光氧化反应研究——Ⅷ.苊酮作为电子给体的电子转移光氧化反应机理

研究了苊酮(ANO)在9,10-二氰蒽(DCA)敏化下的光氧化反应与机理。实验发现,该反应具有逐步氧化模式,依次生成1,8-(3′-羟基)-斗-萘内酯和1,8-萘二甲酸酐。通过循环伏安,荧光淬灭和激基络合物检测,DCA/联苯共敏化反应以及CIDNP效应等研究,证明苊酮可以作为电子给体与单线态DCA发生热力学上有利的电子转移过程。     

1,4-二苯基-1,3-丁二烯的氰基蒽敏化光氧化反应

某些不能与单线态氧(~1O_2)起反应的烯烃、炔烃、硫醚和环氧化合物,在以氰基蒽为敏化剂的条件下,可发生经由光敏电子转移机理的氧化反应.近年来,Santamaria 等,Foote 等和我们都在研究这类反应.本文报道以9,10-二氰基蒽(DCA)为敏化剂、反,反-1,4-二苯基-1,3-丁二烯为反应物的电子转移光敏氧化反应,并讨论了反应机理.     

联苯在β-蒎烯光氧化中的电子中继

β-蒎烯的长时间单重态氧光氧化导致复杂的产物分布。二氰基蒽(DCA)敏化的电子转移光氧化使桃金娘烯醇的产率略有改善, 但是, 添加联苯作共敏化剂使产率几乎翻了一番。在向DCA的竞争性单电子转移中, 联苯超过了β-蒎烯。MNDO计算证实其原因是联苯的HOMO较高。联苯正离子游离基从β-蒎烯回收一个电子, 再生联苯和生成β-蒎烯正离子游离基, 它再与经基态氧与(DCA)^-之间电子转移而生成的超氧负离子(O^-~2)复合。     

光氧化反应的研究 II: 9-苯甲叉芴的电子转移光氧化反应

芳香族烯烃, 芳烃以及稠环芳烃是光氧化反应中的重要研究对象, 本文以9-苯甲叉芴(BF)作为底物, 发现它在9,11-二氰蒽(DCA)敏化作用下易发生电子转移反应, 反应生成芴酮和BF的相应环氧化物, 用紫外光谱测出BF的电荷转移配合物的络合物稳定常数,用循环伏安法测定BF的氧化电位. 由Rehm-Weller方程计算出DCA敏化的单电子转移过程的自由能变化, 并观察到BF对DCA有明显的荧光猝灭作用.     

二氢吡喃光敏氧化反应的研究

本文研究了二氢吡喃的氰基蒽(9,10-二氰基蒽、9-氰基蒽)敏化光氧化反应。在几种不同溶剂(乙腈、二氯甲烷、苯、四氯化碳)中,其敏化光氧化反应所生成的产物、产物分布及溶剂同位素效应与典型单线态氧的氧化反应相同。荧光淬灭、激基复合物的生成和自由能的变化支持了电子转移反应机理。我们认为,反应首先经过敏化剂的激发单线态与反应底物之间的电子转移反应,尔后在反应过程中生成了活性中间体单线态氧1O2。     

SELECTIVE PHOTOOXIDATION OF trans,trans-1, 4-DIPHENYL-1, 3-DIBUTADIENE IN ZEOLITE ZSM-5

本文研究了反式,反式-1,4-二苯基-1,3-丁二烯(DPB)在沸石NaZSM-5中的光敏氧化反应。在溶液中9,10-二氰基蒽(DCA)敏化光氧化反应有两种机制:单重态氧机制和电子转移产生超氧负离子机制。我们把DPB吸附在沸石ZSM-5孔道中,DCA溶解于沸石外部溶剂季戊四醇三甲醚中,溶剂和敏化剂都不能进入沸石孔道。光照反应后,在沸石孔道中只得到DPB的单重态氧的反应产物,没有电子转移的产物产生。反应产物产率为100%。大大提高了反应的选择性。     

MoS2摩擦表面氧化与电子转移

利用电子自旋共振谱(ESR)和X射线光电子谱(XPS)研究了MoS2摩擦表面的氧化行为和摩擦表面氧化的电子转移,发现MoS2在摩擦失效过程中Mo4+与氧作用生成稳定的Mo6+终态氧化物,其间经过Mo5+过渡态。深入揭示了MoS2摩擦表面氧化过程的复杂性,指出Mo在摩擦表面氧化过程中以多种化学状态存在,Mo原子的氧化是Mo4d轨道上的单电子转移过程。     

缺电子芳烃侧链基的光氧化

研究了9,10-二氰蒽(DCA)和四氯对苯二醌(TCBQ)敏化的甲苯、对氯甲苯、对氰基甲苯和对硝基甲苯的电子转移光氧化反应。DCA和TCBQ均可敏化甲苯和对氯甲苯的光氧化。产物为相应的取代苯甲酸和取代苯甲醛。DCA和TCBQ均不能有效敏化对氰基甲苯和对硝基甲苯的光氧化, 但在反应体系中加入与反应物等摩尔的联苯为共敏化剂后, 两者即可顺利氧化为相应的取代苯甲酸和取代苯甲醛。通过荧光淬灭和共敏化剂联苯、无水盐高氯酸镁、O2捕获剂对苯二醌以及电子给体对二甲氧基苯等外加试剂对光氧化的影响讨论了反应历程。     

缺电子芳烃侧链基的光氧化

研究了9,10-二氰蒽(DCA)和四氯对苯二醌(TCBQ)敏化的甲苯、对氯甲苯、对氰基甲苯和对硝基甲苯的电子转移光氧化反应。DCA和TCBQ均可敏化甲苯和对氯甲苯的光氧化。产物为相应的取代苯甲酸和取代苯甲醛。DCA和TCBQ均不能有效敏化对氰基甲苯和对硝基甲苯的光氧化, 但在反应体系中加入与反应物等摩尔的联苯为共敏化剂后, 两者即可顺利氧化为相应的取代苯甲酸和取代苯甲醛。通过荧光淬灭和共敏化剂联苯、无水盐高氯酸镁、O2捕获剂对苯二醌以及电子给体对二甲氧基苯等外加试剂对光氧化的影响讨论了反应历程。     

蒈烯芳氰敏化光氧化反应的研究——Ⅰ.蒈烯对9,10-二腈基蒽荧光的猝灭特性

本文通过研究在不同溶剂中蒈烯对9,10-二腈基蒽(DCA)荧光猝灭的光物理特性及溶剂极性对猝灭速度的影响,温度效应的测定及其在乙腈中双分子猝灭速率常数k_q值与计算所得自由能的变化(△G)之间的关系符合 RehmWeller关系,证明了菇烯对DCA荧光的猝灭是一个电子转移的动态猝灭过程。     

The photochemical preparation of ozonides by electron-transfer photo-oxygenation of epoxides

9,10-Dicyanoanthracene (DCA) sensitizes the electron-transfer photo-oxygenation of epoxides in oxygen-saturated acetonitrile to form ozonides. Epoxides with oxidation potentials lower than 2 V vs SCE quench the fluorescence of DCA and are converted to the ozonides with DCA alone. Epoxides which do not quench the singlet excited state of DCA are unreactive under these conditions. However, the photo-oxygenation of these epoxides can be effected by addition of biphenyl (BP) as a catalyst or co-sensitizer. Investigations of the stereochemistry of the reactions of cis- and trans-2,3-diaryloxiranes has shown that both isomeric epoxides are converted exclusively to the corresponding cis-ozonides. Co-sensitized photo-oxygenation of cis- and trans-2,3-diphenyloxirane affords only cis-3,5-diphenyl-1,2,4-trioxolane. The same stereochemical course is followed for the electron-transfer photo-oxygenation of more easily oxidized 2,3-dinaphthyloxiranes that do not require BP co-sensitization. The stereochemistry of the naphthyl-substituted ozonides has been unequivocably assigned by an X-ray structure of cis-3,5-bis(2'-naphthyl)-1,2,4-trioxolane. The corresponding trans-ozonide was prepared by ozonation of cis-1,2-bis(2'-naphthyl)ethene and stereochemically identified by Chromatographic resolution using high-performance liquid chromatography with optically active (+)-poly(triphenylmethyl methacrylate) as the stationary phase. These stereochemical results have been interpreted in terms of a mechanism involving addition of singlet oxygen as a dipolarophile to intermediate carbonyl ylides.     

Photosensitized oxidation of sulfides: discriminating between the singlet-oxygen mechanism and electron transfer involving superoxide anion or molecular oxygen

The oxidation of diethyl and diphenyl sulfide photosensitized by dicyanoanthracene (DCA), N-methylquinolinium tetrafluoroborate (NMQ(+)), and triphenylpyrylium tetrafluoroborate (TPP(+)) has been explored by steady-state and laser flash photolysis studies in acetonitrile, methanol, and 1,2-dichloroethane. In the Et(2)S/DCA system sulfide-enhanced intersystem crossing leads to generation of (1)O(2), which eventually gives the sulfoxide via a persulfoxide; this mechanism plays no role with Ph(2)S, though enhanced formation of (3)DCA has been demonstrated. In all other cases an electron-transfer (ET) mechanism is involved. Electron-transfer sulfoxidation occurs with efficiency essentially independent of the sulfide structure, is subject to quenching by benzoquinone, and does not lead to Ph(2)SO cooxidation. Formation of the radical cations R(2)S(*+) has been assessed by flash photolysis (medium-dependent yield, dichloroethane>CH(3)CN>CH(3)OH) and confirmed by quenching with 1,4-dimethoxybenzene. Electron-transfer oxidations occur both when the superoxide anion is generated by the reduced sensitizer (DCA(*-), NMQ(*)) and when this is not the case (TPP(*)). Although it is possible that different mechanisms operate with different ET sensitizers, a plausible unitary mechanism can be proposed. This considers that reaction between R(2)S(*+) and O(2)(*-) mainly involves back electron transfer, whereas sulfoxidation results primarily from the reaction of the sulfide radical cation with molecular oxygen. Calculations indeed show that the initially formed fleeting complex RS(2)(+)...O-O(*) adds to a sulfide molecule and gives strongly stabilized R(2)S-O(*)-(+)O-SR(2) via an accessible transition state. This intermediate gives the sulfoxide, probably via a radical cation chain path. This mechanism explains the larger scope of ET sulfoxidation with respect to the singlet-oxygen process.     

高温均相法二醋酸纤维素酯的研究——结构及其溶液微胶粒尺寸

本文用 DSC、WAX 衍射和光电分光光度技术及粘度法研究了高温(100～150℃)均相法二醋酸纤维素酯(DCA)的结构及其微胶粒子尺寸。结果表明,DCA 溶液凝胶由于合成过程的因素失控致使反应不均匀性而产生的该法 DCA 溶液微胶粒子尺寸远小于光波波长,具有很好的可纺性能。     

光氧化反应的研究 V: 氰基蒽敏化苊烯的电子转移光氧化反应

对于容易发生单线态氧(^1O2)反应的稠环烯烃能否在氰基蒽敏化下发生电子转移光氧化研究甚少. 作者曾报道了氰基蒽敏化的9-本甲叉芴的ET光氧化过程. 本文首次探讨了非交替稠环烃, 苊烯(AN), 在9,10-二氰蒽(DCA)或9-氰基蒽(CNA)敏化下的光氧化反应及其机理.     

苊酮对二氰蒽的电子转移荧光猝灭研究──激基络合物的形成机理与动力学

研究了苊酮（ＡＮＯ）对９，１０－二氰蒽（ＤＣＡ）的荧光猝灭与激基络合物形成的动力学与机理。基于瞬态荧光双指数衰减，测定了激基络合物的光化学动力学和有关速度常数，论证荧光猝灭作用主要由ＡＮＯ／ＤＣＡ激基络合物的生成以及快速正向电子转移所致。     

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.     

Solvent friction effect on intramolecular electron transfer

U-shaped donor-bridge-acceptor molecules with different electronic couplings have been investigated as a function of temperature in solvents with slow polarization relaxation, in particular, N-methylacetamide (NMA) and N-methylpropionamide (NMP). At high temperature, the electron-transfer rate is well described by a nonadiabatic model; however, the rate at low temperature is controlled by the solvent friction. The change of the electron-transfer mechanism is discussed and compared with theoretical models.     

α-蒎烯的电荷转移光异构化反应

本文报道一类新的由9,10-二氰基蒽(CcA)敏化的α-蒎烯异构化为苧烯和顺式罗勒烯的光化学反应。在苯溶液中形成苧烯的量子产率为0.32,是乙腈溶液中的8倍,提出了经由单重激发态激态复合物形成苧烯和经由三重激发态激态复合物形成顺式罗勒烯的反应历程,并从实验数据的动力学分析中得到了证实。     

氰基蒽的电子转移荧光猝灭及激基复合物

本文测定了在不同溶剂中一系列化合物以及氧分子对9,10-二氰基蒽(DCA)及9-氰基蒽(CNA)的荧光淬灭常数k_q值及DCA与2,5-二甲基呋喃的激基复合物的发射光谱。这些化合物的k_q值与计算所得自由能的变化△G之间的关系基本符合Rehm-Wdler关系。溶剂极性及溶剂粘度对荧光猝灭反应有影响,影响强电子给体k_q值的主要因素是溶剂的粘度,而弱电子给体的k_q值则主要决定于溶剂的极性。氧分子的k_q值基本上与溶剂扩散速率常数走k_diff值吻合。