Hydrogen Peroxide In Air Research Articles

High Catalytic Activity of Heterometallic (Fe6Na7 and Fe6Na6) Cage Silsesquioxanes in Oxidations with Peroxides

Two types of heterometallic (Fe(III),Na) silsesquioxanes—[Ph5Si5O10]2[Ph10Si10O21]Fe6(O2‒)2Na7(H3O+)(MeOH)2(MeCN)4.5.1.25(MeCN), I, and [Ph5Si5O10]2[Ph4Si4O8]2Fe6Na6(O2‒)3(MeCN)8.5(H2O)8.44, II—were obtained and characterized. X-ray studies established distinctive structures of both products, with pair of Fe(III)-O-based triangles surrounded by siloxanolate ligands, giving fascinating cage architectures. Complex II proved to be catalytically active in the formation of amides from alcohols and amines, and thus becoming a rare example of metallasilsesquioxanes performing homogeneous catalysis. Benzene, cyclohexane, and other alkanes, as well as alcohols, can be oxidized in acetonitrile solution to phenol—the corresponding alkyl hydroperoxides and ketones, respectively—by hydrogen peroxide in air in the presence of catalytic amounts of complex II and trifluoroacetic acid. Thus, the cyclohexane oxidation at 20 °C gave oxygenates in very high yield of alkanes (48% based on alkane). The kinetic behaviour of the system indicates that the mechanism includes the formation of hydroxyl radicals generated from hydrogen peroxide in its interaction with di-iron species. The latter are formed via monomerization of starting hexairon complex with further dimerization of the monomers.

Measurement of reactive species generated by dielectric barrier discharge in direct contact with water in different atmospheres

The formation of hydroxyl radical and long-living chemical species (H2O2, O3, and ) generated in the liquid phase of a water falling film dielectric barrier discharge in dependence on the gas atmosphere (air, nitrogen, oxygen, argon and helium) was studied. The chemical molecular probe dimethyl sulfoxide was employed for quantification of ˙OH, and the influence of hydroxyl radical scavenging on formation of reactive oxygen and nitrogen species was investigated. In addition to liquid analysis, plasma diagnostics was applied to indicate possible reaction pathways of plasma–liquid interaction. The highest ˙OH production rate of 1.19 × 10−5 mol l−1 s−1 was found when water was treated in oxygen, with a yield of 2.75 × 10−2 molecules of ˙OH per 100 eV. Formation of hydrogen peroxide in air, nitrogen and argon discharges is determined by recombination reaction of hydroxyl radicals, reaching the highest yield of about 0.7 g kWh−1 when distilled water was treated in argon discharge. Ozone formation was dominant in oxygen and air discharges. Strong acidification along with formation of reactive nitrogen species was detected in water treated in air and nitrogen discharges.

Alkane oxidation with peroxides catalyzed by cage-like copper(ii) silsesquioxanes

Copper(ii) silsesquioxanes [(PhSiO1.5)12(CuO)4(NaO0.5)4] or [(PhSiO1.5)10(CuO)2(NaO0.5)2] are catalysts for alkane oxidation with H2O2ort-BuOOH.

Oxygenation of saturated and aromatic hydrocarbons with H2O2 catalysed by the carbonyl thiophenolate iron complex (OC)3Fe(PhS)2Fe(CO)3

The compound (OC)3Fe(μ-PhS)2Fe(CO)3 (1) containing a [Fe2S2] diiron moiety catalyses the oxygenation of alkanes and benzene with hydrogen peroxide in air, in acetonitrile solution. Alkyl hydroperoxides are formed as the main reaction products in the alkane oxidation; benzene is transformed into phenol. Addition of pyrazine-2-carboxylic acid (PCA) improves the oxidation. Some lag period can be noticed. If pyridine is simultaneously introduced into this reaction mixture the oxidation rate increases and the duration of the lag period is substantially decreased and in some cases this period can be completely removed. Turnover numbers attain 2300. It is noteworthy that addition of picolinic acid instead of PCA leads to the complete oxidation inhibition. The oxidation proceeds non-stereoselectively and bond selectivity parameters are low, what testifies the participation of hydroxyl radicals in hydrocarbon functionalization. Radical HO attacks the hydrocarbon, RH, to generate alkyl radical, R, which very rapidly reacts with molecular oxygen.

Determination of hydrogen peroxide in air with spectrophotometry

目的 研究一种适用于监测作业场所空气中过氧化氢的测定方法.方法取采样后部 分溶液测过氧化氢和其他强氧化物的总量,然后利用过氧化氢在过氧化氢酶的作用下分解成O2和水,使过氧化氢失去氧化性的特点,测另一部分样品溶液加过氧化氢酶后的其他氧化物含量.根据两次测定结果之差,计算样品中过氧化氢的含量.结果过氧化氢浓度在0～10μg/5 mL范围内有良好的线性关系,方法的相对标准偏差＜1.2%,加标回收率99.3%～102%,定量检测限为0.08μg/mL.最低检测浓度(采样体积为15 L时)为0.053 mg/m3.结论该方法适用于作业场所空气中过氧化氢的测定。

Formaldehyde and hydrogen peroxide in air, snow and interstitial air at South Pole

Abstract Average H2O2 (HCHO) mixing ratios measured above the snowpack at South Pole (SP) were 278 pptv (103 pptv) in December 2000 and between 4 and 43 times (1.4–2.6 times) the value estimated from gas-phase photostationary state (PSS) model calculations. The larger difference is realized if dry deposition of both species is included in the model. H2O2 and HCHO fluxes from the snowpack were independently determined from gradient measurements in the air above the snow surface, from firn-air measurements and from the temporal concentration changes in near-surface snow. On average, the snowpack at SP was releasing on the order of 1×1013 and 2×1012 molecules m−2 s−1 of H2O2 and HCHO, respectively, in December 2000. This is consistent with the volumetric fluxes needed for the PSS model to reproduce the observed atmospheric mixing ratios of both H2O2 and HCHO. The highly elevated levels of both species found in firn air further support the above estimates. In the case of HCHO, it was also shown that there was good agreement between the measured flux and the physical air–snow exchange model as driven by changes in snow temperature from winter to summer. Shading experiments suggest that the net production of HCHO within the snow by heterogeneous photochemical processes may have exceeded photochemical destruction by no more than 20% of the measured fluxes. The very rapid changes observed in atmospheric HCHO, which are also seen in NO and OH, can be understood in terms of dynamical processes that lead to rapid changes in the atmospheric mixing depth.

Detection of gaseous hydrogen peroxide using planar-type amperometric cell at room temperature

An amperometric cell, using two comb-type electrodes, was examined for detection of gaseous hydrogen peroxide in air at room temperature. The planar-type sensor element was composed of the following cell: (cathode)Au/Nafion/Pt (anode). The cell current increased linearly with an increase in concentration of hydrogen peroxide at an applied voltage of 0.5 V (below the decomposition voltage of water). It was also found that the cell could respond sensitively with a fast response to gaseous hydrogen peroxide.

Oxidation with the “O2−H2O2-vanadium complex-pyrazine-2-carboxylic acid” reagent

The oxidation of cyclohexene with hydrogen peroxide catalyzed by a vanadium complex and pyrazine-2-carboxylic acid (PCA) in air results in the formation of cyclohex-2-enyl hydroperoxide as the main product and cyclohex-2-enol, cyclohex-2-enone, cyclohex-3-enyl hydroperoxide, cyclohex-3-enol, cyclohexanol, cyclohexane, and 1,2-epoxycyclohexane in lesser amounts. The composition of the products of oxidation of decalin isomers with the system in question is similar to those obtained in the photochemical oxidation with hydrogen peroxide in air and in the oxidation with air in the presence of anthraquinone. A proposed mechanism for the oxidation includes the initiation by hydroxyl radicals generated from hydrogen peroxide under the action of the V-PCA system.

Evaluation of real-time techniques to measure hydrogen peroxide in air at the permissible exposure limit.

The major occupational concern from bio-decontamination of equipment using vapor phase hydrogen peroxide (VHP) generation systems is potential operator exposure outside the protective barrier from possible VHP leaks or accidental releases from the sealed piece of equipment during decontamination. For this reason, different real time monitoring techniques were evaluated to determine their ability to accurately measure VHP at concentrations ranging from 0.5 ppm to 5 ppm. The results of this laboratory evaluation suggest that two of the four methods evaluated (the ion mobility spectrometer [IMS] and Polytron) will approximate the National Institute for Occupational Safety and Health +/- 25% accuracy requirements for measuring the concentration of VHP at and near the Occupational Safety and Health Administration permissible exposure limit of 1.0 ppm. Over the range of 0.5 ppm to 5.1 ppm VHP, the IMS had an approximate pooled method accuracy of +/- 21%, while the Polytron had a pooled method accuracy of +/- 22%. However, both instruments had false readings when exposed to nominal concentrations of methanol, bleach, and sulfur dioxide. The two additional VHP monitoring techniques evaluated (the single point monitor [SPM] and Draeger tube) were unable to accurately measure the concentration of VHP when the relative humidity was below 20%.

Evaluation of Real-Time Techniques to Measure Hydrogen Peroxide in Air at the Permissible Exposure Limit

Evaluation of Real-Time Techniques to Measure Hydrogen Peroxide in Air at the Permissible Exposure Limit

A method for determination of hydrogen peroxide in air : further discussion

A method for determination of hydrogen peroxide in air : further discussion

Hydrogen peroxide in air during winter over the south‐central United States

Hydrogen peroxide and other atmospheric trace gases were measured along the 91°30′ meridian from near the Iowa border to the Gulf of Mexico during February 1987. The measured H2O2 values were within the range of <0.1 to 1.0 ppbv and an increase in concentration from north to south of 0.04‐0.05 ppbv per degree of latitude was observed on five of six flights. The concentration of H2O2 appeared to be primarily dependent upon air mass history; concentration discontinuities were observed when the aircraft flew across air mass boundaries. H2O2 measurements during flights in air masses of similar histories during daylight and night showed no significant difference in concentration. Neither was there a consistent dependence of the H2O2 concentration upon altitude.

A method for the determination of hydrogen peroxide in air

A method is described for the spectrophotometric determination of atmospheric H 2O 2 at the ppb level. H 2O 2 reacts with pyridine-2,6-dicarboxylic acid and vanadate(V) in acidic solutions forming the stable orange-red coloured oxo-peroxo-pyridine-2,6-dicarboxylato-vanadate(V) chelate. The fairly intense light absorption of this complex at 432 nm is widely unaffected by other atmospheric constituents such as NO x, SO 2,O 3, aldehydes, HCs and metal ions. No changes occurred with variation in pH or reagent concentrations over a wide range. The complex is formed very fast and remains stable for at least several hours. Sampling of atmospheric H 2O 2 is carried out in either a discontinuous manual or a continuous automatic manner. Particular sampling devices have been developed ensuring quantitative absorption of H 2O 2 over wide ranges of H 2O 2 concentration and of sample air flow rate. From preliminary experiments the detection limit has been derived to be about 1 ppbv H 2O 2. The performance characteristics of the method have been determined with the aid of test atmospheres. For the preparation of the test atmospheres two methods were developed.

Measurement of gas phase hydrogen peroxide in air by tunable diode laser absorption spectroscopy

Tunable diode laser absorption spectroscopy has been applied to the determination of gas phase hydrogen peroxide in ambient air with sub‐ppbv (parts per billion by volume) detection limits for measurement times of the order of minutes. The methods for calibrating the instrument and for assuring the absence of spectroscopic and sampling interferences at the level of our present detection limits are described. Ambient air monitoring with our system indicates that the hydrogen peroxide mixing ratio is often < 0.3 ppbv. Five‐minute average mixing ratios of up to 2.9 ppbv have been measured at sites in southwestern Ontario, Canada, during the summer months of 1984 and 1985, while the highest 1‐hour average value observed was 2.1 ppbv.

Automated fluorometric method for hydrogen peroxide in air

A fluorometric method for measuring H/sub 2/O/sub 2/ vapor in air utilizes peroxidase enzyme to catalyze the reaction in which hydroperoxides cause dimerization of (p-hydroxyphenyl)acetic acid. In a second channel, H/sub 2/O/sub 2/ is selectively decomposed by catalase so that the fluorescence signal is due only to organic hydroperoxides. The difference between the two signals is a measure of H/sub 2/O/sub 2/ vapor. The H/sub 2/O/sub 2/ vapor is collected by means of a glass coil though which air and water flow concurrently. The coefficient of variation is 0.5% at 2.5 parts per billion by volume. The standard deviation of the base line is 10 parts per trillion by volume (pptv) under laboratory conditions. This standard deviation has varied between 3 and 33 pptv during ground-based field missions, and was 70 pptv on aircraft flights. Thirty seconds is required for the signal to change from 10 to 90% of its maximum value. 13 references, 4 figures, 1 table.