Oxidation of indole‐3‐acetic acid by peroxomonosulphate: A kinetic and mechanistic study

Kinetics of oxidation of indole‐3‐acetic acid (IAA) by peroxomonosulphate (PMS) in aqueous acetonitrile medium has been investigated. The reaction follows a total second order, first order each with respect to [IAA] and [PMS]. The rate of the reaction was not affected by added [H⁺]. Variation of ionic strength (μ) had no influence on the rate. Increase of percentage of acetonitrile decreased the rate. Absence of any polymerization indicated a nonradical pathway. Activation and thermodynamic parameters have been computed. A suitable kinetic scheme based on these observations is proposed. The reactivity of PMS towards IAA was found to be higher than that with peroxodisulphate. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 569–574, 2002     

Oxidation of some α‐hydroxy acids by tetraethylammonium chlorochromate: A kinetic and mechanistic study

The oxidation of glycolic, lactic, malic, and a few substituted mandelic acids by tetraethylammonium chlorochromate (TEACC) in dimethylsulfoxide leads to the formation of corresponding oxoacids. The reaction is first order each in TEACC and hydroxy acids. Reaction is failed to induce the polymerization of acrylonitrile. The oxidation of α‐deuteriomandelic acid shows the presence of a primary kinetic isotope effect (k_H/k_D = 5.63 at 298 K). The reaction does not exhibit the solvent isotope effect. The reaction is catalyzed by the hydrogen ions. The hydrogen ion dependence has the following form: k_obs = a + b[H⁺]. Oxidation of p‐methylmandelic acid has been studied in 19 different organic solvents. The solvent effect has been analyzed by using Kamlet's and Swain's multiparametric equations. A mechanism involving a hydride ion transfer via a chromate ester is proposed. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 42: 50–55, 2010     

A novel kinetic and mechanistic study of the oxidation of pinacol by acid bromate—homogeneous catalysis of maganous ions

A detailed kinetic study of the Mn(II)-catalyzed and -uncatalyzed oxidation of pinacol by bromate has been carried out in aqueous acetic acid media containing Hg(II) ions. The uncatalyzed reaction exhibits 1.5 order that is, 0.5 order in [pinacol] and 1.0 in [bromate]. A decrease in k₁ by increasing [bromate] has been accounted for due to the formation of Br₂O₅, which is inactive toward reduction. Mn(II)-catalyzed oxidation follows first order in [oxidant], 0.5 order in [manganous ion], and variable order with respect to [pinacol]. At lower [pinacol] (0.005–0.025M) the order is 0.5, but at higher concentration (0.03–0.15M) it becomes negative (?1.0). These observations can be accounted for qualitatively by the formation of 1:1 and 1:2 Mn(II)–pinacol complexes of which only 1:1 is active toward bromate oxidation. At higher [pinacol] the ratio of 1:2 and 1:1 complexes reached 98.2. All reactions were accelerated with acidity, and the rate constant follows the h₀ function. Participation of H₂O in the rate-limiting step and a free-radical mechanism were proposed for the manganous-ion-catalyzed reaction, whereas for the uncatalyzed reaction this was not true. The effects of NaClO₄, Na₄P₂O₇, and the dielectric constant of the media are also in accordance with the proposed mechanism.     

Ruthenium(III)‐mediated oxidation of D‐mannitol by cerium(IV) in aqueous sulfuric acid medium: A kinetic and mechanistic approach

The oxidation of D ‐mannitol by cerium(IV) has been studied spectrophotometrically in aqueous sulfuric acid medium at 25°C at constant ionic strength of 1.60 mol dm^?3. A microamount of ruthenium(III) (10^?6 mol dm^?3) is sufficient to enhance the slow reaction between D ‐mannitol and cerium(IV). The oxidation products were identified by spot test, IR and GC‐MS spectra. The stoichiometry is 1:4, i.e., [D ‐mannitol]: [Ce(IV)] = 1:4. The reaction is first order in both cerium(IV) and ruthenium(III) concentrations. The order with respect to D ‐mannitol concentration varies from first order to zero order as the D ‐mannitol concentration increases. Increase in the sulfuric acid concentration decreases the reaction rate. The added sulfate and bisulfate decreases the rate of reaction. The active species of oxidant and catalyst are Ce(SO₄)₂ and [Ru(H₂O)₆]³⁺, respectively. A possible mechanism is proposed. The activation parameters are determined with respect to a slow step and reaction constants involved have been determined. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 440–452, 2010     

A comparative kinetic and mechanistic study of glutamic acid oxidation by acid permanganate in the absence and presence of sodium dodecyl sulphate

The kinetics and mechanism of glutamic acid (GCO₂H) oxidation by acid permanganate has been carried out in the absence and presence of sodium dodecyl sulphate (SDS). The surfactant enhances the reaction rate without changing the reaction mechanism. The overall rate expression for the reduction of Mn^VII may be written:

Synthesis of novel 3‐ and 5‐substituted indole‐2‐carboxamides

The preparation of several novel 3,5‐substituted‐indole‐2‐carboxamides is described. A 5‐nitro‐indole‐2‐carboxylate was elaborated to the 3‐benzhydryl ester, N‐substituted ester, and carboxylic acid intermedi ates, followed by conversion to the amide and then reduction of the 5‐nitro group to the amine. Indole‐2‐carboxamides with 3‐benzyl and 3‐phenyl substituents were prepared in four steps from either a 3‐bromo indole ester using the Suzuki reaction or from a 3‐keto substituted indole ester. N‐Alkylation of ethyl indole‐2‐carboxylate, followed by amidation and catalytic addition of 9‐hydroxyxanthene gave a 3‐xanthyl‐indole‐2‐carboxamide analog and a spiropyrrolo indole as a side product.     

Controlled release of indole‐3‐butyric acid (IBA)—based on polymeric matrix prepared by ionizing radiation

Polyacrylamide/polyethylene oxide (PAAm/PEO) controlled release matrices were designed to obtain a better control over the concentration of indole‐3‐butyric acid (IBA). PAAm/PEO incorporated IBA was prepared by exposing aqueous solutions of PEO, PAAm, crosslinking agent N,N′‐methylene‐bisacrylamide, and IBA mixtures to electron beam irradiation. PAAm/PEO copolymer structural property relationships that affect its controlled release behavior were determined. Analysis of the results obtained indicated that it is possible to optimize IBA controlled release by adjusting the dimensions and crosslinking degree of the copolymer as well as the concentration of the incorporated IBA. The crosslinking degree of the copolymer can be controlled by governing the irradiation dose, polymer blend composition and/or the amount of crosslinking agent. IBA release rates have been investigated as a function of environmental conditions, such as the changes in pH and temperature to determine the factors, which mostly contribute to the release of IBA. The effect of PAAm/PEO–IBA matrix on the average height of corn (Zea mayz) plant was investigated. The results obtained, revealed that PAAm/PEO‐IBA systems have a capability to deliver IBA slowly and continuously. As a result, the development of root and vegetative systems of Zea mayz plant was greatly promoted. Copyright © 2004 John Wiley & Sons, Ltd.     

A kinetic and mechanistic study of the oxidation of tyrosine by chromium(VI) in aqueous perchloric acid medium

The oxidation of tyrosine by chromium(VI) in aqueous perchloric acid medium has been studied spectrophotometrically at 30 °C and at a constant ionic strength I = 3.10 mol dm⁻³. The main reaction products were identified as chromium(III) and 4-hydroxyphenylacetaldehyde. The stoichiometry is 2:3, i.e., two moles of chromium(VI) react with three moles of tyrosine. The reaction is first order with respect to both chromium(VI) and tyrosine. Increase in perchloric acid concentration increased the rate of reaction. The order with respect to acid concentration was found to be two. Added products, ionic strength and dielectric constant of the medium did not have any significant effect on the reaction rate. A suitable mechanism is proposed. The activation parameters were determined with respect to the slow step of the mechanism. The thermodynamic quantities were also determined and discussed.     

(+)‐Camphor­acetic acid: catemeric hydrogen bonding in a γ‐keto acid

The title compound, (1R)‐4,7,7‐tri­methyl‐3‐oxobi­cyclo­[2.2.1]­heptane‐2‐endo‐acetic acid, C₁₂H₁₈O₃, like its lower homolog, forms carboxyl‐to‐ketone hydrogen‐bonding catemers (Z′ = 2) [O⋯O = 2.729 (5) and 2.707 (5) Å, and O—H⋯O = 165 and 170°] with screw‐related components. The two mol­ecules of the asymmetric unit differ slightly in conformation and produce two counter‐aligned hydrogen‐bonding chains, both aligned with the b axis. Close intermolecular C—H⋯O=C contacts exist for the ketone group of one mol­ecule and for both the ketone and carboxyl functions in the other.     

A kinetic study of the oxidation of α-hydroxy acids and α-hydroxy ketones by potassium bromate

The oxidation of α-hydroxy acids and α-hydroxy ketones by Br(V) follows the rate-law However, the former reaction exhibits a second-order dependence on hydrogen ion concentration while the latter reaction has a third-order dependence. A mechanism involving a slow formation of a bromate ester of the α-hydroxy acid followed by a fast decomposition is proposed. A rate-determining formation of a bromate ester from the conjugate acid of benzoin, followed by a rapid decomposition of the bromate ester, explains the kinetic data for the oxidation of benzoin.     

A kinetic study of the atmospheric photolysis of α‐dicarbonyls

Photolysis frequencies of biacetyl, methyl glyoxal, and glyoxal have been determined relative to the photolysis frequency of NO₂. The values were measured under natural sunlight conditions in a large‐volume outdoor reaction chamber. The experimental results obtained are compared to photolysis frequencies used in current models of tropospheric photo‐oxidant formation. For biacetyl, a ratio of J(biacetyl)/J(NO₂) = (0.0364 ± 0.0026) was found, in good agreement with previous measurements and models. For methyl glyoxal, however, the experimental photolysis frequency ratios were significantly larger than those calculated from models. This could only partly be explained by reaction of methyl glyoxal with HO₂. Due to this inconsistency, it is preferred not to cite a ratio for J(methyl glyoxal)/J(NO₂). The agreement between calculated and experimental photolysis frequency ratios of glyoxal was reasonably good, a ratio of J(glyoxal)/J(NO₂) = 0.0109 has been found, with estimated overall error margins of about 30%. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 33: 9–20, 2001     

Oxidation of L-glutamine by manganese(iii) in aqueous sulfuric acid,acetic acid,and pyrophosphate media: A kinetic and mechanistic study

Manganese(III) solutions were prepared by known electrochemical methods in sulfuric acid, acetic acid, and pyrophosphate media. The nature of the oxidizing species present in manganese(III) solutions was characterized by spectrophotometric and redox potential measurements. Kinetics of oxidation of L-glutamine by manganese(III) in sulfuric acid (1.5 M), acetic acid (60% v/v), and pyrophosphate (pH=1.3) media at 313 K, 323 K, and 328 K, respectively, have been studied. Three different rate laws have been obtained for the three media. Effects of varying ionic strength, solvent composition, and added anions, such as fluoride, chloride, perchlorate, pyrophosphate, and bisulfate, have been investigated. There is evidence for the existence of free radicals as transient species. Activation parameters have been evaluated using Arrhenius and Eyring plots. Mechanisms consistent with the observed kinetic data have been proposed and discussed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 7–19, 1998.     

Conformational studies of hydantoin‐5‐acetic acid and orotic acid

Hydantoin‐5‐acetic acid [2‐(2,5‐dioxoimidazolidin‐4‐yl)acetic acid] and orotic acid (2,6‐dioxo‐1,2,3,6‐tetrahydropyrimidine‐4‐carboxylic acid) each contain one rigid acceptor–donor–acceptor hydrogen‐bonding site and a flexible side chain, which can adopt different conformations. Since both compounds may be used as coformers for supramolecular complexes, they have been crystallized in order to examine their conformational preferences, giving solvent‐free hydantoin‐5‐acetic acid, C₅H₆N₂O₄, (I), and three crystals containing orotic acid, namely, orotic acid dimethyl sulfoxide monosolvate, C₅H₄N₂O₄·C₂H₆OS, (IIa), dimethylammonium orotate–orotic acid (1/1), C₂H₈N⁺·C₅H₃N₂O₄⁻·C₅H₄N₂O₄, (IIb), and dimethylammonium orotate–orotic acid (3/1), 3C₂H₈N⁺·3C₅H₃N₂O₄⁻·C₅H₄N₂O₄, (IIc). The crystal structure of (I) shows a three‐dimensional network, with the acid function located perpendicular to the ring. Interestingly, the hydroxy O atom acts as an acceptor, even though the carbonyl O atom is not involved in any hydrogen bonds. However, in (IIa), (IIb) and (IIc), the acid functions are only slightly twisted out of the ring planes. All H atoms of the acidic functions are directed away from the rings and, with respect to the carbonyl O atoms, they show an antiperiplanar conformation in (I) and synperiplanar conformations in (IIa), (IIb) and (IIc). Furthermore, in (IIa), (IIb) and (IIc), different conformations of the acid O=C—C—N torsion angle are observed, leading to different hydrogen‐bonding arrangements depending on their conformation and composition.     

Evaluation of kinetic parameters for oxidation of thioacids by benzimidazolium dichromate: A mechanistic study

In a non-aqueous medium, oxidation kinetics of thioglycolic, thiolactic and thiomalic acids by benzimidazolium dichromate have been studied. In the temperature range of 20°C–50°C, oxidation kinetics were examined by spectrophotometry. In terms of oxidant, the reaction is dependent on the unitary order. In the case of thioacids, we find the Michaelis-Menten type kinetics. Hydrogen-ions act as catalyst in this process. The reaction rate slows down as the Mn²⁺ ion concentration increases. The reaction does not cause acrylonitrile to polymerize. The formation of a thioester into the pre-equilibrium followed by its progressive degradation was postulated as a mechanism.     

A kinetic and mechanistic study of oxidation of arsenic(III) by hexacyanoferrate(III) in aqueous ethanoic acid

The kinetics of oxidation of As^IIIby Fe(CN)₆ ^3– has been studied spectrophotometrically in 60% AcOH–H₂O containing 4.0moldm^–3HCl. The oxidation is made possible by the difference in redox potentials. The reaction is first order each in [Fe(CN)₆ ^3–] and [As^III]. Amongst the initially added products, Fe(CN)₆ ^4– retards the reaction and As^Vdoes not. Increasing the acid concentration at constant chloride concentration accelerates the reaction. At constant acidity increasing chloride concentration increases the reaction rate, which reaches a maximum and then decreases. H₂Fe(CN)₆ ^–, is the active species of Fe(CN)₆ ^3–, while AsCl₅ ^2– in an ascending portion and AsCl₂ ⁺ in a descending portion are considered to be the active species of As^III. A suitable reaction mechanism is proposed and the reaction constants of the different steps involved have been evaluated.     

A facile synthesis of 7‐chloromethyl‐1H‐indole‐2‐carboxylates: Replacement of a sulfonic acid functionality by chlorine

Valuable new synthetic intermediates, 7‐chloromethyl‐1H‐indole‐2‐carboxylates ( 3a‐d ), were prepared by the facile elimination of sulfur dioxide under the influence of thionyl chloride from 2‐ethoxycarbonyl‐1H‐indole‐7‐methanesulfonic acids ( 1a‐d ), easily accessible by Fischer‐type indolisation. The 7‐chloromethylindoles easily underwent methanolysis and aminolysis.     

Oxidation of metronidazole with sodium N‐bromo‐p‐toluenesulfonamide in acid and alkaline media: A kinetic and mechanistic study

A kinetic study of oxidation of metronidazole (Met) with sodium N‐bromo‐p‐toluenesulfonamide or bromamine‐T (BAT) has been carried out in HClO₄ (30°C) and NaOH (40°C) media. The experimental rate laws obtained are –d[BAT]/dt=k[BAT][Met]^x [H⁺]^y in acid medium and –d[BAT]/dt=k[BAT][Met]^x [OH^?]^y/[PTS]^z in alkaline medium, where x, y, and z are less than unity and PTS is p‐toluenesulfonamide. The reaction was subjected to changes in (a) ionic strength, (b) concentration of added reduction product PTS, (c) concentration of added neutral salts, (d) dielectric permittivity, and (e) solvent isotope effect. In both media, the stoichiometry of the reaction was found to be 1:1, and the oxidation product of metronidazole was identified as its aldehyde. The reaction was studied at different temperatures, and the activation parameters have been evaluated. The reaction constants involved in the proposed schemes were deduced. The reaction was found to be faster in acid medium in comparison with alkaline medium, which is attributed to the involvement of different oxidizing species. Mechanisms proposed and the rate laws derived are consistent with the observed kinetics. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 700–709, 2005     

Electrochemical oxidation of catechols in the presence of ethyl‐2‐chloroacetoacetate. Synthesis and mechanistic study

Electrochemical oxidation of catechol and some of 3‐substituted catechols ( 1a‐c ) has been studied in the presence of ethyl‐2‐chloroacetoacetate ( 3 ) in water/acetonitrile (90:10) solution using cyclic voltammetry and controlled‐potential coulometry. The results indicate that the quinones derived from catechols ( 1a‐c ) participate in Michael addition reactions with ethyl‐2‐chloroacetoacetate( 3 ), with consumption of only two electrons per molecule of 1 , to form the corresponding benzofurans ( 10a‐c ). The electrochemical synthesis of benzofurans ( 10a‐c ) has been successfully performed at a carbon rod electrode and in an undivided cell with good yields and purity. A new two‐electron mechanism for the electrode process is proposed.