Consecutive First-order Reactions Research Articles

Optimizing carboxylated nanocellulose preparation: A kinetic and mechanistic study on the enhancement of TEMPO-mediated oxidation via swelling treatment

This study explored the application of swelling pretreatment as a solution to the high cost and contamination associated with the process of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation for nanocellulose preparation. The results demonstrated that swelling significantly expanded the fibers while preserving the degree of polymerization (DP) of cellulose (approximately 95 %). The native crystal structure and hydrogen bonding of cellulose were disrupted after swelling, leading to a reduction in crystallinity and crystallite size, and the decrease of bonding energy and content of intermolecular O6-H⋯O3′. The TEMPO-mediated oxidation processes of cellulose fibers with or without swelling were successfully fitted using a consecutive first-order reaction kinetic model. The fitting results indicated that swelling significantly reduced the activation energy of TEMPO-mediated oxidation and enhanced the reaction rate. Among three swelling systems, the NaOH/thiourea/water system exhibited the optimal promotion effect. Consequently, the swelling treatment enables a significant reduction of 30 % in the catalyst dose for the TEMPO-mediated oxidation while preserving a competitive reaction rate, yield, and product performance. Lower catalyst dosage helps to reduce cost and environmental impact, facilitating the industrial application of the TEMPO-mediated oxidation process.

Characterization of pyrolysis behavior for rigid polyurethane foam wastes with different densities through TGA-FTIR-DSC-MCC and Hill Climbing Optimization methods

Pyrolysis technology is one of the most effective thermal treatment methods recycling rigid polyurethane foam (RPUF) waste. To optimize pyrolysis recovery efficiency, quantifying the pyrolysis reaction kinetics and the heat required for the thermal treatment process is critical. This work focuses on establishing a systematic methodology to quantify pyrolysis reaction kinetics and thermodynamics for RPUF waste. RPUF waste with two different densities (RPUFρ100 and RPUFρ45) were investigated using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) under anaerobic atmosphere to measure mass and heat flow information. The obtained data were inversely analyzed using a numerical framework known as ThermaKin2Ds. Pyrolysis reaction mechanisms with four and three consecutive first-order reactions were developed to reproduce the TGA data for RPUFρ100 and RPUFρ45, respectively. The Hill Climbing Optimization Algorithm was employed to adjust the reaction kinetics for an improved agreement between the ThermaKin2Ds-reproduced and experimental data. Based on the heat flow data from DSC tests, the specific heat capacity of each condensed-phase component was determined by using the inverse modeling method. Additionally, the micro-scale combustion calorimeter was used to generate the heat release data that served as the target data for inversely determining the heats of complete combustion, hc, of each pyrolyzate. The established pyrolysis reaction models was further validated by predicting the TGA results collected under different external heating conditions. Subsequently, the generated combustion-inhibiting gases (CO2) and combustion-promoting gases (olefins, alkanes, carboxylic acids, etc.) were characterized through TGA coupled with Fourier-transform infrared spectroscopy (TG-FTIR). This allowed us to elucidate the gas-phase combustion phenomena observed in MCC experiments. This work provides a core set of parameters for optimizing the thermal treatment conditions of RPUF waste.

Ionic liquid as regenerable media for simultaneous recovery of melanin and amino acid from waste human hair: An elaborate and efficient biorefining approach

Waste human hair (WHH) is rich in valuable resources like keratin and melanin. However, current resource recovery methods face challenges such as complex procedures, consumption of acidic and alkaline reagents, unsatisfactory yield, and inferior purity of melanin products, primarily due to the difficulty in avoiding the generation of melanin-keratin blends (MKBs). For the first time, this study established an ionic liquid-targeted depolymerization/isolation (IL-TDI) process for the simultaneous recovery of melanin and monomeric amino acids from WHH with both satisfactory yield and superior purity via four steps, including depolymerization, liquid-solid separation, extraction, and recovery of IL. IL-TDI process yielded 6.02% melanin and 34.58% monomeric amino acid, and the environmentally friendly ionic liquid, 1-Butyl-3-methylimidazolium chloride (BMIMCl), was recyclable. SEM and FTIR analyses revealed that the melanin extracted by IL-TDI process retained its native chemical structure and microstructure. In contrast, the traditional base dissolution and acid isolation (BDAI) process achieved only a 2.2% melanin yield and completely destroyed the natural microstructure of melanin. Various characterizations, including UV–visible spectroscopy, quantitative amino acid analysis, and kinetic rate calculations, were conducted to study the separation mechanism of melanin and keratin. In IL-TDI process, disulfide bonds in keratin were initially cleaved by BMIMCl during dissolution. Subsequently, melanin isolation followed two consecutive first-order reactions, and hydrogen ions in BMIMCl preferentially hydrolyzed dissolved keratin, during which preventing the generation of MKB proved essential for achieving high yield of melanin. Economic and E-factor calculations demonstrated this novel biorefining approach's suitability for sustainable WHH recovery.

Decomposition of solid C60–indene adducts by retro Diels Alder reaction – A kinetic and thermodynamic study

Diels-Alder cycloaddition is a common synthetic approach to functionalize fullerenes. However, the stability of such fullerene adducts is hampered by the existence of the Retro Diels-Alder (RDA) reaction. Herein, the RDA reactions in the solid phase of the mono and bisadducts of C60 with indene, IC60MA and IC60BA, were studied by differential scanning calorimetry and thermogravimetric analysis. The RDA reaction in solid IC60MA occurs at a higher temperature than in IC60BA. IC60MA decomposition follows a first-order rate law and in IC60BA it is described by two consecutive first-order reaction steps. The decomposition of both adducts yields a metastable C60 solid. The higher decomposition temperature of IC60MA is due to higher activation energy, Ea, and lower pre-exponential factor, A. The values of Ea for the RDA reactions differ due to crystal packing efficiency in the solids. The measured A values were found to reflect the statistical weight of C60–Indene bonds that can be broken. A reaction mechanism was proposed for the decomposition of the fullerene adducts. The enthalpies of sublimation of IC60MA and IC60BA were estimated based on the enthalpies of their respective RDA reactions. Additionally, the heat capacities of the solid fullerenes (C60, IC60MA, and IC60BA), at T = 298.15 K, were measured by high-precision heat capacity drop calorimetry, indicating that the rotational motion of C60 in the crystal increases its expected heat capacity.

A pyrolysis model for the thermal decomposition of low-density polyethylene blended with ammonium polyphosphate and pentaerythritol

In this work, a semi-empirical pyrolysis model is developed to predict the thermal decomposition behavior of an intumescent fire retardant (IFR) system consisting of ammonium polyphosphate/pentaerythritol (APP/PER) with the ratio 3:1 (wt/wt) in a low-density polyethylene (LDPE) matrix. This work is based on a previously developed semi-global reaction mechanism for the degradation of LDPE and APP/PER, which consists of two consecutive first-order reactions for the LDPE and five first and second-order reactions for the APP/PER combination. The apparent properties that define heat transport inside the pyrolyzing solid are determined via inverse modeling of cone calorimeter experiments for the pure LDPE and then for the complete IFR system. This is achieved by using the Shuffled Complex Evolution optimization algorithm. The flame heat flux in the cone calorimeter experiments is also evaluated by targeting the heat release rate (HRR) data in the optimization process of one of the cone radiative heat setups. The optimized parameters and flame heat feedback are in line with the literature and the robustness of the model is assessed by a comparison with the experimental data for a wide range of cone heat fluxes. Ignition times and peaks of HRR and total HRs are within the engineering accuracy whatever the flux conditions for both pure LDPE and the IFR system.

Investigation of Light-Induced Degradation in B-Doped Mono-Like Silicon PERC Cells by a Cycling Test With Light Soaking and Dark Annealing

We investigated light-induced degradation (LID) of passivated emitter and rear contact cells fabricated from B-doped cast-grown mono-like Si by conducting a cycling test comprising light soaking (illumination intensity of 1 sun at 95 °C) and dark annealing (at 175 °C for 30 min). Degradation and regeneration were observed in both the first light soaking (LS1) and subsequent light soaking after dark annealing (LS2 and LS3), but the extent and timescale were significantly different. The normalized defect density (NDD) during light soaking was analyzed by fitting based on first-order consecutive reaction models. Systematic residuals between the NDD and the three-state consecutive reaction model were observed in the early and regeneration regions during LS1. We discussed the scenarios that could explain the cause of these residuals, and the values of the reaction rate constants and capture cross-section ratio suggested that two types of LIDs occurred simultaneously in LS1. We concluded that one of the two types of LIDs was light- and elevated-temperature-induced degradation, but we could not identify the other LID with a larger extent and timescale.

Impact of the Non-Uniform Catalyst Particle Size on Product Selectivities in Consecutive Reactions

The analysis of consecutive reactions A→B→C in porous catalyst particles, where the simultaneous processes of diffusion and chemical reactions take place and both reactant and products are subjected to diffusion limitations, was performed for catalyst particles with non-uniform sizes, a fact that has not been considered so far. The system comprises first-order consecutive irreversible reactions that proceed on spherical catalyst particles with a log-normal volume particle size distribution (PSD), which is typical in many catalytic applications. Regardless of the prevailing diffusion regime (chemical control, transition situation or intraparticle diffusion control), the yield of the intermediate product (B) reaches a maximum value as a function of the conversion of reactant (A), then decreases as a consequence of the prevalence of the secondary reaction that converts it into the secondary product (C). If intraparticle diffusion resistances affect the reactant species, given the relationship between the kinetic constants and the mean particle size, the selectivity to the intermediate product is negatively affected by the dispersion in PSD. The larger the dispersion in PSD, the stronger the negative impact.

Measurement of the Kinetics and Thermodynamics of the Thermal Degradation for a Flame Retardant Polyurethane-Based Aerogel

The current work aims to study the thermal degradation of the flame retardant polyurethane aerogel (FR_PU_aerogel) through multiple milligram-scale experimental methods. A systemic methodology for measuring the reaction kinetics and thermodynamics of the thermal degradation of FR_PU_aerogel is detailed. Specifically, the thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were performed simultaneously in inert atmosphere to measure the mass loss and heat flow data, and a numerical framework called ThermaKin2Ds was used to inversely model these experimental data. First, a reaction mechanism with six first-order consecutive reactions was developed based on the inverse analysis of the TGA data. The corresponding reaction kinetics were optimized using the hill climbing optimization algorithm. Subsequently, the heat capacities of each condensed phase component and the heat of the reactions were obtained through inversely modeling the heat flow data. Furthermore, the heat of the complete combustion of each gaseous component were derived based on the heat release rates measured in the milligram-scale combustion calorimeter (MCC) experiments. It is noted that the developed reaction mechanism was further validated against the mass loss data obtained at different heating rates. The parameters determined in this work serve as a core subset of inputs for the pyrolysis model development, which is essential for the quantitative understanding of the ignition and the combustion behavior of solid materials.

Biotin-functionalized silica nanoparticles loaded with Erythrosine B asselective photodynamic treatment for Glioblastoma Multiforme

In this contribution, we report the development of a biotin-functionalized silica nanoparticle loaded with Erythrosine B (ERY) to act as a selective cancer nanoplatform via Photodynamic Therapy. Amino silica nanoparticles were synthesized by the co-condensation method and further functionalized via amide linkage with biotin. The silica nanoparticles (mean diameter ∼120 nm) were loaded with ERY yieldings of 34.9 mg g−1 and 16.7 mg g−1, respectively, for the non-biotinylated (ERY/SiNP) and biotinylated (ERY/SiNP-B). The adsorption followed two consecutive first-order reactions, and the isotherms fitted to the Langmuir (SiNP) and Freundlich (SiNP-B) models. The ERY is strongly attached to the silica nanoparticle, which prevents their premature leakage to the biological fluids. The well-established effect of the uric acid as a singlet oxygen scavenger was used to show the 1O2 formation by the nanoplatforms. Trypan blue and MTT cytotoxic assays have shown that ERY/SiNP and ERY/SiNP-B samples are potential systems for PDT applications against Gliobastoma Multiforme (GBM) cancer cells vanishing around 50 % of T98G cells.

Untargeted analysis of TD-NMR signals using a multivariate curve resolution approach: Application to the water-imbibition kinetics of Arabidopsis seeds

The aim of this study is to investigate the ability of Time-Domain Nuclear Magnetic Resonance (TD-NMR) combined with Multivariate Curve Resolution Alternating Least Squares (MCR-ALS) analysis to detect changes in hydration properties of nineteen genotypes of Arabidopsis (Arabidopsis thaliana) seeds during the imbibition process.The Hybrid hard and Soft modelling version of MCR-ALS (HS-MCR) applied to raw TD-NMR data allowed the introduction of kinetic models to elucidate underlying biological mechanisms. The imbibition process of all investigated hydrated Arabidopsis seeds could be described with a kinetic model based on two consecutive first-order reactions related to an initial absorption of water from the bulk around the seed and a posteriori hydration of the internal seed tissues, respectively. Good data fit was achieved (LOF % = 0.98 and r2% = 99.9), indicating that the hypothesis of the selected kinetic model was correct. An interpretation of the mucilage characteristics of the studied Arabidopsis seeds was also provided.The presented methodology offers a novel and general strategy to describe in a comprehensive way the kinetic process of plant tissue hydration in a screening objective. This work also proves the potential of the MCR methods to analyse raw TD-NMR signals as alternative to the controversial and time-consuming pre-processing techniques of this kind of data, known to be an ill-conditioned and ill-posed problem.

Removal of Acetaminophen Residues from Wastewater by Bulk Liquid Membrane Process

The removal of Anit-Inflammatory drugs, namely; Acetaminophen (ACTP), from wastewater by bulk liquid membrane (BLM) process using Aliquat 336 (QCl) as a carrier was investigated. The effects of several parameters on the extraction efficiency were studied in this research, such as the initial feed phase concentration (10-50) ppm of ACTP, stripping phase (NaCl) concentration (0.3,0.5,0.7 M), temperature (30-50oC), the volume ratio of feed phase to membrane phase (200-400ml/80ml), agitation speed of the feed phase (75-125 rpm), membrane stirring speed (0, 100, 150 rpm), carrier concentration (1, 5, 9 wt%), the pH of feed (2, 4, 6, 8, 10), and solvent type (CCl4 and n-Heptane). The study shows that high extraction efficiency for ACTP of about 97% was achieved by a bulk liquid membrane at 50 ppm initial concentration of feed; stirring speed of feed phase 130 rpm; stirring speed of membrane phase 100rpm; 0.5 M NaCl concentration; carrier concentration 1wt%; volume ratio of 200ml feed:80ml membrane; feed pH of ACTP is 6, and 50˚C. The transport kinetics was evaluated using a kinetic model with two consecutive first-order irreversible reactions. The kinetics of (ACTP) transport by bulk liquid membrane was investigated at the best experimental conditions. The activation energy values of the extraction and stripping processes were 1.733 and 1.826 kJ.mol−1. The activation energy confirms that the transport process from solutions is controlled by diffusion.

Hamiltonian classical thermodynamics and chemical kinetics

Classical thermodynamics have recently been formulated as Hamiltonian systems elevating the theory of heat to the same level of description as analytical mechanics. Particularly, mechanical and thermodynamical systems can merge in a single dynamical theory to describe equilibrium and non-equilibrium processes by constructing homogeneous of first degree in momenta Hamiltonian functions on the extended thermodynamic phase space and in a variety of representations. By employing geometric Hamiltonian theory we show that classical chemical kinetics can also be put in a Hamiltonian framework with Massieu–Gibbs function as the generating Hamiltonian at constant temperature and pressure. A metric in the physical state manifold as well as the entropy production in irreversible chemical reactions are defined. This way we establish a common computational platform for chemical kinetics and chemical dynamics. Numerical results are presented from the study of consecutive first-order elementary reactions and the non-linear kinetic equations of a model for autocatalytic symmetry breaking chiral reactions. For the latter example, we have examined two cases; that of a closed system with fixed initial concentrations and the steady-state case.

Production of acetaldehyde from ethanol in coastal waters

Interest in understanding the cycling of ethanol in the environment has grown as ethanol use as a gasoline additive has increased. The production of acetaldehyde from ethanol was measured in Southern California coastal seawater. The rate of increase of acetaldehyde was positively correlated with the rate constant for ethanol biodegradation and bacteria count and was consistent with two consecutive first-order reactions where acetaldehyde is first biologically produced from ethanol then consumed. Correlation with bacteria counts suggested that acetaldehyde degradation was also a biological process. The rate constants for acetaldehyde production from ethanol and acetaldehyde loss averaged 3.0 ± 3.4 × 10-3min-1 and 2.3 ± 4.5 × 10-2min-1 respectively. The branching ratio for acetaldehyde production from ethanol was 0.46 ± 0.26 and estimated acetaldehyde biological production rates ranged from 0.022 to 0.800nMmin-1. With high bacterial counts, biological production rates from ethanol exceeded photochemical production rates from chromophoric dissolved organic matter. Overall, acetaldehyde production rates were larger than biodegradation rates, suggesting these waters are a source of acetaldehyde to the atmosphere. Extrapolation to higher ethanol concentrations associated with spills suggests that the production rate of acetaldehyde will initially increase and then decrease as ethanol concentrations increase.

Photolysis of thiochrome in aqueous solution: A kinetic study

The photolysis of thiochrome (THC), an oxidation product of thiamine (vitamin B1) (THE), used for its fluorimetric assay, has been studied in the pH range 7.0–12.0. THC undergoes photooxidation to oxodihydrothiochrome (ODTHC) which is oxidized to a non-fluorescent compound (OP1) on UV irradiation. The kinetics of the consecutive first-order reactions: THC→k1ODTHC→k2OP1, has been evaluated and the values of first-order rate constants, k1 (0.58–4.20 × 10−5, s−1) and k2 (0.05–2.03 × 10−5, s−1), at pH 7.0–12.0 have been determined. The rates of degradation of THC and ODTHC are enhanced with pH and the second-order rate constants k1ʹ and k2ʹ for the OH– ion-catalyzed reaction are in the range of 0.002–58.3 M−1 s−1. The quantum yields of the photolysis of THC and ODTHC in the pH range 7.0–12.0 have been determined. THC, ODTHC and OP1 have been identified by chromatographic, spectrometric and fluorimetric methods. THC and ODTHC have similar fluorescence characteristics and emit at 450 and 445 nm, respectively. THC, ODTHC and OP1 with distinct absorption maxima (370, 344 and 290 nm, respectively) have been determined by a newly developed and validated multicomponent spectrometric method during the photolysis reactions. The on-line formation of THC by the photooxidation of THE may lead to the degradation of THC and give erroneous results in the fluorimetric assay of THE. A scheme for the photolysis reactions of THC in aqueous solution is presented.

Extensive study on physicochemical properties of polychlorinated biphenyls in a commercial ion trap mass spectrometer, relevance in analytical and environmental chemistry.

Polychlorinated biphenyls (PCBs) exist as 209 congeners, consisting of biphenyl molecules, where the number and substitution positions of halogen atoms are known to affect industrial uses, environmental transport mechanisms, distribution, fate, and toxicity. The complexity of the problem requires accurate physicochemical studies of an increasing number of congeners in order to understand the environmental and biological processes at play. This work presents a systematic study on the thermodynamic and kinetic properties of PCBs by quadrupole ion trap mass spectrometry. A clear relationship between structure and behavior of PCBs in mass spectrometry experiments has been observed. Overall data demonstrate that di-ortho congeners show lower thermodynamic stability and higher fragmentation rate than non/mono-ortho. Congeners follow different fragmentation mechanisms according to the number of chlorine atoms in ortho position of the biphenyl system. Experimental kinetic curves of mono/non-ortho and di-ortho congeners show a strong similarity with classical first-order kinetics curves; in particular, di-ortho congeners follow a first-order consecutive reaction, while mono/non-ortho follow a first-order parallel reaction. For each studied congener, the kinetic constant of reaction (fragmentation) has been determined. Data support environmental levels and biochemical transformations described in literature. The general picture of the PCB behavior inside a quadrupole ion trap provides the basis for the development of reliable and cost-effective analytical methods to the determination of ultra-low level trace of PCB congeners.

Kinetic Study of the Acid Post-hydrolysis of Xylooligosaccharides from Hydrothermal Pretreatment

Hydrothermal pretreatment of sugarcane bagasse is a water-based and environment-friendly process that results in almost complete hemicellulose solubilization in oligomeric form as xylooligossacharides (XOs). However, the soluble XOs cannot be utilized by microorganisms such as yeasts, and therefore, a further break down is necessary to generate pentose (C5) monomers that can be then biotransformed into ethanol or other metabolites. The kinetics of XOs post-hydrolysis with sulfuric, maleic, and oxalic acids (the latter two being dicarboxylic acids) in a sugarcane bagasse hemicellulosic hydrolysate was assessed in a bench-scale reactor (2 L). By means of a 22 full factorial design with center point triplicate, acid mass loading and temperature were varied from 0.5 and 2.0% and from 120 to 150 °C, respectively. An irreversible first-order consecutive reaction model of the hydrolysis of XOs in liquid medium was employed. Based on an Arrhenius-type equation, a kinetic parameter estimation was performed with genetic algorithms and the Runge-Kutta methods. For the three acids, the calculated exponential factors, A 0n (n = 1, 2, and 3), ranged from 1012 to 1015 min−1; the dimensionless parameters, m n (n = 1, 2, and 3), ranged from 0.86 to 1.97; and the activation energies ranged from 89 to 129.8 kJ·mol−1. The model—developed at microscale—correctly described the observed XOs, C5, and furfural post-hydrolysis profiles in bench scale and proved the dicarboxylic acids were more selective towards post-hydrolysis by having slower kinetics than sulfuric acid.

The possibility of using a mathematical model based on consecutive first-order reactions to describe the Cr(III) ions pertraction in DCSLM system

This paper discusses the use of double- carrier supported liquid membrane (DCSLM) for extraction of Cr(III) ions, using the D2EHPA/CYANEX272 mixture as the carriers. Based on the calculated value of the activation energy and on the assumption that the result of transport process in the DCSLM, in particular, depends on the accumulation of intermediate products in the membrane, the mathematical model of the chromium(III) ions separation based on consecutive first-order reactions has been proposed. Transport kinetics of chromium(III) in studied system for different carriers concentrations ratio and their comparison with theoretical prediction was analyzed. The obtained results confirmed the presence of a synergistic effect of selected carriers in DCSLM. Verification of the proposed model has been carried out in the article. Mathematical model describes correctly the membrane transport process only for most effective carriers ratio. It was found that depending on the carriers ratio in DCSLM the transport processes may be controlled by both chemical reaction and diffusion. The described model can be a useful tool for quickly and approximate determination of the transport process parameters in experimental works but is too simple to correctly describe the Cr(III) ions pertraction in supported liquid membrane system under the full range of process parameters (especially concentrations and proportions of the used carrier).

Mechanism and kinetics of the pyrolysis of β-pinene to myrcene

Myrcene, an important intermediate for the production of fine chemicals and pharmaceuticals, is mainly produced by the pyrolysis of β-pinene in the industry. The study of the direct pyrolysis of β-pinene was carried out without a catalyst and carrier gas at 573–873K and under low pressure. In order to clarify the reaction mechanism, the primary intermediates of β-pinene pyrolysis including myrcene and limonene were also used as raw materials for further pyrolysis. The identification of some small molecules and C10H16 isomers in the products proves that both decomposition reaction and ene reaction take place during the pyrolysis process. Based on the qualitative and quantitative analysis of reaction products, a reaction scheme for the pyrolysis of β-pinene was proposed. With appropriate simplification of the reaction scheme, a phenomenological kinetic model of the competitive parallel and consecutive first-order reaction was built, and exhibited good agreement with the experimental data. The activation energy (Ea) and pre-exponential factor (k0) for each pathway were also determined.

Kinetics of Dimethylated Thioarsenicals and the Formation of Highly Toxic Dimethylmonothioarsinic Acid in Environment.

Dimethylmonothioarsinic acid (DMMTAV) is a highly toxic, thiolated analogue of dimethylarsinic acid (DMAV). In comparison, a further thiolated analogue, dimethyldithioarsinic acid (DMDTAV), and DMAV both exhibit lower toxicity. To understand the environmental conditions responsible for forming DMMTAV, the kinetics of DMAV thiolation are examined. The thiolation of DMAV is pH-dependent and consists of two consecutive first-order reactions under excess sulfide conditions. The first thiolation of DMAV to form DMMTAV is faster than the second one to DMDTAV. DMMTAV is therefore an intermediate. The first reaction is first-order in H2S at pH 6.0 and 20 °C; therefore, the overall reaction is second-order and the rate coefficient in this condition is 0.0780 M-1 s-1. The rate coefficient significantly decreases at pH 8.0, indicating that H2S(aq) triggers the thiolation of DMAV. The second reaction rate is significantly decreased at pH 2.5; therefore, reaction under strongly acidic conditions leads to accumulation of highly toxic DMMTAV in the early stages of thiolation. The transformation of DMDTAV to DMMTAV is catalyzed in the presence of ferric iron. Formation of DMMTAV should be considered when assessing risk posed by arsenic under sulfidic or sulfate reducing conditions.

Multi-technique approach for qualitative and quantitative characterization of furazidin degradation kinetics under alkaline conditions

Degradation of drug furazidin was studied under different conditions of environmental pH (11–13) and temperature (30–60°C). The novel approach of hybrid hard- and soft-multivariate curve resolution-alternating least squares (HS-MCR-ALS) method was applied to UV–vis spectral data to determine a valid kinetic model and kinetic parameters of the degradation process. The system was found to be comprised of three main species and best characterized by two consecutive first-order reactions. Furazidin degradation rate was found to be highly dependent on the applied environmental conditions, showing more prominent differences between both degradation steps towards higher pH and temperature. Complimentary qualitative analysis of the degradation process was carried out using HPLC-DAD-TOF-MS. Based on the obtained chromatographic and mass spectrometric results, as well as additional computational analysis of the species (theoretical UV–vis spectra calculations utilizing TD-DFT methodology), the operating degradation mechanism was proposed to include formation of a 5-hydroxyfuran derivative, followed by complete hydrolysis of furazidin hydantoin ring.