The reactivity towards the benzoyloxy radical of 1,4-bis(2-methylstyryl)benzene

It has been found that 1,4-bis(2-methylstyryl)benzene (MSB) is 520 times as effective as methyl methacrylate in capturing the benzoyloxy radicals generated at 60°C by dissociation of benzoyl peroxide. This result has been obtained from examinations of the end groups in samples of poly(methyl methacrylate) prepared using benzoyl peroxide as initiator in the presence of MSB at low concentrations.     

Electrochemical oxidation of oxalate ion in the presence of fluoride ion, and radical analysis by ESR

The problem at hand is the electrochemical oxidation of oxalate ion, which is accelerated by fluoride ion at a platinum anode. The hypothesis that fluoride ion traps incipient hydroxyl radicals as hydroxyfluoride radical anions was not supported by ESR experiments in which hydroxyl radicals were generated in the presence of the spin trap α-(4-pyridyl-1-oxide) N-tert-butyl-nitrone with and without the addition of fluoride ion. The electrochemical oxidation of oxalate at constant current followed current controlled kinetics both at a platinum anode, as observed previously, and at a boron-doped diamond anode, but the rate of the latter reaction was indifferent to the presence of fluoride ion. We propose that the competition of fluoride and hydroxide ions for the Pt/PtO_n surface inhibits the dimerization reactions that lead to oxygen evolution; the displacement of oxygen evolution to more positive potentials overcomes the overpotential for the oxidation of oxalate at this anode. Fluoride ion has no influence on the oxidation of oxalate at BDD because oxygen evolution inherently occurs at more positive potentials at this anode.     

Cationic catalysis and hidden negative differential resistance in reduction of radical anion of nitrobenzene

Well-known reduction of nitrobenzene in acetonitrile yields an anion radical, which is further reduced at more negative potentials. The reduction of anion radical is strongly influenced by the nature of tetraalkylammonium salts (tetramethyl- to tetraheptylammonium) used as supporting electrolytes. At low concentration of tetrahexylammonium hexafluorophosphate the anion radical reduction occurs at extremely negative potential, however, traces of alkali metal cations yield a remarkable acceleration effect. At potentials where alkali metal cations are reduced the acceleration ceases. As a result the current-potential curves show negative or hidden negative slope. Electrochemical impedance spectroscopy sensitively indicates the presence of the negative differential resistance (NDR) or the hidden negative differential resistance (HNDR). Oscillatory behavior based on this type of cationic catalysis is currently under investigation.     

Preparation of modified polybutene‐1 by oxidation and limonene radical grafting using an Nd2O3‐assisted radical initiator system and its characterization

Free radical graft polymerization has been used as a modification method to incorporate functional groups into polyolefins using a melt‐mixing process. In this work, modification of polybutene‐1 (PB) was performed by limonene radical graft polymerization using the Nd₂O₃/dicumyl peroxide (DCP) radical initiator system with various mixing ratios in air. The effects of the modification on the crystallization and tensile behavior were studied in detail. The modified PB samples had ketone and limonene groups. The contents of both the ketone and the limonene groups were highest in the modified PB prepared using Nd₂O₃/DCP (2/0.2 wt%/PB), and a conjugated diene group was found to be produced by a side‐reaction. Excess Nd₂O₃ lowered the limonene graft content in the modified PB. The rate of crystal phase transition (II → I) decreased with an increase of limonene content. The presence of a small amount of the ketone group increased the rate, and the modified PB having a small ketone content exhibited more ductility due to its higher crystal phase transition rate. It was found that there was an optimum mixing ratio of the Nd₂O₃/DCP initiator system for the modification. The ketone and the limonene groups affected the rate of the crystal phase transition and the tensile properties of the modified PB. Copyright © 2010 Society of Chemical Industry     

烃类选择氧化过程中自由基的调控策略与工业氧化应用研究进展

催化烃类氧化是提供合成树脂、合成纤维和合成橡胶等大宗化学品以及各类精细化学品的基本工艺,在化学工业中具有重要的地位。目前工业上的烃类氧化工艺普遍需要高温高压条件,苛刻条件可以使氧气活化及碳氢键断裂产生自由基。本文从均相催化、非均相催化、仿生催化等方面对近年来催化氧化反应的研究进展进行了回顾,梳理了催化氧化中的自由基机理。总结了仿生催化体系中自由基稳定性和定向性调控机制等方面的研究现状,提出了高效催化剂的设计、自由基的传递及调控机制等方面将是催化氧化领域的重要研究方向。     

An efficient and non-precious anode electrocatalyst of NiO-modified carbon nanofibers towards electrochemical urea oxidation in alkaline media

Non-precious NiO nanoparticles were combined with carbon fibers (CFs) to design the novel electrode material; NiO-CFs. The as-synthesized NiO-CFs material was investigated in terms of Field emission scanning electron microscope (FE-SEM), Fourier-transform infrared spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET) surface area, Energy-dispersive X-ray spectroscopy (EDX), UV–vis spectra, Transmission electron microscope (TEM), selected area diffraction (SAED) pattern and X-ray diffraction (XRD) techniques. These analyses indicate the successful synthesis of a nanocomposite of NiO-CFs. Cyclic voltammetry (CV) in addition to chronoamperometric (CA) and electrochemical impedance spectroscopy (EIS) methods were studied in the 3-electrodes system to examine the electrochemical performance of NiO-CFs material for urea oxidation in KOH medium. The synthesized nanocomposite showed improved electrochemical oxidation of urea at various urea concentrations up to 1.5 M. The decreasing of both charge transfer impedance and series resistance indicates the enhanced transfer of electrons in the occurrence of urea which could be related to the high electrochemical performance of NiO-CFs material as an electrocatalyst. The superior electrochemical activity can be due to the assembly of C-structure with NiO nanoparticles during the synthesis steps which enhance electrocatalysis, charge transfer, and structural defects.     

二环己基-苯基膦在燃油体系中的氧化反应的研究

膦化物能显著地改善飞机燃油的高温稳定性能,为新一代高性能飞机燃油潜在的抗氧剂。实验结果表明,膦化物在燃油介质中的氧化反应有两种反应类型同时进行:自由基链反应及膦化物与氧气的直接作用,起始反应速率为拟一级反应速率。因此,膦化物作为新型抗氧剂需与自由基抑制剂相配合使用。     

Chemiluminescence of indole and its derivatives induced by electrogenerated superoxide ion in acetonitrile solutions

Electrochemical behavior of the dioxygen (O₂)/superoxide ion (O₂ ⁻) redox couple in acetonitrile (AN) solutions containing indole compounds and no proton acceptor, and their chemiluminescence have been examined using spectroelectrochemical techniques. In AN solutions, in the presence of indole compounds having a substituent at the N-position (e.g. 1-methylindole and 1,2-dimethylindole), these indole compounds did not work as a proton donor to electrogenerated O₂ ⁻, and did not affect the redox reaction of the O₂/O₂ ⁻ couple. On the other hand, the indole compounds bearing a hydrogen at the N-position (e.g. indole, 3-methylindole (3-MI), tryptamine (TP), 3-indolemethanol and 3-indoleacetic acid) acted as a proton donor to O₂ ⁻. In addition, chemiluminescence was observed for some of the indole compounds having a hydrogen at the N-position and an electron-releasing group at the 3-position (i.e. TP, 2,3-dimethylindole, 2-(3-indole)-ethanol and 3-MI). The intensity of chemiluminescence of 3-MI was by far the strongest among those of the above four compounds. The chemiluminescent reaction of the indole compounds seemed to have close connection with electrogeneration of O₂ ⁻, which functioned as a proton acceptor to the indole compounds, and the chemical stability of a radical species (i.e. a one-electron oxidized form of conjugate base of indole compounds) due to the substituent which is present at the 3-position. The chemiluminescence was considered to occur via the formation of 1,2-dioxetane-like intermediates. The reaction mechanisms of chemiluminescence based on the electrogenerated O₂ ⁻ were briefly discussed.     

Effects of porosity on the electrochemical oxidation performance of Ti4O7 electrode materials

Ti₄O₇ is a kind of conductive ceramic material with a high electrical conductivity and excellent electrochemical performance, rendering it a potential candidate for electrode applications. Here, for the first time, we report the successful preparation of Ti₄O₇ electrodes with different porosities by adding a pore-forming agent. The results showed that the as-prepared Ti₄O₇ electrodes contained both mesoporous and macroporous structures. In addition, with an increase in the porosity of the electrodes, the electrochemical oxidation degradation of high-concentration methyl orange (MO) solution first increased, until reaching a critical point, and then decreased. The Ti₄O₇ electrode with a porosity of 34.9% and an electrical conductivity of 336.1 S cm^-1 exhibited the highest electrochemical oxidation ability. The electrochemical oxidation rate constants for MO and chemical oxygen demand (COD) of the porous Ti₄O₇ electrode were 1.7 times those of the dense Ti₄O₇ electrode. Compared to commercial stainless steel, graphite, and Ti/RuO₂ electrodes, the Ti₄O₇ porous electrode showed superior electrochemical oxidation performance under the same experimental conditions. The result of this study provide new directions for the application of Ti₄O₇ electrode materials.     

Study of the kinetics and the influence of Biirr on formic acid oxidation at Pt2Ru3/C

Electrochemical oxidation of HCOOH in H₂SO₄ and HClO₄ solutions was examined on thin film Pt₂Ru₃/C electrode. XRD pattern revealed that Pt₂Ru₃ alloy consisted of the solid solution of Ru in Pt and the small amount of Ru or solid solution of Pt in Ru. According to STM images, Pt₂Ru₃ particles size was between 2 and 6 nm. It was established that electrochemical oxidation of HCOOH commenced at −0.1 V versus SCE at Pt sites in the catalyst. Kinetic parameters indicated that dehydrogenation path was predominant. Dehydration occurs in parallel, but without significant poisoning by CO_ad owing to oxidative removal by OH species on Ru atoms. The coverage of Pt₂Ru₃ surface by CO preadsorbed from the solution was found to be 24% lower when the surface was modified by irreversibly adsorbed Bi. Modification by Bi also shifted the onset potential for HCOOH oxidation for about 50 mV towards more negative values and consequently, increased the reaction rate for a factor of two. It was proposed that Ru acts through bifunctional mechanism, i.e. OH species adsorbed on Ru oxidizes CO_ad from Pt sites, while Bi hinders the adsorption of CO on Pt sites via electronic and/or ensemble effects.     

Voltammetric oxidation of Hantzsch 1,4-dihydropyridines in protic and aprotic media: relevance of the substitution on N position

A detailed investigation on the electrochemical oxidation of some Hantzsch 1,4-dihydropyridine derivatives with the aim of study the influence of the hydrogen substituent on the N1 position of the heterocyclic ring have been carried out in protic and aprotic media. For this objective we have synthesized two series of compounds wherein the difference was the substituent (H or ethyl) on the N1-position of the heterocyclic ring. Voltammetry, UV-Vis spectroscopy, Controlled potential electrolysis, EPR, ¹H NMR and gas chromatography-mass spectrometry techniques in order to obtain evidences for postulate oxidation mechanisms in both protic and aprotic media have been used. Compounds having the ethyl substituent in the N1 position follow an oxidation mechanism obeying the sequence ECE with the second step as the r.d.e. in both, protic and aprotic media, thus producing the corresponding ethyl substituted pyridinium cation. On the other hand compounds having H in the N1 position follow the same ECE sequence only at acidic media. At basic media, the mechanism consisted of a DISP1 scheme in which rate determining step (r.d.s.) is the uptake of the proton in the N1 position by the OH⁻ ion of the media. In aprotic media both type of compounds follow the same ECEC mechanism with the second step as the r.d.s. but only the H-substituted compounds generates an anionic species that is more easily oxidized than the parent compounds.     

Voltammetric oxidation of Hantzsch 1,4-dihydropyridines in protic media: substituent effect on positions 3,4,5 of the heterocyclic ring

A detailed study was done of the electrochemical oxidation of some 1,4-dihydropyridine (1,4-DHP) derivatives in order to determine the influence of the substituents in the heterocyclic ring. Two types of derivatives were synthesized, namely, 3,5-(substituted)-4-(5′-nitro-2′-furyl)-1,4-DHP for series A, and 3,5-dicarboethoxy-4-(substituted or non-substituted)-1,4-DHP for series B. Voltammetry, coulometry, controlled potential electrolysis, UV-vis spectroscopy and GC-MS techniques were employed to collect data that permitted to postulate oxidation mechanisms in a protic medium. In acid media, at pH < 4, all derivatives follow oxidation mechanisms obeying the ECE sequence. However, at pH > 4, series A derivatives follow an ECEC sequence, while series B derivatives obey a DISP1 mechanism. In both cases, the uptake of proton at N-1 by the OH⁻ ion of the media was the rate-determining step.     

氢氧化锆及其焙烧产物对磷酸根的吸附特性研究

以氢氧化锆作为吸附水溶液中磷酸根的吸附剂,考察了氢氧化锆在不同焙烧温度下的分子式及其对磷酸根吸附效果的影响。通过正交试验确定了最佳实验条件,此条件下氢氧化锆的吸附量为210.9 mg/g。经100、200、300、400、500、600 ℃焙烧后的氢氧化锆对磷酸根的吸附量随温度升高逐渐减小;氢氧化锆经700 ℃焙烧后,焙烧产物氧化锆不具有吸附性。TG、XRD分析表明,随着焙烧温度的升高,氢氧化锆的表面活性基团（-OH）数量逐渐减少。结果表明,吸附剂表面羟基的数量直接影响吸附剂的吸附性。     

枞酸氧化反应及其抗氧剂的研究

采用紫外分光光度分析方法研究了枞酸在聚乙烯膜上的氧化反应,考察了MBP,FMH,DBH,DSB3,DSB65种抗氧剂对枞酸氧化反应的影响,提出了用抗氧化值AO考核抗氧剂的抗氧化能力。实验结果表明,枞酸氧化反应动力学在初期阶段呈表观一级,后期受氧化膜影响不呈表观一级。当反应温度为35,40,45,50,55℃时,5种抗氧剂都表现出不同程度的抗氧化能力,其中MBP,DBH,DSB6抗氧剂的抗氧化能力显著,在35℃下其抗氧化值AO分别是109.92,50.93,209.84。     

TEMPO-NaOCl-NaBr体系选择性氧化壳聚糖及其产物的结构表征

壳聚糖的功能化改性及其生物医学等领域的应用是近年来备受人们关注的重要研究方向.文章研究了TEMPO-NaOCl-NaBr体系对不同形态壳聚糖的氧化过程及其产物的结构表征.发现NaOcl、NaOCl-NaBr、TEMPO-NaOCl和TEMPO-NaOCl-NaBr体系的氧化反应速率递增,溶胀态壳聚糖和壳聚糖纤维由于有着...     

In situ ESR spectroscopic evidence of the spin-trapped superoxide radical, O2, electrochemically generated in DMSO at room temperature

Superoxide radical (O₂⁻) was both electrochemically generated and detected at room temperature. In situ ESR spectroelectrochemistry with spin trapping was used for the radical detection. That is, the O₂⁻ radical was obtained in a DMSO solution under cyclic voltammetry conditions as soon as the potential of the dioxygen electroreduction was reached. This radical reacted then with a 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) spin-trap reagent present in solution to form the DMPO-OOH adduct. The hyperfine coupling constants determined for the adduct were a_N = 1.285 mT, and in accord to those reported in literature.     

厌氧氨氧化反应器的启动及其脱氮性能研究

采用添加多层多孔板的升流式厌氧污泥床接种混合污泥,于78 d内成功启动厌氧氨氧化反应器。第75天,反应器对NH4+-N和NO2--N的去除率达95%以上,容积氮去除负荷达0.525 kg/(m3·d)。启动后,快速提高进水基质浓度,反应器出现抑制现象,且抑制前后三氮之比具有显著变化。运行后期,底部出现红棕色污泥。与普通的升流式厌氧污泥床相比,其具有喷动床效应及水利筛分作用,有利于颗粒污泥的形成。     

Changes in the main components and quality indices of virgin olive oil during oxidation

This work reports on changes in the major and minor components of virgin olive oil during oxidation, details modifications found in the standardized quality indices, and analyzes the most significant relationships between the components of the oil and its oxidative stability. During the induction period or slow phase of oxidation, polyphenols, tocopherols, and pigments undergo the most important alterations. Other compounds, such as FA or volatiles, suffer significant modifications only during the rapid or exponential phase of oxidation when the natural antioxidant systems fall to minimal values. Among the quality indices, PV and the specific extinction coefficients K ₂₃₂ and K ₂₇₀ increase markedly from the earliest stages of oxidation, whereas titratable acidity does not change appreciably during the induction period. The evolution of the different compounds and parameters analyzed suggests that the tocopherol and orthodiphenol contents are the best indices to determine the average life of the oils.     

木素稀硝酸氧化及其与磷酸钙作用的研究

研究了造纸黑液木素稀硝酸氧化法制备活性氧化木素的适宜条件。结果表明,当磷酸含量为4.0%,木素与稀硝酸的质量配比为1∶10,可得到腐殖酸含量达46%的氧化木素。研究了氧化木素和氨化氧化木素对3种磷酸钙的溶解性的影响,讨论并合理地解释了反应机理。