2+PbO2为阳极时，苯酚的转化率只有82.7%和29.8%。对3种电极在苯酚溶液中的伏安特性的研究表明，Ti/SnO2+Sb2O3电极具有比Ti/SnO2+Sb2O3/PbO2和Ti/SnO2+Sb2O3/RuO2+PbO2高的析氧电位，因此有利于有机物的氧化和过程电流效率的提高。     

Solvent Effects on the Selectivity of Palladium-Catalyzed Suzuki-Miyaura Couplings

The use of polar solvents MeCN or dimethylformamide (DMF) was previously shown to induce a selectivity switch in the Pd/P^tBu₃-catalyzed Suzuki-Miyaura coupling of chloroaryl triflates. This phenomenon was attributed to the ability of polar solvents to stabilize anionic transition states for oxidative addition. However, we demonstrate that selectivity in this reaction does not trend with solvent dielectic constant. Unlike MeCN and DMF, water, alcohols, and several polar aprotic solvents such as MeNO₂, acetone, and propylene carbonate provide the same selectivity as nonpolar solvents. These results indicate that the role of solvent on the selectivity of Suzuki-Miyaura couplings may be more complex than previously envisioned. Furthermore, this observation has the potential for synthetic value as it greatly broadens the scope of solvents that can be used for chloride-selective cross coupling of chloroaryl triflates.     

Preparation of pyridinemonocarboxylic acids by catalytic vapour phase oxidation of alkylpyridines. I. Oxidation of 2- and 3-picoline and decarboxylation of 2- and 3-pyridinecarboxylic acid in the vapour phase

The vapour phase oxidation of 2-picoline with air using a singly promoted vanadium catalyst (V₂O₅/SnO₂, mole ratio 1/1.5), at a temperature of 375°C and a space velocity of 6130 h^?1, gave a 69% conversion with a selectivity of 64% for 2-pyridinealdehyde. No pyridoin formation was detected. In the vapour phase oxidation of 3-picoline using a doubly promoted vanadium catalyst (V₂O₅-TiO₂-Na₂O with V/Ti/Na=100/20/1.15) at a temperature of 400°C and a space velocity of 1450 h^?1, a 94% conversion of 3-picoline was obtained with a selectivity of 51% for niacin (3-pyridinecarboxylic acid) and 1% for 3-pyridinealdehyde. By varying the atom ratio V/Ti, the catalyst V/Ti = 100/25 was found to be the most active one. The decarboxylation of 2- and 3-pyridinecarboxylic acid in the vapour phase was also investigated under the conditions used in the oxidation of the picolines to the acids. At 350°C about 90% decarboxylation of picolinic acid occurs under these conditions, while only a few per cent of the niacin decarboxylated to pyridine between 300 and 500°C.     

Reaction of piperidine with formaldehyde over alumina and spinel aluminates

The reaction of piperidine with formaldehyde over -alumina, Na⁺--alumina, NiAl₂O₄ and CuAl₂O₄ was studied as a model system in order to understand the mechanism and selectivity of alkylpyridine formation from piperidine and carbonyl compounds. Along with the expected 3-picoline, 2-picoline and other products were also formed. The selectivity for 3-picoline was high on -alumina whereas on NiAl₂O₄, 2-picoline was selectively formed. The formation of the different products has been rationalized and a probable mechanism for the formation of 2-picoline has been presented.     

Vanadia-molybdena catalysts for the oxidation of 2-picoline

A study has been made of the influence of catalyst composition on the gas phase oxidation of 2-picoline over mixed vanadium and molybdenum oxides supported on kieselguhr. It is shown that the formation of partial oxidation products is associated with the existence of a mixed oxide phase. The selectivity for the formation of pyridine-2-aldehyde reaches a maximum when one in six vanadium(V) ions in the V₂O₅ lattice is replaced by a molybdenum(VI) ion. It is suggested that the origin of the selectivity is the formation of isolated (V⁴⁺-O) species.     

Thermodynamic studies of zinc chloride in mixed aqueous solvents from electromotive force measurements—II. Dioxan,acetone and acetic acid mixtures with water

From the emf measurements of the cell Pt/Zn(Hg)/ZnCl₂, H₂O, organic co-solvent/AgCl/Ag the standard emf of the cell have been determined for dioxan (10,20 and 30 wt%), acetone (10, 20 and 30 wt%) and acetic acid (10, 20, 30, 50, 70 and 90 wt%) mixtures with water at 298 K. These data were used in calculations of: (a) the mean activity coefficients of zinc chloride (b) the primary medium effect (c) the standard Gibbs energies of transfer of zinc chloride from water to mixed solvents. The standard Gibbs energies for the transfer process have been interpreted in regard to the acid-base (in Lewis meaning) properties of the water molecules in mixed solvents.     

Thermodynamic studies of Hydrobromic acid in acetonewater mixtures (10, 30 and 50 wt-%) from electromotive force measurements

The emf of the cell: Pd,H₂(g)/HBr(m), x wt-% acetonewater mixture/AgBr,Ag was measured with x = 10, 30 and 50 at temperatures 15, 25 and 35°C in the molality range for HBr from 0.003 to 0.1 mol kg^?1. From these data the standard potentials for Ag|AgBr electrode are obtained, and used in calculations of: (a) the standard thermodynamic quantities for the cell reaction and the reaction of HBr formation, (b) the mean activity coefficients of HBr, (c) the primary medium effect, and (d) the standard thermodynamic quantities for transfer of HBr from water to the acetonewater mixed solvents. On the basis of the values obtained under (d), the spontaneity of transfer the process for HBr is discussed, the acid—base properties of mixed solvents and their structure.     

Vanadium peroxocomplexes as oxidation catalysts of sulfur organic compounds by hydrogen peroxide in bi-phase systems

New vanadium oxodiperoxocomplexes Bu₄N⁺[VO(O2)₂ L₂]⁻ were synthesized, where L=pyridine (1), 2-methylpyridine (2), 4-methylpyridine (3), 2-oxymethylpyridine (4). All complexes were characterized by NMR (¹H, ⁵¹V) and IR spectroscopy. The oxidation of sulfur organic compounds and diesel fuel desulfurization catalyzed by vanadium peroxocomplexes in bi-phase system was investigated in various solvents. The complexes manifested high catalytic activity and selectivity in oxidation of sulfides.     

Photografting of methyl methacrylate onto high‐density polyethylene initiated by aliphatic ketones

The photografting of a water‐insoluble monomer methyl methacrylate (MMA) onto high‐density polyethylene (HDPE) initiated by an aliphatic ketone/water/alcohol initiating system has been reported. The aliphatic ketones, such as acetone, butanone, and cyclohexanone, could effectively initiate the grafting reaction when they were mixed with water and ethanol to form homogeneous aliphatic ketone/water/ethanol mixed solvents that could dissolve the water‐insoluble monomer. The nature of aliphatic ketone affected the grafting; at the same aliphatic ketone/water/ethanol volume ratio, the grafting system containing acetone or butanone always led to a higher extent of grafting than that containing cyclohexanone. Water also played a very important role in the grafting reaction; in the tested range, the rate of formation of grafted PMMA on HDPE increased with the increase of water : volume ratio. The grafting of MMA carried out in 5 acetone/40 water/55 ethanol mixed solvent led to the highest extent of grafting. ATR‐FTIR characterizations of the grafted samples proved the successful grafting of MMA onto HDPE. SEM investigations of the HDPE surfaces grafted in different aliphatic ketone/water/ethanol mixed solvents indicate the morphologies of grafted surfaces varied with the mixed solvents used. This study broadened the application fields of the aliphatic ketone/water/alcohol initiating system for photografting. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009