scholarly journals SULFONYL CHLORIDES - NOVEL SOURCE OF FREE RADICALS

2021 ◽  
pp. 103-114
Author(s):  
A. A. Seleznev ◽  
D. P. Radchenko ◽  
S. I. Golubova ◽  
S. A. Safronov ◽  
V. A. Navrotskiy
Keyword(s):  
Free Radicals ◽  
Arrhenius Equation ◽  
Degradation Mechanism ◽  
Bond Cleavage ◽  
Preexponential Factor ◽  
Radical Mechanism ◽  
Activation Entropy ◽  
Sulfonyl Chlorides ◽  
Chlorosulfonated Polyethylene ◽  
Bond Scission

Novel free radicals source based on sulfonyl chlorides is discovered. The radical mechanism is confirmed by 2,3-dimethyl-2,3-diphenylbutane formation under chlorosulfonated polyethylene heating in the isopropylbenzene solution. Concerted homolytic C-S and S-Cl bond scission of chlorosulfonated polyethylene thermal degradation mechanism proved by kinetic analysis. The proof of the two bonds simultaneous breaking is provided by the threefold activation energy reduction (83 kJ/mol) in comparison to the C-S and C-Cl bond dissociation energy (280 and 286 kJ/mol respectively), the 6 orders lower preexponential factor (2,46 ∙ 10 s) in Arrhenius equation in comparison to one bond cleavage (≈10-10 s) as well as the strongly negative activation entropy value (-134 J/mol∙K).

Kinetic Studies on the Polymerization of Dicyclohexylmethylmethane-4,4'-Diisocyanate with Polyoxytetramethylene Diol

2013 ◽  
Vol 791-793 ◽  
pp. 32-35
Author(s):  
Jian Cheng Wang
Keyword(s):  
Rate Constant ◽  
Arrhenius Equation ◽  
Activation Enthalpy ◽  
Kinetic Studies ◽  
Activation Entropy ◽  
Dimethyl Acetamide ◽  
Different Temperatures ◽  
Ft Ir ◽  
Temperature Activation

Dicyclohexylmethylmethane-4,4'-diisocyanate is used to react with polyoxytetramethylene diol at different temperatures. N,N-Dimethyl acetamide is used as solvent.In situFT-IR is used to monitor the reaction to work out rate constant, Arrhenius equation and Eyring equation. The polymerization has been found to be a second order reaction, and the rate constant increases with the rise of temperature. Activation energy (Ea), activation enthalpy (ΔH) and activation entropy (ΔS) for the polymerization are respectively calculated out, which are very useful to reveal the reaction mechanism.

scholarly journals A novel mechanism of enzymic ester hydrolysis. Inversion of configuration and carbon-oxygen bond cleavage by secondary alkylsulphohydrolases from detergent-degrading micro-organisms

1977 ◽  
Vol 165 (3) ◽  
pp. 575-580 ◽  
Author(s):  
B Bartholomew ◽  
K S Dodgson ◽  
G W J Matcham ◽  
D J Shaw ◽  
G F White
Keyword(s):  
Bond Cleavage ◽  
Hydrolytic Enzymes ◽  
Ester Hydrolysis ◽  
Enzymic Hydrolysis ◽  
Hydrolysis Products ◽  
Bond Scission ◽  
Micro Organisms ◽  
Hydrolysis Of ◽  
Oxygen Bond ◽  
Comamonas Terrigena

The hydrolysis was studied of potassium (+)-octan-2-yl sulphate by two analogous, optically stereospecific, secondary alkylsulphohydrolases purified from two detergent-degrading micro-organisms, Comamonas terrigena and Pseudomonas C12B. Polarimetry studies have shown that (+)-octan-2-yl sulphate prepared from (+)-octan-2-ol is hydrolysed by both enzymes to yield (-)-octan-2-ol. This inversion of configuration implies that the enzymes are catalysing the scission of the C-O bond of the C-O-S linkage, a type of bond scission apparently not hitherto encountered among hydrolytic enzymes acting on ester bonds. Enzymic hydrolysis of potassium (+)-octan-2-yl sulphate in the presence of H218O and analysis of hydrolysis products for the presence of 18O has confirmed that C-O bond scission (and not O-S bond scission) occurs with both enzymes.

On the Lack of Beneficial Role of Rh Towards C-C Bond Cleavage During Low Temperature Ethanol Electrooxidation on Pt-Rh Nanoalloys

2018 ◽  
Author(s):  
Justyna Piwowar ◽  
Adam Lewera
Keyword(s):  
Low Temperature ◽  
Electrode Potential ◽  
Ethanol Oxidation ◽  
Bond Cleavage ◽  
Ethanol Electrooxidation ◽  
Co Stripping ◽  
Beneficial Role ◽  
Bond Scission ◽  
Oxidation Of Ethanol

Numerous reports in scientific literature claim the increased activity of Rh-containing systems towards C-C bond scission in electrocatalytic oxidation of ethanol at ambient temperatures. Due to the claimed C-C bond breaking ability, Rh-containing systems are intensively investigated and widely recognized as the most promising candidates as anode materials for ethanol-feed low temperature fuel cells. This study aims at verifying the claim of beneficial role of Rh towards C-C bond scission during low temperature ethanol electrooxidation on Pt-Rh nanoparticles. We determined that the surface-normalized amounts of CO<sub>2 </sub>produced during ethanol oxidation are comparable on Pt, Rh and Pt-Rh nanoalloys, and smaller than CO<sub>2</sub> amounts obtained on exactly the same electrode from oxidation of monolayer of adsorbed CO. The whole amount of CO<sub>2</sub> detected during ethanol oxidation, regardless of Rh presence, or lack of thereof, seems to come exclusively from oxidation of submonolayer of CO<sub>ads</sub> produced during dissociative adsorption of ethanol at low electrode potential, and its subsequent oxidation at sufficiently high electrode potential. Our work suggest that Rh-containing alloys are not more active towards C-C bond scission than pure Pt, and on both metals the mechanism of oxidation of ethanol to CO<sub>2</sub> proceeds via the submonolayer of CO<sub>ads</sub>, which limits the quantity of CO<sub>2</sub> produced from ethanol at room temperature to negligible amount. The higher activity of Rh-containing materials towards C-C bond scission claimed in literature was determined to be due to overinterpretation of selectivity data.<br>To characterized the samples we used techniques like XPS, TEM, and cyclic voltammetry. For drove a conclusions we compere amount of CO<sub>2</sub> detected in DEMS during ethanol oxidation reaction and so called CO stripping experiment. <br><br>

Diffusion of He, Ne, and Ar in Vitreous and Partially Devitrified Germani um Dioxide

1972 ◽  
Vol 27 (4) ◽  
pp. 617-623
Author(s):  
W.W. Brandt ◽  
B. Rauch ◽  
J. Wagner
Keyword(s):  
Diffusion Coefficients ◽  
Arrhenius Equation ◽  
Diffusion Mechanism ◽  
Preexponential Factor ◽  
Activation Energies ◽  
Transition Range ◽  
Critical Dimensions ◽  
Glass Transition Range ◽  
Diffusion Paths ◽  
Solubility Coefficients

Abstract The diffusion coefficients of He, Ne, and Ar in various samples of GeO2 and approximate values for the corresponding solubility coefficients were obtained from nonisothermal and isothermal desorption experiments. The data show trends similar to those obtained on fused SiO2 , and are interpreted by assuming that the glasses contain many interstices of different critical dimensions and a variety of diffusion paths corresponding to a range of activation energies. Some annealed and partially devitrified samples were studied and the activation energies of diffusion were found to be relatively high. In a few cases, the measurements were extended into and above the glass transition range (∼570°) ; the resulting activation energy and the preexponential factor of the Arrhenius equation for the diffusion coefficient were markedly increased, indicating that the diffusion mechanism is probably drastically changed.

Cyclopentadienyl–metal bond cleavage and stereospecific bromination. The structure of (η-C5H5)2Ti(OOCPh)2 and its reactions with bromine

1988 ◽  
Vol 66 (3) ◽  
pp. 429-434 ◽  
Author(s):  
C. Robert Lucas ◽  
Eric J. Gabe ◽  
Florence L. Lee
Keyword(s):  
Nmr Spectra ◽  
Bond Cleavage ◽  
The Other ◽  
Ring Cleavage ◽  
Radical Mechanism ◽  
Iodine Monochloride ◽  
Carboxylate Ligands ◽  
X Ray ◽  
H Nmr ◽  
Using Data

The 13C and 1H nmr spectra as well as the X-ray structure determination for (η-C5H5)2Ti(OOCPh)2 are described. The compound crystallizes in space group P21212I with a = 7.5135, b = 12.5166, c = 21.1416 Å, Z = 4, dcalcd = 1.40 g cm−3 (MoKα1, λ = 0.70932 Å). The structure was solved with MULTAN using data collected at 115 K and refined to the final R = 0.059 for 1500 significant reflections. The molecule has two different carboxylate ligands, one of which has a Ti—O—C angle of 135.4(6)° and longer Ti—O (1.976(5) Å) and O—C (1.300(10) Å) bonds while the other has a Ti—O—C angle of 157.0(7)° with shorter Ti—O (1.913(6) Å) and O—C (1.267(10) Å) bonds. With bromine, ring cleavage occurs giving C5H5Br3 or C5H5Br5 in which bromination has occurred stereospecifically. The same reaction occurs with chlorine but not with iodine or iodine monochloride. Related reactions have been observed with (η-C5H5)2MCl2 (M = Ti, Zr, and V). A non-radical mechanism is proposed in which the LUMO and HOMO of Br2 interact simultaneously with one cyclopentadienyl ring and with the metal. This interaction is a consequence of the structure of (η-C5H5)2M(OOCPh)2.

scholarly journals Thermal Degradation Mechanism and Decomposition Kinetic Studies of Poly(Lactic Acid) and Its Copolymers with Poly(Hexylene Succinate)

Polymers ◽  
2021 ◽  
Vol 13 (9) ◽  
pp. 1365
Author(s):  
Iouliana Chrysafi ◽  
Nina Maria Ainali ◽  
Dimitrios N. Bikiaris
Keyword(s):  
Mechanical Properties ◽  
Hydrogen Bond ◽  
Lactic Acid ◽  
Thermal Degradation ◽  
Degradation Mechanism ◽  
Thermal Degradation Kinetics ◽  
Gas Chromatography Mass Spectrometry ◽  
Poly Lactic Acid ◽  
Bond Scission ◽  
New Material

Ιn this work, new block poly(lactic acid)-block-poly(hexylene succinate) (PLA-b-PHSu) copolymers, in different mass ratios of 95/05, 90/10 and 80/20 w/w, are synthesized and their thermal and mechanical behavior are studied. Thermal degradation and thermal stability of the samples were examined by Thermogravimetric Analysis (TGA), while thermal degradation kinetics was applied to better understand this process. The Friedman isoconversional method and the “model fitting method” revealed accurate results for the activation energy and the reaction mechanisms (nth order and autocatalysis). Pyrolysis-Gas Chromatography/Mass Spectrometry (Py-GC/MS) was used to provide more details of the degradation process with PHSu’s mechanism being the β-hydrogen bond scission, while on PLA the intramolecular trans-esterification processes domains. PLA-b-PHSu copolymers decompose also through the β-hydrogen bond scission. The mechanical properties have also been tested to understand how PHSu affects PLA’s structure and to give more information about this new material. The tensile measurements gave remarkable results as the elongation at break increases as the content of PHSu increases as well. The study of the thermal and mechanical properties is crucial, to examine if the new material fulfills the requirements for further investigation for medical or other possible uses that might come up.

scholarly journals Determining Preexponential Factor in Model-Free Kinetic Methods: How and Why?

Molecules ◽  
2021 ◽  
Vol 26 (11) ◽  
pp. 3077
Author(s):  
Sergey Vyazovkin
Keyword(s):  
Activation Energy ◽  
Kinetic Analysis ◽  
Rate Constant ◽  
Condensed Phase ◽  
Compensation Effect ◽  
Preexponential Factor ◽  
Isoconversional Methods ◽  
Activation Entropy ◽  
Model Free ◽  
Kinetics Of

The kinetics of thermally stimulated processes in the condensed phase is commonly analyzed by model-free techniques such as isoconversional methods. Oftentimes, this type of analysis is unjustifiably limited to probing the activation energy alone, whereas the preexponential factor remains unexplored. This article calls attention to the importance of determining the preexponential factor as an integral part of model-free kinetic analysis. The use of the compensation effect provides an efficient way of evaluating the preexponential factor for both single- and multi-step kinetics. Many effects observed experimentally as the reaction temperature shifts usually involve changes in both activation energy and preexponential factor and, thus, are better understood by combining both parameters into the rate constant. A technique for establishing the temperature dependence of the rate constant by utilizing the isoconversional values of the activation energy and preexponential factor is explained. It is stressed that that the experimental effects that involve changes in the preexponential factor can be traced to the activation entropy changes that may help in obtaining deeper insights into the process kinetics. The arguments are illustrated by experimental examples.

scholarly journals Selective Activation of Methane C-H Bond in the Presence of Methanol

2019 ◽  
Author(s):  
Yongjie Xi ◽  
Andreas Heyden
Keyword(s):  
Transition State ◽  
Heterogeneous Catalysts ◽  
State Energy ◽  
Bond Cleavage ◽  
Energy Difference ◽  
Radical Mechanism ◽  
Oxide Surface ◽  
Research Activity ◽  
Bond Dissociation ◽  
Transition State Energy

Direct methane to methanol (MTM) conversion over heterogeneous catalysts is a promising route for valorization of methane. The methane C-H bond activation is considered as the key step of the MTM and is the focus of considerable research activity. However, the formed methanol typically suffers from overoxidation largely due to the cleavage of a methanol C-H bond, whose bond dissociation energy is ca. 0.5 eV lower than that of the methane C-H bond, which usually translates to a transition state energy of the methanol C-H bond cleavage that is ca. 0.55 eV lower than that of methane whenever the reactions proceed through a radical mechanism. Here, we propose a general approach for decreasing the transition state energy difference between the CH4 and CH3OH C-H bond dissociation. When a metal-oxide supported cationic transition metal atom and a neighboring oxygen on the oxide surface serve as the active site, the transition state energy difference through a surface-stabilized pathway can be noticeably narrowed as compared with that of a radical pathway.

A non-innocent pincer H3LONS ligand and its corresponding octahedral low-spin Fe(iii) complex formation via ligand-centric homolytic S–S bond scission

2018 ◽  
Vol 47 (38) ◽  
pp. 13337-13341 ◽  
Author(s):  
Prasenjit Sarkar ◽  
Chandan Mukherjee
Keyword(s):  
Complex Formation ◽  
Bond Cleavage ◽  
Bond Scission

Ligand-based S–S bond cleavage led to an unprecedented, homoleptic, six-coordinate, low-spin Fe(iii) complex comprising two 2-iminobenzosemiquinone and one thiyl π-radical.

In Situ FT-IR Studies on the Catalytic Reaction Kinetics of 1,2-Propanediol with Phenyl Isocyanate

2012 ◽  
Vol 450-451 ◽  
pp. 131-134
Author(s):  
Peng Fei Yang
Keyword(s):  
Rate Constant ◽  
Arrhenius Equation ◽  
Phenyl Isocyanate ◽  
Activation Entropy ◽  
Ir Studies ◽  
Initial Stage ◽  
Different Temperatures ◽  
Ft Ir ◽  
Kinetics Of

Phenyl isocyanate is used to react with 1,2-propanediol in different temperatures. Toluene is used as solvent and triethylamine is used as catalyst. In-situ FT-IR is used to monitor the reaction to work out rate constant, Arrhenius equation and Eyring equation. The urethane reaction has been found to be a second order reaction, and the rate constant seems different between initial stage and final stage. The activation energy (Ea), activation enthalpy (ΔH) and activation entropy (ΔS) for the urethane reaction are calculated out, which are 74.1 kJ•mol-1, 71.3 kJ•mol-1 and -30.5 J•mol-1•k-1, respectively. They are very useful to reveal the reaction mechanism.

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