Perchloric Acid Concentration Research Articles

Electrocatalyst hydrogenation of lignol-derived compounds: Conversion regularity and product selectivity

Phenolic derivatives, crucial components of bio-oil, require thorough understanding of their electrocatalytic hydrogenation (ECH) properties for efficient bio-oil utilization. This study investigated guaiacol, a representative phenolic derivative in bio-oil, focusing on its ECH mechanism, conversion, and product selectivity under varied conditions (temperature: 40–80 °C, perchloric acid concentration: 0.2–1.0 mol/L, current intensity: ((–10)–(–150) mA). Additionally, this study also explored the influence of intermediate products (2-methoxycyclohexanone and cyclohexanone) on both the conversion rate and the selectivity of the products. The experiment had revealed that guaiacol's ECH conversion rate improved with higher temperature and current intensity, whereas an increase in perchloric acid concentration negatively affected the conversion. Significantly, the presence of intermediate products, especially 2-methoxycyclohexanone, markedly enhanced the ECH conversion of guaiacol. Investigating further into the ECH mechanism of other phenolic derivatives, including phenol, pyrocatechol, guaiacol eugenol, and vanillin, as well as their combination, revealed a trend where conversion rates inversely correlated with the complexity of the functional groups on the benzene ring. Specifically, phenol, with its simpler structure, showed the highest conversion rate at 89.34%, in stark contrast to vanillin which, owing to its more complex structure, exhibited the lowest at 46.79%. In our multi-component mixture studies, it was observed that synergistic and competitive interactions significantly alter ECH conversion rates, with some mixtures showing enhanced conversion rate indicative of synergistic effects.

Determination of phosphorus in commercially available milk using ion chromatography with perchloric acid deproteinization.

Suppressed ion chromatography with perchloric acid deproteinization was developed for the determination of phosphorus in commercially available milk. Although the perchloric acid deproteinization method is widely used in the medical field, it sees limited application in the food industry. Herein, the concentration of perchloric acid and hydrolysis conditions were examined, specifically regarding perchloric acid deproteinization, which was used as a deproteinization method in this study. The calibration curve constructed from the peak area of orthophosphoric acid (monohydrogen phosphate ion: HPO42-) was linear, with a correlation coefficient of 0.999. The relative standard deviation of the peak area of 50mg/L of HPO42- from six replicates was 0.35%. The detection and quantitative limits of HPO42-, calculated from its signal-to-noise ratio were 0.033mg/L and 0.100mg/L, respectively. The proposed method was applied to the analysis of phosphorus in commercially available milk. Perchloric acid deproteinization has proved to be useful in the food industry.

Versatile ferrous oxidation-xylenol orange assay for high-throughput screening of lipoxygenase activity.

Lipoxygenases (LOXs) catalyze dioxygenation of polyunsaturated fatty acids (PUFAs) into fatty acid hydroperoxides (FAHPs), which can be further transformed into a number of value-added compounds. LOXs have garnered interest as biocatalysts for various industrial applications. Therefore, a high-throughput LOX activity assay is essential to evaluate their performance under different conditions. This study aimed to enhance the suitability of the ferrous-oxidized xylenol orange (FOX) assay for screening LOX activity across a wide pH range with different PUFAs. The narrow linear detection range of the standard FOX assay restricts its utility in screening LOX activity. To address this, the concentration of perchloric acid in the xylenol orange reagent was adjusted. The modified assay exhibited a fivefold expansion in the linear detection range for hydroperoxides and accommodated samples with pH values ranging from 3 to 10. The assay could quantify various hydroperoxide species, indicating its applicability in assessing LOX substrate preferences. Due to sensitivity to pH, buffer types, and hydroperoxide species, the assay required calibration using the respective standard compound diluted in the same buffer as the measured sample. The use of correction factors is suggested when financial constraints limit the use of FAHP standard compounds in routine LOX substrate preference analysis. FAHP quantification by the modified FOX assay aligned well with results obtained using the commonly used conjugated diene method, while offering a quicker and broader sample pH range assessment. Thus, the modified FOX assay can be used as a reliable high-throughput screening method for determining LOX activity. KEY POINTS: • Modifying perchloric acid level in FOX reagent expands its linear detection range • The modified FOX assay is applicable for screening LOX activity in a wide pH range • The modified FOX assay effectively assesses substrate specificity of LOX.

Effect of Electrolyte Anions on the Activity of Iridium Oxide Catalysts for Water Electrolysis

Developing environmentally friendly and renewable energy sources is essential due to the environmental and energy security issues caused by traditional combustion of fossil fuel-based energy sources. Therefore, as a clean and sustainable energy carrier, hydrogen has attracted great attention in recent years. In this regard, water electrolysis utilizing renewable energy sources to produce hydrogen is considered one of the most promising technologies. It is believed elucidation of the reaction mechanism of highly active iridium oxides is promising for the further development of cost-efficient PEM water electrolysis catalysts. The properties of the MEA could be affected by many parameters such as the catalysts, operating temperature, and pressure1,2. Another important factor is the cation impurities that can be found in the circulating water, which could severely degrade the MEA performance during the operation of a PEM water electrolyze. However, there are less reports on anion impurities such as SO4 2- and PO4 3-. Therefore, in this study, the relationship between electrolyte anions and OER activity was investigated for IrOx catalysts with different crystal structure. By using operando X-ray absorption spectroscopy (XAS), we investigated the electronic state of Ir and O under operation potential.IrOx with different degree of crystallinity (SA3.5 and SA58) were provided by Tanaka Kikinzoku Kogyo K.K., Chemical & Refining Company and named after their BET surface areas. These two samples were then tested for electrochemical properties in different concentrations of phosphoric acid and perchloric acid, respectively. The electrochemical measurements were performed using a standard three-electrode cell connected to an MPG-205-NUC system (Bio-Logic). The cyclic voltammograms (CV) were scanned from 0.1 V to 1.2 V vs. RHE at 50 mV s-1. The electrochemical activities of the catalysts were subsequently investigated using linear sweep voltammetry (LSV) in the range of 1.1 to 1.7 V vs RHE at 10 mV s−1. operando XAS were collected using a home-made flow-type cell, where Pt wire and RHE worked as counter and reference electrodes, respectively. The catalyst ink was coated onto an Nafion membrane to prepare both the X-ray window and working electrode. The electrolyte was circulated at the flow rate of 100 mL min-1.The catalytic performance of IrOx was investigated at different types and content of electrolyte under H3PO4 and HClO4. Figure 1 shows the CVs of SA3.5 and SA58 under different types and content of electrolyte. In the presence of phosphate anions, SA3.5 showed a tendency to decrease Ir redox between 0.6 and 1.1 V with increasing electrolyte concentration. On the other hand, there were no obvious changes in SA58. It was found that IrOx catalysts have an great effect of specific adsorption of anions and low symmetry of monoclinic phase catalysts (SA 3.5) are more susceptible to anion poisoning. Figure 2 shows the result of examining the poisoning mechanism using soft X-ray XAS. O K-edge results present the formation of µ2-O (O-O) bond at around 528.7 eV, which was previously observed by Nong, H. N. et. al. through operando O-K edge measurements during OER process3. The peak intensity at 528.7 eV of the amorphous samples was in the same order as the OER activities. According to potential dependence change of the pre-edge peak, under the presence of phosphate anions, the hole formation to Ir-O hybrid orbitals was suppressed in SA3.5. This result indicates that the anion adsorbs to the active site, poisoning the catalyst surface and inhibiting the reaction. Acknowledgements This work is based on results obtained from a project (JPNP14021) commissioned by the New Energy and Industrial Technology Development Organization (NEDO) of Japan. References Zhang, Y.; Zhu, X.; Zhang, G.; Shi, P.; Wang, A.-L.; et al. J. Mater. Chem. A: 2021, 9, 5890-5914.Chen, Z.; Duan, X.; Wei, W.; Wang, S.; Ni, B.-J.; et al. Nano Energy: 2020, 78, 105270.Nong, H. N.; Falling, L. J.; Bergmann, A.; et al. Nature 2020, 587 (7834), 408-413. Figure 1

Modeling the Environment-Dependent Kinetics of Oxygen Reduction Reaction – a Continuum Model for Electric Double Layer

For proton-exchange-membrane fuel cells (PEMFCs) to achieve broad commercialization, improved energy-conversion efficiency with minimal Pt-based electrocatalyst is required [1]. Because the sluggish rate of oxygen reduction reaction (ORR) limits the efficiency of PEMFCs [2], the efficiency improvement requires a better understanding of ORR kinetics and mechanism to design better catalyst. To understand the ORR mechanism, theoretical and experimental analyses have been conducted. While previous studies reasonably explained the catalyst-dependent activity on single crystal catalysts in 0.1 M perchloric acid solution [3, 4], the explicit effect of electrolyte and related microenvironments [5, 6] is not thoroughly understood. The change in the electrolyte alters the electric-double-layer (EDL) structure and thus the local microenvironment at the electrode/electrolyte interface. Thus, the structure of the EDL should be carefully analyzed to uncover the electrolyte-dependent reaction kinetics. In this talk, we propose a multiscale continuum model to predict the EDL structure and examine the effect of perchloric acid concentration on ORR activity on Pt (111). The model includes Density Potential Functional Theory (DPFT) for electron density and Modified Poisson Boltzmann equation for species’ density and electric potential [7]. Also, the interaction between adsorbents and electric field is taken into account by minimizing the grand potential. After model validation with experimentally measured double-layer capacity data as a function of applied potential and concentration, the effect of the perchloric acid concentration (0.02 M – 0.2 M) on ORR activity is analyzed and discussed. It is shown that the model reproduces the specific activity obtained in the experiments when assuming the oxygen adsorption is limiting the rate, which can be attributed to the large energetic barrier for solvent reorganization [8]. Then, extension of the model to PEMFC ionomer electrolytes will be introduced. Overall, the model framework and findings provide insights into the ORR mechanism and guidance on how to tailor catalyst materials for increased PEMFC performance. Acknowledgements: This work was partially supported by the Hydrogen and Fuel Cell Technologies Office (HFTO), Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy (DOE) through the Million Mile Fuel Cell Truck (M2FCT) consortia, technology managers G. Kleen and D. Papageorgopoulos, under contract number DE-AC02- 05CH11231, as well as by a CRADA with Toyota Central R&D Labs., Inc.. Reference [1] D. A. Cullen, K. C. Neyerlin, R. K. Ahluwalia, R. Mukundan, K. L. More, R. L. Borup, A. Z. Weber, D. J. Myers and A. Kusoglu, Nature Energy, 6, 462 (2021).[2] I. E. L. Stephens, A. S. Bondarenko, U. Grønbjerg, J. Rossmeisl and I. Chorkendorff, Energy & Environmental Science, 5 (2012).[3] M. Shibata, M. Inaba, K. Shinozaki, K. Kodama and R. Jinnouchi, Journal of The Electrochemical Society, 169 (2022).[4] H. A. Hansen, V. Viswanathan and J. K. Nørskov, The Journal of Physical Chemistry C, 118, 6706 (2014).[5] K. Kodama, K. Motobayashi, A. Shinohara, N. Hasegawa, K. Kudo, R. Jinnouchi, M. Osawa and Y. Morimoto, ACS Catalysis, 8, 694 (2017).[6] M. Luo and M. T. M. Koper, Nature Catalysis, 5, 615 (2022).[7] J. Huang, J Chem Theory Comput, 19, 1003 (2023).[8] D. T. Limmer, A. P. Willard, P. Madden and D. Chandler, Proceedings of the National Academy of Sciences, 110, 4200 (2013).

Flash electropolishing of BCC Fe and Fe-based alloys

The preparation of transmission electron microscopy (TEM) samples is a critical step in the characterization of materials, and the focused ion beam (FIB) technique is a commonly used method. However, a significant limitation of this technique is the FIB-induced damages on the foil surfaces, which can obscure the real features of interest, particularly in radiation effects studies. To overcome this limitation, this study presents a detailed description of the flash electropolishing technique, which can be used to remove the FIB damage from samples. The flash electropolishing technique has been successfully applied to a range of materials, including Fe, Fe-based model alloys, commercial Fe-Cr alloys, and advanced Fe-Cr alloys, both in their as-received and ion-irradiated states. Furthermore, the parameters used for Fe-Cr model alloys can be adjusted for commercial and advanced alloys with minimal modifications. The study also examined the effects of electropolishing variables, such as perchloric acid concentration, electropolishing temperature, Cr concentration, and voltage. Qualitatively, a general trend and scoping test strategy is explored in our experiments. Overall, the flash electropolishing technique offers a promising solution to the challenges posed by FIB-induced damages in the preparation of TEM samples.

Proton Relay Effects on Oxygen Reduction Reaction Catalyzed by Dinuclear Cobalt Polypyridyl Complexes with OH Groups on Bipyridine Ligands

Abstract Four-electron oxygen reduction reaction (4e−-ORR) is the foundation of both natural and artificial energy conversion systems. Mechanism studies and catalysis improvements of 4e−-ORR are important research for the actualization of a sustainable society. In this study, we present a dinuclear cobalt complex containing mono-deprotonated forms of 6,6′-dihydroxy-2,2′-bipyridine (6DHBP-H+), [Co2(OH)2(6DHBP–H+)2(btpyxa)](PF6)2 (2) is a highly active 4e−-ORR catalyst in a low acid concentration solution. When ferrocene (Fe(Cp)2) was used as a reductant in PhCN containing a low concentration of perchloric acid (1.0 mmol L−1), 2 showed higher selectivity (99%) and reaction rate (kcat = 6.0 × 103 M−1 s−1) for 4e−-ORR than the bpy analog 1 (kcat = 6.2 × 10 M−1 s−1) and 4DHBP analog 3 (kcat = 1.5 × 102 M−1 s−1). A high catalytic current in the cyclic voltammetry (CV) of 2 indicates a high reaction rate for electrochemical ORR under low acid concentration conditions. Moreover, X-ray crystallography of the corresponding monomeric analog [Co(OH2)(6DHBP–2H+)(trpy)](PF6) (4, 6DHBP–2H+: a doubly deprotonated form of 6DHBP) suggests that OH groups of 2 can form hydrogen bonds with a μ-O2 ligand. Hydroxy groups at the 6,6′-position of bpy would deliver protons to the μ-O2 ligand of the intermediate, thereby promoting O–O bond cleavage in the proton-coupled electron transfer (PCET) process.

Optimization of inhibition efficiencies process of polyvinylpyrrolidone using response surface methodology

Inhibition efficiencies (IE) process in polyvinylpyrrolidone (PVP) which is influenced by independent factors, concentration and size of PVP, temperature, time of immersion, and perchloric acid concentration was investigated in this paper. The relationship between factors and their responses is established by the concept of response surface methodology (RSM) explicitly through regression statistical analysis and probabilistic analysis is used in this work. The concept is a combination of mathematical and statistical techniques allowing the modeling and problems analysis by experimental design. In this study, the results based on statistical analysis showed that the quadratic models for the inhibition efficiencies (IE) were significant at the value of probability P < 0.0001 and the coefficient of multiple regressions R2=0.9997, for further validation of the model, R2Adj=0.9993 indicated a good model. The observed experimental values were in good agreement with predicted ones and the model washighly significant with Q2= 0.9884. The optimal conditions of inhibition efficiencies (IE) obtained are 104.301% for a concentration of 3.55×10−3 mol/L, temperature of 20.15°C, immersion time of 2h, size of PVP 58000 g/mol, and acid concentration of 0.5 mol/L.

Water purification from cationic organic dyes using kaolin-based ceramic materials

The development of effective sorbents based on cheap natural raw materials for water purification from synthetic organic dyes is an important environmental problem. It is known that layered silicates are distinguished by mechanical strength, thermal and chemical resistance, high dispersion, ion exchange, availability and low cost. However, the main disadvantage of natural clays is their insufficiently high sorption capacity with respect to organic toxicants. Therefore, to increase it, the surface of clay minerals is modified by various physical and chemical methods. The object of study is kaolin from the Glukhovets deposit (Ukraine), the main rock-forming mineral of which is kaolinite. After its thermal modification followed by acid activation with chloride acid, sorbents with sufficiently high structural-sorption properties and increased sorption capacity with respect to the synthetic organic dye, methylene blue, are obtained. The influence of the conditions for the synthesis of ceramic materials on the physicochemical features of the dye removal from the aqueous medium is studied. The dependence of the values of methylene blue sorption by silicate sorbents on the temperature of kaolin treatment and the concentration of chloride acid, which was used for its acid activation, is studied. It has been established that the specific surface of the obtained samples is significantly affected by both the kaolin treatment temperature and the concentration of perchloric acid. Thus, under certain experimental conditions, sorption materials were obtained with a specific surface area of 140 m2/g, which significantly exceeds that for the original kaolin, which is 9 m2/g. A significant increase in the sorption capacity of acid-activated samples compared to the original clay and heat-treated forms was established. The value of the maximum sorption of methylene blue for acid-activated samples exceeds that for natural kaolin by almost 2 times and reaches 16 mg/g.

1,2-Bis(4-Pyridyl) Ethane Catalysed Oxidative Conversion of D-Lactose to Lactobionic Acid by Cr(VI) in Aqueous Acetic Acid Medium: A Kinetic and Mechanistic Study

The kinetics of oxidation reactions and the investigations of the reaction mechanisms from the kinetic data have been always the more interesting in the chemical research and industrial applications. The kinetics of oxidation of sugars has been a subject of extensive research in recent years. The biological as well as the economic importance of carbohydrates is responsible for the great interest in the study of their bio- and physio -chemical properties. The kinetics of oxidative degradation of different sugars by metal ions including Cr (VI) has been studied under different conditions. Chomium (VI) compounds are powerful oxidants at low or neutral pH as well as Cr (VI) is a well-known oxidant in acetic media. Aim of our present investigation deals with oxidation of D-Lactose using Cr (VI) Oxidizing agent, Trimethylammonium fluorochromate [TriMAFC] which was carried out in protic solvent as a medium at 308 K in the presence of 1,2-bis(4-pyridyl)ethane as a catalyst . The oxidation of D-Lactose yields the corresponding aldonic acid and Cr3+ as final products. Lactobionic Acid (LBA) has been used for food and pharmaceutical applications. Thus the kinetics and mechanism of carbohydrates using Cr (VI) as oxidant, 1,2-bis(4-pyridyl)ethane as a catalyst is very important from biochemical and kinetic viewpoints. Our experimental studies showed that reaction progressed with first order kinetics with respect to [TriMAFC], [1,2-bis(4-pyridyl)ethane] and [H+] with the fractional Order dependence on [DLactose]. It was found that introduction of sodium perchlorate results in decrement of the reaction rate substantially. The rate constant increased with increase in the concentration of perchloric acid. Also, the rate of reaction decreases with increasing the concentration of acetic acid. For acrylonitrile, no polymerization occurs. The reaction was carried out at four different temperatures to determine the activation parameters. An appropriate mechanism was suggested based on the observed kinetic effects.

Spectral manifestation of protonation of photochromic naphthopyrans

The formation of proton complexes of the photoinduced colored open form of naphthopyrans in solutions was first discovered and investigated by spectral-kinetic method. The complexes exhibit a new absorption band in the visible region, which is bathochromically shifted relative to the absorption band of the photoinduced colored open form. With an increase in the concentration of perchloric or hydrochloric acid, this long-wavelength absorption band appears immediately after the addition of acids to solutions of photochromic compounds. The protonation efficiency depends on the strength of the acids.

Chaotropic chromatography method development for the determination of aripiprazole and its impurities following analytical quality by design principles.

In this paper, development of robust and reliable chaotropic chromatography method for the determination of aripiprazole and its impurities, following Analytical Quality by Design principles is presented. The efficient baseline separation and accurate determination of aripiprazole and its four impurities from tablets were set as Analytical Target Profile. In line with it, the influence of Critical Method Parameters (acetonitrile content, concentration of perchloric acid in water phase, and column temperature) on predefined Critical Method Attributes (separation of the critical pair of peaks, retention of the first and last eluting peak) was investigated with aid of the Central Composite Design. Further on Design Space, where Critical Method Parameters meet predefined acceptance limits with a high level of probability (π ≥ 85%), was computed as a result of performed Monte Carlo simulations. A normal operating conditions corresponding to 34% of acetonitrile, 66% of 42.5mM perchloric acid, and column temperature at 35°C were selected from created Design Space. Robustness testing of the quantitative performances of the developed method was conducted combining Plackett-Burman design with alias matrix approach. Through the additional validation testing, reliability of the developed method for the use in the routine practice was completely confirmed.

Synthesis Biolubricant By Esterification Of Castor Oil (Jatropha Curcas L-Oil) With Chlorate Acid Catalyst

Biolubricant is made by reacting vegetable oil with alcohol with the help of strong acid or strong base catalyst in the esterification process. The goal of this research is to know the flash point of bio-lubricant, and know its characteristics. This research is done by reacting Jatropha oil and methanol reactant with perchloric acid with a variety of reactant mol and variety concentration of perchloric acid as a catalyst with esterification time of 7 hours, after that it will be purified by a various method to get the desired result. Results in this research have the highest flash point on 26 °C and lowest on 242 °C; highest viscosity on 217 cP and lowest on 130, 5 cP at 40 °C. At other temperature, the best viscosity is 184,5 cP at 40 °C and 27,45 cP at 100 °C. Average pour point from this bio-lubricant is -18,8 °C. Almost chemistry compound of Biolubricant contains fatty acid 9,12-Octadecadienoic acid (Z, Z) with methanol resulting monoester compound 9-Octadecenoic acid (Z)-, 2-hydroxy-1-(hydroxymethyl) ethyl ester.

Kinetic models for the extraction of copper by Acorga M5640 after leaching of malachite ore in perchloric acid solutions and the stripping of copper from loaded organic phase

In the present work, the extraction kinetics of copper using the resulting actual leach solution obtained from the leaching of malachite ore in perchloric acid solutions and the stripping kinetics of copper from the loaded organic phase were examined. The organic phase was prepared by using Acorga M5640 and kerosene. In the extraction process, the effects of the initial pH of aqueous solution, initial concentration of copper, extractant concentration, temperature, and stirring speed on the extraction rate were investigated. In the stripping process, the effects of the concentration of perchloric acid, temperature, stirring speed, and extractant concentration on the stripping rate were examined. It was determined that the extraction rate increased with increasing the initial pH of aqueous solution, stirring speed, extractant concentration and temperature, and with decreasing the initial concentration of copper ions. In the stripping process, it was observed that the stripping rate increased with increasing the concentration of perchloric acid, temperature and stirring speed, and with decreasing the extractant concentration. It was determined that both the solvent extraction and stripping processes could be described by the first order pseudo homogenous reaction model. The activation energy for the extraction and stripping processes was calculated to be 50.04 kJ/mol and 32.42 kJ/mol, respectively.

Enhanced electromagnetic wave absorption by optimized impedance matching: covalently bonded polyaniline nanorods over graphene nanoplates

Absorbers based on graphene nanoplates (GNPs) are a promising and low-cost solution to electromagnetic (EM) wave pollution; however, it is well known that GNPs by themselves cannot effectively attenuate an EM wave. To elucidate the limiting factors of GNPs and their mechanism of EM wave absorption, a series of GNP-polyaniline composites (GNPs-PANI) were fabricated by growing polyaniline (PANI) nanorods in situ over GNPs with various concentrations of perchloric acid (HClO4) as a dopant. The correlation between HClO4 doping concentration and microstructures as well as conductivity were investigated. The microwave absorbing performance (MAP) was examined, and it was found that when the doping concentration of HClO4 was 1 M, the effective absorption bandwidth (i.e., the range where the reflection loss (RL) < − 10 dB) was as wide as 5.81 GHz and covered the entire X-band. By investigating the effects of impedance matching and attenuation characteristics, we were able to demonstrate that impedance matching is the limiting factor, and that it can be optimized by coating the GNPs with PANI nanorods. To facilitate practical applications, a coating of phenol–formaldehyde resin (PF) filled with GNPs-PANI (PF/GNPs-PANI) was fabricated by spraying, and the effective absorption bandwidth was 3.5 GHz (14.5–18 GHz).

The role of formic acid/formate equilibria in the oxidation of formic acid on Pt (111)

The formic acid oxidation reaction has been studied in concentrated perchloric acid solutions (up to 9.14 M (60%)) on the Pt (111) surface to explore the relationships between interfacial properties and kinetics. It is found that, as the concentration of perchloric acid in the supporting electrolyte increases, the current markedly decreases, making it possible to detect adsorbed formate on the surface by voltammetric methods. With the aid of DFT calculations, it is shown that the diminution in current is the result of two opposing factors: the reduction in the concentration of free formate in solution and electrode charge effects which encourage the adsorption of formate in a particular configuration. Additionally, the electrochemical behavior under highly acidic conditions suggests the formation of clathrate structures and emphasizes the relevance of the water structure effect in electrode adsorption processes.

Investigation of selective leaching and kinetics of copper from malachite ore in aqueous perchloric acid solutions

ABSTRACTIn this study, the leaching kinetics of malachite in perchloric acid solutions was investigated. The dissolution behaviors of copper, zinc, and iron in the ore matrix were determined at different acid concentrations and reaction temperatures. It was observed that the concentration of perchloric acid had a major effect on the dissolution of copper, zinc, and iron. It was determined that the effect of temperature on the dissolution of these species was not as significant as concentration impact. The results obtained shown that copper in the ore matrix was completely leached while zinc and iron were partially dissolved in perchloric acid solutions. In addition, the effects of the acid concentration, reaction temperature, stirring speed, particle size, and solid-to-liquid ratio on the leaching of malachite were researched. In these experiments, it was observed that the leaching rate of copper increased with increasing solution concentration, stirring speed, and reaction temperature, and with decreasing solid-to-liquid ratio and particle size. A kinetic analysis was performed, and it was found that the rate of leaching reaction obeyed the mixed kinetic control model in the unsteady state. The activation energy of the leaching process was calculated to be 34.69 kJ/mol.

On the reactant concentration and the reaction kinetics in the Villermaux-Dushman protocol

The optimum choice of acid and buffer in the iodide/iodate reaction system known as the Villermaux-Dushman protocol has been under debate for several years. In this paper, the phosphate buffer recently suggested by Pinot et al. is for the first time compared to the established boric acid buffer over a large range of concentrations. The results show that the resulting triiodide yield is a function of the phosphate buffer concentration, which is not the case for boric acid buffer. Furthermore, the evaporation and reactive oxidation of iodine species was identified to significantly influence the sample treatment after mixing, while the dismutation of iodine is less influential. Additionally, a comparison of different hydrochloric, sulfuric, and perchloric acid concentrations was conducted. The catalytic effect of chloride on the Dushman reaction was for the first time quantified within a Villermaux-Dushman protocol, as was the incomplete dissociation of sulfuric acid during the mixing process. Interestingly, it can be found that the presence of chloride and sulfate influences the obtained triiodide yield to the same extent. Finally, this study takes a closer look on the investigation of Dushman kinetics as part of a Villermaux-Dushman protocol and elucidates the role of chemical attenuation for these investigations.

Investigation of reaction conditions on synthesis of steroidal bromohydrin and structural analysis of novel 6α-brom-5β-hydroxy derivative

Reaction conditions variation and its influence on the reaction of 3?- acetoxy-17-oxa-17a-homoandrost-5-en-16-one with in situ generated hypobromous acid was investigated. Hypobromous acid was generated from N-bromoacetamide or Nbromosuccinimide and perchloric acid, and as solvent dioxane, dimethoxyethane or tetrahydrofuran were used. After a series of experiments, it was determined that the number of the reaction products depends on the reagent used, solvents, perchloric acid concentration and the presence/absence of daylight. It has also been found that the yields of certain compounds depend also on the reaction time and temperature. 6?-Bromo-5?- hydroxy derivate is obtained by usage of NBA and 0.28 M perchloric acid in dioxane on daylight. Its structure was confirmed by NMR and X-ray crystal structure analysis.

Design of Experiments–Design Space Approach for Development of Chaotropic Chromatography Method for Determination of Trimetazidine Dihydrochloride and Two Impurities

The quality by design approach has been applied to develop a chaotropic chromatography method for determination of trimetazidine dihydrochloride (TMZ) and two impurities (Y-145, Y-234). Baseline separation and accurate determination of the investigated analytes was set as the target analytical profile, with k Y-145, k TMZ, and α Y-145/TMZ selected as critical quality attributes. The critical process parameters studied in this research were pH of water phase, acetonitrile content in mobile phase, and concentration of perchloric acid in water phase. To compute a design space as a region of the knowledge space having satisfactory values of all critical quality attributes at the desired quality level, Monte Carlo simulations were performed to propagate the error originating from the calculated model coefficients to the predicted responses. At each of 4851 defined grid points, 5000 iterations were performed and the region having probability π ≥ 95% of achieving all defined critical quality attributes was computed. A working point situated in the center of the design space was chosen, corresponding to 27% acetonitrile in mobile phase, 63% 170 mM perchloric acid in water phase, and pH of water phase adjusted to 3.60. The method was validated to confirm its reliability for use in routine pharmaceutical analysis.