Large Excess Of Hydrogen Peroxide Research Articles

Continuous flow disinfection of WWTP secondary effluents by solar photo-Fenton at neutral pH in raceway pond reactors at pilot plant scale

The feasibility of low cost reactors such as raceway pond reactors (RPRs) for micropollutant removal as well as pathogen inactivation has recently been reported. This study presents, for the first time, the inactivation of Total Coliforms, Escherichia coli and Enterococcus sp. in WWTP secondary effluents by the solar photo-Fenton process in continuous flow at neutral pH in open reactors. Firstly, indoor assays were carried out with three hydraulic residence times (HRTs), 15, 30 and 60 min under simulated solar radiation of 30 W m−2, 5 cm liquid depth, 20 mg Fe2+ L−1 and 50 mg H2O2 L−1. At 60 and 30 min of HRT, wastewater disinfection below 1 CFU mL−1 was achieved at steady state for the three microbial groups selected. Nevertheless, at 15 min of HRT only 1-log inactivation was obtained. Taking into account the results obtained at laboratory scale, the best HRTs (60 and 30 min) were tested outdoors in 5 cm-deep RPRs in both summer and winter. The start-up began with a batch operation for 120 min with 20 mg Fe2+ L−1 and 50 mg H2O2 L−1, followed by continuous operation over three consecutive days with 20 mg Fe2+ L−1 and 30 mg H2O2 L−1 to avoid large excess of hydrogen peroxide in steady state. Bacterial inactivation results showed 30 min of HRT to be the most efficient operation condition capable of producing 305 m3 m−2 year−1 of disinfected water while complying with the Spanish Law (RD 1620/2007) for water reuse. Additionally, a reduction in iron supply ranging from 10 to 2.5 mg L−1 in continuous mode with 30 mg H2O2 L−1 was evaluated. Efficient microorganism inactivation was reached for 10 and 5 mg Fe2+ L−1, thus reducing the iron consumption at steady state four-fold. This research opens up a new line of research on the optimisation of wastewater disinfection by large-scale solar photo-Fenton.

EPOXIDATION SYNTHESIS OF LINOLEIC ACID FOR RENEWABLE ENERGY APPLICATIONS

Monoepoxidation linoleic acid (MEOA) has advantages for industrial applications. MEOA was synthesized using immobilized Candida antarctica lipase (Novozym 435). At optimum conditions, higher yield (82.14 %) and medium oxirane oxygen content, OOC (4.91 %) of MEOA were predicted at 15 μL of H2O2, 120 mg of Novozym 435 ® and 7 hours of reaction time. Fourier Transform Infrared Spectroscopy (FTIR) spectra of the MEOA showed monoepoxide group at 820 cm. H NMR analysis confirmed the monoepoxide group at 2.92 – 3.12 ppm while the monoepoxide signals of C NMR appear at 54.59 – 57.29 ppm. LC-MS analysis shows that of MEOA gives m/z at 296.22 as final product. MEOA exhibited good pour point (PP) of -41 oC. Flash point (FP) of MEOA increased to 128 oC comparing with 115 oC of linoleic acid (LA). In a similar fashion, viscosity index (VI) for LA was 224 generally several hundred centistokes (cSt) more viscous than MEOA 130.8. MEOA was screened to measure their oxidative stability (OT) which was observed at 168 oC. It is evident that increasing the hydrogen peroxide amount has a strong effect on the reaction kinetics; however, a large excess of hydrogen peroxide results in accumulation of peracid in the final product.

Kinetic studies on acid- and base-catalyzed aquation of bis-alaninatochromium(III) and on oxidation of tris- and bis-Aa–chromium(III) complexes (Aa = Gly, Ala, Asn) by H2O2

Two aqua derivatives of [Cr(Ala)3] were characterized in solution. Acid-catalyzed aquation of cis-[Cr(Ala)2(H2O)2]+ leads to inert [Cr(Ala)(H2O)4]2+, whereas base hydrolysis of cis-Cr(Ala)2(OH)2]− causes dissociation of both the Ala ligands and formation of chromates(III). Kinetics of these processes have been studied spectrophotometrically in both 0.1–1.0 M HClO4 and 0.2–0.9 M NaOH under first-order conditions. A linear dependence of the kobs,H on [H+] and a small dependence of the (kobs)OH on [OH−] were established. In the proposed mechanism, the rate determining step is Cr–N bond breaking in the reactive form of the substrate, i.e., in the protonated aqua- or dihydroxo complex. The effect of pH on the complex reactivity is discussed. The kinetic results are compared with those determined previously for analogous glycine and asparagine complexes. Additionally, oxidation of tris- and bis-Aa–chromium(III) complexes, where Aa = Gly, Ala or Asn, by hydrogen peroxide in alkaline medium was studied. Two reaction products were detected: thermodynamically stable CrO42− and [Cr(O2)4]3− that under a large excess of hydrogen peroxide is metastable. The rate-limiting stage of this process is an inner sphere two-electron transfer within the peroxido intermediate.

Selective electronalysis of peracetic acid in the presence of a large excess of H2O2 at Au(1 1 1)-like gold electrode

Peracetic acid (PAA) has been selectively electroanalyzed in the presence of a large excess of hydrogen peroxide (H2O2), about 500 fold that of PAA, using Au (111)-like gold electrode in acetate buffer solutions of pH 5.4. Au(111)-like gold electrode was prepared by a controlled reductive desorption of a previously assembled thiol, typically cysteine, monolayer onto the polycrystalline gold (poly-Au) electrode. Cysteine molecules were selectively removed from the Au(111) facets of the poly-Au electrode, keeping the other two facets (i.e., Au(110) and Au(100)) under the protection of the adsorbed cysteine. It has been found that Au(111)-like gold electrode positively shifts the reduction peak of PAA, while, fortunately, shifts the reduction peak of H2O2 negatively, achieving a large potential separation (around 750mV) between the two reduction peaks as compared with that (around 450mV) obtained at the poly-Au electrode. This large potential separation between the two reduction peaks enabled the analysis of PAA in the presence of a large excess of H2O2. In addition, the positive shift of the reduction peak of PAA gives the present method a high immunity against the interference of the dissolved oxygen.

Activation of hydrogen peroxide via bicarbonate, sulfate, phosphate and urea in the oxidation of methyl phenyl sulfide

The presence of bicarbonate had a strong effect on the rate of oxidation of methyl phenyl sulfide (MPS) by hydrogen peroxide. At different concentrations of bicarbonate and hydrogen peroxide, we have observed different proportional amounts of methyl phenyl sulfoxide (MPSO) and methyl phenyl sulfone (MPSO 2). With equimolar amounts of hydrogen peroxide, bicarbonate and methyl phenyl sulfide, the two oxidation products coexisted, and it was very difficult to isolate methyl phenyl sulfoxide. With a large excess of hydrogen peroxide and bicarbonate ion (10-fold), methyl phenyl sulfone appeared as the sole oxidation product, and we never observed methyl phenyl sulfoxide. Other possible activating agents such as H 2PO 4 −, HSO 4 − and urea have also been used. It has been observed that comparative values of k 1 and k 2 for bicarbonate in H 2O were similar and very high, whereas they were distant from one another and lower for other potential activating agents. The same method using H 2O/EtOH (50:50) produced methyl phenyl sulfoxide as the sole reaction product after 2 h at RT.

1,1′‐Binaphthyl‐2‐methylpyridinium‐Based Peroxophosphotungstate Salts: Synthesis, Characterization, and Their Use as Oxidation Catalysts

AbstractA series of 1,1′‐binaphthyl‐2‐methylammonium and pyridinium salts 6, 7, and 8 was synthesized through the coupling reaction of 2‐(bromomethyl)‐1,1′‐binaphthalene (5) with the dendritic tetraallyl pyridinedicarbinol dendron 2 as well as triethylamine and 4‐tert‐butylpyridine. Tetraallyl pyridinedicarbinol dendron 2 was prepared by allylation of commercially available diethyl pyridine‐3,5‐dicarboxylate (1). The allylation of 2 with allyltrimethylsilane in the presence of boron trifluoride was unsuccessful, as tetraallyl pyridinedicarbinol trifluoroboron adduct 3 was obtained instead of expected hexaallylpyridine compound 4. The catalytic hydrogenation of allyl groups of the ammonium salt of 2, namely, tetraallyl 1,1′‐binaphthyl‐2‐methylpyridinium salt 6, successfully led to the corresponding tetra‐n‐propyl 1,1′‐binaphthyl‐2‐methylpyridinium salt 9. The reaction between salts 7, 8, and 9 and the heteropolyacid H3PW12O40 in the presence of a large excess of hydrogen peroxide afforded the corresponding 1,1′‐binaphthyl‐2‐methylammonium‐based polyoxometalate salts 10, 11, and 12, which contain a catalytically active trianionic [H3PW12O40]3– in the core. These binaphthyl–POM salts are soluble in commonly used organic solvents, and their IR and 31P NMR spectroscopic and elemental analysis data indicate the presence of the POM unit in the frameworks. These POM hybrids are efficient, recoverable, and reusable catalysts in the oxidation of thioanisole, cyclooctene, and cyclohexanol, with H2O2 as the oxidant. A study of the countercation effects indicated that the reaction kinetics and the selectivity are sensitive to the structure of the cation. Two cycles of catalytic reactions were performed without a discernible loss in activity. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Regioselective Hydration and Deprotection of Chiral, Dissymmetric Iminodinitriles in the Scope of an Asymmetric Strecker Strategy

AbstractThe controlled, selective decomposition of dissymmetric iminodinitriles (DIDN) of formula RCH(CN)–NH–C(CN)R′R″ (considered as N‐protected alpha‐aminonitriles), is a critical issue for an original asymmetric Strecker strategy previously outlined by us for the enantioselective synthesis of amino acids. This strategy, derived from Harada's work, involves a double sequence of (i) stereoselective Strecker condensation of a chiral ketone R′R″CO with NH3 and HCN, followed by (ii) stereoselective Strecker condensation with an aldehyde RCHO and HCN, then (iii) regioselective retro‐Strecker decomposition of the DIDN intermediate to release the target alpha‐aminonitrile. In addition to the use of quite simple, cheap cyclic ketones (e.g. carvone derivatives) as chiral auxiliaries, another great advantage of this strategy is that step (iii) enables the recovery of the chiral ketone and hence its reuse. While our previous investigations on step (iii) under various conditions, either preceded or followed by the hydration of the secondary nitrile group RH(CN)‐ into an amide, had shown insufficient selectivity, we succeeded in the regioselective hydration of the secondary nitrile of DIDN without significant racemisation, by using a large excess of hydrogen peroxide in methanolic/aqueous ammonia (pH 12.5) at low temperature. The resulting imino nitrile/amide compound was then classically decomposed in acidic medium through a retro‐Strecker reaction, affording the chiral alpha‐amino amide. Alternately, the regioselective retro‐Strecker decomposition of the tertiary moiety of the DIDN was achieved by reaction with silver cation in aqueous nitric acid, also without significant racemisation, thus establishing an original, enantioselective synthesis of alpha‐aminonitriles. In both reactions, the chiral ketonic auxiliary resulting from DIDN decomposition was recovered in good yields. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Potentiometric analysis of peroxyacetic acid in the presence of a large excess of hydrogen peroxide

The potentiometric analysis of peroxyacetic acid (PAA) in the presence of a large excess of hydrogen peroxide (H 2O 2), up to 500 times the concentrations of PAA, has been presented for the first time. This method is based on the detection of the potential change of the glassy carbon indicator electrode in the I −/I 2 potential buffer which is caused by the change in the concentrations of I − and I 2 as a result of the redox reaction of the PAA and/or H 2O 2 with I −. Based on the fact that the reaction rate of PAA and I − is much faster than that of H 2O 2 and I −, a high selective response for PAA was obtained. The different factors, such as the concentrations of I − and I 2 in the potential buffer, affecting the selectivity and sensitivity have been studied. A good calibration curve for PAA, the slope of which is in close agreement with that expected from the Nernst equation, i.e., 29.6 mV per decade, was obtained with a correlation coefficient higher than 0.993. The detection limit for PAA was found to be in the micromolar range depending on the concentration of the coexistent H 2O 2.

Hydrogenperoxo-[(bztpen)Fe(OOH)]2+ and Its Deprotonation Product Peroxo-[(bztpen)Fe(O2)]+, Studied by EPR and Mössbauer Spectroscopy − Implications for the Electronic Structures of Peroxo Model Complexes

The purple hydrogenperoxo species [Fe(bztpen)(OOH)]2+ (1) can be generated in methanol solution by treatment of [Fe(bztpen)Cl]3+ with a large excess of hydrogen peroxide [A. Hazell, C. J. McKenzie, L. P. Nielsen, S. Schindler, M. Weitzer, J. Chem. Soc., Dalton Trans.2002, 310−317]. Addition of 30 equivalents of triethylamine to a solution of [Fe(bztpen)(OOH)]2+ gives the [Fe(bztpen)(O2)]+ (2) species, in which it has been proposed that the peroxo ligand is coordinated in the η2 mode. We have synthesized both 100% 57Fe-enriched non-heme FeIII peroxo species and studied them by EPR and Mossbauer spectroscopy. Species 1 displays a typical S = 1/2 low-spin ferric EPR spectrum, the g values of which have been analysed in terms of the Griffith model [J. S. Griffith, Proc. R. Soc. London, A1956, 234, 23−36]. We have thus obtained insight into the electronic structure of 1. The EPR spectrum of 2 is characteristic of a high-spin FeIII species in a nearly axial ligand field. We have determined all Mossbauer parameters for both complexes by a numerical treatment of applied field Mossbauer data. Species 1 exhibits an isomer shift δ/Fe = 0.16 mm/s and a quadrupole splitting ΔEQ = −2.08 mm/s (T = 4.2 K). In the case of 2, we obtain an isomer shift δ/Fe = 0.63 mm/s and a quadrupole splitting ΔEQ = 1.12 mm/s (T = 4.2 K). These values are close to those published very recently by Bill et al. for [Fe(trispicMeen)(OOH)]2+ (3) and [Fe(trispicMeen)(η2−OO)]+ (4) species, where bztpen and trispicMeen ligands differ by a noncoordinating group [A. J. Simaan, F. Banse, J.-J. Girerd, K. Wieghardt, E. Bill, Inorg. Chem.2001, 40, 6538−6540]. We have also used the extension of the Griffith model developed by Lang et al. for Mossbauer spectroscopy [W. T. Oosterhuis, G. Lang, Phys. Rev. 1969, 178, 439−456] to evaluate the 57Fe hyperfine tensor of 1 and reproduce the experimental data. On comparison with the Mossbauer data available for η2-peroxo FeIII complexes, our Mossbauer study of 2 agrees well with a high-spin FeIII side-on peroxo complex. Very characteristic δ/Fe and ΔEQ ranges for hydrogenperoxo and side-on peroxo FeIII species are now available, which should aid in the detection of comparable species formed in biological systems. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Synthesis, Structures, and Properties of Bis(μ-oxo)nickel(III) and Bis(μ-superoxo)nickel(II) Complexes: An Unusual Conversion of a NiIII2(μ-O)2 Core into a NiII2(μ-OO)2 Core by H2O2 and Oxygenation of Ligand

A six-coordinate bis(μ-oxo)nickel(III) complex, [Ni2(μ-O)2(Me3-tpa)2]2+ (1), was synthesized by the reaction of [Ni2(μ-OH)2(Me3-tpa)2]2+ (2) with 1 equiv of hydrogen peroxide in methanol at −90 °C, where Me3-tpa = tris(6-methyl-2-pyridylmethyl)amine. The 6-methyl groups of Me3-tpa have a significant influence on the formation and stabilization of the high-valent bis(μ-oxo)dinickel(III) species. The reaction of 2 with a large excess of hydrogen peroxide (>10 equiv) afforded a novel bis(μ-superoxo)dinickel(II) complex, [Ni2(μ-O2)2(Me3-tpa)2]2+ (3), thus, the reaction demonstrates a unique conversion of a NiIII(μ-O)2NiIII core into a NiII(μ-OO)2NiII core upon exposure to hydrogen peroxide. Complexes 1, 2, and 3 have been characterized by X-ray crystallography and various physicochemical techniques. Complex 1 has a Ni(μ-O)2Ni core and the average Ni−O and Ni−N bond distances (1.871 and 2.143 Å, respectively) are significantly shorter than those of 2 (2.018 and 2.185 Å, respectively), suggesting that 1 is a bis(μ-oxo)dinickel(III) complex. Complex 3 consists of a Ni(μ-OO)2Ni core with two μ-1,2-O−O bridges to form a six-membered ring with chair conformation and the O−O bond distance is 1.345(6) Å. The resonance Raman spectrum of a powdered sample of 3 measured at ∼110 K showed an isotope-sensitive band at 1096 cm-1 (1044 cm-1 for an 18O-labeled sample), indicating that 3 is a bis(μ-superoxo)dinickel(II) complex. Thermal decomposition of both 1 and 3 in acetone at −20 °C under N2 atmosphere resulted in partial hydroxylation of a methyl group of Me3-tpa in yields of 21−27% for both complexes. For complex 3, a carboxylate complex, [Ni(Me2-tpaCOO)(OH2)]+ (4), where one of the three methyl groups of Me3-tpa is oxidized to carboxylate, was also isolated as a decomposed product under N2 atmosphere. During the decomposition process of 3, dioxygen evolution was simultaneously observed. The electrospray ionization mass spectrometry (ESI-MS) of 3 revealed the formation of 1 during the decomposition process. These results suggest that one possible decomposition pathway of 3 is a disproportionation of two coordinated superoxides to dioxygen and peroxide followed by the O−O bond scission of peroxide to regenerate 1, which is responsible for the hydroxylation and the oxidation of the 6-methyl group of Me3-tpa.

Peroxide analysis in laundry detergents using liquid chromatography

Liquid chromatographic (LC) studies have been conducted to investigate the formation and decomposition of peroxyacetic acid (PAA) and hydrogen peroxide in laundry detergents: Both, methyl- p-tolylsulfide (MTS) and methyl-phenylsulfoxide (MPSO) are suitable reagents for the selective LC determination of peroxycarboxylic acids in the presence of a large excess of hydrogen peroxide. MTS is oxidized in acidic media to the corresponding sulfoxide (MTSO) and MPSO is oxidized in alkaline media to methyl-phenylsulfone (MPSO 2). In both cases, triphenyl phosphine (TPP) can be used for the subsequent determination of hydrogen peroxide using LC. TPP is oxidized to the corresponding phosphine oxide (TPPO). The formation and the decomposition of PAA and hydrogen peroxide in laundry detergents with time have been observed using both methods. Acidification prior to analysis and subsequent application of MTS and TPP for the simultaneous determination of PAA and hydrogen peroxide in alkaline samples has been identified to be best suited as means for preservation of the original sample composition.

Reagent for the high-performance liquid chromatography determination of peroxycarboxylic acids

The synthesis and application of a new thiomethoxy-functionalised azo compound for the determination of peroxycarboxylic acids is described. 2-[(3-{2-[4-Amino-2-(methylsulfanyl}phenyl]-1- diazenyl)phenyl)sulfonyl]-1-ethanol reacts selectively with peroxycarboxylic acids in the presence of a large excess of hydrogen peroxide to yield the corresponding sulfoxide. Sulfide and sulfoxide are separated easily using reversed phase HPLC. An important advantage of the new reagent is the absorption maximum of the sulfoxide at wavelengths higher than 400 nm. The cross selectivity towards colored matrix components in real samples is therefore minimised. The method is characterised by an applicable concentration range over more than two decades and low cross reactivity towards hydrogen peroxide and potassium persulfate. External calibration with the respective sulfoxide leads to accurate and reliable results.

Determination of peracids in the presence of a large excess of hydrogen peroxide using a rapid and convenient spectrophotometric method

Peracids can be determined in the presence of up to a 1000-fold excess of hydrogen peroxide by taking advantage of the much greater rate of reaction of the peracid with iodide. A fast, convenient and accurate spectrophotometric method is described that involves a simple linear extrapolation. The effects of a number of experimental variables on the accuracy, precision, sensitivity and selectivity of the method are described. The method has been applied to the determination of the peracetic acid formed during the perhydrolysis of p-nitrophenyl acetate.

Gas-liquid chromatographic method for the determination of peracids in the presence of a large excess of hydrogen peroxide. Part 2. Determination in alkaline solutions

In aqueous alkaline solutions peroxycarboxylic acids oxidise sulphoxides to sulphones much faster than hydrogen peroxide. Accordingly, when an excess of methyl phenyl sulphoxide is added to a 3 + 1 water-ethanol solution (apparent pH = 12) containing an organic peracid and hydrogen peroxide, formation of methyl phenyl sulphone, equimolar with the peracid, occurs. Under the experimental conditions adopted, hydrogen peroxide is almost unreactive. Therefore, the gas-liquid chromatographic determination of the sulphone produced affords a quantitative measurement of the peracid present.

Process Design and Evaluation of a Continuous Chemical Plant for the Singlet Oxygen-Iodine Laser

Process designs were evaluated for the continuous, large-scale generation of singlet delta oxygen for use in a chemical oxygen-iodine laser. The excited singlet oxygen is generated from the chemical reaction of chlorine gas with basic hydrogen peroxide. The chemical reaction also produces a large waste brine stream that can be controlled by recycling through a chlor-alkali cell, which regenerates the reactants Cl2 and NaOH. To prevent deactivation of this excited oxygen, a large excess of hydrogen peroxide is typically used to change the reaction mechanism. This use of excess hydrogen peroxide or nonstoichiometric generation leads to substantial increases in capital and operating costs when compared with theoretical stoichiometric (no excess) generation. For the generation of singlet oxygen at a 500-kW level of equivalent lasing power, a theoretical stoichiometric plant producing all reactants has an estimated capital cost of $38 million. The capital cost for a nonstoichiometric plant is $98 million. Operating costs are $0.68 and $2.12/lb of singlet oxygen, respectively. The energy efficiency of generation is ∼6.3% for the theoretical stoichiometric flow sheet and 3.3% for the nonstoichiometric flow sheet. At this nonstoichiometric efficiency, the use of a chemical oxygen iodine laser for photoneutralization of negative ion beams is probably not competitive with other technologies below a 750-keV neutral beam level.

The degradation of cytochrome c by hydrogen peroxide

Cytochrome c is degraded by a large excess of hydrogen peroxide, leading to opening of the heme porphyrin ring and loss of the Soret absorption bands. The kinetic parameters of this reaction have been determined, and it is shown that a small concentration of oxygen is liberated at the same rate as degradation. Low-level chemiluminescence and release of a hydroxylating species also accompany heme destruction. It is proposed that heme iron activates hydrogen peroxide to a more powerful oxidant, perhaps the hydroxyl radical, which remains bound to the heme iron and initiates attack on the porphyrin ring. Chemiluminescence appears to result from a side reaction involving singlet oxygen attack on the α-methene bridge, yielding a dioxetane. The in vivo degradation of cytochrome c by excess hydrogen peroxide may interfere with respiration, accelerate aging, and enhance the metabolism of carcinogens.

Gas-liquid chromatographic method for the determination of peracids in the presence of a large excess of hydrogen peroxide

The oxidation of organic sulphides is very fast with peracids and very slow with hydrogen peroxide. Thus, addition of an excess of methyl p-tolyl sulphide to a mixture of an organic peracid and hydrogen peroxide results in the formation of methyl p-tolyl sulphoxide equimolar with the peracid. The gas-chromatographic determination of the residual sulphide, or of the produced sulphoxide, affords a quantitative evaluation of the peracid present in the mixture. The method has been applied to the determination of m-chloroperbenzoic acid and peracetic and perpropionic acids.

ChemInform Abstract: THE KINETICS OF THE REACTION BETWEEN THE CHROMIUM(III) ION AND THE ETHYLENEDIAMINE‐N,N,N′,N′‐TETRAACETATE ION IN THE PRESENCE OF HYDROGEN PEROXIDE

AbstractKinetische Untersuchung der Bildung von Aquoäthylendiamintetraacetatochromat?II).

The Kinetics of the Reaction between the Chromium(III) Ion and the Ethylenediamine-N,N,N′,N′-tetraacetate Ion in the Presence of Hydrogen Peroxide

Abstract The rate of the reaction between chromium(III) ion and ethylenediamine-N,N,N′,N′-tetraacetate was found to be accelerated upon the addition of a large excess of hydrogen peroxide. Under such a condition the rate of CrIII(edta)(H2O)− formation shows a first-order dependence on the concentrations of hydrogen peroxide and chromium(III) ions, but is independent of the concentration of EDTA. The rate of CrIII(edta)(H2O)− formation catalyzed by the hydrogen peroxide increases with an increase in the pH and decreases with an increase in the acetate ion concentration. The kinetic study suggested that the initiation of the reaction takes place as follows: Cr(III)+H2O2→Cr(IV)+OH·+OH− The reaction mechanism of the hydrogen-peroxide catalysis is discussed in terms of the formation of the chromium(IV)– and /or the chronium(V)–EDTA complex in the course of the reaction. It was found that monohydroxochromium(III) is much more reactive than the chromium(III) ion toward hydrogen peroxide.

Studies on organosulfur compounds. XIII. The substituent effect on the acid dissociation of thioanilides and on the rate of oxidation by hydrogen peroxide.

2-Thiopicolinoanilide and its meta-and para-substituted derivatives were synthesized. These thioanilides were converted readily to the corresponding O-amides by hydrogen peroxide in alkaline solution. The oxidations of the thiopicolinoanilides by use of a large excess of hydrogen peroxide were kinetically carried out and the activation energies were determined. The small increase in the rates is attributed primarily to the electron-attracting effect of the substituents. On the other hand, these acid dissociation constants were measured in 20% ethanol-water at 20° by spectrophotometry and fitted the Hammett equation with the use of σ (ρ=1.4), but the p-carboethoxy group deviates from the straight line because of its much lower pKa (8.42) value. In the reaction between 2-thiopicolinoanilides and o-aminophenol, the yield of 2-(2-pyridyl) benzoxazole increased with increasing electron-attracting effect of the substituent in the order of the observed acidity of thioanilides.