Electrochemical oxidation of aniline at boron-doped diamond electrodes

The electrochemical oxidation of aniline at boron-doped diamond (BDD) electrodes was investigated by cyclic voltammetry, steady-state polarization measurements and bulk electrolysis under potentiostatic control. It was found that acidic media is suitable for efficient electrochemical oxidation of aniline, because at low pH, the potential required for avoiding electrode fouling is lower than in neutral and alkaline media. The results of the longtime polarization measurements suggested that more anodic potentials ensure slightly higher efficiency for the conversion of aniline to CO₂, while the direct oxidation process does not play a prominent part in the overall electrochemical incineration of aniline. The current efficiencies (44%) and the efficiency of aniline conversion to CO₂ (80%) favourably compare with those reported for other electrochemical methods for aniline destruction. The results demonstrate the possibility of using BDD as an electrode material for electrochemical wastewater treatment, mainly when very high anodic potentials are required.     

微波/H_2O_2协同降解苯胺废水的研究

采用微波催化氧化处理模拟苯胺废水。实验结果表明,在微波、H2O2及微波-H2O23个条件下,苯胺降解都是先增大后趋于平衡。微波达到平衡时降解率为31.22%,H2O2条件下降解率为21.98%,微波-H2O2条件下降解率为46.36%,说明微波与H2O2两者之间有很好的协同作用。对反应机理进行了初步的分析。     

催化超临界水氧化苯胺

研究了在催化超临界水氧化体系中苯胺废水的处理(催化剂采用MnO2/CeO2),结果表明该催化剂有较高的催化活性,使苯胺彻底去除的温度、压力大大降低。实验得出了反应的最佳工艺条件为:温度380℃、压力26 MPa、停留时间5 s、氧气过量15倍,反应后的苯胺含量<1 mg/L、总有机碳(TOC)含量28.56 mg/L,二者均达到了国家的排放标准。     

Conjugated polyaniline as a result of the benzidine rearrangement

The mechanism of the oxidative polymerization of aniline is reviewed on the basis of the experimental evidence and reaction schemes proposed in the literature. It is demonstrated that the balance between the non‐protonated and protonated forms of the monomer and the growing chain is responsible for the diversity of the molecular structure, morphology and properties of aniline oxidation products. Various forms are oxidized by two oxidation mechanisms: (1) chain reaction of electrophilic substitution and (2) coupling of cation‐radical centres. At pH > 2.5, the non‐protonated reagents are oxidized with a chain reaction controlled by electrophilic substitution of the aromatic ring. The reaction leads to the formation of non‐conducting aniline oligomers with heterogeneous molecular structures. At pH = 2.5–4, the electrophilic substitution is reduced because of the protonation of the aniline, and the cyclic dimer, phenazine, becomes the main product of the oxidation. The growth of the conjugated chain proceeds at pH < 2.5, when the reactants are protonated. The reaction proceeds through coupling between the terminal cation radical and the monomer cation radical with formation of a π‐complex. The transformation of the π‐complex into a para‐substituted monomer unit is thermodynamically controlled and is produced through an intramolecular benzidine (semidine) rearrangement. The regular structure of the growing chains is a result of the high regioselectivity of the sigmatropic rearrangements and significant energy gain attained by the formation of protonated polyconjugated chains in the agglomerated state. © 2015 Society of Chemical Industry     

Selective catalytic oxidation of aniline to azoxybenzene over titanium silicate molecular sieves

The oxidation of aniline using aqueous H₂O₂ and titanium silicates, TS-1 and TS-2 as catalysts was carried out in a batch reactor in the temperature range 333–353 K. TS-1 catalyzes aniline selectively to azoxybenzene and is superior to TS-2. The influence of different solvents, concentration of H₂O₂ and the catalyst in the reaction mixture on the conversion and product distribution has been studied. Acetonitrile is a suitable solvent in this reaction, while acetone is not. For the TS-1 catalyzed oxidation reaction,t-butyl hydroperoxide is not a suitable oxidant. At optimum conditions, a H₂O₂ efficiency of about 100% for aniline conversion is obtained with a selectivity of 97% to azoxybenzene in the product.     

An NMR spectroscopic investigation of the oxidation reactions of DL-selenomethionine

Oxidation reactions of DL -selenomethionine (DL -SeMet) with hydrogen peroxide and ozone were investigated by ¹H and ¹³C NMR spectroscopy. Chemical shifts of the reaction products were measured at different pD values in D₂O solutions. In the moderate (4–8) pD range, a pair of singlets of equal intensity appeared at 2·71 and 2·80 ppm, with the disappearance of the DL -SeMet methyl peak at 2·04 ppm. As the pD of the solution decreased, the chemical shifts of both peaks increased relative to 3-trimethylsilylpropionic acid-d₄ sodium salt. In strongly acidic solutions (pD<3), the pair collapsed to one singlet at 3·18 ppm. As pD values increased the chemical shifts decreased in numerical value with only a singlet at 2·69 ppm observed in strongly basic solutions (pD>10). These data were assigned to Met selenoxide in basic solution, stabilized by intermolecular hydrogen bonding, and to the hydration of Met selenoxide to Met dihydroxyselenide in acidic solutions. In moderate pD solutions (pD = 4–8), both forms of the selenoxide can exist. For the reaction of DL -SeMet with CNBr, two parallel reactions occur, i.e. oxidation and bond cleavage with cyanization: the bond cleavage giving the expected products, i.e. 2-amino-4-butyrolactone and methyl selenocyanate, with an additional singlet observed at 2·54 ppm. © 1988 SCI     

Studies in mineralization of aqueous aniline using Fenton and wet oxidation (FENTWO) as a hybrid process

A hybrid process for mineralization of aqueous aniline using Fenton and wet oxidation (FENTWO) is studied. It is important to have maximum conversion of ‘N’ atoms from the waste to N₂. The conversion of input ‘N’ atoms in aniline to N₂ was 15% during wet oxidation without the Fenton process and was improved to 50% with the Fenton process. Therefore, a hybrid process of Fenton followed by wet oxidation was studied for mineralization of the aqueous aniline stream. The parameters for the Fenton process were optimized (pH, catalyst, H₂O₂ to catalyst (FeSO₄) ratio, quantity of H₂O₂). The waste obtained after the Fenton process was then treated by wet oxidation for mineralization by having homogeneous CuSO₄ as the catalyst by keeping FeSO₄ therein. This combined catalyst was found to be more effective for the degradation of the intermediates formed in the Fenton process. Wet oxidation (WO) was studied in the temperature range 473–513 K and the oxygen partial pressure range 0.345–1.38 MPa at pH 6.5. The kinetic data was modeled using a power law rate expression in terms of chemical oxygen demand (COD). The optimum temperature for formation of more N₂ gas was found to be 493 K. The treated waste stream was found to contain oxalic acid using HPLC, and NH₄⁺, NO₃^? and NO₂^? ions using ion chromatography analysis. Copyright © 2007 Society of Chemical Industry     

Electrocatalytic oxidation of readily available disaccharides in alkaline medium at gold electrode

The electrooxidation of some readily available disaccharides, i.e. trehalose, maltose, isomaltulose and cellobiose, was investigated in alkaline medium. The reaction products were identified and quantified using chromatographic and spectroscopic methods. Important conversion yields and high selectivities towards mono carboxylic acids of some of these disaccharides were obtained. The pH effect on the product distribution was also determined.     

Oxidative degradation of polyaniline during the chemical oxidative polymerization of aniline in aqueous methanol medium

The course of chemical oxidative polymerization of aniline using ammonium persulfate as the initiator in acidic (1 M HCl) aqueous methanol (30 to 70 vol%) was studied spectrophotometrically. It was found that at temperatures greater than about 10 °C the reaction leads to degradation of polyaniline, the effect being greater with increasing methanol concentration. This is quite unlike the situation in aqueous ethanol where the product is the usual emeraldine hydrochloride form of polyaniline. Copyright © 2005 Society of Chemical Industry     

Electrochemical copolymerization of aniline and aniline-2,5-disulfonic acid

Electrochemical copolymerization of aniline and aniline-2,5-disulfonic acid (ADSA) was carried out in HCl solutions. The presence of ADSA inhibited significantly the growth of polyaniline (PAn), although the voltammetry of the copolymer was still similar to that of conventional PAn. As the ADSA concentration increased, the deposition rate of the copolymer decreased rapidly and finally no solid film was deposited on the electrode surface. When the ADSA concentration was lower than ˜ 5 mM, the depression effect of ADSA on the growth rate of the copolymer is mainly due to its stronger adsorption at the electrode surface. For higher ADSA concentrations, the inhibiting effect of ADSA was dominated by its termination effects, which led to more soluble oligomers and in turn resulted in lower deposition efficiency. Electrolysis of ADSA solution might result in a water-soluble fully sulfonated PAn.     

Electrocatalytic oxidation of methanol on Cu modified polyaniline electrode in alkaline medium

Electrolytically deposited Cu on polyaniline film covered Pt substrate (Cu/PANI/Pt) is used as anode for the electrooxidation of methanol in alkaline medium. The electrochemical behavior and electrocatalytic activity of the electrode were characterized using cyclic voltammetry, impedance spectroscopy, chronomethods, rotating disc voltammetry and polarization studies. The morphology and composition of the modified film were obtained using SEM and EDAX techniques. The electrooxidation of methanol in NaOH is found to be more efficient on Cu/PANI/Pt than on bare Cu (Cu), electrodeposited Cu on Cu (Cu/Cu) and electrodeposited Cu on Pt (Cu/Pt) substrates. Partial chemical displacement of dispersed Cu on PANI with Pt or Pd further improved its performance towards methanol oxidation.     

苯胺废水预处理组合工艺试验

采用铁炭微电解法对苯胺废水进行预处理,微电解的作用使苯胺废水中的大部分苯胺降解,而且出水中含有足够的Fe2+,从而减少了催化氧化过程中双氧水的消耗量。结果表明:当进水苯胺、CODCr的质量浓度分别为204、448mg/L,色度为500倍时,在最佳工艺条件(微电解工艺的铁炭体积比1∶1、废水pH值为5,停留时间90min;催化氧化工艺条件为双氧水(30%)用量0.3mL/L,pH值调节至5,反应时间60min)下,该方法对苯胺的去除率为95.32%,对CODCr的去除率达到66.96%,色度的去除率为92%。     

苯胺氧化制对苯二酚中二氧化锰的回收利用

苯胺氧化法生产对苯二酚的二氧化锰废水经熟石灰除杂,用氨水调pH至碱性,用双氧水氧化,硫酸精制得到二氧化锰固体粉末。最佳回收条件为:双氧水用量为64%(占废液体积),反应液pH为10.0,反应温度为25℃,反应时间为1 h,二氧化锰的回收率可达到80%,采用回收的二氧化锰氧化苯胺可使对苯醌的收率从72.48%提高到83.90%。     

无机盐高铁酸钾去除微污染水中苯胺的研究

以苯胺为代表性污染物,借用全自动六联混凝试验搅拌机,实验研究了自制的高铁酸钾对微污染水中难降解有机物的去除功效、影响因素及其去除作用机制。结果表明,高铁酸钾对苯胺具有比较好的去除作用,但受高铁酸钾的投加量、反应时间、体系的pH、苯胺初始浓度等的影响,其最佳反应时间为30 min,pH=9.0~9.5。通过高铁酸钾作用过程中氧化与絮凝作用的定量研究发现,高铁酸钾去除苯胺主要是通过氧化作用实现的。     

N-烯丙基苯胺的合成研究

以溴丙烯和苯胺为原料合成了N-烯丙基苯胺,通过IR和~1HNMR对化合物的组成和结构进行了表征,探讨了优化反应条件,该路线具有操作简便、反应快、收率高的特点。     

Synthesis,characterization and SEESR spectroscopic investigations of indole/aniline copolymers

Indole/aniline copolymers were synthesized electrochemically and the polymerization mechanism was investigated via in‐situ simultaneous electrochemical electron spin resonance (SEESR) spectroscopy. The Radical cationic intermediates of substituted indole and aniline were detected during the electrochemical oxidation. The resulting ESR‐spectra with hyperfine splitting were simulated and radicalic structures were identified. It was suggested that the polymerization occurs over positions C‐3 and C‐6 of indole molecule and over the nitrogen and para‐position of aniline. Furthermore, aniline, indole and aniline/indole copolymers were investigated depending on applied potential via electrochemical impedance spectroscopy (EIS). © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Electrospray ionization MS of high M.W. TAG oligomers

Reported are the on-line LC/electrospray ionization MS of large, high M.W. oligomers formed from heated triolein, a TAG used as a model for dietary oils. Triolein, the major component of olive oil, canola oil, and other dietary oils, was heated at frying temperature, and the TAG oxidation products were separated using RP-HPLC coupled to an ion trap mass spectrometer via an electrospray ionization interface. Ammonium formate was added as a sheath liquid to promote ammonium adduct formation. Masses corresponding to ammonium adducts of intact carbon-linked dimers (m/z 1783–1787), trimers (m/z 2666–2672), and tetramers (m/z 3547–3557) of triolein, with and without additional sites of unsaturation, were observed. Also, dimers, trimers, and tetramers containing one, two, or three additional oxygens, also with and without additional sites of unsaturation, are reported. Based on the formation of some types of triolein dimers, we believe that tristearin might also form dimers, even though it has no readily oxidizable sites of unsaturation. Oxidized tristearin monomers, tristearin dimers, chainaddition products, and chain-shortened products are observed.     

Polyaniline co‐doped with camphor sulfonic and hydrochloric acids by chemical oxidation in aqueous solution

A co‐doped polyaniline was prepared from aniline camphorsulfonate (ANICSA) and aniline hydrochloride (ANIHCl), which was soluble in common organic solvents, such as m‐cresol. Without any additional doping, it possessed a higher conductivity (2 S/cm) than those prepared from ANICSA or ANIHCl alone (0.4 S/cm). In other words, a synergistic effect arose through the chemical oxidative polymerization of a mixture of ANICSA and ANIHCl. The mole ratio of (CSA + HCl)/aniline was 1; if additional HCl was introduced, the conductivity reached a value as high as 7.9 S/cm. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 80–85, 2001     

Destruction of aniline by mediated electrochemical oxidation with Ce(IV) and Co(III) as mediators

Mediated electrochemical oxidation has been employed to test the feasibility of treating soluble organic wastes. We report Ce(IV)- and Co(III)-mediated electrochemical oxidation of aniline at various electrodes in acidic media as an example of organic waste. Aniline was oxidized by an electrogenerated electron transfer mediator, Ce⁴⁺ or Co³⁺, in the anolyte and carbon dioxide was produced as a final oxidation product. Carbon dioxide was collected by bubbling through a barium hydroxide solution. When a powerful oxidizing agent, Ce(IV) or Co(III), was used as an electron shuttling mediator, parameters affecting the coulombic efficiency for aniline oxidation were the standard oxidation potentials of the mediators, their concentrations and the reaction temperature. Intermediate species produced during the oxidation of aniline were identified by cyclic voltammetric and absorption spectroscopic measurements.     

微波/Fenton试剂/钛掺杂笼型八聚倍半硅氧烷体系降解苯胺宏观反应动力学研究

本文建立了以颗粒钛掺杂笼型八聚倍半硅氧烷为催化剂的微波诱导氧化工艺处理苯胺废水模型,并深入开展了相关基础研究。基于钛掺杂笼型八聚倍半硅氧烷对有机污染物的吸附能力和对微波的强吸收能力,利用微波能量实现对有机物的分解和炭化。考察了微波辅助催化氧化剂处理苯胺废水过程中各种参数对处理效果的影响,建立了微波辅助催化氧化降解苯胺废水过程的宏观动力学模型。