The Theoretical and Experimental Studies on Oxidation of Straight Chain Amino Acids in Moderately Concentrated Sulfuric Acid Medium

The kinetics of the permanganic oxidation process of some straight chain amino acids in moderately concentrated sulfuric acid medium have been investigated using a spectrophotometric technique. Conclusive evidences have proven autocatalytic activity of Mn(II) for these reactions. It is determined that even and odd effects of the number carbon atom in a carbon chain are annihilated when it's the number of carbon atoms is increased more than of three in a noncatalytic oxidation pathway. Thus, rate constants belonging to glycine, l ‐α‐amino‐n‐butyric acid, l ‐norleucine, and l ‐α‐amino‐n‐heptanoic acid satisfy Taft's equation involving the induction factor in the noncatalytic pathway, whereas l ‐α‐amino‐n‐heptanoic acid has an odd number of carbon atom in its chain carbon. On the other hand, in the catalytic pathway, rate constants satisfy Taft' equation including inductive and steric factors, when rate constants belonging to amino acids with an even number of carbon atoms are separated from those with an odd number of carbon atoms. The oxidation process of amino acids in the noncatalytic pathway and those with the even number of carbon atoms in the carbon chain in the catalytic pathway speeds up by an increase in the length of chain that is accompanied with an increase in the carbon chain's electron‐donating characteristic. On the other hand, an increase in the length of the carbon chain is accompanied with more steric hindrance, which counteracts its electron‐donating character, thereby decreasing reaction rate in the catalytic pathway. Finally, amino acid–Mn(II) complexes were studied using a density functional theory method. Results obtained show that such a complex is less stable than reactants, namely it is formed in an endothermic reaction. The number and strength of hydrogen bonding belonging to amino acid is more than those of the amino acid–Mn(II) complex. Besides, it has been illustrated that natural bond orbital analysis and molecular orbital calculations satisfy the findings.     

Kinetics and Mechanism of Oxidation of l‐Histidine by Permanganate Ions in Sulfuric Acid Medium

The reaction kinetics for the oxidation of l ‐histidine by permanganate ions have been investigated spectrophotometrically in sulfuric acid medium at constant ionic strength and temperature. The order with respect to permanganate ions was found to be unity and second in acid concentration, whereas a fractional order is observed with respect to histidine. The reaction was observed to proceed through formation of a 1:1 intermediate complex between oxidant and substrate. The effect of the acid concentration suggests that the reaction is acid catalyzed. Increasing the ionic strength has no significant effect on the rate. The influence of temperature on the rate of reaction was studied. The presence of metal ion catalysts was found to accelerate the oxidation rate, and the order of effectiveness of the ions was Cu²⁺ > Ni²⁺ > Zn²⁺. The final oxidation products were identified as aldehyde (2‐imidazole acetaldehyde), ammonium ion, manganese(II), and carbon dioxide. Based on the kinetic results, a plausible reaction mechanism is proposed. The activation parameters were determined and discussed with respect to a slow reaction step.     

Anodic Oxidation of Copper in Concentrated Sulfuric Acid Solutions

Copper oxidation in 1–10 M sulfuric acid solutions is studied using cyclic voltammetry and x-ray diffraction methods. Copper passivation is shown to be caused by the formation of a resistive porous layer of copper(I) oxide via an electrochemical mechanism. The primary product of the electrode reaction is unstable and, depending on the acid concentration, either enters chemical reactions with electrolyte components or is oxidized electrochemically to give copper(II) oxide.     

Anodic Oxidation of Silver Alloys in Concentrated Sulfuric Acid Solutions

Anodic oxidation of Ag–Cu and Ag–Pd alloys in concentrated sulfuric acid solutions is studied by cyclic voltammetry. Influence of electronegative (Cu) and electropositive (Pd) constituents on the rate and mechanism of the silver electrooxidation in non-steady-state conditions is revealed. The maximum silver oxidation current increases with the copper content due to a decreased H₂SO₄ concentration in the near-electrode layer and increased solubility of passivating phase Ag₂SO₄. The mechanism of ionization of palladium-doped silver is complicated by two electrochemical reactions involving the formation of Ag₂SO₄ and Ag⁺ _solv.     

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.     

Kinetics and Mechanism of the Autocatalyzed Oxidation of Theophylline by Permanganate in Aqueous Perchloric Acid Medium

The reaction kinetics for the oxidation of theophylline by permanganate ions have been investigated in perchloric acid medium using spectrophotometric techniques at 25?^°C, and at constant ionic strength 1.60 mol?dm^?3, under pseudo first order conditions. An autocatalyzed reaction is observed due to one of the products formed is Mn(II). The orders with respect to theophylline and Mn(VII) were both found to be unity, whereas fractional order is observed with respect to the autocatalyst, Mn(II). The rate of the reaction increases as the concentration of acid increases, but the order with respect to acid concentration is less than unity. The influence of temperature on the rate of reaction was studied. Based on the experimental results a suitable mechanism is proposed. The activation and thermodynamic parameters were determined with respect to slow reaction step.     

Kinetics and Mechanism of the Autocatalytic Oxidation of Mn(II) by Bromine

The oxidation of Mn(II) by bromine is an autocatalytic reaction, which seems to be important for a detailed elucidation of chemical oscillators, based on manganese chemistry. With regard to the mechanism proposed previously, an alternative reaction mechanism is proposed, based on a micro-heterogeneous oxidation of Mn(II) ion, adsorbed on a surface of the MnO₂ colloid. This revised version was published online in June 2006 with corrections to the Cover Date.     

探究铁和铝在浓硫酸和浓硝酸中的电化学行为

铁和铝在冷的浓硫酸和浓硝酸中都因被钝化而阻止其进一步被腐蚀,通过用Fe、Al做原电池的电极材料,考察其在浓硫酸、浓硝酸中的钝化情况：Fe、Al的钝化快慢、钝化后金属表面氧化膜的致密程度、酸液温度等对钝化的影响等均有所不同。     

V(IV)在不同电极上氧化还原动力学研究

分别以导电塑料集流板、石墨棒、铂片作工作电极,应用循环伏安法和稳态极化法研究V(IV)的阳极氧化动力学过程,计算V(IV)在不同材料电极上的反应动力学参数.结果表明,以导电塑料板作电极,硫酸氧钒有较宽的水稳定区,且析氧电位较高;在石墨电极上,V(V)/V(IV)的交换电流密度较大,表现出较好的可逆性;而在铂电极上,硫酸氧钒更易析氢.     

Kinetics and Mechanism of Cathodic Reduction of Nitrate Ions in a Sulfuric Acid Solution

Russian Journal of Physical Chemistry A - The cathodic reduction of nitrate ions in aqueous solutions of sulfuric acid in the presence of chromium(III) ions is studied via potentiometry. It is...     

Kinetics and Mechanism of Oxidation of Adipic Acid by Ce(IV) Ion in Acidic Medium

Kinetic study of oxidation of adipic acid by Ce(IV) ion in aqueous solution of sulphuric acid shows that the reaction follows first order kinetics in both Ce(IV) and adipic acid and the over all reaction order ascertained is two. The specific rate constant increases with an increase in the concentration of adipic acid. Effects of hydrogen ion concentration, bisulphate ion and temperature have been studied in detail. Various kinetic parameters have been computed. The experimental findings are consistent with the mechanism involving rapid resersible formation of an activated complex between Ce(IV) and adipic acid followed by a rate determining step involving C-C bond fission.     

Kinetics and Substrate Selectivity of the Oxidation of Saturated Hydrocarbons by Adamantyl Cations in Sulfuric Acid

It was shown that at 70 °C sulfuric acid ([H₂SO₄] > 85 wt.%) solutions of 1-hydroxyadamantane and the solutions obtained in the reaction of adamantane with concentrated sulfuric acid oxidize saturated hydrocarbons (RH). Data on the kinetics, selectivity, kinetic isotope effect, and the effect of the acidity of the medium on the oxidation rate of RH indicate cleavage of the C—H bond in the substrate at the rate-determining stage and the direct participation of adamantyl carbocations.     

Kinetics and Mechanism of the Oxidation of 4-Oxo-4-arylbutanoic Acids by N-bromophthalimide in Aqueous Acetic Acid Medium

The kinetics of oxidation of a series of substituted 4-oxobutanoic acids (Y–C₆H₄COCH₂CH₂COOH: Y = H, OCH₃, CH₃, C₆H₅, Cl, Br or NO₂) by N-bromophthalimide have been studied in aqueous acetic acid medium at 30 °C. The total reaction is second-order, first-order each in oxidant and substrate. The oxidation rate increases linearly with [H⁺], establishing the hypobromous acidium ion, H₂O⁺Br, as the reactive species. A variation in ionic strength has no effect on the reaction rate. The order of reactivity among the studied 4-oxoacids is: 4-methoxy > 4-methyl > 4-phenyl > 4-H > 4-Cl > 4-Br > 3-NO₂. The effect of changes on the electronic nature of the substrate reveals that there is a development of positive charge in the transition state. The activation parameters have been computed from Arrhenius and Eyring plots. Based on the kinetic results, a suitable mechanism has been proposed.     

Thermodynamic and Kinetic Studies of Oxidation of L-histidine by Manganese(VII) in Concentrated Sulfuric Acid Medium in the Absence and Presence of Silver(I)

Abstract

Thermodynamic and kinetic studies and mechanism of manganese(VII) oxidation of L-histidine has been studied both in the absence and presence of silver(I) in aqueous sulfuric acid medium. Various hypotheses for the mechanism of acid catalysis have been tested and it has been found that rate is related to the activity of water in accord with Bunnett's hypothesis. The energy and entropy of activation and frequency factor have been calculated using the Arrhenius and Eyring plots. Mechanisms in agreement with the observations are reported. The experimental rate law for the both uncatalyzed reaction and in the presence of silver was found. The applicability of Burnett's theory has been tested.     

Mechanical Activation of Kaolinite in the Presence of Concentrated Sulfuric Acid

Physicochemical processes that occur in mechanical activation of kaolinite in centrifugal-planetary mills in the presence of concentrated sulfuric acid were studied. A scheme of formation of aluminum sulfate in the course of acid activation was analyzed.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 1, 2005, pp. 36–40.Original Russian Text Copyright © 2005 by Dudkin, Loukhina, Isupov, Avvakumov.     

铜与浓硫酸反应的热力学分析

在铜与浓硫酸反应实验中,我们发现:铜片上总有大量黑色物质附着。这种黑色物质是什么?在反应中起了什么作用?为了解决这个问题,我们作了下列实验。实验(1)仔细观察铜与浓硫酸的反应,发现:开始给试管中的铜与浓硫酸加热,无现象。反应是在有气泡产生,随之铜片表面变黑时开始的。当大量气泡产生,体系达沸腾后,铜片表面的黑色物质不断脱落,并在沸腾的溶液中由大到小,铜片表面继续变黑。停止加热,铜片上仍有黑色物质附着,试管底部有黑白相间的固体,溶液并无明显的蓝色。     

Kinetics and Mechanism of Iridium（Ⅲ）-Catalyzed Oxidation of Ethanol Amine by Cerium（ Ⅳ ） in Sulfuric Acid Media

In this study, the kinetics and mechanism of the iridium(Ⅲ)-catalyzed oxidation of ethanol amine(EAN) by cerium(Ⅳ) in a sulfuric acid medium was investigated using titrimetric technique of redox in a temperature range of 298—313 K. It was found that the reaction is of first order with respect to Ce(Ⅳ) and Ir(Ⅲ), and a positive fractional order with respect to EAN. It was also found that the pseudo-first-order([EAN][Ce(Ⅳ)]) rate constant kobs decreases with the increase of [H ] and [HSO-4]. Under the protection of nitrogen gas, the reaction system can initiate the polymerization of acrylonitrile, indicating the generation of free radicals. On the basis of the experimental results, a suitable mechanism was proposed. From the dependence of kobs on the concentration of hydrogen sulfate, Ce(SO4)2 was found to be the kinetically active species. The rate constants of the rate-determining step together with the activation parameters were evaluated.     

Nitrilotriacetamide: Synthesis in Concentrated Sulfuric Acid and Stability in Water

Acid hydrolysis of N(CH₂CN)₃ leads either nitrilotriacetamide, 1, and/or 3,5-dioxopiperazineacetamide, 4, in quantitative yield. 1 slowly and cleanly converts to 3,5-dioxopiperazineacetic acid, 5, in water, although ammonium salts prevent this reaction.     

浓硫酸性质实验的整合创新设计

对浓硫酸的几个性质(吸水性、脱水性、强氧化性、遇水放热性、催化性)实验进行了整合创新设计, 解决了教材实验中的药品耗量大、不易操作、药品易撒落、易污染水源、耗时长、不适合学生分组实验等缺点。整合创新后设计的实验不仅操作简便、体现绿色实验理念, 而且操作安全, 适合中小学生开展课外活动。