用离子色谱法测定水中的二氧化氯、氯、亚氯酸根及氯酸根

建立了一种测定水中的ClO2、Cl2、ClO2^-、ClO3^-离子色谱法,在含有碳酸氢钠缓冲溶液的中性条件下,用NaNO2将ClO2、Cl2还原为ClO2^-、Cl^-,通过测定ClO^-和NO3^-的变化值,间接测定ClO2和Cl2。加入硫代乙酰胺(TAA)作掩蔽剂测定ClO2^-。     

电子活度和pH对二氧化氯制备和稳定性的影响

建立了氯体系电子活度（pε）和pH优势区域图（pε-pH）图,从酸化、氧化和还原的角度,探讨了标准状态下pε和pH对二氧化氯制备和稳定性的影响。实际生产不可能制备绝对纯净的二氧化氯。对于不同的水体,由于其pε和pH值不同,因而可能使二氧化氯表现出不同的稳定性特征。如果水溶液中二氧化氯不歧化为氯酸根,二氧化氯相对稳定,并与亚氯酸根、氯分子或氯离子稳定共存。当氯体系实现最终平衡时,二氧化氯仅在强酸介质中优势存在,随着酸度降低,二氧化氯歧化为氯酸根和氯气,水溶性和二氧化氯在常规pH条件下不稳定。     

Catalytic reactions of chlorite with a polypyridylruthenium(II) complex: disproportionation, chlorine dioxide formation and alcohol oxidation

cis-[Ru(2,9-Me(2)phen)(2)(OH(2))(2)](2+) reacts readily with chlorite at room temperature at pH 4.9 and 6.8. The ruthenium(II) complex can catalyze the disproportionation of chlorite to chlorate and chloride, the oxidation of chlorite to chlorine dioxide, as well as the oxidation of alcohols by chlorite.     

Studies of selectivity in the amaranth method for chlorine dioxide

Studies were designed to evaluate the amaranth method for measuring chlorine dioxide in water. Specifically, the effects of pH and temperature are examined for the amaranth method. The results of interference studies are reported for free available chlorine species, chlorite ion, chlorate ion, iron (III) ion, oxidized manganese, and monochloramine. Additional research focused on selectivity enhancement for chlorine dioxide over free available chlorine using ammonia/ammonium chloride buffer and gas diffusion-flow injection analysis. The results of method detection limit and accuracy and precision studies are reported for measuring chlorine dioxide in the presence of free available chlorine.     

Three autocatalysts and self-inhibition in a single reaction: a detailed mechanism of the chlorite-tetrathionate reaction

The chlorite-tetrathionate reaction has been studied spectrophotometrically in the pH range of 4.65-5.35 at T = 25.0 +/- 0.2 degrees C with an ionic strength of 0.5 M, adjusted with sodium acetate as a buffer component. The reaction is unique in that it demonstrates autocatalysis with respect to the hydrogen and chloride ion products and the key intermediate, HOCl. The thermodynamically most-favorable stoichiometry, 2S(4)O(6)2- + 7ClO2- + 6H2O --> 8SO(4)2- + 7Cl- + 12H+, is not found. Under our experimental conditions, chlorine dioxide, the chlorate ion, or both are detected in appreciable amounts among the products. Initial rate studies reveal that the formation of chlorine dioxide varies in an unusual way, with the chlorite ion acting as a self-inhibitor. The reaction is supercatalytic (i.e., second order with respect to autocatalyst H+). The autocatalytic behavior with respect to Cl- comes from chloride catalysis of the chlorite-hypochlorous acid and hypochlorous acid-tetrathionate subsystems. A detailed kinetic study and a model that explains this unusual kinetic behavior are presented.     

Dissection of the mechanism of manganese porphyrin-catalyzed chlorine dioxide generation

Chlorine dioxide, an industrially important biocide and bleach, is produced rapidly and efficiently from chlorite ion in the presence of water-soluble, manganese porphyrins and porphyrazines at neutral pH under mild conditions. The electron-deficient manganese(III) tetra-(N,N-dimethyl)imidazolium porphyrin (MnTDMImP), tetra-(N,N-dimethyl)benzimidazolium (MnTDMBImP) porphyrin, and manganese(III) tetra-N-methyl-2,3-pyridinoporphyrazine (MnTM23PyPz) were found to be the most efficient catalysts for this process. The more typical manganese tetra-4-N-methylpyridiumporphyrin (Mn-4-TMPyP) was much less effective. Rates for the best catalysts were in the range of 0.24-32 TO/s with MnTM23PyPz being the fastest. The kinetics of reactions of the various ClO(x) species (e.g., chlorite ion, hypochlorous acid, and chlorine dioxide) with authentic oxomanganese(IV) and dioxomanganese(V)MnTDMImP intermediates were studied by stopped-flow spectroscopy. Rate-limiting oxidation of the manganese(III) catalyst by chlorite ion via oxygen atom transfer is proposed to afford a trans-dioxomanganese(V) intermediate. Both trans-dioxomanganese(V)TDMImP and oxoaqua-manganese(IV)TDMImP oxidize chlorite ion by 1-electron, generating the product chlorine dioxide with bimolecular rate constants of 6.30 × 10(3) M(-1) s(-1) and 3.13 × 10(3) M(-1) s(-1), respectively, at pH 6.8. Chlorine dioxide was able to oxidize manganese(III)TDMImP to oxomanganese(IV) at a similar rate, establishing a redox steady-state equilibrium under turnover conditions. Hypochlorous acid (HOCl) produced during turnover was found to rapidly and reversibly react with manganese(III)TDMImP to give dioxoMn(V)TDMImP and chloride ion. The measured equilibrium constant for this reaction (K(eq) = 2.2 at pH 5.1) afforded a value for the oxoMn(V)/Mn(III) redox couple under catalytic conditions (E' = 1.35 V vs NHE). In subsequent processes, chlorine dioxide reacts with both oxomanganese(V) and oxomanganese(IV)TDMImP to afford chlorate ion. Kinetic simulations of the proposed mechanism using experimentally measured rate constants were in agreement with observed chlorine dioxide growth and decay curves, measured chlorate yields, and the oxoMn(IV)/Mn(III) redox potential (1.03 V vs NHE). This acid-free catalysis could form the basis for a new process to make ClO(2).     

A new sensitive and selective fluorescence method for determination of chlorine dioxide in water using rhodamine S

A new simple, selective and sensitive method for the determination of trace chlorine dioxide in water has been developed, based on the oxidation by chlorine dioxide to reduction the fluorescence of rhodamine dyes in ammonia-ammonium chloride buffer solution. Four rhodamine dyes systems such as rhodamine S, rhodamine G, rhodamine B and butyl-rhodamine B were tested. The rhodamine S system is the best, with a linear range of 0.0060-0.450 μg mL⁻¹ and a detection limit of 0.0030 μg mL⁻¹ ClO₂. It was applied to the determination of chlorine dioxide in synthetic samples and real samples, with satisfactory results. This method has good selectivity, especially, other chlorine species such as chlorine, hypochlorite, chlorite and chlorate do not interfere the determination. The mechanism of fluorescence reduction was also considered.     

Untersuchungen an Stickstoff-Chlor-Verbindungen. VIII. Tieftemperatur-Umsetzungen von Aminen mit Chlordioxid in wasserfreien Medien – Darstellung von Chlorsäureamiden und Amin-Chlordioxid-Addukten

Studies on Nitrogen-Chlorine Compounds. VIII. Low Temperature Reactions between Amines and Chlorine Dioxide in Non-Aqeous Solutions – Preparation of Chloric Acid Amides and Adducts between Amines and Chlorine Dioxide The radicalic redox reaction between amines and chlorine dioxide leads to different reaction products dependent on the kind of amine: reactive protons in α position to nitrogen are abstracted, and azomethinium chlorite is formed besides the chlorite or chlorate of the protonated base. In case of absence of reactive protons in α position to nitrogen these are abstracted from nitrogen if possible; amidochlorates are formed – which are described here for the first time – besides the salt of the protonated base. In case of absence of reactive protons at nitrogen the reaction stops after formation of an adduct between amine and chlorine dioxide. For this several new examples are reported.     

Photochemical formation of perchlorate from aqueous oxychlorine anions

Evidence of atmospherically produced perchlorate is being accumulated, yet information regarding its formation process is largely unknown. For the first time, the present study demonstrates that perchlorate can be generated as an end-product of photochemical transformation reactions of chlorine precursors such as aqueous salt solutions of hypochlorite, chlorite, and chlorate upon exposure to ultraviolet (UV) radiation. For example, under exposure to UV light from photochemical reactor lamps at a peak wavelength of 253.7 nm for 7 days, the observed perchlorate concentrations were 5, 25, and 626 μg/L at initial chlorite concentrations of 100, 1000, and 10,000 mg/L, respectively. In addition, perchlorate was generated within 7 days from aqueous chlorite solutions at mid-latitude (33°59′N, 101°89′W) spring and summer solar radiation. Via UV radiation from the artificial lamps and sunlight, chlorite was converted to chloride (68%) and chlorate (32%) as end-products on the basis of molar percentage. However, perchlorate was not detected from aqueous chloride solutions at initial concentrations up to 10,000 mg/L under the experimental conditions. Relevant mechanistic pathways were proposed based on the fact that chlorine dioxide (as a primary intermediate) may play a significant role in phototransformation of the precursors leading to perchlorate.     

S-oxygenation of thiocarbamides II: Oxidation of trimethylthiourea by chlorite and chlorine dioxide

The kinetics of the oxidation of a substituted thiourea, trimethylthiourea (TMTU), by chlorite have been studied in slightly acidic media. The reaction is much faster than the comparable oxidation of the unsubstituted thiourea by chlorite. The stoichiometry of the reaction was experimentally deduced to be 2ClO2- + Me2N(NHMe)C=S + H2O --> 2Cl- + Me2N(NHMe)C=O + SO4(2-) + 2H+. In excess chlorite conditions, chlorine dioxide is formed after a short induction period. The oxidation of TMTU occurs in two phases. It starts initially with S-oxygenation of the sulfur center to yield the sulfinic acid, which then reacts in the second phase predominantly through an initial hydrolysis to produce trimethylurea and the sulfoxylate anion. The sulfoxylate anion is a highly reducing species which is rapidly oxidized to sulfate. The sulfinic and sulfonic acids of TMTU exists in the form of zwitterionic species that are stable in acidic environments and rapidly decompose in basic environments. The rate of oxidation of the sulfonic acid is determined by its rate of hydrolysis, which is inhibited by acid. The direct reaction of chlorine dioxide and TMTU is autocatalytic and also inhibited by acid. It commences with the initial formation of an adduct of the radical chlorine dioxide species with the electron-rich sulfur center of the thiocarbamide followed by reaction of the adduct with another chlorine dioxide molecule and subsequent hydrolysis to yield chlorite and a sulfenic acid. The bimolecular rate constant for the reaction of chlorine dioxide and TMTU was experimentally determined as 16 +/- 3.0 M(-1) s(-1) at pH 1.00.     

Utilisation of kinetic-based flow injection methods for the determination of chlorine and oxychlorine species

Automated selective iodometric methods for the determination of chlorine and oxychlorine species have been developed for use in the drinking water industry. By utilising kinetic-based methods, linear ranges observed were: chlorine, 0.2–10 mg l^?1; chlorine dioxide, 0.3–10 mg l^?1; chlorite ion, 0.08–5 mg l^?1; and chlorate ion, 0.08–5 mg l^?1.     

Alternative spectrophotometric method for standardization of chlorite aqueous solutions

The chlorite ion is the principal by-product of the treatment of drinking water by chlorine dioxide. In function of the chlorite salt instability, standard solutions of this ion need standardization by iodometric titration, which is a reliable method although labor intensive and time consuming. An alternative method to standardization of aqueous chlorite solutions, based on its direct UV absorption measurement, was presented. Besides the maximum absorption (260 nm) generally used in other studies, the minimum (239 nm) and isosbestic (248 nm) wavelengths were proposed as supplementary points to chlorite quantification and their molar absorptivity coefficients were estimated (155.2 ± 0.6, 104.5 ± 1.0 and 69.0 ± 1.2 L cm⁻¹ mol⁻¹, respectively). The direct spectrophotometric determination of chlorite could be made selectively even in the presence of high concentration of major contaminants (chorine dioxide, chloride and chlorate), being a simple and rapid method, consuming very low volume of sample and generating low quantities of laboratory wastes.     

Application of an amperometric sensor to in-line monitoring of pulp bleaching with chlorine dioxide

Chlorine dioxide is replacing chlorine as the active compound in pulp bleaching in order to reduce the amount of chlorine used in the process and hence also in the waste waters. In bleaching with chlorine dioxide part of the effective bleaching chemical is usually chlorite. The electrochemistry of chlorine dioxide and chlorite at solid electrodes was studied by cyclic voltammetry at different pH values. The observed voltammograms indicated that reduction of chlorine dioxide gives chlorite and oxidation of chlorite gives chlorine dioxide. Both voltammograms were well developed, indicating a reversible process. Both platinum and glassy carbon were used as the working electrode. The dependence of the limiting current of chlorine dioxide and chlorite on pH was studied at both electrodes. The method was tested in the chlorine dioxide bleaching stage D1 in a typical bleaching process. A good correlation was found between the concentrations of chlorine dioxide and chlorite measured by the in-line amperometric method and a standard titrimetric method.     

Simultaneous determination of inorganic disinfection by-products and the seven standard anions by ion chromatography

For the first time, an ion chromatographic method for the simultaneous determination of the disinfection by-products bromate, chlorite, chlorate, and the so-called seven standard anions, fluoride, chloride, nitrite, sulfate, bromide, nitrate and orthophosphate is presented. The separation of the ten anions was carried out using a laboratory-made high-capacity anion-exchanger. The high capacity anion-exchanger allowed the direct injection of large sample volumes without any sample pretreatment, even in the case of hard water samples. For quantification of fluoride, chloride, nitrite, sulfate, bromide, nitrate, orthophosphate and chlorate, a conductivity detection method was applied after chemical suppression. The post-column reaction, based on chlorpromazine, was optimized for the determination of chlorite and bromate. The method detection limit for bromate measured in deionized water is 100 ng/l and for chlorite, it is 700 ng/l. In hard drinking water, the method’s detection limits are 700 ng/l (bromate) and 3.5 μg/l (chlorite). The method’s detection limits for the other eight anions, determined by conductivity detection, are between 100 μg/l (nitrite) and 1.6 mg/l (chlorate).     

Determination of low concentrations of chlorite and chlorate ions by using a flow-injection system

A flow-injection method is reported for the determination of chlorite ion and chlorite and chlorate ions in mixtures at the submilligram per liter level in drinking water. The chlorite ion concentration is selectively determined by using its reaction with iodide ion at pH 2, which liberates iodine. Both species react with iodide ion in6 M HCl to produce iodine, the concentration of which is measured spectrophotmetricaly at 370 nm. The individual species are determined using multiplel regression. The method exhibits a linear range from 2 to 150 μM (0.1–10.1 mg l^-1) for chlorite ion and from 2 to μM (0.1–8.3 mg l^-1 for chlorate ion, with relative standard deviations of 0.4 and 1.2%, respectively.     

Selectivity enhancement by flow injection analysis

Flow injection analysis offers numerous possibilities for significantly increasing the selectivity of existing methods by utilizing knowledge of the chemistry of those methods. It also enables new selective methods to be created by utilizing kinetic methods and fast separation techniques such as gas diffusion, dialysis, extraction and ion-exchange columns. Selectivity enhancements and increased sensitivity can be achieved by incorporating the kinetic techniques of kinetic discrimination and/or kinetic enhancement into the timing of the system or the reagent concentrations and conditions for a given method. Methods have been developed for quantifying ozone, chlorine dioxide, chlorate ion, and chlorite and chlorate ions sequentially. A dual-phase gas diffusion system for hydride generation provides significant decreases in the interferences observed for transition metals.     

Oxyhalogen-sulfur chemistry: kinetics and mechanism of oxidation of N-acetylthiourea by chlorite and chlorine dioxide

The oxidation reactions of N-acetylthiourea (ACTU) by chlorite and chlorine dioxide were studied in slightly acidic media. The ACTU-ClO(2)(-) reaction has a complex dependence on acid with acid catalysis in pH > 2 followed by acid retardation in higher acid conditions. In excess chlorite conditions the reaction is characterized by a very short induction period followed by a sudden and rapid formation of chlorine dioxide and sulfate. In some ratios of oxidant to reductant mixtures, oligo-oscillatory formation of chlorine dioxide is observed. The stoichiometry of the reaction is 2:1, with a complete desulfurization of the ACTU thiocarbamide to produce the corresponding urea product: 2ClO(2)(-) + CH(3)CONH(NH(2))C=S + H(2)O --> CH(3)CONH(NH(2))C=O + SO(4)(2-) + 2Cl(-) + 2H(+) (A). The reaction of chlorine dioxide and ACTU is extremely rapid and autocatalytic. The stoichiometry of this reaction is 8ClO(2)(aq) + 5CH(3)CONH(NH(2))C=S + 9H(2)O --> 5CH(3)CONH(NH(2))C=O + 5SO(4)(2-) + 8Cl(-) + 18H(+) (B). The ACTU-ClO(2)(-) reaction shows a much stronger HOCl autocatalysis than that which has been observed with other oxychlorine-thiocarbamide reactions. The reaction of chlorine dioxide with ACTU involves the initial formation of an adduct which hydrolyses to eliminate an unstable oxychlorine intermediate HClO(2)(-) which then combines with another ClO(2) molecule to produce and accumulate ClO(2)(-). The oxidation of ACTU involves the successive oxidation of the sulfur center through the sulfenic and sulfinic acids. Oxidation of the sulfinic acid by chlorine dioxide proceeds directly to sulfate bypassing the sulfonic acid. Sulfonic acids are inert to further oxidation and are only oxidized to sulfate via an initial hydrolysis reaction to yield bisulfite, which is then rapidly oxidized. Chlorine dioxide production after the induction period is due to the reaction of the intermediate HOCl species with ClO(2)(-). Oligo-oscillatory behavior arises from the fact that reactions that form ClO(2) are comparable in magnitude to those that consume ClO(2), and hence the assertion of each set of reactions is based on availability of reagents that fuel them. A computer simulation study involving 30 elementary and composite reactions gave a good fit to the induction period observed in the formation of chlorine dioxide and in the autocatalytic consumption of ACTU in its oxidation by ClO(2).     

饮用水中氯酸盐、亚氯酸盐的离子色谱测定方法

建立了饮用水中微量氯酸盐以及亚氯酸盐的离子色谱测定方法。结果表明,亚氯酸盐和氯酸盐在0～0.50 mg/L范围内线性良好,精密度高,亚氯酸盐r2=0.999 8,样品加标平均回收率91.5%～99.4%,相对标准偏差(RSD)0.64%～1.78%,检出限为3.98μg/L;氯酸盐r2=0.999 6,样品加标平均回收率94.7%～101.6%,相对标准偏差(RSD)0.94%～1.35%,检出限为4.65μg/L;方法操作简单、快速、准确、灵敏度高、干扰少,适用于饮水消毒副产物亚氯酸盐和氯酸盐的检测。     

Potentiometric titration of chlorine and its oxy compounds in water

Potentiometric titrations at constant current with identical platinum electrodes are applied to mixtures of chlorine, chlorine dioxide and chlorite. The procedure is compared with the common amperometric method. Chlorine can be titrated with phenylarsine oxide at pH 7 even in mixtures with chlorine dioxide and chlorite, and three-component mixtures can be resolved by titrations at pH 2 and 7 with and without iodide addition. The behavior of chlorine and chlorite mixtures can be characterized by appropriate titrations.     

Kinetics of the Sodium Chlorate Formation in Electrolysis of Chloride Solutions with Use of Dimensionally Stable Anodes

The kinetics of the formation of sodium chlorate during electrolysis of chloride solutions with use of dimensionally stable anodes is studied. An analysis and calculations suggest that the experimental results are well described by the proposed set of differential equations under the assumption that the homogeneous chemical reaction of chlorate formation has second, rather than third, order by active chlorine.