Simple Reaction Scheme Research Articles

Cobalt(II)-catalyzed oxidation of 2,6-xylenol in toluene

The oxidation of 2,6-xylenol with molecular oxygen has been studied using toluene as a solvent and bis( n-butyl- N-salicylideneiminato)cobalt(II) as a catalyst. The products of the oxidation were 3,5,3′,5′-tetramethyldiphenoquinone-4,4′ and low molecular weight poly(2,6-dimethylphenylene-l,4-oxide). During this reaction the irreversible oxidation of cobalt (II) chelate has been observed. A simple reaction scheme has been suggested to describe the complex kinetic behavior.

Formation and decay of triplet excimers as revealed by their absorption spectra: Intramolecular excimers of α,α-dinaphthylalkanes

Transient absorptions, which can be assigned to the triplet—triplet absorptions of excimers, have been observed from fluid solutions of α,α-dinaphthylalkanes. The temporal characteristics of the absorptions are identical to those of the emission previously assigned to excimer phosphorescence. Analysis of the monomer and the excimer absorptions indicate that the kinetics of formation and decay of the triplet excimer can be represented by a simple consecutive reaction scheme: 3M* → 3D* → 1M.

Etudes stéréochimiques XIV. Adduits de Diels‐Alder en série résiniques; action des peracides et ouvertures acido‐catalysées d'époxydes

Studies in Stereochemistry XIV. Diels‐Alder adducts in the resin series; action of peracids and acid‐catalysed ring opening of epoxidesThe synthesis of Diels‐Alder compounds of type 2 with a 17‐nor‐13(14)‐atisène skeleton is described (cf. Schemes 1–3). Depending on the nature and configuration of substituents R1 and R2 on the carbon atoms 15 and 16, an epoxide (24–33) or a ketone (35–38) or a mixture of epoxide, ketone and lactone is obtained by the action of p‐nitroperbenzoic acid on the double bond of these adducts (cf. Scheme 4). A simplified reaction scheme is suggested to explain the formation of the various products. In an acid‐catalysed reaction, the epoxides isomerize mainly into ketones. Nevertherless, in some cases, dienes (e.g. 52) or hydroxy‐γ‐lactones of (13R*, 14S*)‐configuration (e.g. 50) resulting from the opening of the epoxide ring with retention of configuration were obtained.

Reactions of ammonia and nitric oxide in the burnt gases of fuel-rich hydrocarbon-air flames

Measurements of HCN, NH i and NO have been made in a number of fuel-rich ethylene- and acetylene-air flames, seeded with varying amounts of fuel-nitrogen (ammonia, pyridine or nitric oxide). The behaviour of NH i (mostly NH 3) and HCN have been analyzed in terms of the overall reaction scheme ▪ Assuming that the NH i system {NH 3, NH 2, NH, N} is internally equilibrated, the NO-forming and removing reactions have been identified as the nitrogen atom reactions (1) N+ OH→ NO+ H , (2) N+ NO→ N 2+ O . The ratio of the rate constants k 1 k 2 is found to be 1.0 ± 0.2 in the temperature range 1950 to 2380 K. The simplified reaction Scheme I may need modification to include some N 2 formation by NH i + NH i processes. In the presence of hydrocarbons removal of NO by reaction with these species may also need to be considered.

Steady states and stability analysis of a bimolecular non-equilibrium reaction scheme with general hinshelwood-langmuir saturation-inhibition law

The stability analysis of a simple two-component bimolecular reaction scheme involving a Hinshelwood-Langmuir law of nth-order [X/(1 + qX)n, n ≥ 2], is presented.

Kinetics of the chlorine-photosensitized oxidation of hydrogen at 1 atmosphere pressure, 306 K

The chlorine-photosensitized oxidation of hydrogen has been studied at 1 atmosphere total pressure and 306 K in a stopped-flow system. Hydrogen peroxide is the main oxidation product and its formation kinetics at high hydrogen concentrations are consistent with the following simple reaction scheme involving Cl, H and HO2: Cl2+hv→Cl + Cl, Cl + H2→HCl + H, H + O2+ M→HO2+ M, HO2+ HO2→H2O2+ O2. At lower hydrogen concentrations, a marked inhibition in the H2O2 production and Cl2 decay rates was observed, due to the reactions (5b) and (6), Cl + ClOO→Cl2+ O2, Cl + HO2→HCl + O2. (6) Computer analysis of the experimental data gave k5b=(2–1+2)× 10–11 and k6=(2.5 ± 1)× 10–11 cm3 molecule–1 s–1 at 306 K, 1 atmosphere pressure.

Stability diagram and nonlinear structures in a simple reaction scheme involving inhibition forward

Linear stability portrait, limit cycle and dissipative structures exhibited by a reaction scheme involving inhibition forward and diffusion of the intermediate reactants are shown.

Synthesis and N.M.R. spectral analysis of leucine -dgamma.

A simple reaction scheme for the synthesis of leucine totally deuterated in the γ position is described. The n.m.r. spectral properties of this derivative are analyzed and its potential usefulness as a probe of leucine sidechain stereochemistry in peptides is discussed.

Kinetics of recombination of the subunits of human chorionic gonadotropin. Effect of subunit concentration.

The rate of formation of human chorionic gonadotropin from its alpha and beta subunits has been measured at neutral pH and 37 degrees C as a function of subunit concentration, using the fluorescence probe, 1,8-anilinoaphthalene-sulfonate (ANS), to monitor the reaction. The subunits were prepared by acid dissociation of the intact hormone (pH less than or equal to 2, 37 degrees C). Following neutralization, the rate of appearance of ANS fluorescence was identical with the rate of recovery of receptor binding activity and both of these properties were completely recovered. Kinetic data obtained over a 100-fold range of subunit concentrations (1.5 to 146 muM) were not compatible with a simple second-order reaction scheme, but required at least one additional step. The data were best fit by a model in which the subunits reversibly form an intermediate complex (alpha + beta in equilibrium alphabeta) which then undergoes a conformational rearrangement to form the native structure (alphabeta leads to H). Ultraviolet difference absorption measurements suggest that most of the change in the environment of the tyrosyl residues occurs during this second step.

Liquid helium quenching experiments on impure aluminium

Abstract Liquid helium quenching and post-quench annealing experiments have been made on slightly impure Al. The energy of monovacancy formation, the apparent activation energies for Stage I annealing, and the temperature range for Stage I recovery are compatible with previously published data for pure Al. Simplified reaction schemes are discussed in an attempt to explain the annealing behaviour. Although the annealing models appear to describe observed kinetics and, in the divacancy case, give reasonable values for the vacancy/vacancy binding energy, they do not provide a full description of the annealing process. In particular, values of the apparent activation energy for Stage I decay obtained from cross-cut analyses of annealing isotherms are low in comparison with model predictions.

Stereochemistey of nucleophilic addition reactions to ketones with acetylene bonds

1. The addition of thiols (CH3SH, t-C4H9SH) to methyl ethynyl ketone in methanol, in the presence of Triton B, leads to the unstable hemithioketal, the 1,2-addition product. The hemithioketal decomposes at −20°, with the resultant formation of the addition products of the thiol to the C=C bond as a mixture of the cis- and trans-alkylthiovihyl alkyl ketones. 2. Within the framework of the self-consistent MO LCAO method, taking into account all of the valence electrons (CNDO/2), we calculated the energies of the two “transition” complexes that characterize the possible competing attack of alcoholate ion on the fourth or second C atom of methyl ethynyl ketone. The results of the calculation disclosed that attack on the C4 atom should be more probable in the case of the simple bimolecular reaction scheme, despite the seeming disadvantage from the standpoint of the distribution of the charges in the methyl ethynyl ketone molecule.

Spatial instability in simple reaction schemes

A few simple reaction schemes with suitable values of diffusion coefficients and rate constants have been found to be spatially unstable. The conditions for this and for homogeneous oscillations are presented graphically.

Kinetics of free‐radical copolymerization of α‐methylstyrene and styrene

AbstractThe free‐radical copolymerization of α‐methylstyrene and styrene has been studied in toluene and dimethyl phthalate solutions at 60°C. Gas chromatography was used to monitor the rate of consumption of monomers. For styrene alone, the measured rate of polymerization Rp and M̄n of the polymer coincided with values expected from previous studies by other workers. Solution viscosity η affected Rp and M̄n of styrene homopolymers and copolymers as expected on the basis of an inverse proportionality between η1/2 and termination rate. The rate of initiation by azobisisobutyronitrile appears to be independent of monomer feed composition in this system. Molecular weights of copolymers can be accounted for by considering combinative termination only. The effects of radical chain transfer are not significant.A theory is proposed in which the rate of termination of copolymer radicals is derived statistically from an ideal free‐radical polymerization model. This simple theory accounts quantitatively for Rp and M̄n data reported here and for the results of other workers who have favored more complicated reaction models because of the apparent failure of simple copolymer reactivity ratios to predict polymer composition. This deficiency results from systematic losses of low molecular weight copolymer species in some analyses. Copolymer reactivity ratios derived with the assumption of a simple copolymer model and based on rates of monomer loss can be used to predict Rp values measured in other laboratories without necessity for consideration of depropagation or penultimate unit effects. The 60°C rate constants for propagation and termination in styrene homopolymerization were taken to be 176 and 2.7 × 107 mole/l.‐sec, respectively. The corresponding figures for α‐methylstyrene are 26 and 8.1 × 108 mole/l.‐sec. These constants account for the sluggish copolymerization behavior of the latter monomer and the low molecular weights of its copolymers. The simple reaction scheme proposed here suggests that high molecular weight styrene–α‐methylstyrene copolymers can be produced at reasonable rates at 60°C by emulsion polymerization. This is shown to be the case.

The kinetics and mechanism of the cathodic reduction of monomolecular oxide layers electrochemically formed on platinum in bisulphate melts under constant ageing conditions

Summary The kinetics of the electrochemical reduction of a monolayer oxide film anodically formed on platinum in bisulphate melts is studied by means of single potential sweep voltammetry. Under constant ageing conditions, the kinetics of the process is discussed in terms of an irreversible process comprising a simple consecutive reaction scheme involving a second order process as the rate determining step.

ChemInform Abstract: POLYMERISATION BY GLOW DISCHARGE ELECTROLYSIS

Abstract A glow discharge passed from a metal anode to the surface of aqueous solutions of acrylamide produces radicals which initiate polymerisation. The yield of polymer together with its relative molecular mass has been examined as a function of monomer concentration and pressure in neutral solutions. The form of the variations can be explained in terms of a simplified reaction scheme. On the basis of the proposed mechanism there are two reaction zones. In the primary reaction zone no polymerisation occurs, the radical concentration being too high. About 0·2% of the radicals escape into the secondary reaction zone to initiate polymerisation, the volume of this zone being about 0·4 cm 3 . In alkaline solutions the yields and relative molecular masses of the polymers are very low and this is attributed to chain termination by oxygen which rises from the destruction of hydrogen peroxide in alkaline solution.

The radiolysis of acetic acid in aqueous solutions and acetic acid-water mixtures

The radiation chemical yields of stable products were measured in deaerated and oxygenated solutions at low absorbed doses (⩽ 10 krad), different pH values (1–3 and 7·8) and various acetic acid concentrations (0·1–17 mol dm −3). For a dilute solution (0·1 mol dm −3) the results obtained support a simple reaction scheme. At larger acetic acid concentrations, yields of stable products change proportionally to the electron fraction of acetic acid in irradiated mixture. Determinations of molecular hydrogen in deaerated solutions and some measurements of nitrite ion yield in the presence of nitrate point to the reaction of acetic acid with the precursor of the hydrated electron. Optical absorption spectra of intermediates in deaerated acetic acid-water mixtures were obtained by pulse radiolysis.

Polymerisation by glow discharge electrolysis

A glow discharge passed from a metal anode to the surface of aqueous solutions of acrylamide produces radicals which initiate polymerisation. The yield of polymer together with its relative molecular mass has been examined as a function of monomer concentration and pressure in neutral solutions. The form of the variations can be explained in terms of a simplified reaction scheme. On the basis of the proposed mechanism there are two reaction zones. In the primary reaction zone no polymerisation occurs, the radical concentration being too high. About 0·2% of the radicals escape into the secondary reaction zone to initiate polymerisation, the volume of this zone being about 0·4 cm 3. In alkaline solutions the yields and relative molecular masses of the polymers are very low and this is attributed to chain termination by oxygen which rises from the destruction of hydrogen peroxide in alkaline solution.

Thermal dissipative structures: Limit-cycle oscillations in high temperature fluids

Thermochemical analogues of the dissipative structures studied by Prigogine are realized in fluids that feature certain simple reaction schemes at high temperatures.

Glow-discharge electrolysis of sulphuric acid solutions

A glow discharge passed from a metal anode to the surface of sulphuric acid solutions produces hydrogen peroxide and peroxymonosulphuric acid. The yield of each product has been examined as a function of sulphuric acid concentration. The peroxide yield shows a maximum, which is attributed to the scavenging by sulphuric acid of radicals which attack peroxide. The yields of the products have also been examined as a function of pressure and the form of the variations can be explained in terms of a simplified reaction scheme. On the basis of the proposed mechanism the concentration of radicals is of the order of 10−5 mol/dm3 in the primary reaction zone, which extends effectively to a depth of about 400 nm into the solution.

Interactions entre l'oestradiol et des sites récepteurs utérins

The oestradiol‐binding protein of calf uterine cytosol forms a slowly reversible complex with oestradiol. Kinetic studies on the formation of this complex, carried out with crude or partially purified uterine cytosol preparations, indicate a reaction of the second order. The rate constant shows an inverse relationship with protein concentration. Dissociation of the complex appears to occur in two stages, both following first order reaction rate kinetics. Affinity constants calculated from association‐dissociation kinetics, decrease with increasing temperature. The affinity constant measured under equilibrium conditions shows an inverse relationship with protein concentration, and does not appear to vary at temperatures between 0° and 18°. The treatment of the data from binding studies at equilibrium suggests a cooperative effect.These findings indicate that the interaction between the oestradiol‐binding protein, and its ligand cannot be described by simple reaction schemes; work with purified material, now under progress, could simplify interpretation by eliminating ambiguities due to eventual specific or unspecific protein‐protein interactions in our present impure system.