The Reaction of Organophosphorus Radicals With Vinyl Acetate and Acrylonitrile in the Presence of an Aminoxyl Radical Scavenger

1995 ◽  
Vol 48 (3) ◽  
pp. 625 ◽  
Author(s):  
WK Busfield ◽  
ID Grice ◽  
ID Jenkins
Keyword(s):  
Vinyl Acetate ◽  
Hydrogen Abstraction ◽  
Phosphate Esters ◽  
Radical Scavenger ◽  
Diphenylphosphine Oxide ◽  
Dimethyl Phosphite ◽  
Radical Trapping ◽  
Diffusion Controlled ◽  
Order Of Magnitude

The radical-trapping technique employing 1,1,3,3-tetramethyl-1,3-dihydro-2H-isoindol-2-yloxyl (1) as a radical scavenger has been used to study the reaction of diphenylphosphinoyl (2) and dimethoxyphosphinoyl (3) radicals with vinyl acetate and acrylonitrile. The phosphorus- centred radicals were generated by hydrogen abstraction from diphenylphosphine oxide and dimethyl phosphite respectively. Diphenylphosphine oxide was approximately three times as reactive as dimethyl phosphite towards hydrogen abstraction by t- butoxyl radicals and four times as reactive as tetrahydrofuran (towards abstraction of an α-hydrogen). Diphenylphosphinoyl radicals were found to be relatively nucleophilic and, in competition experiments, reacted about an order of magnitude faster with acrylonitrile than with vinyl acetate. Dimethoxyphosphinoyl radicals were rather less nucleophilic and reacted only twice as fast with acrylonitrile as they did with vinyl acetate. In the presence of excess aminoxyl (1), both diphenylphosphinoyl and dimethoxyphosphinoyl radicals were efficiently scavenged to produce stable phosphinic and phosphate esters respectively. The rate of scavenging was close to diffusion-controlled (c. 1.8×109 1. mol-1 s-1).

Zinc dissolution in Leclanche electrolyte

1974 ◽  
Vol 27 (11) ◽  
pp. 2467 ◽  
Author(s):  
DB Matthews ◽  
PG Capps
Keyword(s):  
Corrosion Rate ◽  
Metallic Impurity ◽  
Cathodic Reaction ◽  
Electrolyte Layer ◽  
Zinc Surface ◽  
Diffusion Controlled ◽  
Layer 2 ◽  
Order Of Magnitude ◽  
Zinc Dissolution

The rate and morphology of zinc dissolution were studied in a Leclanche electrolyte of composition 0.5 mol dm-3 ZnCl2 and 5 mol dm-3 NH4Cl. A gelled electrolyte layer 2 x 10-3 m thick on the zinc surface was found to reduce the corrosion rate by an order of magnitude and to promote even dissolution. The corrosion results are interpreted in terms of a diffusion-controlled cathodic reaction involving O2 dissolution and metallic impurity deposition.

A kinetic study of the reaction of adamantanethione with 2-adamantanethiol

1976 ◽  
Vol 54 (21) ◽  
pp. 3407-3411 ◽  
Author(s):  
J. C. Scaiano ◽  
J. P.-A. Tremblay ◽  
K. U. Ingold
Keyword(s):  
Benzene Solution ◽  
Hydrogen Abstraction ◽  
Chain Process ◽  
Radical Chain ◽  
Diffusion Controlled ◽  
Carbon Centered Radical ◽  
Photochemical Initiation ◽  
Kinetics Of ◽  
Radical Chain Process ◽  
Termination Process

The title reaction is a free radical chain process which yields di(2-adamantyl)disulfide(2). The kinetics of this reaction have been studied in benzene solution at 50 °C using both thermal and photochemical initiation. Thermal initiators which yield resonance stabilized carbon-centered radicals were surprisingly inefficient at starting the reaction. The kinetics indicate that the rate controlling propagation step is hydrogen abstraction from the thiol, AdHSH, by the carbon-centered radical, AdHSSAd•. Rotating sector studies gave a rate constant for this step, k2 = 4 × 104 M−1 s−1. There is some kinetically first order chain termination, but the predominant termination process involves the diffusion-controlled bimolecular self-reactions of AdHSSAd• radicals, 2kt = 1.8 × 1010 M−1 s−1.

Investigations on the thermal decomposition of olefins

1962 ◽  
Vol 265 (1323) ◽  
pp. 519-537 ◽  
Keyword(s):  
Nitric Oxide ◽  
Thermal Decomposition ◽  
Double Bond ◽  
Carbon Atom ◽  
Chromatographic Analysis ◽  
Indirect Method ◽  
Hydrogen Abstraction ◽  
Reaction Products ◽  
A Value ◽  
Order Of Magnitude

It has been shown that at 530 °C there is practically no decomposition of olefins not possessing b C—C bond β to the double bond. The rate constants for the decomposition of various olefins at 530 °C over the range of p 0 from 25 to 300 mm have been measured. The relative rates of decomposition and polymerization of ethylene at 530, 600 and 630 °C have been studied. On the basis of chromatographic analysis of the reaction products both in the presence and in the absence of nitric oxide it is concluded that the ethane formed comes mainly from the secondary decomposition of polymers. At 530 °C the inhibitory activity of nitric oxide is exerted only on some olefins and even then it is rather small. All olefins are, however, subject to a remarkable stimulatory activity of nitric oxide. Over the range of pressures investigated this accelerating effect on the decomposition depends linearly on the olefin and nitric oxide pressures r 0 = k 0 [RK] + k 2 [RH] [NO]. The values of the constants for different olefins have been determined. The order of magnitude of the constant k 2 was found to be the same for all olefins investigated except ethylene and propylene, the values lying between 1.0 x 10 -4 and 3.0 x 10 -4 min -1 (mm NO) -1 . Propylene, which possesses an unusually small number (3) of weak C—H bonds and only primary ones, gave (by an indirect method) the lower value (2 ± 1) x 10 -6 min -1 (mm NO) -1 . Ethylene, the only olefin without weak C—H bonds, gave (by an indirect method), a value of k 2 of about (4 ± 1) x 10 -6 min -1 (mm NO) -1 . The reaction of hydrogen abstraction from the olefin molecule by nitric oxide is assumed responsible for the stimulatory phenomenon. The low value of k 2 for ethylene compared with the values for other olefins and for paraffins can be explained as a result of the strengthening influence of the double bond on the C—H bond with the doubly bound carbon atom. The different roles of the inhibitory and accelerative functions of nitric oxide in the decomposition of paraffins and olefins are considered to be mainly responsible for the changes in the shape of the ∆p –time curves as P NO is varied. On this basis the phenomenon of the apparently transistory activity of nitric oxide as an inhibitor in some cases can be explained.

Synthesis of the radical scavenger 1,1,3,3-Tetramethylisoindolin-2-yloxyl

1983 ◽  
Vol 36 (2) ◽  
pp. 397 ◽  
Author(s):  
PG Griffiths ◽  
G Moad ◽  
E Rizzardo
Keyword(s):  
Free Radical ◽  
Small Proportion ◽  
Radical Scavenger ◽  
Grignard Reaction ◽  
Radical Trapping ◽  
Methylmagnesium Iodide ◽  
Trapping Agent

A versatile free-radical trapping agent, 1,1,3,3-tetramethylisoindolin-2-yloxyl, has been prepared from N-benzylphthalimide by reaction with 'methylmagnesium iodide' in refluxing toluene followed by hydrogenolysis and oxidation. The Grignard reaction gives 2-benzyl-1,1,3,3-tetramethylisoindoline along with a small proportion of an unexpected by-product, 2-benzyl-1-ethyl-1,3,3-trimethyliso-indoline.

scholarly journals Tetraalkyl Hydroxymethylene-bisphosphonate and Dialkyl 1-Diphenylphosphinoyl-1-hydroxy-ethylphosphonate Derivatives by the Pudovik Reaction and Their Rearranged Products

Molecules ◽  
2021 ◽  
Vol 26 (24) ◽  
pp. 7575
Author(s):  
Zsuzsanna Szalai ◽  
György Keglevich
Keyword(s):  
Carbon Atom ◽  
Phenyl Group ◽  
Diethyl Phosphite ◽  
Diphenylphosphine Oxide ◽  
Central Carbon Atom ◽  
Dimethyl Phosphite ◽  
Pudovik Reaction ◽  
Central Carbon ◽  
Catalyst Temperature ◽  
The Pudovik Reaction

The reaction of diethyl α-oxoethylphosphonate and diethyl oxobenzylphosphonate with diethyl phosphite, dimethyl phosphite, and diphenylphosphine oxide affords, depending on the substrates and conditions (nature and quantity of the amine catalyst, temperature, and solvent), the Pudovik adduct and/or the corresponding >P(O)–CH–O–P(O)< product formed by rearrangement. The nature of the substituent on the central carbon atom (a methyl or phenyl group) influences the inclination for the rearrangement. The asymmetric products (either adducts or rearranged species) with different P(O)Y functions (Y = RO or Ph) exhibit interesting NMR features.

Reaction of Acyclic Hydrocarbons Towards t-Butoxy Radicals. A Study of Hydrogen Atom Abstraction by Using the Radical Trapping Technique

1998 ◽  
Vol 51 (12) ◽  
pp. 1113 ◽  
Author(s):  
Peter Dokolas ◽  
Steven M. Loer ◽  
David H. Solomon
Keyword(s):  
Hydrogen Atom ◽  
Hydrogen Abstraction ◽  
Hydrogen Atom Abstraction ◽  
Aromatic Solvent ◽  
Radical Trapping ◽  
Sterically Demanding ◽  
Butoxy Radical ◽  
Hydrocarbon Solution ◽  
Acyclic Hydrocarbons

The reaction of 3-methylpentane and 2,4-dimethylpentane toward t-butoxy radicals has been investigated, in neat and benzene solutions, by using the radical trapping technique. Abstraction occurs principally from the tertiary and secondary C-H reaction sites of 3-methylpentane and the tertiary position of 2,4-dimethylpentane. The tertiary and in particular secondary C-H reaction sites of 2,4-dimethylpentane are shown to be considerably less susceptible towards t-butoxy radical facilitated abstraction compared with the equivalent reaction sites of 3-methylpentane. As a result, the latter is three times as reactive as 2,4-dimethylpentane as a neat hydrocarbon solution and seven times as reactive in a diluted mixture of benzene. Diferences in selectivity and rate of hydrogen abstraction, between the substrates, are interpreted in terms of non-bonding interactions retarding t-butoxy radicals from approaching sterically demanding C-H reaction sites. The selectivity from 3-methylpentane is solvent-insensitive whereas abstraction from 2,4-dimethylpentane is modified in benzene. Further, the rate of hydrogen abstraction, from either substrate, to t-butoxy radical β-scission is considerably smaller in benzene. Both observations are interpreted in terms of t-butoxy radical solvation by the aromatic solvent.

The Role of H in the Growth Mechanism of PECVD a-Si:H

1999 ◽  
Vol 557 ◽  
Author(s):  
M.C.M. Van de Sanden ◽  
W.M.M. Kessels ◽  
A.H.M. Smets ◽  
B.A. Korevaar ◽  
R.J. Severens ◽  
...  
Keyword(s):  
Growth Mechanism ◽  
Atomic Hydrogen ◽  
Defect Density ◽  
Hydrogen Abstraction ◽  
High Rate ◽  
Kinetic Growth ◽  
Surface Hydrogen ◽  
Order Of Magnitude ◽  
Direct Abstraction

AbstractThis paper describes an extension of the silyl radical based kinetic growth model by atomic hydrogen induced surface hydrogen abstraction processes. It is shown that by including this direct abstraction process several problems of the SiH 3 based model are resolved. The defect density can be predicted with the proper temperature dependence and order of magnitude. The implications for high rate deposition of a-Si:H are discussed

Controlled Release of Trimaterene from Poly(DL-Lactide-Co-Glycolide) Microspheres

1993 ◽  
Vol 331 ◽  
Author(s):  
Amy D. Ouellete ◽  
Nicholas A. Peppas
Keyword(s):  
Controlled Release ◽  
Drug Loading ◽  
Release Behavior ◽  
Release Rates ◽  
Diffusion Controlled ◽  
Order Of Magnitude ◽  
Lower Drug ◽  
Biphasic Release ◽  
Silicone Matrix

AbstractRelease of triamterene from 150–300 gm poly(DL-lactide-co-glycolide) (PLGA) microspheres was investigated in vitro as a function of lactic acid/glycolic acid (LA/GA) copolymer ratio and drug loading both with free microspheres and with microspheres embedded in a silicone matrix. Biphasic release consisting of diffusion controlled release followed by erosion controlled release corresponding to polymer degradation was observed in all samples. Drug release from PLGA 50:50 copolymer microspheres was three times faster than the release from PLGA 75:25 microspheres for the higher drug loading (20 wt%) and slightly faster for the lower drug loading (10 wt%). Release rates from spheres containing the higher drug loading were approximately one order of magnitude faster than release from spheres containing the lower drug loading for the same PLGA copolymer. The same qualitative results were observed for the spheres embedded in silicone matrices; however, the overall release was much slower. The results demonstrate that release behavior may be altered by changing LA/GA copolymer ratio, drug loading, and microsphere environment to obtain the desired release characteristics.

A thermocouple method of following the non-stationary state of chemical reactions - II. The evaluation of velocity coefficients and energies of activation for the propagation and termination reactions for the initial and later stages of the polymerization of vinyl acetate

1955 ◽  
Vol 230 (1183) ◽  
pp. 429-447 ◽  
Keyword(s):  
Activation Energy ◽  
Vinyl Acetate ◽  
Viscous Medium ◽  
Energy Of Activation ◽  
Solid Polymer ◽  
Polymer Gel ◽  
Kcal Mole ◽  
Continuous Increase ◽  
Diffusion Controlled ◽  
Thermocouple Method

A study has been made of the changes which occur in the velocity coefficients and energies of activation for the propagation and termination reactions in the polymerization of vinyl acetate, photosensitized with 0·0009 mole/1. 1. 1'-azo-bis- cyclo hexanecarbonitrile. The rate of polymerization increases from the early stages of the reaction until about 50% conversion and subsequently decreases rapidly to an extremely low value at about 75% conversion, while the overall energy of activation decreases from 4·2 kcal/mole initially to 1·9 kcal/mole at 50% conversion and then increases rapidly as the polymerization continues towards completion. This decrease in the overall energy of activation is due to a continuous increase in the activation energy for the termination reaction as the polymerization progresses, and this is believed to be due to an increase in the activation energy for the diffusion of polymer radicals in the increasingly viscous medium. Beyond 50% conversion the activation energy for the propagation reaction begins to increase, presumably due to the propagation step becoming diffusion controlled as the system becomes a solid polymer gel. The energies of activation for the propagation and termination reactions have been shown to vary from less than 5 and 1 kcal/mole respectively initially, to values of greater than 14 kcal/mole at about 70% conversion.

scholarly journals ELEMENTARY ACTS OF PHOTOREACTIONS OF 2,6-DIPHENYL-1,4-BENZOQUINONE IN VARIOUS SOLVENTS

2018 ◽  
Vol 62 (1) ◽  
pp. 26-30
Author(s):  
Dmitriy N. Gurulev ◽  
Lyubov V. Palatkina ◽  
Natalia A. Kuznetsova ◽  
Vladimir I. Porkhun
Keyword(s):  
Exchange Process ◽  
Nmr Spectrum ◽  
Meta Position ◽  
Semiquinone Radicals ◽  
Diffusion Controlled ◽  
Order Of Magnitude ◽  
Diffusion Rate Constant ◽  
Wide Line ◽  
The Stability ◽  
Increasing Temperature

In order to determine the effect of the polarity of solvents on the reactivity and the course of the reactions of semihinone radicals, their complexes, this study of 2,6-diphenyl-1,4-benzoquinone, (class of substituted benzoquinones) and its dimer D was carried out. It was found that in the NMR spectrum of the dimer solution, with increasing temperature, the lines widen, and there is one wide line close to the chemical shift to the protons of the meta-groups of quinone. The NMR spectrum of a solution D in deuterochloroform at low temperatures contains lines corresponding to the aromatic part of the protons in the meta position, respectively (7.05 M.d, 6.89 M.d.). That is, the exchange process between the non-equivalent parts of the diamagnetic dimer molecule of the preceding dissociation takes place with the constant of the velocity k-1, coinciding in order of the inverse spin-spin relaxation time. The value of k-1 increases by more than an order of magnitude with the increasing polarity of the solvent. This effect is due to the stronger solvent solvation of the activated complex in the transition state compared to the molecule. The reaction of dimerization of semiquinone radicals is diffusion-controlled, since the values of ∆H1≠ in all solvents differ from the activation energy of viscosity by no more than 1 kcal/M and the values of the velocity constant in 5-8 times differ from the diffusion rate constant calculated by Debye. The solvation of radicals leads to a decrease in the diffusion coefficients of radicals and, possibly, to the shielding of the reaction center, which causes a decrease in k1. With the decrease of the constant in the specified number of solvents, the stability of the radical increases, which is manifested in a symbiotic increase in the equilibrium constant K. The reason for the increase of the direct constant k1 in solvents with high permittivity is explained.  

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