Palladium-catalyzed reaction of aryl iodides with tertiary propargylic amides.: Highly substituted allenes through a regioselective carbopalladation/β-NPd elimination reaction

The palladium-catalyzed reaction of aryl iodides with tertiary propargylic amides affords highly substituted allenes. Best results have been obtained by using Pd(OAc)₂, ⁿBu₃N, HCOOH, and ⁿBu₄NCl or LiCl in DME at 100 °C. The reaction is highly regioselective and the carbopalladation step is controlled by the strong directing effect of the tertiary amide group.     

Kinetics and mechanism of the chain reaction of N-phenyl-1,4-benzoquinone monoimine with 2,5-dimethylhydroquinone

The kinetics of the reaction of N-phenyl-1,4-benzoquinone monoimine with 2,5-dimethyl-1,4-hydroquinone in chlorobenzene was studied at 298.2 and 340 K. The reaction occurs by a chain mechanism with a chain length of ～10²?10³ units, depending on temperature and reactant concentrations. The orders of reaction with respect to components and the rate constants (or estimated values) were determined for all of the elementary steps at 298.2 and 340 K. The experimental data were compared with the results obtained previously for the reaction of N-phenyl-1,4-benzoquinone monoimine with 2,5-di-tert-butyl-1,4-hydroquinone. The nature of substituents in hydroquinone exerts a strong effect on the kinetic parameters of this new class of chain reactions. The effect of the final product, 2,5-dimethylquinone, on the reaction kinetics at 298.2 and 340 K was studied, and it was found that 2,5-dimethylquinone additives has only a weak inhibiting effect. The rate constant of the reaction of 2,5-dimethylquinone with semiquinone radicals, which were produced from 4-hydroxydipheny-lamine, was estimated: k _?2 ～ 10⁴?10⁵ l mol^?1 s^?1.     

Nucleophilic displacement in polyhalogenoaromatic compounds. Part 12.[1] Additivity of fluorine substituent effects in methoxydefluorination

The rates of methoxydefluorination of all twelve polyfluorobenzenes in dimethyl sulphoxide-methanol mixtures (DMSO-MeOH; 9:1, v/v; 298.2 K) have been measured. Three substituent rate factors (f_o, 60; f_m, 180; f_p, 0.75) are sufficient to reproduce the effect of the fluorine substituent in this reaction upon each member of the series. The solvent effect, comparing these results with an earlier and more limited study in methanol is predominantly a simple acceleration. The effects of substituents upon the rate of methoxydefluorination of fluorobenzene itself are slightly greater (?^?, 6.9) than in the corresponding reaction of pentafluorobenzene derivatives (?^?, 5.8), but the change in sensitivity is much less than that found with nitrobenzene derivatives.     

Selenosulfonation of allenes

Se-Phenyl p-tolueneselenosulfonate (1a) undergoes highly regioselective, photoinitiated, free-radical addition to allenes (R₁CHCCR₂R₃) to afford the regioisomer R₁CH(SePh)C(SO₂Ar)CR₂R₃ (13) arising from addition of the p-tolylsulfonyl group to the central carbon of the allene and transfer of the phenylseleno group to the less highly substituted of the two terminal carbons. This regioselectivity, which contrasts with that observed in the majority of radical additions to allenes, can be explained by reference to concepts proposed by Heiba as being important in determining the orientation in different radical additions to allenes. Oxidation of the PhSe group in 13 to PhSe(O) gives allylic selenoxides that undergo a reaction sequence of facile, concerted, [2,3]-sigmatropic rearrangement followed by hydrolysis of the resulting selenenate to afford β-tolylsulfonyl-substituted allylic alcohols, R₁CHC(SO₂Ar)C(OH)R₂R₃ (14) in 70–98% yield. Photoaddition of 1a to allenes, followed by the conversion of 13 to 14 thus provides a simple, high-yield route to a wide variety of 14, a class of compounds that would seem to have a number of interesting possible uses in synthesis.     

Vibrational energy exchange of the DF (ν=2) state with DF (ν=0)

The energy transfer rate for the reaction DF (ν=1) + DF (ν=1)^k_νν→ DF (ν=0) + DF (ν=2) + ΔE=91.6 cm^?1 has been studied in a combined shock-tube laser-induced fluorescence experiment at temperatures from 295 to 720°K. The rate coefficient k_νν for the exothermic reaction was found to vary as T^?1 when expressed in units of cm³/mole sec. At T=295°K, the probability of the reaction is approximately 0.2 per collision.     

Rate of the reaction I2 + F2 → products

The rate coefficient, k1, for the reaction I2+F2k1→ products has been measured at room temperature to be k1 = (1.9 = 0.4) × 10?15 cm3/molecule s. The macroscopic rate is compared to microscopic cross-section data obtained from molecular beam experiments and is found to be consistent with the bimolecular reaction I2 + F2→ I2F + F.DG|National Research Council/Resident Research Associate.     

Kinetics of the reaction of NH2 with NO2

The absolute rate constant of the reaction of NH₂ with NO₂ has been measured using a flash-photolysis laser resonance-fluorescence technique. The value obtained at room temperature is k₁ = 2.3 (± 0.2) × 10^?11 cm³ molecule ^?1 s^?1. A negative temperature coefficient has been found between 298 and 505 K for this reaction, k₁ = 3.8 × 10^?8 × T^?1.30 cm³ molecule^?1 s^?1. It is thought that this is the major reaction of NH₂ in the troposphere.     

Rhodium(III) as a homogeneous catalyst for the oxidative decolorization of ethyl orange with aqueous acidic chloramine-T: a spectrophotometric, kinetic and mechanistic study

The kinetics and mechanism of sodium N-chloro-p-toluenesulfonamide oxidative decolorization of ethyl orange (EO) in aqueous perchloric acid have been studied at 303 K in the presence of rhodium(III) chloride as catalyst. The reaction exhibits first-order dependence on [EO]_o and a fractional-order dependence on [CAT]_o, [H⁺] and [Rh^III]. The dielectric effect is positive. The stoichiometry of the reaction was found to be 1:1, and the oxidation products of EO were identified as N-(4-diethylamino-phenyl)-hydroxylamine and 4-nitroso-benzenesulfonic acid. The rhodium(III)-catalyzed reaction is about fourfold faster than the uncatalyzed reaction. The proposed mechanism and derived rate law are in agreement with the observed kinetic results.     

Kinetic and mechanistic study of the reduction of 2,6-dichlorophenol indophenol by dithionites

The reaction of 2,6-dichlorophenolindophenol (DCPI) and dithionites is studied kinetically by applying the stopped-flow technique. Reaction rate constants are given for the pH range 1.30–6.80. The reaction was found to follow first-order kinetics with respect to each of the reactants. For pH 3.97, 5.10 and 6.80, the second-order reaction rate constant was determined by applying four different technique. Mean values of k = 172±5, 200±2 and 276±4 l mol^?1s^?1 are given for pH 3.97, 5.10 and 6.80, respectively. A mechanism is proposed for the reaction, which suggests partial reactions of all possible species of DCPI and dithionites at any pH. An equation for the calculation of k at any pH is derived, which gives k as a function of [H⁺], the partial reaction rate constants and the dissociation constants of DCPI and H₂S₂O₄. Values of reaction rate constants of all possible partial reactions are also presented.     

Kinetic control of the transmetalation of labile metalloporphyrins in individual and mixed solvents

Transmetalation reactions of cadmium complexes of tetraphenylporphine (CdTPP, I) and tetrabenzoporphine (CdTBP, II) in individual and mixed solvents have been investigated. For individual solvents, provided that the reaction proceeds via the same mechanism, its rate generally increases as the donor number increases in the order DMSO < DMF < PrOH-1 < MeCN (CdTPP-Zn(OAc)₂-Solv system). On passing to the CdTPP-Cu(OAc)₂-Solv system, the reaction rate order changes to DMSO < PrOH-1 < MeCN < DMF because the transmetalation mechanism changes from mixed to associative, as follows from the reaction order with respect to the salt being zero. The effect of the DMSO-DMF mixed solvent on the transmetalation reaction is limited to changing the reaction rate through alteration of the stability of the [CuX₂(Solv¹) _{n ? m ? 2}(Solv²) _m ] solvated salts. The trans effect of the ligands in the solvated salts does not increase the transmetalation rate.     

Theoretical studies on the kinetics and mechanism of the reaction of atomic hydrogen with carbon dioxide

The potential energy surface for the reaction of hydrogen atom with carbon dioxide is explored by using various quantum chemical methods including W1BD, CBS-QB3, G4, G3B3, CCSD(T), QCISD(T), CCSD, M06-2X, and BB1K.Transition state theory and a modified strong collision/RRKM model are employed to calculate the thermal rate coefficients for the reaction. The results of calculation show that the overall rate constant for the reaction H + CO₂ are pressure-independent over the temperature range of 300 to 3500 K. By using the energies at the W1BD level, the non-Arrhenius expression k = 9.8T ^2.9exp(?74.8 kJ/mol/RT) L mol^?1 s^?1 was found for the reaction.     

Kinetics and mechanism of the redox reaction between malachite green and iron(III) in aqueous and micellar media

The kinetics of the oxidation of malachite green (MG⁺) by Fe(III) were investigated spectrophotometrically by monitoring the absorbance change at 618 nm in aqueous and micellar media at a temperature range 20–40 °C; I = 0.10 mol dm^?3 for [H⁺] range (2.50–15.00) × 10^?4 mol dm^?3. The rate of reaction increases with increasing [H⁺]. The reaction was carried out under pseudo-first-order conditions by taking the [Fe(III)] (>10-fold) the [MG⁺]. A mechanism of the reaction between malachite green and Fe(III) is proposed, and the rate equation derived from the mechanism was consistent with the experimental rate law as follows: Rate = (k ₄ + K ₁ k ₅[H⁺]) [MG⁺][Fe(III)]. The effect of surfactants, such as cetyltrimethylammonium bromide (CTAB, a cationic surfactant) and sodium dodecylsulfate (SDS, an anionic surfactant), on the reaction rate has been studied. CTAB has no effect on the rate of reaction while SDS inhibits it. Also, the effect of ligands on the reaction rate has been investigated. It is proposed that electron transfer proceeds through an outer-sphere mechanism. The enthalpy and the entropy of the activation were calculated using the transition state theory equation.     

Rate determination for F + CH4 by real-time competitive kinetics

The rate constant for the title reaction was found to be (5.72 ± 0 30) × 10^?11 cm³ molecule^?1 s^?1. Fluorine atoms were generated via IR multiphoton dissociation of SF₆ in a mixture of CH₄, D₂, and Ar. The time-dependent concentration of fluorine atoms, and hence the rate of reaction, could be monitored either by HF IR luminescence or by DF luminescence. We have thus established that real-time observation of competitive kinetics can be used to measure a variety of reaction rates.     

Influence in kinetic studies by competitive photocurrent methods of a post-competition link between parallel reactions chains: Part II. OH radical addition to phenol and aniline

The rate constants for the homogeneous reaction of OH radicals of O^? ions with phenol and aniline have been determined by a photoelectrochemical method involving studies of the suppressive effect of mixtures of aniline and of phenol with methanol on the nitrous oxide photocurrent at a DME. Fairly good agreement with absolute rate constants obtained by conventional radiation chemical methods is obtained if use is made of the theory developed in Part I of this paper which takes account of the possibility of interaction between the photocurrent reaction chains following competition between the two organic solutes for OH radicals. The present work points to a value of 1.75±0.6 10¹⁰M^?1 s^?1 for the capture of OH by phenol at pH 9.5. The reaction product, the cyclohexadienyl radical Φ (OH)₂, is able to extract H atoms from methanol with a rate constant of the order of 10⁷M^?1 s^?1, this reaction tending to lessen the suppressive effect of a phenol + methanol mixture on the nitrous oxide photocurrent. Similar complications are observed at higher pH, and also when using aniline + methanol mixtures.     

Mechanism of the reaction of N-p-tosylsulphilimine and related compounds with thiophenolate ion

The reaction of alkyl aryl N-p-tosylsulphilimines with thiophenolate ion was found to afford quantitatively the sulphide that arises by an S_N2 like reaction on the carbon atom adjacent to the tri-valent sulphur atom. This reaction was also found to proceed smoothly with such compounds as sulphoxides and sulphones and sulphoxmanes. The kinetic study on the reaction between aryl methyl N-p-tosylsulphilimine with thiophenolate ion in DMF reveals that the reaction is of second order, namely, first order with respect to each thiophenolate ion and the sulphilimine. The enthalpy and entropy of activation for the reaction are ΔH^≠ = ?17· kcal/mol and ΔS^≠ = ?5·7 eu respectively. The effect of substituents in the reaction, p-XC₆H₄⁺(^?SO₂C₆H₄Y-p)CH₃ + p-ZC₆H₄SK is nicely correl with Hammett σ values giving ?_x = + 2·4, ?_y = + 1·2 and ?_z = ?1·8 respectively. Meanwhile, a marked steric retardation by a bulky alkyl group in alkyl phenyl N-p-tosylsulphilimine is observed. Furthermore, from the stereochemical study of the reaction using an optically active sec-octyl phenyl N-p-tosylsulphilimine with thiophenolate ion it is concluded that the reaction proceeds via a typical S_N2 process on α-carbon atom attached to the tri-valent sulphur atom.     

The oxidized complex of nickel with 4-carboxy-1,2-cyclohexanedionedioxime in alkaline media

The reaction of oxygen with a nickel(II) complex of 4-carboxy-1,2-cyclohexanedionedioxime in alkaline media was studied spectrophotometrically, polarographically, and by spectrophotometric titrations with tin(II) chloride. Magnetic susceptibility measurements were also performed. The rate of formation of the oxidized complex was found to be first order at 25° and 50°. The average values obtained for the rate constant k'₁ are (2.71 ± 0.23) x 10^-2 h^-1 (25°), spectrophotometrically; (5.99 ± 0.83) x 10^-2 h^-1 (50°), polarographically; (4.98 ± 0.90) x 10^-2 h^-1 (50°), titrimetrically; (2.87 ± 0.29) x 10^-2 h^-1 (50°), curve fitting. The value obtained for the rate constant K'₂ is (1.59 ± 0.16) x 10^-2 h^-1 (50°), curve fitting, The effect of reducing agents on the formation of the oxidized complex was studied. It was found that tin(II) chloride, hydrazine sulfate, and hydroxylammonium chloride prevented the formation of the oxidized complex. A reaction mechanism for the formation and decomposition of the oxidized complex is proposed.     

Experimental design for copper cementation process in fixed bed reactor using two-level factorial design

This work deals with cementation of copper onto iron grid in a fixed bed reactor. The influence of several parameters is studied, namely: initial concentration of copper [Cu²⁺]₀, temperature and flow rate. Moreover, their influence on the copper cementation reaction is investigated statistically by the experimental design in view of industrial application. The estimation and the comparison of the parameter’s effects are realized by using two-level factorial design. The analysis of these effects permits to state that the most influential factor is initial concentration of copper [Cu²⁺]₀ with an effect of (+2.4566), the second in the order is the temperature with an effect of (+0.18959), the third is the flow rate of the electrolytic solution with an effect of (?0.4226). The significance interactions found by the design of experiments are between initial concentrations of copper ions–flow rate (x₁x₃) with an effect (b₁₃ = +0.6965).     

Solvated positron chemistry. The reaction of hydrated positrons with chloride ions

The reaction of hydrated positrons (c_aq⁺ with cloride ions in aqueous solutions has been studied by means of positron annihilation angular correlation measurements. A rate constant of k = (2.5 ± 0.5) × 10¹⁰ M^?1 s^?1 was found. Probably the reacting positrons annihilated from an e⁺ Cl^? bound state resulting in an angular correlation curve 8% narrower than for the hydrated positron. Carbontetrachloride in benzene seems to give similar, but smaller effect.     

Kinetic study on reactions between polymer chain-ends. Coupling reactions of living polystyrene with chloro-ended polystyrene

The reaction of living polystyrene with chloro-ended polystrene was studied to examine “the kinetic excluded volume effect” on the intermolecular reaction between reactive chain-ends of two monodisperse polymers. The reaction of living polystyrene with 1-chloropentane was also studied as a model reaction (small molecule-polymer reaction). The second-order rate constants, k₂, for the polymer polymer reaction in benzene (with a small amount of tetrahydrofuran to break the association of living-ends) is independent of the degree of polymerization, DP, for the range of DP studied (up to 400). The ratios of the rate constants for the polymer-polymer and the polymer-small molecule reactions, k₂/k₂⁰, are the same in benzene and in cyclohexane (good and poor solvent for polystyrene respectively), showing that the effect of the coil expansion is not large enough to be detected. These results confirm the Flory basic concept that the reactivity of a functional group attached to an inert polymer is not affected by the presence of the polymer chain in activation-controlled reactions.     

Kinetics of the Decomposition of α-Phenylethyl Hydroperoxide in the Presence of <Emphasis Type="Italic">N,N,N′,N′</Emphasis>-Tetramethyl-<Emphasis Type="Italic">para</Emphasis>-Phenylenediamine

It is found that the tertiary amine N,N,N′,N′-tetramethyl-para-phenylenediamine (TMPD) causes the decomposition of α-phenylethyl hydroperoxide (ROOH), and the interaction between the components occurs in accordance with a complicated rate law. It is demonstrated that more than 30 hydroperoxide molecules (n) can be degraded at a molecule of TMPD; this fact suggests that the amine has a catalytic effect on the process. The value of n increases with the [ROOH]₀/[TMPD]₀ ratio. The initial rates of consumption of ROOH and TMPD linearly increase with the initial concentrations of both of the reactants. The apparent rate constant of the reaction is k = 0.4 l mol^?1 s^?1 (393 K), as calculated from the initial rates of ROOH consumption. As a result of the interaction, TMPD is converted into an inhibitor. The rate constant of the reaction of this inhibitor with ethylbenzene peroxy radicals is about 2 × 10⁴ l mol^?1 s^?1.