Influence of nitrogen base ligation and hydrogen bonding on the rate constants for oxygen transfer from percarboxylic acids and alkyl hydroperoxides to (meso-tetraphenylporphinato)manganese(III) chloride

1986 ◽  
Vol 108 (7) ◽  
pp. 1643-1650 ◽  
Author(s):  
Lung Chi. Yuan ◽  
Thomas C. Bruice
Keyword(s):  
Hydrogen Bonding ◽  
Rate Constants ◽  
Oxygen Transfer ◽  
Nitrogen Base ◽  
Alkyl Hydroperoxides

Oxygen transfer from percarboxylic acids and alkyl hydroperoxides to (meso-tetraphenylporphinato)iron(III) and -chromium(III)

1988 ◽  
Vol 110 (13) ◽  
pp. 4277-4283 ◽  
Author(s):  
William A. Lee ◽  
Lung Chi. Yuan ◽  
Thomas C. Bruice
Keyword(s):  
Oxygen Transfer ◽  
Alkyl Hydroperoxides

The antioxidant activities of phenolic antioxidants in free radical peroxidation of phospholipid membranes

1990 ◽  
Vol 68 (12) ◽  
pp. 2258-2269 ◽  
Author(s):  
Lawrence Ross Coates Barclay ◽  
Kimberly Ann Baskin ◽  
Kelly Andrea Dakin ◽  
Steven Jefffrey Locke ◽  
Melinda Ruth Vinqvist
Keyword(s):  
Hydrogen Bonding ◽  
Free Radical ◽  
Rate Constants ◽  
Antioxidant Activities ◽  
Hydrogen Abstraction ◽  
Peroxyl Radicals ◽  
Phenolic Antioxidants ◽  
Inhibition Rate ◽  
Radical Chain ◽  
Tert Butyl

Autoxidation of dilinoleoylphosphatidylcholine (DLPC) bilayers photoinitiated by benzophenone takes place by a free radical chain mechanism according to product studies of the cis, trans and trans, trans-9- and -13-linoleate hydroperoxides formed and kinetic studies of the reaction order as a function of light intensity. The absolute rate constant for hydrogen abstraction from DLPC bilayers by peroxyl radicals is found to be 36.1 M−1 s−1 at 37 °C. Preliminary measurements of activities of phenolic antioxidants, α-tocopherol (α-T), 2,2,5,7,8-pentamethyl-6-hydroxychroman (PMHC), 2,5,7,8-tetramethyl-6-hydroxychroman-2-carboxylate (Trolox), and 2,6-di-tert-butyl-4-methylphenol (BHT) by oxygen uptake studies during inhibition periods using photoinitiation gave uncorrected inhibition rate constants, Kinh, for α-T, PMHC, and Trolox several orders of magnitude lower than observed earlier in chlorobenzene. Three series of phenolic antioxidants, (a) polyalkyl-6-hydroxychromans, (b) polyalkyl-4-methoxyphenols, and (c) trialkylphenols, were examined for their antioxidant activities in DLPC membranes during thermally initiated autoxidation by azobis-2,4-dimethylvaleronitrile (DMVN). The corrected inhibition rate constants, kinh, observed in (a), α-T (5.8 × 103), PMHC (17.8 × 103), Trolox (5.8 × 103), 2,2-dimethyl-5,7-diisopropyl-6-hydroxychroman, 4a (55 × 103), and 2,2,5-trimethyl-7-tert-butyl-6-hydroxychroman, 5a (61 × 103) M−1 s−1, are dramatically lower, by several orders of magnitude, than those measured earlier in chlorobenzene and significantly lower (about 1/40–1/10) than those measured in solution in tert-butyl alcohol and less than kinh measurements (1/2–1/5) in aqueous SDS micelles. The kinh values for series (b) were 2,3,5,6-tetramethyl-4-methoxyphenol (TTMMP) (2.1 × 103), 2,3,6-trimethyl-4-methoxyphenol (TMMP) (10.4 × 103), and 2,6-di-tert-butyl-4-methoxyphenol (DBHA) (27.5 × 103) M−1 s−1 and for (c) were 2,6-di-tert-butyl-4-methylphenol (BHT) (3.7 × 103) and 2,4,6-trimethylphenol (TMP) (0.56 × 103) M−1 s−1. The results show an overall leveling and depression of antioxidant activities in DLPC membranes in the series (a), (b), (c) compared to those reported in solution in chlorobenzene, where large differences were attributed to steroelectronic effects of the para ether oxygen stabilizing the derived phenoxyl radicals in (a) and (b) types. The results in aqueous micellar and membrane systems are interpreted in terms of polar solvation effects. Hydrogen bonding by water at both the ether and phenolic groups decreases the activity of the (a) series. Hydrogen bonding at the phenolic hydroxyl appears to be the more significant factor since steric hindrance to H-bonding at hydroxyl allows 4a and 5a to be the most active antioxidants of the α-tocopherol series (a) and DBHA to be the most active antioxidant of the (b) series. Keywords: antioxidant activities, phenols, membranes, peroxidation, kinetics.

Accurate Calculation of the Energy Barriers and Rate Constants of the Large-size Molecular Reaction System for Abstraction from Alkyl Hydroperoxides

2018 ◽  
Vol 76 (4) ◽  
pp. 311 ◽  
Author(s):  
Fangfang Chen ◽  
Xiaohui Sun ◽  
Qian Yao ◽  
Zerong Li ◽  
Jingbo Wang ◽  
...  
Keyword(s):  
Rate Constants ◽  
Reaction System ◽  
Accurate Calculation ◽  
Energy Barriers ◽  
Large Size ◽  
Alkyl Hydroperoxides ◽  
Molecular Reaction

Infrared Investigation of H2S Adsorption and Decomposition on Alumina and on Alumina Supported Molybdenum Sulfide

1972 ◽  
Vol 50 (21) ◽  
pp. 3416-3423 ◽  
Author(s):  
T. L. Slager ◽  
C. H. Amberg
Keyword(s):  
Hydrogen Bonding ◽  
Rate Constants ◽  
Kinetic Data ◽  
Surface Reaction ◽  
Molybdenum Sulfide ◽  
Subsequent Reaction ◽  
Alumina Support ◽  
First Order ◽  
H2s Adsorption ◽  
Surface Bond

Adsorption and subsequent reaction of H2S on alumina gave major i.r. bands at 1341, 1568, 1625, and 3400 cm−1. Relative band intensities were used to follow the first order decomposition of adsorbed H2S and formation of H2O. Rate constants of the surface reaction at 23, 55, and 80 °C were 0.70, 1.48, and 3.42 × 10−3 s−1, respectively. A mechanism consistent with the observed spectral and kinetic data involved adsorption to an exposed Al ion forming an Al—S surface bond, and hydrogen bonding to neighboring O and OH species. It was assumed that the sulfur remained on the surface as a sulfide. The 1568 cm−1 band was discussed in terms of an Al—O species.With adsorption on MoS2–Al2O3, bands appeared at 1330 and 1575 cm−1. Behavior in all respects was similar to that observed on the alumina support alone.

Hydrolysis of amides. IV. Dilute acid hydrolysis of amides of the type R2CH-CONH2 and R3C-CONH2

1971 ◽  
Vol 24 (3) ◽  
pp. 471 ◽  
Author(s):  
PD Bolton ◽  
GL Jackson
Keyword(s):  
Free Energy ◽  
Hydrogen Bonding ◽  
Acid Hydrolysis ◽  
Rate Constants ◽  
Hydrolysis Rate ◽  
Dilute Acid ◽  
Dilute Acid Hydrolysis ◽  
Reasonable Explanation ◽  
Hydrolysis Of

Enthalpies and entropies of activation have been derived from rate constants measured over a range of temperature for the dilute acid hydrolysis of isobutyramide, diethylacetamide, α-methylbutyramide, cyclohexaneoarboxamide, cyclopentane-carboxamide, and trimethylacetamide. ��� These data, in combination with data for other amides produced earlier, show the hydrolysis rate constants to be dominated by steric influences but with a perturbing effect which is proportional to the number of α-hydrogens present in the substituent. The "α-hydrogen bonding" concept of hyperconjugation appears to offer a reasonable explanation of these perturbations. ��� Controlled steric changes are shown to be non-additive for this reaction and to exert their influence primarily through the enthalpy component of the observed free energy changes.

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