Chemistry of O-Benzoquinones and Masked O-Benzoquinones I. Diels-Alder Reactions of O-Benzoquinones with Dimethyl Acetylenedicarboxylate and Phenylacetylene

Diels-Alder reactions of six o-benzoquinones with dimethyl acetylenedicarboxylate has been examined. The yields of adducts vary with the natures of the o-benzoquinones, 3,4-Di-n-propyl-(1c), 3,6-di-n-propyl (1d). 3. 4-diallyl-(1e) and 3, 6-diallyl-o-benzoquinone (1f) are found to give bicyclic a-diketones exclusively without the formation of 1,4-dioxine derivatives, the yields ranging from 20 to 70%. In the case of 4, 5-dimethoxy-o-benzoquinone, dimethyl 4, 5-dimethoxyphthalate is produced in 42% yield, presumably derived from the decomposition of the corresponding initially formed α-diketone. 3, 6-Di-n-propyl-4, 5-dimethoxy-o-benzoquinone deteriorates without addition to dimethyl acetylenedicarboxylate upon heating. The additions of o-benzoquinones 1c , 1d and 1f to phenylacetylene are also studied. The yields of adducts, α-diketones, range from 23% to 82%.     

Mechanical and electrochemical effects on surface convection and on emulsification new criteria

Theoretical and experimental studies of surface instability for charged and polarized interfaces between two immiscible liquids are reviewed. A linear analysis of stability shows the role of mechanical and electrochemical para meters for the onset of interfacial convection. Three cases are studied: 1) For the restored Boltzman distribution in bulk phases, the stability is only governed by the interfacial tension through the composition between mechano-chemicaland electrical contributions to the surface free energy; 2) for the non-restored Boltzman distribution, the stability is also governed by the discontinuity of mechanical quantities (density-viscosity) associated with the discontinuity of electrochemical and electrical quantities (dielectric constant-solute concentration-diffusion coefficient, potential drop); and 3) for concentrated charged and dipolar monolayers, the convection criteria of stability are directly related to the discontinuity of mechanical quantities (density-viscosity) associated with the discontinuity of electrochemical quantities (dielectric constant).Additional experiments on emilsification and demulsification were performed in order to verify this last theoretical prediction.     

Spectrophotometry Determination of Cobalt after Extraction of its Ternary Complex with 3-(4-Phenyl-2-Pyridyl)-5,6-Diphenyl-1,2,4-Triazine and Tetraphenylborate into Molten Naphthalene

The reaction of 3-(4-phenyl-2-pyridyl)-5,6-diphenyl-1,2,4-triazine (PPDT) and tetraphenylborate (TPB) with cobalt (II) has been studied to determine the optimum conditions for the extraction and quantitative spectrophotometry determination of this metal. The ternary complex is extracted into molten naphthalene at pH 3.6–7.4. The solid naphthalene containing the cobalt associated complex is separated by filtration and dissolved in acetonitrile. Beer's law is obeyed in the concentration range 8–140 μg cobalt in 10 ml of acetonitrile solution. The molar absorptivity and sensitivity are 4.2×10³ l·mol^?1·cm^?1 and 0.01408 μg/cm², respectively. The other factors such as pH, amounts of reagents and naphthalene, shaking and standing times, and the effect of diverse ions are studied. The method has been applied to the determination of cobalt in iron steel alloys.     

FFC-1离子交换纤维对酸碱有害气体吸附性能的研究

系统考察了不同直径及反离子形式的FFC-1聚羧酸离子交换纤维对酸碱有害气体的穿透吸附,各种温、湿度条件下的吸水率,以及作为有害气体吸附滤除材料的重复使用与再生性能。研究表明:FFC-1纤维直径的减小有利于提高对有害气体的动态吸附容量。在体系温度、相对湿度分别为15℃、50%时,以3D腈纶为起始原料的钠型FFC-1离子交换纤维的吸水率≥350mg/g.纤维;对SO2的穿透吸附容量可达200mg/g.纤维。FFC-1离子交换纤维具有良好的重复使用与再生能力,经20次再生循环使用后,纤维交换容量未见明显变化。     

Structural and bonding characteristics in transition metal-silane complexes

Transition metal-silane complexes containing metal-eta 2-H-Si coordination display different structural and bonding characteristics in comparison to other sigma-complexes, such as dihydrogen and alkane (agostic) complexes. The different characteristics can be related to the strong sigma*-accepting properties of the eta 2-silane ligand(s) because of the weaker H-Si sigma bond. Various examples of metal-silane complexes have been reviewed and their structural stabilities have been systematically discussed. Silyl-hydride complexes having substantial silyl-hydrido interactions have also been emphasized.     

Electronic-to-vibrational energy transfer reactions.X* + CO (X = O,I and Br)

The vibrational distribution of CO produced from the following two electronic-to-vibrational energy transfer reactions:

have been determined by means of infrared resonance absorption measurements employing a cw CO laser. The CO molecules formed in both reactions were found to be vibrationally excited up to the limits of available electronic energies carried by the excited atoms. A similar result was also observed in the Br(4²P_{$\text{1}\text{2}$}) + CO reaction, in which absorption occurred only in the 1 → 2 band. For the O^* + CO reaction the efficiency of E → V energy transfer was determined to be 16%. Our present results were found to be inconsistent with the impulsive (half-collision) model.     

Fluorescent sensors for the enantioselective recognition of mandelic acid: signal amplification by dendritic branching

Novel chiral bisbinaphthyl compounds have been synthesized for the enantioselective fluorescent recognition of mandelic acid. By introducing dendritic branches to the chiral receptor unit, the fluorescence signals of the receptors are significantly amplified because of the light-harvesting effect of the dendritic structure. This has greatly increased the sensitivity of the sensors in the fluorescent recognition. Study of the three generation sensors demonstrates that the generation zero sensor is the best choice for the recognition of mandelic acid because of its greatly increased fluorescence signal over the core and its high enantioselectivity. This sensor is potentially useful for the high throughput screening of chiral catalysts for the asymmetric synthesis of alpha-hydroxycarboxylic acids.     

人工神经网络X射线荧光光谱法测定钢中酸溶铝

建立了一种人工神经网络-X射线荧光光谱法测定钢中酸溶铝的方法，用X射线荧光光谱法测定低合金钢中总铝值，应用所建立的ANN-BP网络模型，输入总铝含量直接预测出酸溶铝含量。同时使用改进的BP算法，避免了神经网络学习中可能产生的麻痹现象。该方法用于钢中酸溶铝的测定，结果满意。     

Kinetics of the reaction of C6H5 with HBr

The rate constant for the reaction of phenyl radical with hydrogen bromide has been measured with the cavity-ring-down method at six temperatures between 297 and 523 K. The Arrhenius expression for the H abstraction reaction can be effectively given by: . The values of these parameters are similar to those for the H + HBr reaction, but are in sharp contrast to those for alkyl radical reactions. The gross difference between the alkyl radical reactions and the phenyl and H-atom reactions could be rationalized in terms of the inductive effects of these radicals as measured by Taft's σ* (polar) constants. © 1993 John Wiley & Sons, Inc.     

Synthesis and electrospray ionization mass spectra of AZT/d4T boranophosphates

New anti-HIV prodrugs, conjugates of AZT and d4T with boranophosphates, were prepared by the H-phosphonate method. Their structures were determined by negative ion electrospray ionization mass spectrometry (ESI-MS) in conjunction with tandem mass spectrometry (MS/MS). The fragmentation pathways were investigated, and most of the fragment ions contained the boranophosphate or phosphinate group.