Aqueous Sulfuric Acid Medium Research Articles

Surface morphology and corrosion behavior of pure aluminum and its alloys in aqueous sulfuric acid medium

AbstractAluminum and aluminum alloys are light materials with some of the preferences such as lightweight, high specific strength, good elasticity, and good workability that play an important role in today's modern and industrial world. The economic loss and environmental and safety problems are also the most concerning aspects of these materials. As a result, numerous studies are performed by the researchers to improve the overall environment throughout the materials world. That is why, in this study, the surface morphology and corrosion behavior of pure aluminum and its alloys, such as 7S10 and 7003H, were investigated in aqueous sulfuric acid medium through immersion process at different temperatures. Open‐circuit potential and potentiodynamic polarization techniques were used to evaluate the resistance to corrosion of pure aluminum and its alloys 7S10 and 7003H. The current density increased with increasing temperature in the case of the alloys, and pure aluminum showed the highest corrosion resistance properties. The surface roughness measurement was performed using atomic force microscope to find out the amount of roughness of the used materials before and after the immersion process. Surface roughness was higher on the alloys than in pure Al, which indicates that less corrosion was formed in pure Al than in the alloys. The surface morphology analysis was also carried out using scanning electron microscopic data. The results revealed that the alloy 7003H undergoes more corrosion than pure aluminum and 7S10 in sulfuric acid medium, which clearly indicates that pure aluminum has higher corrosion resistance than the alloys 7S10 and 7003H. The corrosion rate of the test materials decreased with increasing immersion time.

Spectrophotometric Study of Kinetics of Redox Reaction between Caffeine and Permanganate Ion in Aqueous Acidic Medium

The kinetics of redox reaction between caffeine (hereafter referred to as CAF) and permanganate ion [MnO4-] has been studied spectrophotometrically in aqueous sulfuric acid medium. One mole of CAF was oxidized by one mole of [MnO4-].The reaction showed first-order kinetics with respect to both [CAF] and [MnO4-]. The investigation was carried out under pseudo-first order condition atI= 0.5 mol dm–3, (Na2SO4), T = 24± 0.1℃ and [H+] = 1.0 × 10–1mol dm-3. The reaction obeys the rate law: -d[MnO4-]/dt = (a+b [H+]) [CAF ] [MnO4-]. The reaction was retarded by increased in ionic strength of the reaction medium. The rate of the reaction showed dependence on acid (in the range used).Added anions and cations were observed to catalyze the reaction rate. Spectroscopic investigation and kinetic study did not suggest intermediate complex formation. An outer–sphere mechanism is proposed for the reaction.

An Experimental and Theoretical Investigation of the Efficacy of Pantoprazole as a Corrosion Inhibitor for Mild Steel in an Acidic Medium

The corrosion behavior of mild steel in a 1 M aqueous sulfuric acid medium in the presence and absence of the drug Pantoprazole was investigated using potentiodynamic polarization and quantum chemical calculations as well as Monte Carlo and molecular dynamic simulations. The potentiodynamic experiments indicated that this molecule, as a result of its adsorption on a mild steel surface, functioned as a mixed inhibitor. The goal of the study was to use theoretical calculations to acquire a better understanding of how inhibition works. The adsorption behavior of the examined compounds on the Fe (1 1 0) surface was calculated using a Monte Carlo simulation. Furthermore, the molecules were studied using density functional theory (DFT), especially the PBE functional, to determine the relationship between the molecular structure and the corrosion inhibition behavior of the chemical under research. The adsorption energies of Pantoprazole (in its three different protonation states) iron were calculated more precisely using molecular mechanics with periodic boundary conditions (PBC). The predicted theoretical parameters were found to be in agreement with the experimental data, which was a considerable help in understanding the corrosion inhibition mechanism displayed by this chemical.

Corrosion study of copper in aqueous sulfuric acid solution in the presence of (2E,5E)-2,5-dibenzylidenecyclopentanone and (2E,5E)-bis[(4-dimethylamino)benzylidene]cyclopentanone: Experimental and theoretical study

AbstractThe corrosion behavior of copper in 0.1 M aqueous sulfuric acid medium has been studied using potentiodynamic polarization measurements, quantum chemical calculations, and molecular dynamic simulations in the presence and absence of (2E,5E)-2,5-dibenzylidenecyclopentanone (M1) and (2E,5E)-bis[(4-dimethylamino)benzylidene]cyclopentanone (M2). The compounds were freshly prepared in high yields via the Claisen–Schmidt reaction between the cyclopentanone and the corresponding aryl aldehyde. The results from the potentiodynamic measurements imply thatM1andM2act as mixed inhibitors due to their adsorption on the copper surface. The more pronounced corrosion inhibition performance of theM2molecule in comparison toM1was related to the fact that this molecule contains two basic nitrogen atoms (in 4-dimethylamino group).

Oscillatory Reaction Rates in the Electro-Oxidation of Formaldehyde on Palladium

Formaldehyde has been used as a model system to investigate the electro-oxidation of small organic molecules, mainly on platinum[1]. This reaction is extremely dependent on the control conditions (potential and current) and it is also known to display self-organized oscillations on platinum[2]. In the present work we report a study of the oscillating reaction rates in the electro-oxidation of formaldehyde on polycrystalline palladium and in aqueous sulfuric acid media. The mapping of the existence region of potential oscillations was obtained by a slow current scan. Galvanodynamic oscillations were observed to range from 0.50 to 0.85 V. Further analysis was performed by galvanostatic measurements. The amplitude of potential oscillations increases in time. The potential-increase part of the cycle is formed by a rapid increase to about 0.60 V and then a slow one to 0.85 V, followed by an abrupt drop, with an average oscillation frequency of 0.15 Hz. Both the morphology and the frequency of oscillations differ from that observed for the electro-oxidation of formaldehyde on platinum, where the electrode potential varies from 0.40 to 0.90 V, and the it increases slowly until reaching 0.60 V followed by a rapid potential increase of up to 0.90 V, and then it decreases abruptly. Oscillations on platinum under comparable conditions were also about three times faster [3]. Overall, our results suggest the surface chemistry underlying the dynamics of formaldehyde elector-oxidation on palladium and platinum is considerably different, particularly under oscillatory regime. Some mechanistic aspects of the, far less studied, palladium system will be discussed.

Determination of Nalbuphine Hydrochloride in Pharmaceutical Formulations Using Diperiodatoargentate(III)-Rhodamine-B Chemiluminescence System by Flow Injection Analysis.

A novel method for the analysis of nalbuphine hydrochloride (NAL) is reported based on its enhancement effect on a diperiodatoargentate(III)-rhodamine-B (Ag(III) complex-Rh-B) chemiluminescence (CL) system in an aqueous sulfuric acid medium using flow-injection analysis (FIA). The optimal conditions of the CL reaction were: sulfuric acid, 10-2 M; Ag(III) complex, 2.0 × 10-4 M; Rh-B, 2.0 × 10-5 M; Brij-35, 0.01%; sample loop volume, 300 μL; and flow rate, 3.0 mL/min/stream. The limit of detection (LOD) and limit of quantification (LOQ) were 0.001 and 0.003 mg/L (S/N = 3 and 10); linear calibration range, 5 × 10-3 - 5.0 mg/L (R2 = 0.9999) and injection throughput, 150/h. The relative standard deviation (RSD) was from 0.8 - 3.2% over the range studied. The suggested technique was applied for the determination of NAL in pharmaceutical injections, compared with a reported spectrophotometric method, and obtained results were found to be satisfactory. Based on spectrophotometric studies, the most probable mechanism of the CL reaction has been briefly described and drawn schematically.

Studying Properties of Prospective Biologically Active Extracts from Marine Hydrobionts

Biologically active substances (BAS) extracted from marine hydrobionts are characterized by high diversity and efficiency. They are represented by carotenoids, phospholipids, saponins and other compounds possessing high antioxidant (AOA), antitumor, immunomodulatory, radioprotective, and hypolipidemic activities. Because of extremely high marine BAS activity, the BAS dose necessary for treatment and prevention of many diseases is very small. The aim of present work was to assess biological properties of BAS complexes extracted from Black Sea marine inverterbrates for their following using in pharmacological preparations including liposomal drug delivery. BAS complexes were extracted from marine invertebrate tissues by two-phase extraction in combination with ultrasonication. Antioxidant activity of BAS extracts was determined with potassium permanganate discoloration method in an aqueous sulfuric acid medium. Antimicrobial activity was investigated by germination of BAS extracts. BAS influence on lymphocyte proliferative activity was studied with help of cytogenetic analysis. In this paper, the assessment of antioxidant, antimicrobial and mitogenic activities of biologically active complexes extracted from marine invertebrate tissues is presented. BAS properties in the oil and alcohol-water phases are compared. For the first time BAS complexes from Black Sea invertebrates are extracted by the resource-light method of two-phase extraction in combination with ultrasonication. Conditions for obtaining BAS extracts with optimal characteristics are proposed.

A SIMPLE SPECTROPHOTOMETRIC METHOD FOR THE QUANTITATIVE ANALYSIS OF PHOSPHATE IN THE WATER SAMPLES

A simple spectrophotometric method was used to determine the phosphate content in the water sampels. The method is based on the formation of molybdenum blue complex from the reaction of orthophosphate and ammonium molybdate followed by reduction with ascorbic acid in the aqueous sulfuric acid medium. The color intensity of the molybdenum blue complex is proportionally to the phosphate content in the solution. The system obeys Lamber-Beer’s Law at the 890 nm in the concentration range of 0.1-1 mg P/L and the linier calibration graph was obtained with the slope, 0.6334, intercept, 0.0074 and correlation coefficient of 0.9988. This official method was also used for the quantitative analysis of phosphate in the water samples and the satisfactory result was obtained. The range of phosphate concentration in the water samples are 0.033 – 2.943 mg P/L.

A SIMPLE SPECTROPHOTOMETRIC METHOD FOR THE QUANTITATIVE ANALYSIS OF PHOSPHATE IN THE WATER SAMPLES

A simple spectrophotometric method was used to determine the phosphate content in the water sampels. The method is based on the formation of molybdenum blue complex from the reaction of orthophosphate and ammonium molybdate followed by reduction with ascorbic acid in the aqueous sulfuric acid medium. The color intensity of the molybdenum blue complex is proportionally to the phosphate content in the solution. The system obeys Lamber-Beer’s Law at the 890 nm in the concentration range of 0.1-1 mg P/L and the linier calibration graph was obtained with the slope, 0.6334, intercept, 0.0074 and correlation coefficient of 0.9988. This official method was also used for the quantitative analysis of phosphate in the water samples and the satisfactory result was obtained. The range of phosphate concentration in the water samples are 0.033 – 2.943 mg P/L.

Mn(II) Catalyzed Oxidation of Atenolol by Cerium(IV) in Aqueous Sulfuric Acid Medium: A Spectrophotometer Aided Kinetic, Mechanistic and Thermodynamic Study

Abstract The kinetics and mechanism of manganese(II) catalyzed oxidation of atenolol by cerium(IV) sulfate in aqueous H2SO4 at a constant ionic strength of 0.50 mol dm-3 was studied spectrophotometrically. The reaction showed first order kinetics in cerium(IV) whereas fractional order in both manganese(II) and atenolol. Addition of products showed no effect on the rate of the reaction. The main product, 2-(4-(2-hydroxy-3-oxopropoxy)phenyl)acetamide, was identified with the aid of IR and mass spectral data. Stoichiometry with respect to the drug substrate and reagent was established as 2:1. Added H2SO4, SO4 2− and HSO4 − showed negligible effect on the rate of the reaction. HCe(SO4)3 − was found to be the predominant reactive species under the specified experimental conditions. The rate constants (k), catalytic constant (kc ) and equilibrium constant (K 6) for the proposed mechanism were determined. The kinetic and thermodynamic activation parameters were computed for both the slow rate determining step and complex forming equilibrium step.

Corrosion Study of Mild Steel in Aqueous Sulfuric Acid Solution Using 4-Methyl-4H-1,2,4-Triazole-3-Thiol and 2-Mercaptonicotinic Acid-An Experimental and Theoretical Study.

The corrosion behavior of mild steel in 0.1 M aqueous sulfuric acid medium has been studied using weight loss, potentiodynamic polarization measurements, quantum chemical calculations, and molecular dynamic simulations in the presence and absence of 4-methyl-4H-1,2,4-triazole-3-thiol and 2-mercaptonicotinic acid. Potentiodynamic measurements indicate that these compounds mostly act as mixed inhibitors due to their adsorption on the mild steel surface. The goal of the study was to use theoretical calculations to better understand the inhibition. Monte Carlo simulation was used to calculate the adsorption behavior of the studied molecules onto Fe (1 1 1) and Fe2O3 (1 1 1) surface. The molecules were also studied with the density functional theory (DFT), using the B3LYP functional in order to determine the relationship between the molecular structure and the corrosion inhibition behavior. More accurate adsorption energies between the studied molecules and iron or iron oxide were calculated by using DFT with periodic boundary conditions. The calculated theoretical parameters gave important assistance into the understanding the corrosion inhibition mechanism expressed by the molecules and are in full agreement with the experimental results.

Influence of structure of poly(o-phenylenediamine) on the doping ability and conducting property

Poly(o-phenylenediamine) with ladder-type structure was formed in aqueous hydrochloric acid medium below pH 1, while open ring-type amine derivative, i.e., −NH2 functional group substitution of polyaniline structure, was obtained in 1:1 aqueous sulfuric acid medium from the chemical synthesis of the monomer o-phenylenediamine. However, poly(o-phenylenediamine) having structure like polyaniline derivative with free =NH functional groups was obtained by chemical synthesis in dimethyl sulfoxide medium. The ladder-type polymer was almost insoluble but the other two types of synthesized polymers having polar functional group substitutions were well soluble in polar organic solvent like dimethyl sulfoxide, N,N-dimethyl formamide, and tetrahydrofuran. The freestanding films were cast from dimethyl sulfoxide solution of both the soluble functional polymers. The polymers having different structures were doped with inorganic acid by solution doping technique and the doped polymers were characterized by various standard characterizations. In order to explore the electronic uses of the polymers like sensor and actuators, the influences of their structure on the doping ability as well as ionic properties of the sulfuric acid-doped polymers were compared.

Autocatalytic Oxidation of Thiamine Hydrochloride (Vitamin B1 ) by Permanganate in Aqueous Sulfuric Acid Medium: A Kinetic and Mechanistic Study

The reaction kinetics of autocatalytic oxidation of thiamine hydrochloride (vitamin B1) by the permanganate ion in aqueous sulfuric acid medium has been investigated spectrophotometrically under the pseudo–first-order condition at 25°C. The observed stoichiometry is 6:5 in terms of the mole ratio of permanganate ions and thiamine hydrochloride. Formation of products was confirmed by UV–vis, IR, GC-MS, and NMR spectral data. Usually in the permanganate oxidation–reduction reactions, one of the products, Mn2+ autocatalyzes the reaction, but in the present investigation the autocatalytic effect is due to the (4-methyl–thiazol-5-yl) acetic acid, a product formed from the oxidation of vitamin B1, which is a rare case. The added Mn2+ does not have any significant effect on the rate of reaction. The reaction is first order with respect to both permanganate and thiamine hydrochloride concentrations. An increase in the sulfuric acid concentration decreases the rate of reaction. A composite scheme and rate laws were proposed. The activation parameters with respect to the slow step and reaction constants involved in the mechanism were determined and discussed.

Oxidation of clindamycin phosphate by chromium(VI) in aqueous sulfuric acid medium—A kinetic and mechanistic study

AbstractKinetics and mechanism of oxidation of clindamycin phosphate by potassium dichromate in aqueous sulfuric acid medium is studied spectrophotometrically at 25°C at a constant ionic strength of 3.60 mol dm−3. The stoichiometry of the reaction is determined and it was found that one mole of clindamycin phosphate consumes two moles of chromium(VI) (1:2). The oxidation products are characterized and confirmed by spectral studies such as IR, GC-MS and LC-MS. The reaction is first order each in chromium(VI) and clindamycin phosphate concentrations. An increase in the sulfuric acid concentration causes an increase of the reaction rate. The order with respect to acid concentration is found to be 1.65. From the results of kinetic studies, reaction stoichiometry and product analysis a suitable free radical mechanism is proposed. Based on investigation of the reaction at different temperatures, computation of the activation parameters with respect to the slow step of the proposed mechanism was evaluated.

Theoretical and experimental studies of the corrosion behavior of some thiazole derivatives toward mild steel in sulfuric acid media

<p>The corrosion behavior of iron in diluted aqueous sulfuric acid medium has been studied in the presence and absence of 6-ethoxybenzo[<em>d</em>]thiazol-2-amine (EBT), 5-bromothiazol-2-amine (BTA) and 4,5-dimethylthiazol-2-amine (DTA). Potentiodynamic measurements showed the shift of corrosion potential towards a more negative potential indicating that these compounds mostly act as cathodic inhibitors due to their adsorption on the iron surface. The adsorbed film of these molecules hinders the transport of metal ions from the metal to the solution and also retards hydrogen evolution reaction by acting as a physical barrier. The molecules were also studied by density functional theory (DFT), using the B3LYP functional in order to determine the relationship between molecular structure and the corrosion inhibition efficiencies.</p>

Conclusive evidence for autocatalytic behaviour of manganese(II) ions in the oxidative degradation of ondansetron by permanganate in aqueous sulfuric acid medium – a kinetic and mechanistic approach

The oxidation of ondansetron by permanganate in aqueous sulfuric acid medium has been investigated spectrophotometrically under the pseudo-first order condition at 25°C and at constant ionic strength, I=0.60moldm−3. The reaction between ondansetron and permanganate in acid medium exhibits 2:1 stoichiometry. The products are identified and characterised by IR and GC–MS spectral studies. The identified oxidation products are 1-methyl-2-((E)-4-(2-methyl-1H-imidazol-1-yl)but-3-enyl)-1H-indole-3-carboxylic acid and Mn(II), which are different from those obtained by hepatic metabolism. The reaction is autocatalysed due to one of the product, Mn(II). The reaction is first order with respect to MnO4− and less than unit order with respect to ondansetron, acid and Mn(II) concentrations. The oxidation reaction in acid medium proceeds through a permanganate–ondansetron complex that decomposes slowly in a rate-determining step followed by other fast steps to give the products. The reaction constants involved in different steps of the mechanism are calculated at different temperatures. The activation parameters with respect to the slow step of the mechanism are computed, and thermodynamic quantities are also determined.

Micellar catalysis of quinquivalent vanadium oxidation of methanol to formaldehyde in aqueous medium

The kinetics of oxidation of methanol by quinquivalent vanadium in aqueous sulfuric acid medium has been studied at 313 K under pseudo-first-order condition by UV–vis spectrophotometry. Nonfunctional sodium dodecyl sulfate (SDS) surfactant solution was used as a microheterogeneous micellar catalyst. The reaction rate and selectivity strongly depend on the chosen surfactant, and in some cases also on the surfactant concentration. The critical micelle concentration (CMC) values of the SDS surfactant in aqueous medium as well as in the presence of the substrate methanol were determined by the conductivity method, matching well with the kinetically determined CMC value. SDS was found to be an excellent catalyst for oxidation of methanol by vanadium(V) in aqueous sulfuric acid medium, leading to the corresponding oxidized product (formaldehyde), which was detected by 1H nuclear magnetic resonance (NMR). The micellar catalysis by SDS is due to strong binding of the cationic oxidant with the anionic surfactant. Formation of aggregates by the catalytic surfactant was studied using optical microscopy, and the change in shape and size of the aggregates in the reaction condition was studied by using scanning electron microscopy and the dynamic light scattering method. Mechanisms for this oxidation reaction in aqueous medium as well as with micellar catalyst are proposed, being completely supported by our experimental results.

Radicals and radical cations of thioacetamide and thiobenzamide in aqueous sulfuric acid media

Studies on the radical cations and radicals of thioacetamide [(CH3)(NH2)C=S] and thiobenzamide [(C6H5)(NH2)C=S], in aqueous sulfuric acid media of various strengths were carried out using pulse radiolysis technique. In this system, the formation time of thioacetamide/thiobenzamide radical cation was observed to be different at different acid strengths. At acid system of pH/H0 = −3.5, the slow growth kinetics signifies a dominating reaction of SO4•− radical with these solutes (reaction rate constants found in the range of 1–4 × 108 M−1 s−1). Two different reactions (solute molecule with •OH and SO4•−) lead to the formation of lone intermediate species (radical cation) following immediate (fast) and delayed (slow) kinetics. By this process, the transient yield increased by 65 % (as the transients’ absorbance at 400 nm increased to 0.090 from 0.055) in the case of thiobenzamide, whereas in the case of thioacetamide, this figure was higher. The general mechanism for the formation of radical cations of these solutes during radiation chemical studies has been revisited wherein the electron transfer reactions are more favorable.

A Kinetic Study on Catechol‐Based Belousov–Zhabotinsky Reaction

AbstractThe present investigation pertains to the kinetic study on bromate‐driven and manganese ion catalyzed Belousov–Zhabotinsky oscillatory chemical reaction having catechol (1,2‐dihydroxybenzene) as the organic substrate in aqueous acid media at 30 ± 0.1oC under stirred conditions. Although some polyphenols as chemical oscillators are known in the literature but the role of catechol has been marginalized. The reaction system with catechol shows long‐time series of periodic as well as aperiodic oscillations, which were monitored potentiometrically in the oxidation reduction potential (ORP) mode under batch conditions. The various oscillatory parameters such as induction time (tin), time period (tp), amplitude (A), and number of oscillations (N) were obtained by drawing a plot between redox potential (mV) versus time (s). It is found that the oscillatory parameters of the system vary with the concentration of the reacting species. The reaction system was also studied in different aqueous acid media, but the detailed studies with respect to experimental parameters have been made in aqueous sulfuric acid medium as it showed a broad oscillatory window and better oscillatory characteristics. Moreover, the oscillatory parameters in general and induction time in particular vary significantly with temperature (15 to 45 ± 0.1oC). The activation parameters of the system have also been calculated. The oscillatory behavior of the reaction system was also confirmed spectrophotometrically. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 45: 141–151, 2013

Oxidation of Lactic Acid by Manganese(III) in Sulfuric Acid Medium: Kinetics and Mechanism

The kinetics of oxidation of lactic acid (LA) by manganese(III) in sulfuric acid solutions at 293 K has been studied. A solution of the mild oxidant, Mn(III) sulfate, in aqueous sulfuric acid medium was prepared by a standard electrochemical method. The oxidation reaction was monitored by spectrophotometry at a fixed wavelength (λmax = 491 nm), varied temperature, and varied solution conditions. The Mn(III)-LA reaction stoichiometry of 4:1 was determined and the products were characterized. The experimental rate law is: rate = kobs [Mn(III)][LA]x [H+ ] y , where x, and y are fractional orders. The effects of varying ionic strength, solvent composition (dielectric constant), acid, and the reduction product, Mn(II), on the rate of the reaction were investigated. Activation parameters evaluated using Arrhenius and Eyring plots suggest the occurrence of an entropy controlled reaction. A mechanism consistent with the observed kinetic data has been proposed. A rate law has been derived based on the mechanism