金属卟啉催化环己烷羟基化反应中环己酮的形成机理研究

单金属卟啉和双金属卟啉催化下PhIO常温氧化环己烷的羟基化反应中金属卟啉结构和反应溶剂、反应温度、反应时间等环境因素对产物酮含量及酮形成反应动力学的影响进行了系统研究, 并与金属卟啉催化下PhIO氧化环己醇的反应进行了对比, 提出了金属卟啉催化下环己烷羟基化反应中产物酮的形成机理。     

金属卟啉催化环己烷羟基化反应中环己酮的形成机理研究

单金属卟啉和双金属卟啉催化下PhIO常温氧化环己烷的羟基化反应中金属卟啉结构和反应溶剂、反应温度、反应时间等环境因素对产物酮含量及酮形成反应动力学的影响进行了系统研究, 并与金属卟啉催化下PhIO氧化环己醇的反应进行了对比, 提出了金属卟啉催化下环己烷羟基化反应中产物酮的形成机理。     

钴分子筛催化剂的制备及其分子筛载体对环己烷氧化选择性的影响

为了考察催化剂载体的孔道结构和择形性能对环己烷部分氧化反应的影响,采用直接水热法制备出了Co/S-1,Co/TS-1以及Co/MCM-41分子筛催化剂.XRD,FT-IR和SEM结果表明合成的样品具有较高的结晶度,晶粒大小均匀,其活性组分钴进入了分子筛骨架.采用氧气为氧化剂,考察了合成的钴催化剂样品对环己烷部分氧化的催化性能,并与CoAPO-5、Co/A l2O3、均相Co(OAc)2.4H2O催化剂以及无催化氧化的结果进行了比较.实验结果表明:分子筛载体能利用其孔道结构和择形性能,降低环己醇(酮)选择性对环己烷转化率的依赖性,且反应的选择性随分子筛载体孔径的增加而下降.孔道较小的Co/TS-1和Co/S-1做催化剂时,过氧化物含量低,环己烷转化率可达5%以上,同时反应总选择性为95%左右.     

环己烷氧化反应:有机小分子的催化作用简

考察了酮、醛、酯、醇与胺等几类有机小分子在环己烷氧化反应中的催化作用. 结果表明,有机小分子催化剂的活性与其极性的强弱、与环己烷形成氢键的强弱、α氢的活性及清除自由基的能力有关. 因此,对于环己烷氧化反应,溶剂很可能存在催化作用. 三丙胺在环己烷氧化反应中表现出较高的催化活性,具有进一步开发应用的前景.     

GoAggⅡ体系催化氧化环己烷为环己酮

研究了Gif体系成员之一GoAggⅡ体系催化氧化环己烷为环己酮的反应.考察了催化剂用量、氧化剂用量、溶剂配比、反应温度和反应时间等对产率的影响.最佳反应条件为:1 40 mmol,催化剂[NH4Fe(SO4)2]1mmol,氧化剂[30%H2O2]80 mmol,溶剂[y(吡啶):V(乙酸)=5.6:1.0]33 mL,于40℃反应16 h.在此条件下,收率达10.33%,n(环己酮):n(环己醇)=5.61.     

在醛基化交联聚苯乙烯微球表面同步合成与固载卟啉及固载化金属卟啉的高效催化氧化性能

采用Kornblum氧化反应, 先将氯甲基交联聚苯乙烯(CMCPS)的氯甲基氧化为醛基, 制得醛基(AL)化改性微球ALCPS, 然后使改性微球ALCPS与溶液中的苯甲醛(或取代的苯甲醛)、吡咯之间发生固-液相之间的Adler反应, 成功地实现了卟啉在交联聚苯乙烯微球表面的同步合成与固载, 制得了固载有苯基卟啉(PP) 、对氯苯基卟啉(CPP)、对硝基苯基卟啉(NPP)的功能微球, 最后使功能微球与钴盐发生配合反应, 制备了固载有三种钴卟啉的固体催化剂. 研究重点有两方面: (1)考察主要因素对卟啉同步合成与固载过程的影响|(2)考察固载化钴卟啉在催化分子氧氧化环己烷羟基化过程中的催化特性. 实验结果表明, 以醛基化改性微球ALCPS与溶液中的吡咯及小分子苯甲醛(或取代的苯甲醛)为共反应物, 通过固-液之间的Adler反应, 可以顺利地实现卟啉在微球ALCPS表面的同步合成与固载, 这是制备固载化卟啉的新途径|苯甲醛的取代基结构、催化剂的酸性与溶剂的性质对卟啉的同步合成与固载都有较大的影响|所制备的固体催化剂对分子氧氧化环己烷羟基化的反应, 具有很高的催化活性(环己烷最高转化率约为40%)与选择性(环己醇的选择性在90%以上), 这是由固体催化剂特殊的化学结构所决定的.     

离子液体中Mn(salen)催化环己烯环氧化反应

 研究了离子液体中Mn(salen)络合物催化环己烯的环氧化反应,考察了反应介质、 Mn(salen)络合物催化剂结构和反应条件等对环氧化反应的影响. 在离子液体-CH2Cl2混合溶剂中,以相对廉价的H2O2为氧化剂,得到了高的环己烯转化率和环氧环己烷选择性. 当以邻苯二胺和水杨醛制备的Mn(salen)络合物为催化剂,反应温度为273 K时,在［bmim］BF4-CH2Cl2的混合溶剂中,环己烯的转化率和环氧环己烷选择性分别可达100%和94.0%. 此外,反应结束后,产物可以由正己烷萃取出来,解决了传统均相催化体系中催化剂与产物不易分离的问题.     

Au/ZSM-5催化选择氧化环己烷制环己酮和环己醇的研究

利用水热合成的方法制备了ZSM-5分子筛担载的纳米金催化剂．对合成的样品进行了XRD，XPS，Uv-Vis征分析,以环己烷催化氧化为探针反应．发现该催化剂对选择氧化环己烷制备环己酮和环己醇表现了优异的活性,环己烷的最高转化率可达到～16％．环己酮和环己醇的总选择性达到～92％．     

多功能Na2WO4-离子液体催化体系催化环己醇一锅合成己内酰胺

己内酰胺是合成尼龙-6和工程塑料的关键中间体.工业上己内酰胺的合成工艺分三步:以环己醇为原料合成环己酮,环己酮氨肟化合成环己酮肟,环己酮肟重排生成己内酰胺.该工艺存在工艺流程长、重排过程中使用发烟硫酸腐蚀设备、形成大量低值副产物硫酸铵等问题.随着人们对环境保护意识的提高,发展环境友好、经济效益高的直接合成己内酰胺工艺已经迫在眉睫.多步串联反应具有设备投资少、中间分离步骤少、反应效率高等优点,其关键问题之一是多功能催化剂的开发.环己醇作为环己烷氧化反应的副产物,能够直接用于己内酰胺的合成,具有理论研究价值和工业应用意义.本文构建了以环己醇氧化、环己酮肟化和环己酮肟重排反应构成的串联反应系统,可缩短己内酰胺合成工艺流程,降低能耗,减小环境污染.合成了九种离子液体,并与Na2WO4组成催化体系,以环己醇、过氧化氢和羟胺为原料,催化环己醇直接合成己内酰胺.首先研究了不同Na2WO4-离子液体催化体系对环己醇直接氧化合成环己酮反应的影响.反应介质的酸性和离子液体水油两相中的相转移功能是影响氧化过程的两个主要因素.Na2WO4-磺酸基功能化的离子液体催化剂具有较高的氧化活性.这是由于磺酸基的引入提高了催化剂酸性,另外磺酸基功能化的离子液体随碳链的增长,催化剂的亲油性增强,即该催化剂相转移功能增强.考察了九种离子液体对氧化过程的影响,其中Na2WO4-[BSTma]HSO4在氧化过程中催化活性最高,因此将其用于催化环己酮与羟胺合成己内酰胺的反应,并考察了环己酮与[BSTma]HSO4的摩尔比对该反应的影响,发现该摩尔比为1:0.08时,反应效果最好.最后,将Na2WO4-[BSTma]HSO4体系用于催化环己醇直接合成己内酰胺的反应.考察了反应温度、反应时间和环己醇与[BSTma]HSO4摩尔比的影响.在氧化时间为300 min,肟化和重排时间为150 min,反应温度为80℃,环己醇:H2O2:(NH2OH)2·H2SO4:Na2WO4·2H2O:[BSTma]HSO4的摩尔比为1.00:1.50:0.50:0.06:0.08的条件下反应效果最好,环己醇转化率为97.3%,己内酰胺收率为76.0%.Na2WO4-[BSTma]HSO4催化体系活性较高的原因是离子液体阳离子的相转移作用,以及在氧化过程中离子液体与过氧钨酸盐的配位作用和对Beckmann重排过程中中间产物的稳定作用.研究了Na2WO4-[BSTma]HSO4催化体系的普适性,发现该催化体系对所考察的脂肪醇和芳香醇直接合成酰胺均具有较好的催化活性.另外,回用的Na2WO4-[BSTma]HSO4催化剂仍具有较好的催化活性.因此,该催化体系具有高效易回收、操作简单和反应条件温和的优点.     

金催化剂催化环己烷液相选择氧化研究

采用溶胶-凝胶法制备了一系列担载纳米金催化剂,用于催化环己烷液相选择氧化反应.在反应体系中没有加入任何溶剂或助催化剂,考察了反应温度、时间、压力和不同焙烧温度对催化剂活性的影响.实验结果表明,催化剂在250℃焙烧和金含量为0.032%时,环己烷选择氧化可以达到10.8%的转化率和90.8%的目的产物(环己醇和环己酮)选择性,相应转化频率高达5.2×104.     

附加试剂及反应介质对TPPFeCl催化环己烷仿生氧化反应性能的影响

研究了某些附加试剂及反应介质对四苯基卟吩合铁(Ⅲ)[TPPFeCl或(TPPFe)₂O]模拟细胞色素P-450催化PhIO羟化环己烷反应的影响。发现适量的异丙醇、吡啶及NaOH能促进反应,加入盐酸及增大介质的极性对反应不利。证明了副产物环己酮主要是由PhIO直接氧化主产物环己醇生成的,TPPFeCl的存在不利于酮的生成,醇的存在能延长催化剂的寿命。     

Oxidation of Cyclohexane by Molecular Oxygen Photoassisted by meso-Tetraarylporphyrin Iron(III)-Hydroxo Complexes

The photochemical and photocatalytic properties of iron meso-tetraarylporphyrins bearing an OH(-) axial ligand and different substituents in the beta-positions of the porphyrin ring are reported. Irradiation (lambda = 365 nm) in the absence of dioxygen leads to the reduction of Fe(III) to Fe(II) with the formation of OH(*) radicals. Substituents at the pyrrole beta-positions are found to markedly affect the photoreduction quantum yields. Under aerobic conditions, this photoreaction can induce the subsequent oxidation of cyclohexane to cyclohexanone and cyclohexanol by O(2) itself. The process occurs under mild conditions (22 degrees C; 760 Torr of O(2)) and without the consumption of a reducing agent. The polarity of the solvent and the nature of the porphyrin ring have a remarkable effect on the selectivity of the photooxidation process, likely controlling the cleavage of O-O bonds of possible iron peroxoalkyl intermediates. In particular, in pure cyclohexane, oxidation occurs with the selective formation of cyclohexanone; in contrast, in dichloromethane/cyclohexane mixed solvent, the main oxidation product is cyclohexanol. Phenyl-tert-butylnitrone (pbn) has been found to quench the radical chain autooxidation of the substrate thus increasing the yield of cyclohexanol. This becomes the only oxidation product when iron 5,10,15,20-tetrakis(2,6-dichlorophenyl)porphyrin hydroxide (Fe(III)(TDCPP)(OH)) is used as photocatalyst.     

Radical Cation of Pyrazine-di-N-oxide as a Mediator in Electrocatalytic Oxidation of Organic Compounds

The mechanism of oxidation of cyclohexanol, methanol, diethyl ether, triethyl orthoformate, and cyclohexane in the presence of a mediator—electrochemically generated radical cation of pyrazine-di-N-oxide (PyrDNO)—is studied on glassy carbon and platinum in a 0.1 M LiClO₄ solution in acetonitrile employing cyclic voltammetry, ESR electrolysis, and gas chromatography. Effect of temperature, additives of acid and water, oxygen, and the nature of the substrate and solvent on the shape of cyclic voltammograms and intensity of ESR signal of PyrDNO is examined. ESR spectra for radical cations and anions of PyrDNO with g factors equal to, respectively, 2.0090 and 2.0031 are recorded. A mechanism for the overall two-electron catalytic oxidation of an organic substance, which involves a stage in which it complexes with the radical cation of PyrDNO, is suggested.     

三氯化钌催化下环己烷和环己醇在离子液体中的氧化反应研究

在三氯化钌催化下,使用叔丁基过氧化氢在离子液体中可将环己烷和环己醇氧化为环己酮,结果表明环己醇的氧化具有较高的转化率和选择性．离子液体(bmim)^ PF6^-和催化剂三氯化钌均有一定的重复使用性．     

NaY分子筛固载席夫碱钴配合物的制备、表征及其催化性能研究

利用“瓶中造船”（ship-in-a-bottle） 技术将双水杨醛缩乙二胺合钴（Cosalen）配合物封装于Y型沸石分子筛的超笼中，制备出固载型席夫碱钴金属配合物Cosalen/Y（SB）。同时采用浸渍方法将Cosalen负载于Y型分子筛的表面，制备了浸渍型的负载物Cosalen/Y（IM）。采用原子吸收、红外光谱、紫外光谱、X射线衍射、热重 差热和电镜扫描等方法对两者进行了表征。 结果表明 ，固载物Cosalen/Y（SB）中Cosalen已成功地进入了分子筛的孔道内。以分子氧为氧源，考察了Cosalen/Y（SB）对环己烷的催化氧化性能以及催化剂用量、溶剂、氧气压力对反应的影响。结果表明，Cosalen/Y（SB）具有较高的催化氧化活性和对环己醇、环己酮以及己二酸的选择性，有一步氧化环己烷生成己二酸的潜力。重复实验表明，催化剂稳定性较好，没有明显的活性组分流失。     

Increasing the ketone selectivity of the cobalt-catalyzed radical chain oxidation of cyclohexane

A variety of heterogeneous catalysts for the radical chain oxidation of cyclohexane has been prepared by immobilization of the well-defined cobalt acetate oligomers [py(3)Co(3)(mu(3)-O)(OH)(O(2)CCH(3))(5)](PF(6)) (1) and [py(4)Co(2)(OH)(2)(O(2)CCH(3))(3)](PF(6)) (2) on carboxy-modified mesoporous silica supports A-D by carboxylate exchange. The catalytic oxidation of cyclohexane with tert-butyl hydroperoxide (TBHP) in the presence of these homogeneous and immobilized cobalt acetate complexes afforded the corresponding alcohol and ketone in high yield. The immobilization of 1 and 2 results in a significant increase of catalytic activity. TBHP acts as a radical initiator and as source of molecular oxygen, which is also involved in the overall oxidation process. The rate of cyclohexane conversion is limited by the diffusion of molecular oxygen, and steady-state concentrations of cyclohexanone (K, ketone) and cyclohexanol (A, alcohol) are established; these determine the maximum K:A ratio.     

Electrochemical and ESR-study of the mechanism of organic compound oxidation in the presence of mediators—Radical cations of substituted pyrazin-di-N-oxydes

The mechanism of methanol, ethanol, diethyl ether, triethyl-o-formate, cyclohexanol, and cyclohexane oxidation in the presence of electrochemically generated radical cations of 2,5-dimethyl-, 2,3,5,6-tetramethyl-, 2,3-dimethyl-5,6-cyclohexa-, and 3-phenyl-5,6-cyclohexapyrazin-di-N-oxydes as mediators was studied by cyclic voltammetry, ESR-electrolysis, and gas chromatography. The studies were carried out at glassy-carbon-, Pt-, and Au-electrodes in 0.1 M LiClO₄ solutions in acetonitrile and methanol, the alcohol being used as a solvent and substrate simultaneously. ESR-spectra of the radical cations of the pyrazin-di-N-oxydes were recorded. Effects of temperature, oxygen, admixtures of water and acid, and the nature of substrate and solvent on the shape of the cyclic voltammograms and intensity of the ESR-spectra of the pyrazin-di-N-oxydes are elucidated. By comparing experimental and calculated voltammograms, the rate constants for the interaction between the pyrazin-di-N-oxydes and the substrates C-H-bonds are determined. Mechanism of the ultimate two-electron catalytic oxidation of the organics as a constituent of complexes, formed with the radical cations of the mediators (pyrazin-di-N-oxydes), is suggested.     

Radical autoxidation and autogenous O2 evolution in manganese-porphyrin catalyzed alkane oxidations with chlorite

A manganese porphyrin catalyst employing chlorite (ClO(2)(-)) as a "shunt" oxidant displays remarkable activity in alkane oxidation, oxidizing cyclohexane to cyclohexanol and cyclohexanone with >800 turnover numbers. The ketone is apparently formed without the intermediacy of alcohol and accounts for an unusually large fraction of the product ( approximately 40%). Radical scavenging experiments indicate that the alkane oxidation mechanism involves both carbon-centered and oxygen-centered radicals. The carbon-radical trap CBrCl(3) completely suppresses cyclohexanone formation and reduces cyclohexanol turnovers, while the oxygen-radical trap Ph(2)NH inhibits all oxidation until it is consumed. These observations are indicative of an autoxidation mechanism, a scenario further supported by TEMPO inhibition and (18)O(2) incorporation into products. However, similar cyclohexane oxidation activity occurs when air is excluded. This is explained by mass spectrometric and volumetric measurements showing catalyst-dependent O(2) evolution from the reaction mixture. The catalytic disproportionation of ClO(2)(-) into Cl(-) and O(2) provides sufficient O(2) to support an autoxidation mechanism. A two-path oxidation scheme is proposed to explain all of the experimental observations. The first pathway involves manganese-porphyrin catalyzed decomposition of ClO(2)(-) into both O(2) and an unidentified radical initiator, leading to classical autoxidation chemistry providing equal amounts of cyclohexanol and cyclohexanone. The second pathway is a "rebound" oxygenation involving a high-valent manganese-oxo intermediate, accounting for the excess of alcohol over ketone. This system highlights the importance of mechanistic studies in catalytic oxidations with highly reactive oxidants, and it is unusual in its ability to sustain autoxidation even under apparent exclusion of O(2).     

Electrochemical and ESR study of the mechanism of oxidation of phenazine-di-N-oxide in the presence of cyclohexanol on glassy carbon and single-walled carbon nanotube electrodes

The mechanism of oxidation of phenazine-di-N-oxide in the presence of cyclohexanol was studied by cyclic voltammetry on glassy carbon (GC) and single-walled carbon nanotube (SWCNT) electrodes in 0.1 M LiClO₄ solutions in acetonitrile. The effect of cyclohexanol on the shape of the cyclic voltammograms of phenazine-di-N-oxide and the intensity of the ESR signal of its radical cation was investigated. It was shown by ESR that the products of the one-electron oxidation and reduction of phenazine-di-N-oxide were radical cations and anions. The catalytic currents were recorded during the oxidation of phenazine-di-N-oxide on the SWCNT and GC electrodes in the presence of cyclohexanol. The results were explained in terms of the E₁C₁E₂C₂ mechanism of the two-stage electrode process characterized by the catalytic current recorded at the second electrode stage. The overall two-electron catalytic oxidation of cyclohexanol in the complex with the phenazine-di-N-oxide radical cation was assumed to occur. It was shown that SWCNT electrodes can be used in the electrocatalytic oxidation of organic compounds in the presence of the electrochemically generated phenazine-di-N-oxide radical cation.