A mechanistic study of the fragmentation of ferrocenyldiarylmethylium ions in aqueous acidic acetonitrile

Ferrocenylcarbocations of the type Fc$\text{c}\text{+}$ArAr′ (Ar, Ar′ = aryl groups) decompose in aqueous acidic acetonitrile liberating the 6,6-diarylpentafulvene ligand. The mechanism of the reaction has been studied by product analysis and by kinetic measurements.     

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 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.     

Autocatalytic oxidation of β‐alanine by peroxomonosulfate in the presence of copper(II) ion

Kinetics and mechanism of oxidation of β‐alanine by peroxomonosulfate (PMS) in the presence of Cu(II) ion at pH 4.2 (acetic acid/sodium acetate) has been studied. Autocatalysis was observed only in the presence of copper(II) ion, and this was explained due to the formation of hydroperoxide intermediate. The rate constant for the catalyzed (k) and uncatalyzed (k) reaction has been calculated. The kinetic data obtained reveal that both the reactions are first order with respect to [PMS]. k values initially increase with the increase in [β‐alanine] and reach a limiting value, but k values decrease with the increase in [β‐alanine]. k values increase linearly with the increase in [Cu(II)], whereas k values increase with [Cu(II)]². Furthermore, k values are independent of [acetate], but k values decrease with the increase in acetate. A suitable mechanism has been proposed to explain the experimental observation. The reaction has been studied at different temperatures, and the activation parameters are calculated. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 40: 44–49, 2008     

Reaction of copper(II) with ferrocene and 1,1'-dimethylferrocene in aqueous acetonitrile: the copper(II/I) self-exchange rate

The kinetics of the reactions of copper(II) with ferrocene (Fc) and 1,1'-dimethylferrocene (Dmfc) have been studied at 25 degrees C in aqueous acetonitrile (AN) containing 50-97.5 vol % AN. With increasing % AN, the rate constant increases along with the driving-force for the reaction. The results are analyzed in terms of Marcus theory to estimate the Cu(II/I) electron self-exchange rate constant (k11) for the system. Over the solvent range studied, the calculated k11)changes from 1.1 x 10(-9) to 17 x 10(-9) M(-1) s(-1), with an average value of 5 x 10(-9). In addition, the structures of the trifluoromethanesulfonate salts of [Cu(AN)4]+, [Cu(OH2)2(AN)2]2+, and [Cu(AN)4]2+ are reported. It is found that the Cu-NCCH3 bond-length difference between the Cu(I) and Cu(II) oxidation states is only approximately 0.02 A.     

Manganese(II) catalysed oxidation of glycerol by cerium(IV) in aqueous sulphuric acid medium: a kinetic and mechanistic study

The manganese(II) catalysed oxidation of glycerol by cerium(IV) in aqueous sulphuric acid has been studied spectrophotometrically at 25 °C and I = 1.60 mol dm⁻³. Stoichiometry analysis shows that one mole of glycerol reacts with two moles of cerium(IV) to give cerium(III) and glycolic aldehyde. The reaction is first order in both cerium(IV) and manganese(II), and the order with respect to glycerol concentration varies from first to zero order as the glycerol concentration increases. Increase in sulphuric acid concentration, added sulphate and bisulphate all decrease the rate. Added cerium(III) retards the rate of reaction, whereas glycolic aldehyde had no effect. The active species of oxidant and catalyst are Ce(SO₄)₂ and [Mn(H₂O)₄]²⁺. A mechanism is proposed, and the reaction constants and activation parameters have been determined.     

TI(III) oxidation of alkenes and alkynes and Ru(III) catalysis in the oxidation of alkenes: A kinetic and mechanistic study

The oxidation of trans-stilbene, phenylacetylene, and diphenylacetylene by Tl(OAc)₃ in aqueous acetic acid medium in the presence of HClO₄ follows the rate law in [H⁺] of 0.1–1.0M, the [H⁺] dependence below 0.1M being marginal. The reactions are strongly dielectric dependent. The order of reactivity among the substrates is styrene > phenylacetylene and trans-stilbene > diphenylacetylene. A mechanism involving the oxythallation adduct by the Tl⁺(OAc)₂ species has been discussed. The use of Ru(III) as a homogeneous catalyst brings a change in the kinetic orders for trans-stilbene, the rate law being The formation constants K for the Ru(III)–alkene π complex at 40, 50, and 60°C are 90.14M^?1, 105.2M^?1, and 127.7M^?1, respectively. Interestingly the oxidation of phenylacetylene and diphenylacetylene does not undergo catalysis by Ru(III). The mechanism involving the metal–arene π complex is discussed.     

Effect of substituent on the mechanism of oxidation of anilines by acidic iodate. A kinetic study

The nature of the substituent is found to exhibit a profound influence on the mechanism of oxidation of anilides by iodate. The process appears to be smooth with electron-releasing groups, while it involves consecutive reactions with electron-withdrawing groups. Azobenzenes and quinones are obtained as the major products with electron-releasing and withdrawing groups, respectively.

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Quenching of superoxide ions by curcumin. A mechanistic study in acetonitrile

The quenching of superoxide ions, O2.-, by curcumin has been studied by electrogenerating this anion radical from oxygen dissolved in acetonitrile solvent (that is, at best, a mimic of the lipofilic layer of biological membranes), containing known amounts of curcumin. Voltammetric tests, combined with coulometric and spectrophotometric measurements, pointed out that each mol of curcumin is able to react with six mols of such anion radical, through a process initiated by an acid-base step, which provides the perhydroxyl radical, HO2.; that disproportionates rapidly to the anionic form of hydrogen peroxide, HO2-, and oxygen, which is thus partially regenerated. At the same time, curcumin is converted to the corresponding three-charged anion. The strict resemblance existing between the mechanism of the rapid superoxide radical decay caused by curcumin and that involved in the presence of the superoxodismutase enzyme (SOD) is also underlined.     

A kinetic and mechanistic study on the oxidation of indole‐3‐acetic acid by peroxodisulfate

The kinetics of oxidation of indole‐3‐acetic acid (IAA) by peroxodisulfate (PDS) has been carried out in aqueous acetic acid medium. First‐order dependence of rate each with respect to [IAA] and [PDS] was observed. The reaction rate was unaffected by added [H⁺]. Increase of percentage of acetic acid decreased the rate. Variation of ionic strength (μ) had negligible influence on the rate. A suitable kinetic scheme based on these observations involving a nonradical mechanism is proposed. The reactivity of peroxodisulfate toward indole‐3‐acetic acid was found to be lower than that with peroxomonosulfate. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 355–360, 2005     

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 kinetic and mechanistic study on the oxidation of L-cystine by alkaline diperiodatocuprate(III): A free radical intervention

The kinetics of oxidation of L-cystine (L-CYS) by diperiodatocuprate (III) (DPC) in aqueous alkaline medium at a constant ionic strength of 0.20 mol/1 was studied spectrophotometrically at 298 K. The reaction between DPC and L-cystine in alkaline medium exhibits 1: 4 stoichiometry (L-cystine: DPC = 1: 4). The reaction is of first order in [DPC] and has less than unit order in [L-CYS] and [alkali], negative fractional order in [periodate] and intervention of free radicals was observed in the reaction. The oxidation reaction in alkaline medium has been shown to proceed via a monoperiodatocuprate(III)-L-ystine complex, which decomposes slowly in a rate determining step followed by other fast steps to give the products. The main products were identified by spot test, IR and GC-MS. The reaction constants involved in the different steps of the mechanism are calculated. The activation parameters with respect to slow step of the mechanism are computed and discussed and thermodynamic quantities were also determined.     

Oxidation of aniline and some para-substituted anilines by benzimidazolium fluorochromate in aqueous acetic acid medium – A kinetic and mechanistic study

The oxidation kinetics of some para-substituted anilines by benzimidazolium fluorochromate (BIFC) have been studied in aqueous acetic acid media in the presence of perchloric acid. The reaction is first order with respect to both aniline and BIFC and is catalysed by a hydrogen ion. The rate data obey Hammett relationship. The products of oxidation are the corresponding azo benzenes. Based on the kinetic results and product analysis, a suitable mechanism has been proposed for the reaction of BIFC with anilines.     

PMR study of mixed complexes of Co(II) in aqueous pyridine and aqueous acetonitrile solutions

Journal of Structural Chemistry -     

Osmium(VIII) mediated oxidation of mercury(I) by cerium(IV) in aqueous sulphuric acid – a kinetic and mechanistic study

The oxidation of Hg^I by Ce^IV has been studied in aqueous H₂SO₄. A minute amount (10^–6 mol dm^–3) of Os^VIII is sufficient to catalyse the reaction. The active catalyst, substrate and oxidant species are H₂OsO₅, [Hg₂(SO₄)HSO₄]^– and H₃Ce(SO₄)^– ₄, respectively. Possible mechanisms are proposed and the reaction constants involved have been determined.     

Complexation of cobalt(II) with histidinato(pentaammine)cobalt(III) in aqueous medium. A kinetic and mechanistic study

Summary The kinetics of formation and dissociation of the binuclear complex of Co^II with histidinato(pentaammine)Co^III have been studied at 10.0°Ct°C25°C and I = 0.3 mol dm^–3 (ClO _inf4 ^sup– ). The formation of the binuclear complex, [(NH₃)₅Co^IIILCo^II]⁴⁺ (L = histidinate), in the 5.7–6.8 pH range involves the reaction of Co(OH₂) _inf6 ^sup2+ with the deprotonated, (NH₃)₅CoL²⁺, and monoprotonated, (NH₃)₅CoLH₃₊, forms of the complex. The rate and activation parameters for the formation are consistent with an I _d mechanism. The binuclear species undergoes dissociation to yield the parent Co^III substrate and Co(OH₂) _inf6 ^sup2+ via spontaneous and acid-catalysed paths. Comparison of spontaneous dissociation rate of the binuclear complex with other related systems indicated the chelate nature of the binuclear species.     

Osmium(VIII) catalysed and uncatalysed oxidation of aspirin drug by diperiodatocuprate(III) complex in aqueous alkaline medium: A mechanistic approach

The kinetics of oxidation of a non-steroidal analgesic drug, aspirin (ASP) by diperiodatocuprate(III)(DPC) in the presence and absence of osmium(VIII) have been investigated at 298 K in alkaline medium at a constant ionic strength of 0.10 mol dm⁻³ spectrophotometrically. The reaction showed a first-order in [DPC] and less than unit order in [ASP] and [alkali] for both the osmium(VIII) catalysed and uncatalysed reactions. The order with respect to Os(VIII) concentration was unity. The effects of added products, ionic strength, periodate and dielectric constant have been studied. The stoichiometry of the reaction was found to be 1:4 (ASP:DPC) for both the cases. The main oxidation product of aspirin was identified by spot test, IR, NMR and GC–MS. The reaction constants involved in the different steps of the mechanisms were calculated for both reactions. Activation parameters with respect to slow step of the mechanisms were computed and discussed for both the cases. The thermodynamic quantities were also determined for both reactions. The catalytic constant (K_C) was also calculated for catalysed reaction at different temperatures and the corresponding activation parameters were determined.     

Aquation of α-cis-chloroaquoethylenediamine-N,N'-diacetatocobalt(III) in aqueous and in mixed solvents: A mechanistic study

Summary The displacement of chloride ligands from -cis-chloro-aquoethylenediamine-N,N-diacetatocobalt(III) in nonacidic aqueous solutions was followed conductimetrically at 30–45° and the products of aquation were characterised by conductance, spectral and ion-exchange techniques. The rate constants for aquation in aqueous media and in 1 : 4 v : v mixed solvents at 25° are: 4.0 × 10^–5 s^–1 in H₂O, 2.71 × 10^–5 s^–1 in MeOH : H₂O, 2.74 × 10^–5 s^–1 in EtOH: H₂,O and 2.58 × 10^–5 s^–1 n in Me₂CO : H₂O. The corresponding H* and S* values have also been evaluated. Solvent polarity has a marked influence on the rate of chloride ion release. The aquation rate constants and the activation parameters have been correlated with solvent parameters,e.g. D, Y-values, Dimroth's E_T and Kosower's Z-values and, based on these correlations, a dissociative interchange (I_d) mechanism is proposed rather than dissociative as observed for some other cobalt(III) complexes.Senior author.