Potentiometric titration of hydrogen peroxide with an electropolished stainless steel electrode

The preparation and use of a stainless steel indicator electrode in the accurate potentiometric titration of aqueous hydrogen peroxide are described. The results agree excellently with those obtained by a standard colorimetric weight-titration procedure. The nature of the titration curves, potential changes and the factors affecting them are discussed. Rapid potentiometric titrations directly to the equivalence-point potential are possible, owing to the nature of the titration curve.     

The influence of non-covalent interactions on the hydrogen peroxide electrochemistry on platinum in alkaline electrolytes

The potential range of the transition region between the diffusion-limited reduction to oxidation of hydrogen peroxide depends strongly on the nature of the cation of the supporting alkaline electrolyte. Non-covalent interactions between the hydrated alkali metal cations and chemisorbed OH species on platinum influence the potential-dependent reaction kinetics.     

Self‐immolative nanoparticles triggered by hydrogen peroxide and pH

The azomethine‐based oligomers bearing boronate groups and imine moieties in the main chain were synthesized from a dialdehyde monomer and an aromatic (oligomer 4 ) diamine or an aliphatic diamine (oligomer 5 ). Based on the oligomers, the nanoparticles with hydrogen peroxide (H₂O₂) and pH dual‐responsive properties were constructed and encapsulated nile red inside. The nanoparticles disassembled either by the trigger of H₂O₂ or by the attack of H⁺, thus leading to the release of loaded species. Compared to oligomer 4 , oligomer 5 showed a faster degradation rate in the presence of H₂O₂, especially in a weak acidic environment. No significant cytotoxicity was observed as HeLa cells incubated in the nanoparticles with the concentration up to 200 μg/mL evidenced by cytotoxicity assay in vitro. Such a system capable of dual response of H₂O₂ and H⁺ may have potential application as a carrier for drug delivery. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1962–1969     

The influence of aggregation of porphyrins on the efficiency of photogeneration of hydrogen peroxide in aqueous solution

The pH-dependence of the ability of coproporphyrin (CP) and uroporphyrin (UP) to photogenerate hydrogen peroxide (H2O2) in aqueous solution was investigated, with special attention to the structure-activity relationship related to the aggregation of the porphyrins. It was found that the efficiency was strongly dependent on the aggregation of CP and UP mediated by changes in the pH of the solution, and a dimeric form had a weak ability to produce H2O2, while a highly aggregated form had a good ability. The increased efficiency of the highly aggregated porphyrin to produce H2O2 was further demonstrated using a different type of aggregate formed by the electrostatic interaction of cationic tetrakis-5,10,15,20-(N-methyl-4-pyridyl)porphin (TMPyP) with anionic tetrakis-5,10,15,20-(4-sulfonatophenyl)porphin (TSPP). The present results demonstrated the importance of the state of aggregation of porphyrin to photogenerate H2O2, and the results may help to develop a new type of medicine for photodynamic therapy.     

Oxidations with alkaline permanganate using monovalent thallium for the back titration: Estimation of hydrogen peroxide

Owing to the instability of hydrogen peroxide in alkaline solutions, direct oxidation with KmnO₄ did not yield accurate results.The back titration of KmnO₄ in the presence of IN NaOH and Ba⁺² ions also gave inaccurate results. The reaction could not be checked at the manganate state. However, in the presence of 2N NaOH and telluric acid quantitative data were obtained, which is not the case if telluric acid is absent.Another advantageous method is the oxidation of hydrogen peroxide with excess KmnO₄ in the presence of 1N NaOH and telluric acid, followed by back titrating excess oxidant with monovalent thallium.     

Sustained self-organizing pH patterns in hydrogen peroxide driven aqueous redox systems

Many pattern developments in nature are believed to result from the interplay between self-activated (bio)chemical processes and the diffusive transport of constituents. Though the details are difficult to work out, the relevance of reaction-diffusion processes is widely accepted in many aspects of biological development. Due to their easier manipulation and control, aqueous phase chemical reactions are commonly preferred to probe the patterning capacity of reaction-diffusion processes. Nonetheless, sustained patterns of such a type were observed only in reactions involving oxyhalogen compounds. We report on halogen free solution chemistry systems which lead to stationary or oscillatory spatiotemporal pH patterns. They are based on the acid autocatalytic oxidation of sulfite ions by hydrogen peroxide in combination with two significantly different proton consuming feedback reactions. Besides the chemical novelty, yet experimentally and even theoretically undocumented pattern dynamics are uncovered. This success, based on a well-defined method, further paves the way to the discovery of stationary patterns in delicate biochemical reactions.     

Oscillatory reactions involving hydrogen peroxide and thiosulfate-kinetics of the oxidation of tetrathionate by hydrogen peroxide

The reaction between tetrathionate and hydrogen peroxide forms an important part of several pH oscillators based on the oxidation of thiosulfate. The kinetics of this reaction were examined in a batch reactor by measurement of the initial pH values in the range from 8 to 10.5. Experimental data were evaluated by the method of initial reaction rates combined with the assumption of instantaneously equilibrated acid-base reactions. The rate-determining step was found to be of the first order with respect to tetrathionate, hydrogen peroxide, and OH- ions with the value of rate constant k = (1.50 +/- 0.03) x 10(2) (M2 s)(-1) at 25 degrees C. In the alkaline solution, no distinct catalytic effect of Cu2+ was observed in contrast to earlier assumptions. The waveform of measured pH over the course of the reaction indicates that thiosulfate is probably an intermediate because characteristics of the curves are very similar to those for the oxidation of thiosulfate. We also measured the time evolution of concentrations of major components by the attenuated total internal reflectance infrared spectroscopy to further elucidate the underlying reaction mechanism. These measurements confirm the suspected role of thiosulfate as an intermediate in the studied reaction and provide valuable detailed information on the time evolution of thiosulfate, sulfite, sulfate, tetrathionate, and trithionate. These experimental observations are included in a simple mechanism that accurately simulates the reaction course in an alkaline solution. The results provide considerable new insights into the nature of autocatalysis in the hydrogen peroxide-thiosulfate-Cu2+ reaction and suggest that a new role for Cu2+ in the oscillatory dynamics observed in a flow-through reactor needs to be found.     

Thermometric titration of cadmium with sodium diethyldithiocarbamate, with oxidation by hydrogen peroxide as indicator reaction

A new method of end-point indication is described for thermometric titration of cadmium with sodium diethyldithiocarbamate (DDTC). It is based on the redox reaction between hydrogen peroxide added to the system before titration, and the first excess of DDTC. Amounts of cadmium in the range 10-50 mumoles are titrated within 1% error.     

The oxidation of aminophenazone by hydrogen peroxide

Aqueous solutions of aminophenazone were oxidized by excess hydrogen peroxide in acidic, neutral and alkaline media and the reaction was followed using thin-layer chromatography and spectrophotometry in the visible and uv regions. The oxidation course is explained on the basis of detection of the products formed (4-methylaminoantipyrine, 4-aminoantipyrine, 1-phenyl-3-methyl-4-(phenylazo)-5-pyrazolone, 1-acetyl-1-methyl-2-di-methyl-oxanil-2-phenylhydrazine, oxalic acid, dimethylamine).     

Flow-injection analysis of hydrogen peroxide based on carbon nanospheres catalyzed hydrogen carbonate-hydrogen peroxide chemiluminescent reaction

A flow-injection chemiluminescence (CL) system with high sensitivity, selectivity, rapidity, and reproducibility is proposed for the determination of hydrogen peroxide (H(2)O(2)) in water samples. The system is based on the reaction of hydrogen peroxide and hydrogen carbonate solution. Carbon nanospheres (CNSs) prepared from aqueous glucose solution are used to enhance the weak CL. The CL intensity was found to be directly proportional to the concentration of H(2)O(2) present in the sample solutions. The effects upon the CL of several physicochemical parameters, including the concentration of the reagents, the mixing order of the reagents, flow rate, pH, particle size of CNSs and other relevant variables, were studied and optimized. The proposed method exhibited advantages in a larger linear range of 5.0 × 10(-8) to 3.0 × 10(-6) mol L(-1) and a lower limit of detection of 1.0 × 10(-9) mol L(-1) (S/N = 3). This method has been successfully applied to the evaluation of H(2)O(2) in tap water and snow water with recoveries from 80 to 110%. The relative standard deviation (RSD) was less than 8% for intra- and inter-assay precision. Based on the kinetic curve, the CL spectrum, fluorescence spectrum, UV-visible spectrum, and electron spin resonance (ESR) spectrum of NaHCO(3)-H(2)O(2)-CNSs system, a possible CL mechanism was proposed. Superoxide ion radical (˙O(2)(-)) and hydroxide radical (˙OH) were generated during the reaction of NaHCO(3) and H(2)O(2). They were the key intermediates for the production of hole-injected and electron-injected CNSs in the CL process.     

Determination of sulphate by pH titration

A simple and inexpensive method has been developed for the determination of sulphate and other very weak bases and acids. It utilizes the partial protonation of the weak base or the partial dissociation of the weak acid, which has not been exploited for analytical purposes thus far. The procedure consists of three pH titrations: one with a test solution of known sulphate content, the second with the sulphate sample, and the third with a blank. This method can be used in the presence of several inorganic ions and organic matrices, including non-aqueous solvents. In aqueous medium sulphate contents above 10(-3)M can be determined. The use of solvent mixtures may increase the sensitivity of the method by two orders of magnitude.     

The influence of hydrogen peroxide on carbon monoxide electrooxidation at Pt/C and Pt:Ru/C electrodes

Polymer electrolyte fuel cells constitute one of the most important efficiency energy converters for non-centralised uses. However, the use of fuels arising from reformate processes significantly lowers the current efficiency because of anodic catalytic poison coming from adsorbed carbon monoxide (CO_ad). In this work, the influence of the addition of hydrogen peroxide in the flow current is studied, considering the adsorption and electrochemical oxidation of carbon monoxide on carbon-supported Pt (20% Pt/Vulcan) and Pt:Ru (1:1, 20% Pt:Ru/Vulcan) catalysts in 2 M sulphuric acid. The investigation was conducted applying cyclic voltammetry and on-line differential electrochemical mass spectrometry. A series of experiments has been performed to investigate the influence of the temperature as well as the time of contact and the concentration of hydrogen peroxide. Oxidation of CO_ad to carbon dioxide occurs at lower potentials in the presence of hydrogen peroxide. Moreover, it is possible to remove ca. 70% of CO_ad on Pt/C electrodes. On the other hand, for PtRu/C electrodes, similar charge values to those of Pt/C electrodes were obtained for the CO stripping, but the process occurs at more negative potentials. In this case, the effect of partial desorption for CO_ad by interaction with hydrogen peroxide is added to the bifunctional mechanism usually considered for this alloy. This paper is dedicated to Prof. Francisco Nart, in memoriam.     

Reactions of hydrogen atom with hydrogen peroxide

Rate coefficients are calculated using canonical variational transition state theory with multidimensional tunneling (CVT/SCT) for the reactions H + H2O2 --> H2O + OH (1a) and H + H2O2 --> HO2 + H2 (1b). Reaction barrier heights are determined using two theoretical approaches: (i) comparison of parametrized rate coefficient calculations employing CVT/SCT to experiment and (ii) high-level ab initio methods. The evaluated experimental data reveal considerable variations of the barrier height for the first reaction: although the zero-point-exclusive barrier for (1a) derived from the data by Klemm et al. (First Int. Chem. Kinet. Symposium 1975, 61) is 4.6 kcal/mol, other available measurements result in a higher barrier of 6.2 kcal/mol. The empirically derived zero-point-exclusive barrier for (1b) is 10.4 kcal/mol. The electronic structure of the system at transition state geometries in both reactions was found to have "multireference" character; therefore special care was taken when analyzing electronic structure calculations. Transition state geometries are optimized by multireference perturbation theory (MRMP2) with a variety of one-electron basis sets, and by a multireference coupled cluster (MR-AQCCSD) method. A variety of single-reference benchmark-level calculations have also been carried out; included among them are BMC-CCSD, G3SX(MP3), G3SX, G3, G2, MCG3, CBS-APNO, CBS-Q, CBS-QB3, and CCSD(T). Our data obtained at the MRMP2 level are the most complete; the barrier height for (1a) using MRMP2 at the infinite basis set limit is 4.8 kcal/mol. Results are also obtained with midlevel single-reference multicoefficient correlation methods, such as MC3BB, MC3MPW, MC-QCISD/3, and MC-QCISD-MPWB, and with a variety of hybrid density functional methods, which are compared with high-level theory. On the basis of the evaluated experimental values and the benchmark calculations, two possible recommended values are given for the rate coefficients.     

The oxidation of cinnamaldehyde with alkaline hydrogen peroxide

The oxidation of cinnamaldehyde (3-phenyl-2-propenal) by alkaline peroxide results in epoxidation of the double bond to form cinnamaldehyde epoxide (3-phenyl-2,3-epoxy-propanal) which undergoes further reaction by ring opening and side chain cleavage to yield benzaldehyde and acidic fragments. The reactions are first-order in the organic substrates and perhydroxyl anion and second-order overall. In the presence of alkali alone, two further reactions take place in which cinnamaldehyde and cinnamaldehyde epoxide side chains are cleaved by reaction with hydroxide ion to form benzaldehyde and side chain fragments. These reactions are first-order in the organic substrates and hydroxide ion and second-order overall. Increasing solvent polarity accelerates the rates of reaction and reaction mechanisms have been proposed to describe the observed kinetic behavior. The stereoselectivity of the epoxidation reaction has been examined in terms of an existing model for epoxidation of α, β-unsaturated ketones by alkaline peroxide. © 1993 John Wiley & Sons, Inc.     

The formation of hydrogen peroxide in metallic reductors

The formation of hydrogen peroxide in various types of metallic reductors both in the presence and absence of oxygen has been studied. Only when oxygen is rigorously excluded is peroxide undetectable. The oxidimetric determination of iron is seriously affected by this peroxide when the test solution and reductor are open to atmospheric oxygen. Systems which are completely oxygen-free give satisfactory results.     

过氧化氢光化学的理论研究

介绍了研究过氧化氢光解离的重要意义及目前的理论研究现状,分析了存在的问题,并对今后该领域的理论研究进行了展望.     

The effects of carbon nanotubes on the electrocatalysis of hydrogen peroxide by metallo-phthalocyanines

The pre-grafted screen-printed gold electrode modified with phenyl-amino monolayer was investigated for covalent immobilization of phenyl-amine functionalized single-walled carbon nanotubes (PA-SWCNT) and metal tetra-amino phthalocyanine (MTAPc) using Schiff-base reactions with benzene-1,4-dicarbaldehyde (BDCA) as cross-linker. The PA-SWCNT and MTAPc modified electrodes were applied as hybrids for electrochemical sensing of H₂O₂. The step-by-step fabrication of the electrode was followed using electrochemistry, impedance spectroscopy, scanning electron microscopy and Raman spectroscopy and all these techniques confirmed the fabrication and the immobilization of PA-SWCNT, MnTAPc and CoTAPc onto gold surfaces. The apparent electron transfer constant (k_app) showed that the carbon nanotubes and metallo-phthalocyanines hybrids possess good electron transfer properties compared to the bare, pre-grafted and the MTAPc modified gold electrode surfaces without PA-SWCNT. The electrochemical sensing of hydrogen peroxide was successful with PA-SWCNT-MTAPc hybrid systems showing higher electrocatalytic currents compared to the other electrodes. The analytical parameters obtained using chronoamperometry gave good linearity at H₂O₂ concentrations ranging from 1.0 to 30.0 μmol L⁻¹. The values for the limit of detection (LoD) were found to be of the orders of 10⁻⁷ M using the 3δ for all the electrodes. The PA-SWCNT-MTAPc modified SPAuEs were much more sensitive compared to PA-MTAPc modified SPAuEs.     

Transformations of furoyl peroxide and hydroperoxide in the presence of water and hydrogen peroxide

In the presence of water, furoyl peroxide and hydroperoxide are hydrolyzed to pyromucic acid and hydrogen peroxide, between which there is a partial reaction.