scholarly journals Alkaline oxidative degradation of diphenylmethane structures — Activation energy and computational analysis of the reaction mechanism

2001 ◽  
Vol 79 (9) ◽  
pp. 1394-1401
Author(s):  
Lubo Jurasek ◽  
Lívia Krištofová ◽  
Yujun Sun ◽  
Dimitris S Argyropoulos
Keyword(s):  
Activation Energy ◽  
Reaction Mechanism ◽  
Computational Analysis ◽  
Model Compound ◽  
Degradation Products ◽  
Oxidative Degradation ◽  
Semiempirical Method ◽  
Activation Energies ◽  
Ring Cleavage ◽  
Residual Lignin

A diphenylmethane model compound (2,2'-methylenebis[6-methoxy-4-methylphenol]) and residual kraft lignin were treated with alkaline hydrogen peroxide. Kinetic data for the disappearance of the model and the diphenylmethane structures in the residual lignin was collected. The activation energies for the degradation were found to be similar (54 ± 11 kJ mol–1 for the model and 58 ± 5 kJ mol–1 for the residual lignin). A comparison of the activation energies with the data of a previous study on a biphenyl model compound (3,3'-dimethoxy-5,5'-dimethyl-[1,1'-biphenyl]-2,2'-diol) showed a substantially higher activation energy for the degradation of the latter. Pathways for the degradation of 2,2'-methylenebis[6-methoxy-4-methylphenol] were proposed and the intermediates subjected to computational analysis using a semiempirical method (PM3). The results suggest that initially a common pathway exists, resulting in 2-[2-hydroxy-3-methoxy-5-methyl-phenylmethyl]-4-methyl-2,4-hexadienedioic acid. Then the pathway branches into three, resulting in three major degradation products. The main driving force of the reactions is the formation of radical sites after reaction with hydroxyl radicals and subsequent radical coupling with perhydroxyl radicals to form peroxides. All the reactions on the pathways are exothermic except for the transformations of peroxides into dioxetanes. The dioxetanes cleave exothermically resulting in ring cleavage and fragmentation. The computed data permitted for the rationalization as to why the diphenylmethane structures appear to be more labile than biphenyl structures under alkaline oxidative conditions.Key words: activation energy, alkaline oxidative degradation, computational chemistry, lignin, reaction mechanism.

scholarly journals Oxidation of Polyphenols by Extracellular Peroxidase in Suspension Cell Culture of Liverwort Heteroscyphus planus

2007 ◽  
Vol 2 (6) ◽  
pp. 1934578X0700200
Author(s):  
Leily Tjandrawaskitasari ◽  
Rie Hata ◽  
Hanami Chiba ◽  
Makoto Hashimoto ◽  
Kosaku Takahashi ◽  
...  
Keyword(s):  
Cell Culture ◽  
Model Compound ◽  
Degradation Products ◽  
Oxidative Degradation ◽  
Oxidation Products ◽  
Suspension Cell ◽  
Suspension Cell Culture ◽  
Lignin Model Compound ◽  
Culture Filtrates ◽  
Lignin Model

Peroxidase secretion and activity in the oxidation of polyphenols bisphenol A (BPA, 2,2-bis(4-hydroxyphenyl)propane) and lignin model compound (LMC, guaiacylglycerol-β-guaiacylether) were observed in a suspension cell culture of liverwort Heteroscyphus planus. When BPA was co-incubated in a suspension cell culture of liverwort for 5 days, it was depleted by approximately 63%. Oxidation of BPA was observed in culture filtrates of liverwort, and most of the oxidation products were insoluble higher molecular-weight compounds (30%). The oxidative degradation products of BPA and LMC were analyzed by GC-MS and were identified by comparing their retention time and MS spectra with those of the authentic compounds. BPA was degraded to 4-isopropenylphenol and p-hydroxyacetophenone. The formation of these products was examined using [2H14]-BPA. The lignin model compound was degraded to guaiacol, vanillin, coniferyl alcohol and ferulic acid. Biphenyl dehydrodimer was detected in both the reaction mixtures of the suspension cell culture and the culture filtrates incubated with the LMC. The dimer was identified as 1,1′-(4,4′-dihydroxy-3,3′-dimethoxy-5,5′-biphenylene)- bis[8-(2″-methoxyphenoxy)-7,9-propanediol] by 1D and 2D NMR analysis. The activity of secreted peroxidase in the suspension cell culture (0.045 U/mL) was slightly enhanced by addition of LMC (0.059 U/mL), p-cresol (0.064 U/mL), and 2,6-dimethoxyphenol (0.082 U/mL) 7 days after the beginning of incubation.

REACTIONS OF ARYLSULPHONIC ESTERS: V. AN INTERPRETATION OF ACTIVATION ENERGIES OF SOLVOLYSIS OF METHYL BENZENESULPHONATE IN MIXED HYDROXYLIC SOLVENTS

1956 ◽  
Vol 34 (7) ◽  
pp. 931-941 ◽  
Author(s):  
J. B. Hyne ◽  
R. E. Robertson
Keyword(s):  
Activation Energy ◽  
Reaction Mechanism ◽  
Aliphatic Alcohol ◽  
Activation Energies ◽  
Physical Significance ◽  
Activation Entropy ◽  
Experimental Uncertainty ◽  
Extended Form ◽  
Uncertainty Product ◽  
Alcohol Water

The rates of solvolysis of methyl benzenesulphonate at 50 ° and 75 °C. in several binary aliphatic alcohol–water mixtures have been determined over the composition ranges. The derived activation energies are compared with those calculated from an extended form of the equation employed in accounting for solvolytic activation energies in pure hydroxylic solvents. The physical significance of the equation is discussed in terms of a spectrum of solvolytic mechanisms covering the range between SN1 and SN2 mechanisms. The equation predicts activation energy values well within the experimental uncertainty. Product ratio and activation entropy data are shown to be in keeping with the reaction mechanism proposed.

scholarly journals High-Temperature Deformation of Naturally Aged 7010 Aluminum Alloy

Metals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 581
Author(s):  
Abdulhakim A. Almajid
Keyword(s):  
Activation Energy ◽  
Aluminum Alloy ◽  
High Temperature ◽  
Threshold Stress ◽  
Activation Energies ◽  
Temperature Deformation ◽  
High Temperature Range ◽  
Temperature Range ◽  
True Activation Energy ◽  
Two Temperatures

This study is focused on the deformation mechanism and behavior of naturally aged 7010 aluminum alloy at elevated temperatures. The specimens were naturally aged for 60 days to reach a saturated hardness state. High-temperature tensile tests for the naturally aged sample were conducted at different temperatures of 573, 623, 673, and 723 K at various strain rates ranging from 5 × 10−5 to 10−2 s−1. The dependency of stress on the strain rate showed a stress exponent, n, of ~6.5 for the low two temperatures and ~4.5 for the high two temperatures. The apparent activation energies of 290 and 165 kJ/mol are observed at the low, and high-temperature range, respectively. These values of activation energies are greater than those of solute/solvent self-diffusion. The stress exponents, n, and activation energy observed are rather high and this indicates the presence of threshold stress. This behavior occurred as a result of the dislocation interaction with the second phase particles that are existed in the alloy at the testing temperatures. The threshold stress decreases in an exponential manner as temperature increases. The true activation energy was computed by incorporating the threshold stress in the power-law relation between the stress and the strain. The magnitude of the true activation energy, Qt dropped to 234 and 102 kJ/mol at the low and high-temperature range, respectively. These values are close to that of diffusion of Zinc in Aluminum and diffusion of Magnesium in Aluminum, respectively. The Zener–Hollomon parameter for the alloy was developed as a function of effective stress. The data in each region (low and high-temperature region) coalescence in a segment line in each region.

The kinetics of hydration of tricalcium silicate

1970 ◽  
Vol 48 (21) ◽  
pp. 3291-3299 ◽  
Author(s):  
K. G. McCurdy ◽  
B. P. Erno
Keyword(s):  
Reaction Mechanism ◽  
Intermediate Product ◽  
Activation Energies ◽  
Tricalcium Silicate ◽  
Rate Data ◽  
Large Excess ◽  
First Order ◽  
Kinetics Of ◽  
Subsequent Decomposition

An investigation has been made of the kinetics of hydration of tricalcium silicate at several temperatures in a large excess of water in the presence of various added ions. The rate data have been interpreted by a reaction mechanism which involves: (a) the first order hydration of tricalcium silicate to form an intermediate product, 1.5CaO•SiO2, which can react by two pathways, (b) the direct first order decomposition of intermediate, 1.5CaO•SiO2, to form lime and silica or (b′) complexing of intermediate with silica and subsequent decomposition to form lime and silica. This reaction mechanism predicts the rate of production of base during the hydration. The effect of various added ions is interpreted in terms of the proposed mechanism.Rate constants and activation energies for the various steps in the proposed mechanism are reported.

scholarly journals Effect of CaO on catalytic combustion of semi-coke

2021 ◽  
Vol 10 (1) ◽  
pp. 011-020
Author(s):  
Luyao Kou ◽  
Junjing Tang ◽  
Tu Hu ◽  
Baocheng Zhou ◽  
Li Yang
Keyword(s):  
Activation Energy ◽  
Apparent Activation Energy ◽  
Combustion Rate ◽  
Activation Energies ◽  
Combustion Reaction ◽  
Tg Analysis ◽  
Conversion Rates ◽  
Apparent Activation Energies ◽  
Ozawa Integral Method ◽  
Addition Amount

Abstract Generally, adding a certain amount of an additive to pulverized coal can promote its combustion performance. In this paper, the effect of CaO on the combustion characteristics and kinetic behavior of semi-coke was studied by thermogravimetric (TG) analysis. The results show that adding proper amount of CaO can reduce the ignition temperature of semi-coke and increase the combustion rate of semi-coke; with the increase in CaO content, the combustion rate of semi-coke increases first and then decreases, and the results of TG analysis showed that optimal addition amount of CaO is 2 wt%. The apparent activation energy of CaO with different addition amounts of CaO was calculated by Coats–Redfern integration method. The apparent activation energy of semi-coke in the combustion reaction increases first and then decreases with the increase in CaO addition. The apparent activation energies of different samples at different conversion rates were calculated by Flynn–Wall–Ozawa integral method. It was found that the apparent activation energies of semi-coke during combustion reaction decreased with the increase in conversion.

scholarly journals The Effect of α-Al(MnCr)Si Dispersoids on Activation Energy and Workability of Al-Mg-Si-Cu Alloys during Hot Deformation

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Xiaoguo Wang ◽  
Jian Qin ◽  
Hiromi Nagaumi ◽  
Ruirui Wu ◽  
Qiushu Li
Keyword(s):  
Activation Energy ◽  
Aluminum Alloys ◽  
Constitutive Equation ◽  
Hot Deformation ◽  
Flow Instability ◽  
Void Formation ◽  
Activation Energies ◽  
Compression Tests ◽  
Softening Mechanism ◽  
Dynamic Softening

The hot deformation behaviors of homogenized direct-chill (DC) casting 6061 aluminum alloys and Mn/Cr-containing aluminum alloys denoted as WQ1 were studied systematically by uniaxial compression tests at various deformation temperatures and strain rates. Hot deformation behavior of WQ1 alloy was remarkably changed compared to that of 6061 alloy with the presence of α-Al(MnCr)Si dispersoids. The hyperbolic-sine constitutive equation was employed to determine the materials constants and activation energies of both studied alloys. The evolution of the activation energies of two alloys was investigated on a revised Sellars’ constitutive equation. The processing maps and activation energy maps of both alloys were also constructed to reveal deformation stable domains and optimize deformation parameters, respectively. Under the influence of α dispersoids, WQ1 alloy presented a higher activation energy, around 40 kJ/mol greater than 6061 alloy’s at the same deformation conditions. Dynamic recrystallization (DRX) is main dynamic softening mechanism in safe processing domain of 6061 alloy, while dynamic recovery (DRV) was main dynamic softening mechanism in WQ1 alloy due to pinning effect of α-Al(MnCr)Si dispersoids. α dispersoids can not only resist DRX but also increase power required for deformation of WQ1 alloy. The microstructure analysis revealed that the flow instability was attributed to the void formation and intermetallic cracking during hot deformation of both alloys.

Chemistry of renieramycins. Part 6: Transformation of renieramycin M into jorumycin and renieramycin J including oxidative degradation products, mimosamycin, renierone, and renierol acetate

Tetrahedron ◽  
2004 ◽  
Vol 60 (17) ◽  
pp. 3873-3881 ◽  
Author(s):  
Naoki Saito ◽  
Chieko Tanaka ◽  
Yu-ichi Koizumi ◽  
Khanit Suwanborirux ◽  
Surattana Amnuoypol ◽  
...  
Keyword(s):  
Degradation Products ◽  
Oxidative Degradation
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