Electrochemical oxidation of hydroquinone, resorcinol, and catechol on boron-doped diamond anodes

The electrochemical oxidation of aqueous wastes polluted with hydroquinone, resorcinol, or catechol on boron-doped diamond electrodes has been studied. The complete mineralization of the organic waste has been obtained independently of the nature of each isomer. No aromatic intermediates were found during the treatment, and solely aliphatic intermediates (carboxylic acids C4 and C2, mainly) were detected in the three cases. Although as from the bulk electrolyses study no differences in the electrochemical oxidation of dihydroxybenzenes seem to exist, different voltammetric behavior between resorcinol and the other two isomers was obtained in the voltammetric study. Catechol and hydroquinone have a reversible quinonic form, and a cathodic reduction peak appears in their voltammograms. The characterization of the first steps in the electrochemical oxidation of the three dihydroxybenzenes showed the formation of a larger number of intermediates in the oxidation of catechol, although no carbon dioxide was detected in its oxidation. Conversely, the oxidation of resorcinol and hydroquinone lead to the formation of important concentrations of carbon dioxide. The nondetection of aromatic intermediates, even if small quantities of charge are passed, confirms that the oxidation must be carried out directly on the electrode surface or by hydroxyl radicals generated by decomposition of water.     

Formation of PCDD/Fs from the copper oxide-mediated pyrolysis and oxidation of 1,2-dichlorobenzene

Formation of polychorinated dibenzo-p-dioxins (PCDDs) has been demonstrated to occur via surface-mediated reactions of chlorinated phenols. However, polychlorinated dibenzofurans (PCDFs) are observed in much lower yields in laboratory studies than in full-scale combustors where PCDFs are in higher concentrations than PCDDs. This has led to the suggestion that at least PCDFs are formed from elemental carbon in the de novo process. However, the potential for PCDF formation from reactions of chlorinated benzenes has been largely overlooked. In this study, we investigated the potential contribution of chlorinated benzenes to formation of PCDD/Fs using 1,2-dichlorobenzene as a surrogate for reactions of other chlorinated benzenes and CuO/silica (3 wt % Cu) as a surrogate for fly ash. Results were similar for oxidative and pyrolytic conditions with a slight increase in more chlorinated products under oxidative conditions. Reaction products included chlorobenzene, polychlorinated benzenes, phenol, 2-monochlorophenol (2-MCP), dichlorophenols, and trichlorophenols with yields ranging from 0.01 to 2% for the phenols and from 0.01 to 10% for chlorinated benzenes. 4,6-Dichlorodibenzo furan (4,6-DCDF) and dibenzofuran (DF) were observed in maximum yields of 0.2% and 0.5%, respectively, under pyrolytic conditions and 0.1% and 0.3%, respectively, under oxidative conditions. In previous studies of the pyrolysis of 2-MCP under identical conditions, 4,6-DCDF and dibenzo-p-dioxin (DD) were observed with maximum yields of ～0.2% and ～0.1%, respectively, along with trace quantities of 1-monochlorodibenzo-p-dioxin (1-MCDD). Under oxidative conditions, 1-MCDD, DD, and 4,6-DCDF were observed with maximum yields of 0.3%, 0.07% and 0.1%, respectively. When combined with the fact that measured concentrations of chlorinated benzenes are 10-100× that of chlorinated phenols in full-scale combustion systems, the data suggest surface-mediated reactions of chlorinated benzenes can be a significant source of PCDD/F emissions.     

Formation of bromochlorodibenzo-p-dioxins and furans from the high-temperature pyrolysis of a 2-chlorophenol/2-bromophenol mixture

The homogeneous, gas-phase pyrolytic thermal degradation of a 50:50 mixture of 2-bromophenol and 2-chlorophenol was studied in a 1 cm i.d., fused silica flow reactor at a total concentration of 88 ppm, reaction time of 2.0 s, and temperatures from 300 to 1000 degrees C. Observed products included (in decreasing yield) naphthalene, dibenzo-p-dioxin (DD), phenol, dibenzofuran (DF), bromobenzene, chloronaphthalene, 4-bromo-6-chlorodibenzofuran (4-B,6-CDF), bromonaphthalene, benzene, 4,6-dichlorodibenzofuran (4,6-DCDF), chlorobenzene, 4-monobromodibenzofuran (4-MBDF), 4-monochlorodibenzofuran (4-MCDF), 1-mono-bromodibenzo-p-dioxin (1-MBDD), 2-chloro,4-bromophenol, 2,4-dibromophenol, and 2-bromo-4-chlorophenol. Unlike the case for the pyrolysis of pure 2-chlorophenol, 4,6-DCDF was observed, but the analogous 4,6-DBDF remained undetected similar to the individual results with 2-MBP. This indicates that the presence of bromine increases the concentration of chlorine atoms available for the formation of 4,6-DCDF. Due to bromine atoms acting as better leaving groups than chlorine atoms, the yield of DD was increased over that observed for the pyrolysis of 2-chlorophenol. The addition of bromine to a chlorinated hydrocarbon system results in an increase in the total yield of PCDD/Fs as well as PBDD/Fs and mixed PBCDD/Fs due to the ease of bromine elimination reactions as well as an increase of the chlorine atom concentration.     

Formation of dehydrodiisoeugenol and dehydrodieugenol from the reaction of isoeugenol and eugenol with DPPH radical and their role in the radical scavenging activity

The aim of this work was to investigate the products of the reactions between isoeugenol and eugenol with the stable 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical and their role in the radical scavenging mechanism. The reaction of isoeugenol and eugenol with the DPPH radical produced, as evidenced by GC–MS and HPLC–MS, a complex mixture of dimeric species in which dehydrodiisoeugenol and its adducts with methanol (reaction solvent) and dehydrodieugenol were the main reaction products, respectively. The antioxidant activity of dehydrodiisoeugenol, determined by the DPPH method, resulted lower than that of isoeugenol considering both the parameters Effective Concentration (EC₅₀) and Antiradical Efficiency (AE). In particular, due to its very slow kinetic behaviour (), the possible contribution of dehydrodiisoeugenol to the DPPH radical scavenging activity of isoeugenol () was practically negligible. On the contrary, dehydrodieugenol had an antioxidant activity higher than that of eugenol and its lower T_EC50 (85 min with respect to 126 min) made it possible to contribute to the DPPH radical scavenging activity of eugenol.     

Rate constants for the gas-phase reactions of a series of alkylnaphthalenes with the nitrate radical

Naphthalene and its methyl-, ethyl-, and dimethyl-derivatives are semivolatile polycyclic aromatic hydrocarbons expected to be in the gas phase in ambient atmospheres and are subject to nighttime degradation by gas-phase reactions with the nitrate (NO3) radical. Using a relative rate method, rate constants for the gas-phase reactions of NO3 radicals with a series of alkylnaphthalenes have been measured at 298 +/- 2 K and atmospheric pressure of air. The compounds studied were 1- and 2-methylnaphthalene (1- and 2-MN), 1- and 2-ethylnaphthalene (1- and 2-EN), and the 10 dimethylnaphthalene isomers (1,2-, 1,3-, 1,4-,1,5-, 1,6-, 1,7-, 1,8-, 2,3-, 2,6-, and 2,7-DMN). Sampling in Riverside, CA showed that these alkylnaphthalenes were readily detected in ambient air, with the exception of 1,8-DMN. The reactions of naphthalene and the alkylnaphthalenes with NO3 radicals proceed by initial addition of the radical to form an aromatic-NO3 adduct (with rate constant k(a)) which either decomposes back to reactants (with rate constant kb) or reacts with NO2 to form products (with rate constant k(c). Using naphthalene as the reference compound, the values of (k(a)k(c)/k(b)) obtained for the NO3 radical reactions (in units of 10(-28) cm(6) molecule(-2) S(-1), indicated errors are two least-squares standard deviations) were as follows: 1-MN, 7.15 +/- 0.37; 2-MN, 10.2 +/- 1.0; 1-EN, 9.82 +/- 0.69; 2-EN, 7.99 +/- 0.99; 1,2-DMN, 64.0 +/- 2.3; 1,3-DMN, 21.3 +/- 1.2; 1,4-DMN, 13.0 +/- 0.5; 1,5-DMN, 14.1 +/- 1.3; 1,6-DMN, 16.5 +/- 1.8; 1,7-DMN, 13.5 +/- 0.7; 1,8-DMN, 212 +/- 59; 2,3-DMN, 15.2 +/- 0.5; 2,6-DMN, 21.2 +/- 1.6; 2,7-DMN, 21.0 +/- 1.5.     

Rate constants for the gas-phase reactions of a series of alkylnaphthalenes with the OH radical

Naphthalene and its C1- and C2-alkyl derivatives are semivolatile polycyclic aromatic hydrocarbons expected to be in the gas phase in ambient atmospheres and subject to degradation by gas-phase reactions with the hydroxyl (OH) radical. Using a relative rate method, rate constants for the gas-phase reactions of OH radicals with a series of alkylnaphthalenes have been measured at 298 +/- 2 K and at atmospheric pressure of air. The compounds studied include naphthalene, 1- and 2-methylnaphthalene (1-, 2-MN), 1- and 2-ethylnaphthalene (1-, 2-EN), and the 10 dimethylnaphthalene isomers (1,2-; 1,3-; 1,4-; 1,5-; 1,6-; 1,7-; 1,8-; 2,3-; 2,6-; and 2,7-DMN). Using 1,2,3-and 1,3,5-trimethylbenzene as reference compounds, the rate constant obtained for the OH radical reaction of naphthalene was (2.39 +/- 0.09) x 10(-11) cm3 molecule(-1) s(-1). Relative to naphthalene, the rate constants measured for the alkylnaphthalenes were (in units of 10(-11) cm3 molecule(-1) s(-1), where the errors given are two standard deviations and include the above uncertainty in the naphthalene rate constant) 1-MN, 4.09 +/- 0.20; 2-MN, 4.86 +/- 0.25; 1-EN, 3.64 +/- 0.41; 2-EN, 4.02 +/- 0.55; 1,2-DMN, 5.96 +/- 0.55; 1,3-DMN, 7.49 +/- 0.39; 1,4-DMN, 5.79 +/- 0.36; 1,5-DMN, 6.01 +/- 0.35; 1,6-DMN, 6.34 +/- 0.36; 1,7-DMN, 6.79 +/- 0.45; 1,8-DMN, 6.27 +/- 0.43; 2,3-DMN, 6.15 +/- 0.47; 2,6-DMN, 6.65 +/- 0.35; 2,7-DMN, 6.87 +/- 0.43. These data show that, under atmospheric conditions, the DMN isomers react most rapidly with the OH radical with calculated lifetimes of 1.9-2.4 h, followed by the MNs and ENs with lifetimes of 2.9-3.8 h and naphthalene with a lifetime of 5.8 h. These differences in reactivity were confirmed by the nighttime/daytime concentration ratios of the alkylnaphthalenes measured in ambient Riverside, CA, samples.     

Formation of methane sulfinic acid in the gas-phase OH-radical initiated oxidation of dimethyl sulfoxide

Dimethyl sulfoxide (CH3S(O)CH3: DMSO) is an important product of dimethyl sulfide (CH3SCH3: DMS) photooxidation. The mechanism of the OH-radical initiated oxidation of DMSO is still highly uncertain and a major aim of recent studies has been to establish if methane sulfinic acid (CH3S(O)OH: MSIA) is a major reaction product In the present work the products of the OH-radical gas-phase oxidation of dimethyl sulfoxide have been investigated in the absence and presence of NOx All experiments were performed in a 1,080 L reaction chamber in 1,000 mbar synthetic air at 284 +/- 2 K using long-path FT-IR spectroscopy and ion chromatography to monitor and quantify reactants and reaction products. Formation of methane sulfinic acid in high yield (80-99%) was observed in both in the absence and presence of NOx, and the results support that it is the major primary reaction product Other products observed included dimethyl sulfone (CH3S(O)2CH3: DMSO2), sulfur dioxide (SO2), methane sulfonic acid (CH3S(O)2OH: MSA), and methane sulfonyl peroxynitrate (CH3S(O)2OONO2: MSPN). The formation behavior of these products is in line with their source being mainly secondary production via oxidation of a primary product, i.e. MSIA.     

新型抗氧化剂芝麻酚的合成研究

以邻苯二酚、二氯甲烷为起始原料,于碱性130℃条件下环化得到胡椒环,然后与乙酰氯于冰浴条件下经Friedel-Crafts酰基化得到3,4-亚甲二样基苯乙酮,最后经过Bayer-Villiger氧化、水解酸化得到目标产物芝麻酚,总产率达36.6%。对各个步骤中催化剂的种类对产率的影响进行了对比,并得出优化条件;对各步骤的主产物进行了提纯及结构的分析鉴定。      

Constitutive synthesis, purification, and characterization of catechol 1,2-dioxygenase from the aniline-assimilating bacterium Rhodococcus sp. AN-22

A catechol 1,2-dioxygenase (CD) was found, which was synthesized constitutively in the aniline-assimilating bacterium Rhodococcus sp. AN-22 grown on a medium without aniline, as well as on aniline medium. The bacterium synthesized CD in its cells grown on all the 21 non-aromatic substrates examined, including four natural media such as meat and yeast extracts, one sugar, six organic acids, and 10 amino acids as carbon, energy, and nitrogen sources. When the bacterium was incubated on a medium with D-glucose, L-malate, isoleucine, leucine, etc., it synthesized more CD than that in cells grown on aniline. Two CDs, which were prepared from cells grown on aniline and L-malate, were purified separately to homogeneity and characterized. The two enzymes were apparently identical in molecular and catalytic properties including molecular mass, optimal pH, stability to heating, and substrate specificity for catechol analogues. However, they differed in the substrate specificity and resistance to sulfhydryl and chelating agents from the inducible CDs produced by other aniline-assimilating bacteria reported previously.     

特丁基对苯二酚(TBHQ)应用与检测

本文综述特丁基对苯二酚(TBHQ)应用与检测。TBHQ对大豆油、鱼油等食用油具有良好抗氧化作用,在油中其抗氧化能力优于叔丁基对羟基茴香醚、2,6-二叔丁基对甲苯和没食子酸丙酯。柠檬酸对TBHQ抗氧化作用具有一定增效作用。在高温环境中(如160℃),TBHQ抗氧化效果不好,要使用微胶囊抗氧剂才能获得较好效果。可采用气相色谱配氢火焰离子化检测器和液相色谱配紫外检测器定量分析TBHQ。     

Quantitative determination of arbutin and hydroquinone in leaves of Arctostaphylos, Vaccinium vitis-idaea, and the plant preparations

The optimal conditions of arbutin and hydroquinone extraction from plant raze, materials and biologically active supplements based on Vaccinium vitis-idaea and Arctostaphylos uva-ursi leaves were developed. 25% ethanol was used for extraction in quantitation. Based on isocratic fluorometric HPLC chromatographic method of arbutin and hydroquinone detection in Vaccinium vitis-idaea and Arctostaphylos uvaursi leaves was developed. Fluorometric detector increases selectivity and sensitivity of the method. Detection limit averaged 0,1 mg/kg.     

Speciation of gas-phase and fine particle emissions from burning of foliar fuels

Fine particle matter with aerodynamic diameter <2.5 microm (PM2.5) and gas-phase emissions from open burning of six fine (foliar) fuels common to fire-prone U.S. ecosystems are investigated. PM2.5 distribution is unimodal within the 10-450 nm range, indicative of an accumulation mode. Smoldering relative to flaming combustion shows smaller particle number density per unit time and median size. Over 100 individual organic compounds in the primarily carbonaceous (>70% by mass) PM2.5 are chemically speciated by gas chromatography/mass spectrometry. Expressed as a percent of PM2.5 mass, emission ranges by organic compound class are as follows: n-alkane (0.1-2%), polycyclic aromatic hydrocarbon (PAH) (0.02-0.2%), n-alkanoic acid (1-3%), n-alkanedioic acid (0.06-0.3%), n-alkenoic acid (0.3-3%), resin acid (0.5-6%), triterpenoid (0.2-0.5%), methoxyphenol (0.5-3%), and phytosterol (0.2-0.6%). A molecular tracer of biomass combustion, the sugar levoglucosan is abundant and constitutes a remarkably narrow PM2.5 mass range (2.8-3.6%). Organic chemical signatures in PM2.5 from open combustion of fine fuels differ with those of residential wood combustion and other related sources, making them functional for source-receptor modeling of PM. Inorganic matter [PM2.5 - (organic compounds + elemental carbon)] on average is estimated to make up 8% of the PM2.5. Wavelength dispersive X-ray fluorescence spectroscopy and ion chromatography identify 3% of PM2.5 as elements and water-soluble ions, respectively. Compared with residential wood burning, the PM2.5 of fine fuel combustion is nitrate enriched but shows lower potassium levels. Gas-phase C2-C13 hydrocarbon and C2-C9 carbonyl emissions are speciated by respective EPA Methods T0-15 and T0-11A. They comprise mainly low molecular weight C2-C3 compounds and hazardous air pollutants (48 wt % of total quantified volatile organic carbon).     

油脂热解生成丙烯醛的途径及规律研究

考察了油脂降解产物——甘油和脂肪酸受热降解生成丙烯醛的情况及其生成丙烯醛的途径。结果表明:在175℃加热条件下,甘油每小时生成丙烯醛平均量为106.95μg/kg,棕榈酸为551.33μg/kg,硬脂酸为263.23μg/kg,油酸为34 795.96μg/kg,亚油酸为24 395.15μg/kg;油脂热解生成的丙烯醛主要来自于脂肪酸的分解而非甘油,且不饱和脂肪酸生成丙烯醛的量远远高于饱和脂肪酸的;甘油主要通过脱水生成丙烯醛,饱和脂肪酸主要由于碳链在高温下断裂生成丙烯醛,而不饱和脂肪酸生成丙烯醛则是通过氧化,继而发生夺氢反应生成烯丙自由基,进一步断裂得到丙烯醛。     

Simultaneous analysis and exposure assessment of migrated bisphenol analogues,phenol, and p-tert-butylphenol from food contact materials

ABSTRACT

A simple, rapid, and novel liquid chromatography tandem-mass spectrometry (LC-MS/MS) method was developed and validated to determine levels of eight bisphenol analogues (A, S, F, B, P, AF, AP, and Z), phenol, and p-tert-butylphenol migrated from food contact material (FCM) into food simulants. Method validation showed acceptable values in terms of linearity, precision, and accuracy. The limits of detection and quantification were 0.53–29.6 and 1.77–29.6 μg L^?1, respectively. Water, 4% acetic acid, 50% ethanol, and n-heptane were employed as food simulants for the migration tests, and the proposed method was applied to 234 articles of 11 FCMs including polycarbonate, polyethersulfone, polypropylene, and polyethyleneterephthalate, obtained from domestic markets and manufacturers in Korea. Only phenol was found in the FCMs poly(cyclophexane-1,4-dimethylene terephthalate), polylactide, and thermoplastic polyurethane. Eight bisphenol analogues and p-tert-butyl phenol were not found in any samples. Using the obtained migration results, the estimated daily intake (EDI) of phenol was calculated. Exposure assessments were carried out to compare the EDI with the tolerable daily intake (TDI), showing a low percentage (0.18%) of the TDI reported. This is the first study to examine eight bisphenol analogues and two phenols simultaneously in FCMs using the LC-MS/MS.     

鲜切茭白酚类物质测定及POD特性研究

采用紫外光谱扫描及高效液相色谱法对茭白酚提取物进行初步定性分析,同时研究了鲜切茭白的POD特性。结果表明,茭白中的主要酚类物质是咖啡酸和没食子酸,分别占茭白酚提取物总量的25.57%和29.54%,两种酚均可作为鲜切茭白POD的底物,咖啡酸同时也是木质素合成的前体物质,表明茭白不仅具有很强的褐变潜力,而且具备了快速木质化的物质基础。鲜切茭白POD活力很高,其最适pH为6.0,pH5.0～7.0范围内较稳定;最适温度为40.0℃,60℃以上稳定性较差;H2O2浓度在12.25mmol/L以下时,POD活力随H2O2浓度增加直线上升,浓度进一步增加POD活力上升不大,超过14.71mmol/L对POD活力有抑制作用。鲜切茭白POD对焦性没食子酸、咖啡酸、愈创木酚、表儿茶酚、儿茶酚、没食子酸、酪氨酸、肉桂酸及H2O2的Km分别为1.75、5、12、16、41.5、76.2、∞、∞、4.91mmol/L,且与愈创木酚结合时表现出最大酶活力。      

Mechanisms of dioxin formation from the high-temperature pyrolysis of 2-bromophenol

Brominated hydrocarbons are the most commonly used flame retardants. Materials containing brominated hydrocarbons are frequently disposed in municipal and hazardous waste incinerators as well as being subjected to thermal reaction in accidental fires. This results in the potential for formation of brominated dioxins and other hazardous combustion byproducts. In contrast to chlorinated hydrocarbons, the reactions of brominated hydrocarbons have been studied only minimally. As a model brominated hydrocarbon that may form brominated dioxins, we studied the homogeneous, gas-phase pyrolytic thermal degradation of 2-bromophenol in a 1-cm i.d., fused-silica flow reactor at a concentration of 90 ppm, with a reaction time of 2.0 s, and over a temperature range of 300 to 1000 degrees C. Observed products included dibenzo-p-dioxin (DD), 1-monobromodibenzo-p-dioxin (1-MBDD), 4-monobromodibenzofuran (4-MBDF), dibenzofuran (DF), naphthalene, bromonaphthalene, 2,4- and 2,6-dibromophenol, phenol, bromobenzene, and benzene. These results are compared and contrasted with previous results reported for 2-chlorophenol. At temperatures lower than 700 degrees C, formation of 2-bromophenoxyl radical, which decomposes through CO elimination to form a bromocyclopentadienyl radical, forms naphthalene and 2-bromonaphthalene through radical recombination/rearrangement reactions. However, unlike the results for 2-chlorophenol, where naphthalene is the major product, DD becomes the major product for the pyrolysis of 2-bromophenol. The formation of DD and 1-MBDD are attributed to radical-radical reactions involving 2-bromophenoxyl radical with the carbon- (bromine) centered radical and the carbon- (hydrogen) centered radical mesomers of 2-bromophenoxyl radical, respectively. The potential product, 4,6-dibromodibenzofuran (4,6-DBDF) for which the analogous product, 4,6-dichlorodibenzofuran (4,6 DCDF), was observed in the oxidation of 2-chlorophenol, was not detected. This is attributed to the pyrolytic conditions of our experiments (e.g., shorter reaction times and higher temperatures) that favor reaction intermediates that form DD and 1-MBDD.