Low molecular weight by-products in the Ziegler polymerization of higher terminal olefins

For the polymerization of n-octadecene-1 with catalysts derived from titanium tetrachloride and triethylaluminum, it has been shown that, in addition to polymerization of the olefin, the formation of isomerized olefin occurs. The latter is predominantly trans-n-octadecene-2 and its formation is favored by increase in Al:Ti mole ratio, in catalyst concentration, and in reaction temperature. It has also been shown that 1,1-disubstituted ethylene is present in the nonpolymeric reaction products. The influence of added trans-n-octadecene-2 or trans-n-octadecene-7 on the polymerization of n-octadecene-1 has been studied, and it is shown that the 2-isomer has the more pronounced effect on polymer yield and intrinsic viscosity. It has also been shown that no significant copolymerization of terminal with nonterminal octenes or octadecenes occurs under these conditions. Results indicate that, in polymerizations of this kind, the interaction of catalyst with isomerized monomer is probably an important factor in determining polymer yield and molecular weight. The isomerization reaction is also of interest as a general preparative method for trans-2-olefins.     

Reactions of 2,2,4,4-tetramethyl-1,3-cyclobutanedione with amines and other nucleophiles. II

The reaction of 2,2,4,4-tetramethyl-1,3-cyclobutanedione with various nucleophiles has been demonstrated to be dependent on the reaction conditions, steric factors and the nucleophilicity of the attacking species. In the reaction with primary amines the intermediate has been established as the N-substituted imine which is hydrolyzed to the corresponding amide in the presence of water. The reaction of diamines with the dione has been shown to be a method of synthesizing 2-substituted imidazolines and 1 H-4,5-dihydropyrimidines.     

Study of the reaction of MoOS2(S2CNR2)2 with PPh3 in 1,2-dichloroethane: Part II. Detection of reaction intermediate pentavalent molybdenum using ESR method at low temperature

Intermediate product of the reaction of MoOS₂(S₂CNR₂)₂ and PPh₃ in dichloroethane has been detected by ESR spectroscopy. Two ESR signals have been observed at low temperature in the reaction system which was stopped by quenching it in liquid nitrogen. The g values are 2.020 ± 0.001 and 1.972 ± 0.001 respectively. The signal at g = 2.020 is attributed to a reaction intermediate with pentavalent molybdenum. A reaction mechanism has been proposed which is consistent with the observation of pentavalent molybdenum as the intermediate in the process of reaction.     

Ruthenium(III) catalyzed oxidation of paracetamol by chloramine-T in aqueous alkaline medium – A kinetic and mechanistic pathway

The kinetic study of ruthenium(III) chloride catalyzed oxidation of paracetamol by N-chloro-p-toluene sulfonamide (chloramine-T) in the alkaline medium has been performed. The reaction exhibits second order nature and the effect of the catalyst indicates the occurrence of uncatalyzed reaction simultaneously. Rate is decelerated by hydroxide ions. A plausible reaction mechanism has been suggested and the rate law is derived to account for such experiential observations. The activation parameters have been calculated. No evidence of the participation of free radicals is observed.     

Kinetics and mechanism of the reaction of substituted benzyl bromides with copper in dimethylformamide

The reaction of copper metal with various substituted benzyl bromides in dimethylformamide has been studied and the kinetic and thermodynamic parameters of the reaction have been obtained. Hammett plots of log(k/k°) vs the substituent constant σ gave good correlations (ρ = 0.24, S_ρ = 0.03, r = 0.951). The structure of the organic group has little effect on the rate of reaction of substituted benzyl bromides with copper. In the absence of atmospheric oxygen, oxidative dissolution of copper occurred by the mechanism of single‐electron transfer with the formation of 1,2‐diphenylethanes and copper(I) complexes. The stereochemistry and intermediate compound were also studied and the reaction mechanism is discussed. Copyright © 2005 John Wiley & Sons, Ltd.     

Polyesters. I. Rate of polyesterification of γ-arylitaconic acids with ethylene glycol

A kinetic study of the polyesterification reaction of γ-phenyl- γ-p-methoxyphenyl-, and γ-p-chlorophenylitaconic acids (1 mole) with ethylene glycol in the presence or in absence of p-toluenesulfonic acid as a catalyst has been carried out in order to show the effect of substituents on the rate and degree of polymerization. The reaction of 1 mole of the acid and an excess of ethylene glycol has also been studied. In all cases the reaction is found to follow the second-order rate equation. The mechanism of polyesterification has been discussed. In catalyzed polyesterification electron-withdrawing groups (CI) decrease the velocity of the reaction. The low values of ρ in both the auto-catalyzed and catalyzed reaction indicate that this polyesterification is slightly sensitive to the polar nature of the substituent.     

The Roles of Counterion and Water in a Stereoselective Cysteine‐Catalyzed Rauhut–Currier Reaction: A Challenge for Computational Chemistry

The stereoselective Rauhut–Currier (RC) reaction catalyzed by a cysteine derivative has been explored computationally with density functional theory (M06‐2X). Both methanethiol and a chiral cysteine derivative were studied as nucleophiles. The complete reaction pathway involves rate‐determining elimination of the thiol catalyst from the Michael addition product. The stereoselective Rauhut–Currier reaction, catalyzed by a cysteine derivative as a nucleophile, has also been studied in detail. This reaction was experimentally found to be extremely sensitive to the reaction conditions, such as the number of water equivalents and the effect of potassium counterion. The E1cB process for catalyst elimination has been explored computationally for the eight possible stereoisomers. The effect of explicit water solvation and the presence of counterion (either K⁺ or Na⁺) has been studied for the lowest energy enantiomer pair (1S, 2R, 3S)/(1R, 2S, 3R).     

Kinetics and mechanism of the reaction of benzyl bromide with copper in hexamethylphosphoramide

The reaction of copper with benzyl bromides in hexamethylphosphoramide has been studied. The kinetic and thermodynamic parameters of the reaction have been obtained. Hammett plots of log (k/k^o) vs the substituent constant σ gave good correlations (ρ = 0.15, S_ρ = 0.02, r = 0.954). The structure of the organic group has little effect on the rate of reaction of benzyl bromide with copper. In the absence of atmospheric oxygen, the oxidative dissolution of copper occurred by the mechanism of single‐electron transfer with the formation of 1,2‐diphenylethane and copper(I) complexes. The stereochemistry and intermediates compound was also investigated. The reaction mechanism is discussed. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 296–305, 2005     

Kinetic and mechanistic studies of some aliphatic amines' oxidation by sodium N‐bromo‐p‐toluenesulfonamide in hydrochloric acid medium

Oxidations of n‐propyl, n‐butyl, isobutyl, and isoamyl amines by bromamine‐T (BAT) in HCl medium have been kinetically studied at 30°C. The reaction rate shows a first‐order dependence on [BAT], a fractional‐order dependence on [amine], and an inverse fractional‐order dependence on [HCl]. The additions of halide ions and the reduction product of BAT, p‐toluenesulfonamide, have no effect on the reaction rate. The variation of ionic strength of the medium has no influence on the reaction. Activation parameters have been evaluated from the Arrhenius and Eyring plots. Mechanisms consistent with the preceding kinetic data have been proposed. The protonation constant of monobromamine‐T has been evaluated to be 48 ± 1. A Taft linear free‐energy relationship is observed for the reaction with ρ* = −12.6, indicating that the electron‐donating groups enhance the reaction rate. An isokinetic relationship is observed with β = 350 K, indicating that enthalpy factors control the reaction rate. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 776–783, 2000     

5-Aryl-1,3,4-oxadiazoline-2(3H)-thiones in reactions with alkyl haloacetates

The reaction of 5-aryl-1,3,4-oxadiazoline-2(3H)-thiones with alkyl haloacetates has been studied. It was shown that the reaction proceeds to give S-substituted products. The effect of the nature of the substituents in the molecules of both the thiones and the haloacetates on the reaction route and yields has been examined.     

Kinetic studies on the mechanism of the relative catalytic activities of surfactants in the oxidation of amino-acids by chloramine-T

The kinetics of oxidation of amino-acids by chloramine-T in the presence of two different surfactants (cationic and anionic surfactants) in acidic medium has been studied. The kinetic results show that the reaction is fractional and first order with respect to substrate and oxidant respectively. The influence of halides, ionic strength and solvent on the rate has been studied. The effect of surfactants on the reaction show that the reaction velocity is highly sensitive to the variation of surfactant concentration. The micelle-substrate binding constant (K) and co-operativity index have been calculated indicating the stability of the catalyst substrate micelles (complex) so formed. A probable reaction path has been suggested and discussed in the light of various experimental results and findings.     

Kinetics and mechanism of tris (p-bromophenyl) aminium hexachloroantimonate induced decomposition of 9-diazofluorene

The kinetics and products of the decomposition of 9-diazofluorene by tris (p-bromophenyl) aminium hexachloroantimonate in acetonitrile solvent has been investigated. The reaction is first order with respect to the concentration of both 9-diazofluorene and tris (p-bromophenyl) aminium hexachloroantimonate. A reaction mechanism has also been proposed.     

Mechanistic investigation of the oxidation of vitamin B1 with sodium N-chlorobenzenesulfonamide in presence of ruthenium(III) catalyst in hydrochloric acid medium: a kinetic approach

The oxidative cleavage of vitamin B₁ (thiamine hydrochloride, THM) with sodium N-chlorobenzenesulfonamide (chloramine-B, CAB) has been kinetically investigated in HCl medium in presence of ruthenium(III) catalyst at 308 K. The oxidation reaction follows the rate law, −d[CAB]/dt = k [CAB] [Ru(III)] [H⁺] [THM]^a [Cl⁻]^b, where a and b are less than unity. Variation of ionic strength of the medium and addition of the reaction product, benzenesulfonamide (BSA) had no significant effect on the reaction rate. The change in relative permittivity of the medium affected by changing the solvent composition with acetonitrile has been studied. The stoichiometry of the reaction was found to be 1:1, and N-[(4-amino-2-methylpyrimidine-5-yl)methyl]benzensulfonamide and 2-(4-methylthiazol-5-yl)ethanol were identified as the oxidation products of vitamin B₁. The reaction constants involved in the mechanism were computed. The reaction was studied at different temperatures and the overall activation parameters have been evaluated. C₆H₅SO₂NHCl has been postulated as the reactive oxidizing species. The observed results have been explained by plausible mechanisms and the relative rate laws have been deduced. Correspondence: Kikkeri Narasimhasetty Mohana, Department of Studies in Chemistry, University of Mysore, Manasagangotri, Mysore 570 006, India.     

The reactivity of organothallium compounds. Kinetics and mechanism of iodination of diarylthallium salts by molecular iodine in dioxane

The kinetics and mechanism of the reactions of diarylthallium, trifluoroacetates with molecular iodine in dioxane solutions have been studied. The reaction has the overall second order with the first order with respect to each reagent. The effect of substituents in the aromatic ring on the rate constant of iodination is described by the equation logk ₂ρσ⁺(ρ=-1.60, r=0.97). The reaction is catalyzed by the iodide ion. The activation enthalpies and entropies of iodination of diarylthallium trifluoroacetates in dioxane and di(p-anisyl)thallium trifluoroacetate in various solvents have been calculated. The effect of solvents on the rate constant of iodination of di(p-anisyl)thallium trifluoroacetate has been studied. The reaction mechanism is considered as an electrophilicS _EC process. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 451–455, March, 1999.     

Copper‐catalyzed Clauson–Kass pyrroles synthesis in aqueous media

An efficient and convenient copper‐catalyzed Clauson–Kass reaction of 2,5‐dimethoxytetrahydrofuran with amines in aqueous media has been developed, providing a wide range of N‐substituted pyrroles in good yields. It is noteworthy that the Clauson–Kass reaction of 2,5‐dimethoxytetrahydrofuran with p‐phenylenediamine or m‐phenylenediamine proceeds smoothly to afford the corresponding monopyrroles and bispyrroles with high selectivity in impressive yields. A plausible mechanism for the formation of N‐substituted pyrroles has been proposed. Copyright © 2012 John Wiley & Sons, Ltd.     

Kinetic energy release in metastable ions from β-keto esters

The kinetic energy release, T, in metastable ion transitions accompanying the main fragmentation reaction by electron impact has been determined for methyl-, ethyl- and propyl-pivaloyl acetates. The measurements have been made using a MAT 311 mass spectrometer with inverse Nier–Johnson geometry, by high voltage and mass-analysed ion kinetic energy methods. The peak width at 50% height has been used in the calculations. The T values and the shape of the metastable peaks are correlated to reaction types and to the alcohol radical.     

Kinetics of the oxidative degradation of d-xylose in the presence and absence of cationic and anionic surfactants

The oxidative degradation of d-xylose by cerium(IV) has been found to be slow in acidic aqueous solution with the evidence of autocatalysis. The reaction is accelerated in the cetyltrimethylammonium bromide (CTAB) micellar medium but sodium dodecyl sulfate (an anionic surfactant) has no effect. The pseudo first-order rate constants have been determined at different [reductant], [oxidant], [H₂SO₄], temperature, and [CTAB]. The reaction rate increased with increasing [d-xylose] and decreased with increase in [H₂SO₄]. The CTAB-micelle-catalyzed kinetic results can be interpreted by the pseudophase model. The kinetic parameters such as association constant (K _s), micellar medium rate constant (k _m), and activation parameters (E _a, ΔH ^# and ΔS ^#) are evaluated and the reaction mechanism is proposed. The reaction rate is inhibited by electrolytes and the results provide an evidence for the exclusion of the reactive species from the reaction site.     

Structure and Reactivity of Xanthocorrinoids. Part II. Influence of the c-acetic-acid chain on the course of the hydroxylation of the corrin chromophore by oxygen in the presence of ascorbic acid

The yield of the main product from the reaction of heptamethyl dicyanocobyrinate with O₂ in the presence of ascorbic acid has been optimised by systematic variation of the reaction conditions, and the structure of the obtained ‘stable yellow corrinoid’ has been established by X-ray analysis. From the relationship between the structures of analogous xanthocorrinoids obtained likewise from a series of dicyanocobyrinic-acid derivatives, which has been prepared by systematic modifications of the c-acetic-acid chain, and the functionality of the substituent at C(7), a reaction mechanism is suggested.     

The Electrochemical Oxidation of N,N‐Diethyl‐p‐Phenylenediamine in DMF and Analytical Applications. Part I: Mechanistic Study

The electrochemical oxidation of N,N‐diethyl‐p‐phenylenediamine in dimethylformamide has been studied at platinum and gold microdisk electrodes of various radii between 6.7 and 66 μm. The voltammetric responses revealed two electrochemically reversible waves the second of which becomes larger at higher concentrations and bigger electrode radii. The voltammetric signals have been modelled and the electrochemical oxidation reaction is not inconsistent with an EC_revECE reaction. Kinetic parameters are reported.     

Photochromism in the arylaroylaziridine system

Photochromism of a number of arylaroylaziridines has been observed in the solid state or in the rigid matrix. The photochromic behavior is dependent on the intensity of the incident radiation, the reaction medium, the wavelength of light used and on the relationship of the substituents on the three-membered ring. From the visible absorption spectra it is clear that cis-arylaroylaziridines give different colored species than do the trans isomers. These results suggest that the coloration is due to an extensive electrical interaction between the bent bonds of the aziridine ring and the π orbitals of the benzoyl and phenyl groups. Attempts to trap the colored species by co-irradiation with substrates containing a multiple bond failed. A reaction has been found to occur upon heating various arylaroylaziridines with dimethylacetylene dicarboxylate in inert solvents.