Temperature oscillations in bromate–gallic acid system: A calorimetric study

The oscillatory reaction between potassium bromate and gallic acid in sulfuric acid medium has been studied calorimetrically with and without ferroin indicator. Enthalpy changes during oscillations have increased with increasing bromate concentration in presence and absence of the indicator. Prominent catalytic activity of the indicator has been observed. An initial large enthalpy change has been observed in both uncatalyzed and catalyzed conditions prior to the starting of oscillation. Attempts have been made to correlate the main thermal events with the proposed mechanism of the reaction. © 1995 John Wiley & Sons, Inc.     

Coexistence of two bifurcation regimes in a closed ferroin-catalyzed Belousov-Zhabotinsky reaction

The ferroin-catalyzed Belousov-Zhabotinsky (BZ) reaction was studied in a batch reactor under anaerobic conditions and was found to evolve through two separated regimes of complex oscillations. Significantly, the two bifurcation regimes exhibited qualitatively different dependence on compositions of the reaction mixture, i.e., initial concentrations of bromate, sulfuric acid, malonic acid, and ferroin. The reaction temperature also showed opposite effects on the two bifurcation regimes, in which complexities of the first bifurcation regime were enhanced while oscillations in the second bifurcation regime became simpler as a result of decreasing temperature. Numerical simulations with a 12-variable model developed specifically for the ferroin-BZ system were able to reproduce transient complex oscillations observed in experiments. These calculations further illustrated that reactions such as ferroin and HOBr, ferroin and HBrO2, and ferriin and Br- were not essential in describing complex dynamics of the ferroin-BZ reaction.     

Transient complex oscillations in a closed chemical system with coupled autocatalysis

In this study, hydroquinone was introduced to the classic Belousov-Zhabotinsky (BZ) reaction to build up coupled autocatalytic feedbacks. Various complex dynamical behaviors including successive period-adding bifurcations, irregular oscillations, and frequency modulations were observed in the coupled reaction system. Not only the complexity of oscillations but also the time period during which complex oscillations persist were found to depend greatly on the initial concentration of hydroquinone, which was expected to manifest the coupling strength in the studied system. Dependence of the observed transient complex oscillations on concentrations of ferroin, sulfuric acid, bromate, and malonic acid was also characterized systematically. Numerical simulations with a modified BZ model via incorporating reactions involving hydroquinone and products of hydroquinone qualitatively reproduced the influence of hydroquinone seen in experiments.     

Chemical oscillations in the metal ion-catalyzed bromate-4-aminophenol reaction

Temporal oscillations of the bromate-4-aminophenol system have been studied in the presence of four different catalysts:tris(1,10-phenanthroline)iron(II) sulfate(ferroin),Ce(III),Mn(II),and Fe(II).Transient temporal oscillations were observed in the four catalyzed systems when the reactions were conducted in a stirred batch reactor.The induction time was prolonged by the presence of ferroin,but it was shortened in the Ce(III)-and Mn(II)-catalyzed systems.On the other hand,the number of peaks was significantly decreased in the presence of ferroin.The development of oscillatory behaviour was found to be more sensitive to the ratio of bromate and 4-aminophenol concentration than to their absolute concentrations.The reaction rates of 4-aminophenol with Ce(IV) and 4-aminophenol with ferritin were measured directly by spectroscopic methods in a sulfuric acid medium.     

Chemical oscillations and waves in the catalyzed bromate-pyrocatechol reaction

Long time series of temporal oscillations and wave formation are observed in the catalyzed bromate-pyrocatechol reaction conducted in a batch reactor, in which the induction time is insensitive to the presence of ferroin but is greatly shortened by Ce(III) or Mn(II). On the other hand, the number of oscillations is significantly increased by ferroin, while it is less sensitive to Ce(III) and Mn(II). The ferroin-catalyzed system also exhibits strong photosensitivity, in which illumination could quench the oscillatory behavior. A phase diagram illustrates that the oscillatory behavior of the studied system is more sensitive to the ratio of [pyrocatechol]/[bromate] than their absolute concentrations. Reactions conducted in a spatially extended medium show that the ferroin-catalyzed system supports a two-stage pattern formation with the wave activity surviving for up to 10 h.     

Complex Nonlinear Behavior in the Bromate–2‐Aminophenol Reaction

The bromate–2‐aminophenol reaction in a batch reactor was investigated in this research, in which both simple and sequential oscillations were observed. The occurrence of sequential oscillations were found to be very sensitive to changes of the initial concentrations, where decreasing the concentration of sulfuric acid or sodium bromate or increasing the 2‐aminophenol concentration caused the two oscillation windows to coalesce. Lowering the reaction temperature from 30 to 5°C also caused the two oscillation windows to merge into one. A phase diagram in the bromate–sulfuric acid concentration plane demonstrates that sequential oscillations only occur within a narrow band of conditions. Mechanistic studies of the system through employing ¹H NMR and mass spectrometry suggest that a dibrominated ortho‐benzoquinone is a major product. The oxidation of 2‐aminophenol, on the other hand, can lead to the formation of pyrocatechol, which may be the substrate responsible for the second set of oscillations.     

Transient Chemical Oscillations in the 4‐(N,N‐Dimethylamino) Benzoic Acid–Bromate Reaction

The bromination and oxidation of 4‐(N,N‐dimethylamino) benzoic acid (DMABA) by acidic bromate was investigated in a batch reactor through following their redox potential and UV/vis absorption spectra, in which transient oscillations with a long induction time were observed. Different from most of the bromate‐aromatic compound oscillators reported earlier, the addition of metal catalysts such as manganese, cerium, and ferroin does not significantly affect the nonlinear phenomena, but the induction time could be greatly shortened by adding bromide ions as a starting reagent. The reaction between bromine and DMABA was identified through ¹H NMR spectroscopy to form 3‐bromo‐4‐(N,N‐dimethylamino) benzoic acid. The compound 3‐bromo‐DMABA was also found to occur relatively early during the bromate‐DMABA reaction and was determined to be a major component prior to the onset of oscillations. Periodic evolution of 3‐bromo‐4‐(N,N‐dimethylamino) benzoic acid has been detected with a UV/vis spectrophotometer.     

Experimental study of a closed system in the chlorine dioxide–iodine–ethyl acetoacetate–sulfuric acid oscillation reaction by UV–vis and online FTIR spectrophotometric methods

The appearance of oscillations depends critically on the pH for a closed system of ClO₂–I₂–ethyl acetoacetate in the absence of sulfuric acid, and was investigated by determining the absorbance of I₃⁻ with reaction time at 280 nm. The pH should be 2.2–3.8. The initial concentration of ethyl acetoacetate, chlorine dioxide, iodine, and sulfuric acid has great influence on the oscillation at 581 nm for I₃⁻–starch complex (SI₃⁻). The oscillation occurs as long as the reactants are mixed at 280 nm. There is no pre-oscillatory period. However, at 581 nm, there is an induction period. The curve’s shape at 581 nm is very different from that at 280 nm. The oscillation becomes more obvious by adding starch at 581 nm for I₃⁻–starch complex (SI₃⁻) than that observed without adding starch at 280 nm. The oscillation curve is more regular and smooth by adding starch at 581 nm than that without adding starch at 280 nm. The amplitude and the number of oscillations are associated with the initial concentration of reactants. The higher the initial concentration of ethyl acetoacetate, the bigger the amplitude. Also, the number of oscillations becomes small. An opposite influence exists for chlorine dioxide and iodine. The higher the initial concentration of sulfuric acid, the bigger the amplitude. Also, the number of oscillations becomes large. The equations for the triiodide ion reaction rate changing with reaction time and the initial concentrations on the oscillation stage were obtained. The intermediates were detected by the online FTIR analysis. Based upon the experimental data in this work and in the literature, a plausible reaction mechanism was proposed for the oscillation reaction.     

Analysis of the effect of temperature on complex self-oscillation regimes in the belousov-zhabotinskii reaction in a constant-agitation flow-through reactor

Modeling of the influence of temperature on complex self-oscillation regimes in the BZ reaction in a CAFT has been carried out. It is shown that the onset of relaxation oscillations as the temperature is raised results from bifurcation of the onset of an infinite period. The disappearance of the oscillations as the temperature is raised further is due to a Hopf bifurcation. The results of the modeling are in qualitative agreement with the experimental data. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 252039 Kiev, Prosp. Nauki, 32. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 33, No. 3, pp. 159–164, May–June, 1997.     

Experimental Study of a Closed System in the Chlorine Dioxide–Iodine–Ethyl Acetoacetate–Sulfuric Acid Oscillation Reaction by UV-vis and Online FTIR Spectrophotometric Methods

The appearance of oscillations for the closed system ClO₂–I₂–ethyl acetoacetate depends critically on the pH in the absence of sulfuric acid, and was investigated by determining changes in the absorbance of I₃ ^-\mathrm{I}_{3}^{ -} with reaction time at the wavelength 280 nm. The pH should be 2.2–3.8 for this reaction. The initial concentrations of ethyl acetoacetate, chlorine dioxide, iodine and sulfuric acid have great influences on the oscillations observed at wavelengths of 280 nm or 350 nm. The oscillations at 280 nm occur as long as the reactants are mixed. However, at 350 nm the oscillation is preceded by a pre-oscillatory or induction period. The oscillation curve is more regular and smooth at 350 nm than that at 280 nm. The amplitude and the number of oscillations are associated with the initial concentration of each reactant. (1) The higher the initial concentration of ethyl acetoacetate, the greater is the amplitude while the number of oscillations becomes smaller. The amplitude is small at the beginning stage but increases with reaction time. An opposite influence exists for chlorine dioxide. Finally, the oscillation suddenly ceases. (2) When the initial concentration of iodine is higher, the amplitude is small at the beginning stage but then increases with reaction time. When the initial concentration of iodine is lower, the amplitude is large at the beginning stage and then decreases with reaction time. An opposite influence exists for sulfuric acid. Equations for the triiodide ion reaction rate were obtained as functions of reaction time and initial concentrations at the oscillation stage. The intermediates were detected by online FTIR analysis. Based upon the experimental data in this work and in the literature, a plausible reaction mechanism was proposed for the oscillation reaction.     

Bifurcation of irregular oscillatory regimes in the Belousov-Zhabotinskii reaction in a closed reactor

We describe the bifurcation diagram for irregular oscillatory regimes in the Belousov-Zhabotinskii reaction in a closed reactor upon variation of the initial concentrations of ferroin and potassium bromate. We formulate rules for transition from one regime to another.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol, 28, No. 5–6, pp. 474–478, September–December, 1993.     

Complex behavior in coupled bromate oscillators

In this study, coupled bromate-oscillators constructed by adding 1,4-cyclohexanedione (1,4-CHD) to the ferroin-catalyzed Belousov-Zhabotinsky reaction are investigated in a batch reactor under anaerobic conditions. Various complex behaviors such as sequential oscillations and bursting phenomena are observed. At low concentrations of ferroin or malonic acid (MA), the development of sequential oscillations is found to depend on the ratio of [1,4-CHD]/[ferroin] and [1,4-CHD]/[MA] rather than their absolute concentrations. As the concentration of MA or ferroin was increased gradually, however, the minimum 1,4-CHD concentration required to induce complex oscillations reaches a plateau. Perturbations by light illustrate that the first oscillatory window is governed by the ferroin-MA-BZ mechanism, whereas the 1,4-CHD-bromate oscillator plays a prominent role during the non-oscillatory evolution and the second oscillatory window. Our conclusion is further supported by numerical simulations in which sequential oscillations observed in experiments are qualitatively reproduced by a modified FKN mechanism.     

Electrochemical dehydrochlorination initiation for vinylidene chloride-vinyl chloride copolymers

Direct electrochemical initiation of dehydrochlorination is possible for polyvinylidine chloride VDC and copolymers of VDC with vinyl chloride VC. The ratio of the VDC and VC links in the initial polymer affects the rate of the dehydrochlorination and the structure of the products. Institute for Bioorganic Chemistry and Petrochemistry, National Academy of Sciences of Ukraine, 50 Kharkovskoe Shosse, 252660 Kiev-94, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 33, No. 3, pp. 180–183, May–June, 1997.     

Experimental study of a closed system in the sodium chlorite–iodine–ethyl acetoacetate oscillation reaction by UV–Vis and online FTIR spectrophotometric method

The sodium chlorite–iodine–ethyl acetoacetate (EAA) chemical oscillatory reaction system was studied by UV–Vis and online FTIR spectrophotometric method. The oscillation phenomenon does not occur as long as the reactants are mixed. There is a pre-oscillatory or induction period. The amplitude is small at the beginning stage and then increases with reaction time. Finally, the oscillation ceases suddenly. The amplitude and the number of oscillations are associated with the initial concentration of sodium chlorite, iodine, EAA and sulfuric acid. The equations for the triiodide ion reaction rate changing with reaction time and the initial concentrations on the oscillation stage were obtained. The intermediates were detected by the online FTIR analysis. Based upon the experimental data in this work and in the literature, a plausible reaction mechanism was proposed for the oscillation reaction.     

Bromide/bromate speciation by NTI-IDMS and ICP-MS coupled with ion exchange chromatography

 Two different mass spectrometric methods, negative thermal ionization isotope dilution mass spectrometry (NTI-IDMS) and inductively coupled plasma mass spectrometry (ICP-MS), off-line and on-line coupled with anion exchange chromatography, have been developed for simultaneous bromide and bromate determinations in water samples. The detection limits of these methods are in the range of 0.03–0.09 μg/L using a 50 mL sample.The results are independent of the content of other anions, which could be demonstrated by the analyses of six mineral waters containing chloride and sulfate of up to 160 mg/L and 1500 mg/L, respectively. Bromide has been analyzed by the NTI-IDMS method in the range of 10–500 μg/L and bromate in the range of 1–50 μg/L with relative standard deviations of 0.3–1.2% and 0.4–6%. Quantification for the ICP-MS method was carried out by the standard addition technique, which resulted in relative standard deviations of 5.5% for bromide at the 500 μg/L level and of 13% for bromate at the level of about 3 μg/L. These results are compared with those described in the literature for ion chromatographic (IC) and other methods and those obtained in this work by IC using UV detection, which allows high concentrations of chloride in the bromate fraction. The detection limits of this IC method are 6 μg/L for bromide and 30 μg/L for bromate. NTI-IDMS and ICP-MS therefore fit the recommendations of the European Union (detection limit<2.5 μg/L; precision and accuracy better than 25% at the 10 μg/L level) for methods analyzing the carcinogenic bromate much better than IC and other methods applied up to now. As a definitive but time consuming method, NTI-IDMS is preferably applicable as a calibration technique, whereas ICP-MS, with relatively short analysis times, due to on-line coupling with chromatography, can be used as a sensitive and powerful routine method for trace bromide and bromate species in water samples. Received: 5 July 1996/Accepted: 7 August 1996     

Bromide/bromate speciation by NTI-IDMS and ICP-MS coupled with ion exchange chromatography

 Two different mass spectrometric methods, negative thermal ionization isotope dilution mass spectrometry (NTI-IDMS) and inductively coupled plasma mass spectrometry (ICP-MS), off-line and on-line coupled with anion exchange chromatography, have been developed for simultaneous bromide and bromate determinations in water samples. The detection limits of these methods are in the range of 0.03–0.09 μg/L using a 50 mL sample.The results are independent of the content of other anions, which could be demonstrated by the analyses of six mineral waters containing chloride and sulfate of up to 160 mg/L and 1500 mg/L, respectively. Bromide has been analyzed by the NTI-IDMS method in the range of 10–500 μg/L and bromate in the range of 1–50 μg/L with relative standard deviations of 0.3–1.2% and 0.4–6%. Quantification for the ICP-MS method was carried out by the standard addition technique, which resulted in relative standard deviations of 5.5% for bromide at the 500 μg/L level and of 13% for bromate at the level of about 3 μg/L. These results are compared with those described in the literature for ion chromatographic (IC) and other methods and those obtained in this work by IC using UV detection, which allows high concentrations of chloride in the bromate fraction. The detection limits of this IC method are 6 μg/L for bromide and 30 μg/L for bromate. NTI-IDMS and ICP-MS therefore fit the recommendations of the European Union (detection limit<2.5 μg/L; precision and accuracy better than 25% at the 10 μg/L level) for methods analyzing the carcinogenic bromate much better than IC and other methods applied up to now. As a definitive but time consuming method, NTI-IDMS is preferably applicable as a calibration technique, whereas ICP-MS, with relatively short analysis times, due to on-line coupling with chromatography, can be used as a sensitive and powerful routine method for trace bromide and bromate species in water samples. Received: 5 July 1996/Accepted: 7 August 1996     

Electrochemical oxidation of sulfodifluoroacetic acid in the presence of halogens

The electrochemical oxidation of sulfodifluoroacetic acid (HOSO₂CF₂CO₂H) in the presence of Cl₂ or Br₂ gives halodifluoromethanesulfonic acid. The anodic oxidation of sulfodifluoromethanecarboxylate ion to form the sulfodifluoromethyl radical as an intermediate is proposed as the rate-determining step. Institute of Organic Chemistry, National Academy of Sciences of Ukraine, 5 Murmanskaya ul., Kiev 253094, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 4, pp. 246–248, July–August, 1999.     

Titrimetric and Spectrophotometric Determination of Some Phenothiazine Psychotropics in Pure Form and in Pharmaceutical Formulations with Metavanadate

 Two simple, fast, accurate and precise methods for the determination of six phenothiazines and a number of their pharmaceutical formulations are described. The titrimetric method involves the oxidation of the drugs by metavanadate in sulphuric acid medium and titration of vanadium(IV) formed, with cerium(IV) using ferroin indicator and acetone as catalyst. In spectrophotometry, vanadium(IV) formed was reacted with ferriin and the resulting ferroin measured at 510 nm. Phenothiazines in the ranges 5–100 mg and 2.5–25.0 μg mL⁻¹ can be determined by titrimetry and spectrophotometry, respectively, with detection limits of 0.96–2.05 mg and 0.0359–0.0565 μg mL⁻¹, respectively. Both methods were applied successfully to the determination of the studied drugs in pharmaceutical preparations. The reliability of the assays was established by parallel determination by the official methods of British Pharmacopoeia and the results being statistically evaluated. Received September 26, 2000. Revision March 25, 2001.     

Modeling of the kinetics of the heterogeneous-homogeneous conversion of methane into ethane and ethylene in the absence of oxygen in the gas phase

Computer calculations were carried out on the kinetics of the gas phase chain process for the conversion of methyl radicals into higher hydrocarbons in an oxygen-free atmosphere based on a scheme of reactions consisting of 23 homogeneous elementary steps and the heterogeneous stage of methyl radical formation. The results of the calculations are in good agreement with experimental kinetic results obtained for the interaction of methane with the oxidized surface of the perovskite catalyst KNaSrCoO₃. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Prospekt Nauki, Kiev 03039, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 36, No. 4, pp. 222–225, July–August, 2000.     

Three useful bromimetric methods for the determination of salbutamol sulfate

Three different methods developed for the determination of salbutamol sulfate (SBS), in pure drug form and in dosage forms, are discussed. The methods are based on the oxidation–bromination reaction of the drug by bromine generated in-situ by the interaction of bromate with bromide in acid medium. In titrimetry the drug is titrated directly with bromate in the presence of a large excess of bromide and in sulfuric acid medium using methyl red as indicator. Spectrophotometry is based on addition of a measured excess of bromate–bromide mixture to the sample solution in sulfuric acid medium followed by the estimation of surplus bromine by reacting it with a definite amount of methyl orange dye and measuring the absorbance at 510 nm. The amount of bromate reacting corresponds to the sample content. The kinetic method depends on the linear relationship between the concentration of the drug and time for oxidation and bromination as indicated by the bleaching of the methyl orange acid colour by the bromine generated in situ. Titrimetry is applicable in the 2–20 mg range. In spectrophotometry, Beer's law is obeyed in the 0.5–5.0 g mL^–1 range whereas concentrations in the 5.0–25.0 g mL^–1 range can be determined by the kinetic method. The effect of common excipients and additives in tablets is discussed. The procedures have been successfully applied to dosage forms; the results agree well with those obtained by use of a reference method. The methods can be used to determine SBS at mg or g levels.