Pyrolysis of Aryl Azides.X. Effects of Azide Concentration on Rate Constants and Product Yields

1990 ◽  
Vol 43 (6) ◽  
pp. 997 ◽  
Author(s):  
LK Dyall ◽  
PAS Smith
Keyword(s):  
Free Radical ◽  
Rate Constants ◽  
Aryl Azides ◽  
Radical Chain ◽  
Initial Concentration ◽  
Azo Compound ◽  
Product Yields ◽  
First Order ◽  
Induced Decomposition ◽  
Group Effects

First-order rate constants (k1) have been measured for pyrolysis of azidobenzenes in decalin solution, in the presence of a free-radical chain inhibitor to prevent any induced decomposition. The new values of k1 for the spontaneous unimolecular thermolysis are lower than previously reported ones, and require revision of published neighbouring group effects. Product yields ( azo compound and primary amine) vary with initial concentration of azide in ways which suggest the species responsible for induced decomposition is not triplet arylnitrene , but a solvent-derived free radical. There is no evidence for induced decomposition when nitrobenzene is the solvent. For aryl azides with no neighbouring group effects operating in their pyrolysis, the Arrhenius parameters Eact and ΔSactobey a precise linear relationship.

Absolute rate constants for hydrocarbon autoxidation. 32. On the self-reaction of 1,1-diphenylethylperoxyl in solution

1982 ◽  
Vol 60 (20) ◽  
pp. 2566-2572 ◽  
Author(s):  
J. A. Howard ◽  
J. H. B. Chenier ◽  
T. Yamada
Keyword(s):  
Free Radical ◽  
Rate Constants ◽  
The Self ◽  
Absolute Rate ◽  
Radical Process ◽  
First Order ◽  
Hydroperoxide Decomposition ◽  
Solvent Cage ◽  
Induced Decomposition ◽  
Free Radical Process

The major products of the self-reaction of 1,1-diphenylethylperoxyl have been determined from product studies of the autoxidation of 1,1-diphenylethane, induced decomposition of 1,1-diphenylethyl hydroperoxide, and decomposition of 2,2,3,3-tetraphenylbutane under an atmosphere of oxygen. Overall self-reaction is a complex free-radical process involving the intermediacy of 1,1-diphenylethoxyl and 1-phenyl-1-phenoxyethoxyl which undergo H-atom abstraction, β-scission and, in the case of the former radical, rearrangement. Hydroperoxide decomposition under an atmosphere of 36O2 has shown that 1,1-diphenylethylperoxyl undergoes β-scission faster than α-cumylperoxyl at 303 K in solution. The values of the rate constants for self-reaction of Ph2C(Me)O2• relative to those for tert-butylperoxyl are, however, not affected by this reaction. Furthermore they are not affected to any appreciable extent by the efficiency with which Ph2C(Me)O•, formed in nonterminating self-reactions, escape from the solvent cage. They are influenced principally by the first-order rate of decomposition of Ph2C(Me)OOOOC(Me)Ph2.

IRRADIATION OF AQUEOUS CHLORAL HYDRATE WITH Sr90–Y90 BETA RAYS

1959 ◽  
Vol 37 (6) ◽  
pp. 1022-1028 ◽  
Author(s):  
R. F. Platford ◽  
J. W. T. Spinks
Keyword(s):  
Free Radical ◽  
Rate Constants ◽  
Chloral Hydrate ◽  
Average Lifetime ◽  
Chain Reaction ◽  
Radical Chain ◽  
Acid Yield ◽  
Initial Concentration ◽  
Free Radical Chain Reaction ◽  
Radical Chain Reaction

Air-saturated aqueous chloral hydrate has been irradiated with beta rays and the acid yield as determined by titration has been studied as a function of dose rate, temperature, and initial concentration of the chloral hydrate.The average lifetime of the intermediates has been found, by means of the rotating sector technique, to be about 0.5 second. Propagation and termination rate constants for the reaction have been calculated and an effort has been made to explain the results observed in terms of a free radical chain reaction.

ChemInform Abstract: Pyrolysis of Aryl Azides. Part 10. Effects of Azide Concentration on Rate Constants and Product Yields.

ChemInform ◽  
1990 ◽  
Vol 21 (37) ◽  
Author(s):  
L. K. DYALL ◽  
P. A. S. SMITH
Keyword(s):  
Rate Constants ◽  
Aryl Azides ◽  
Product Yields

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.

Pyrolysis of 1-methylcyclohexene and methylenecyclohexane

1976 ◽  
Vol 29 (3) ◽  
pp. 599 ◽  
Author(s):  
JL Garnett ◽  
WD Johnson ◽  
JE Sherwood
Keyword(s):  
Rate Constants ◽  
Alder Reaction ◽  
Diels Alder ◽  
Reaction Pathways ◽  
Main Reaction ◽  
Confidence Limits ◽  
Radical Chain ◽  
First Order ◽  
Diels Alder Reaction ◽  
Ring Fission

At 495� the decomposition of both 1-methylcyclohexene and methylenecyclohexane is homogeneous and first order overall, the rate constants (with 90% confidence limits) being (6.01 � 0.40) x 10-4 and (6.53 � 0.23) x 10-4 s-1 respectively. Pressure is not a good measure of the rate of decomposition of either isomer. Toluene inhibits the decomposition of both olefins, although the effect is more marked for the exo-isomer. The two main reaction pathways for 1-methylcyclohexene are a reverse Diels-Alder reaction, giving 2-methylbuta-1,3-diene and ethene, and a radical chain dehydrogenation to give toluene and benzene. Methylenecyclohexane cannot react through a reverse Diels-Alder reaction and ring fission gives a mixture of C3 and lower hydrocarbons. Dehydrogenation to give benzene and toluene is also important. Isomerization is a much more favoured pathway for methylenecyclohexane as expected from the relative thermodynamic stabilities of the isomers.

Pyrolysis of aryl azides. III. Steric and electronic effects upon reaction rate

1975 ◽  
Vol 28 (10) ◽  
pp. 2147 ◽  
Author(s):  
LK Dyall
Keyword(s):  
Transition State ◽  
Rate Constants ◽  
Reaction Rate ◽  
Steric Effects ◽  
Electronic Effects ◽  
Aryl Azides ◽  
Phenyl Azide ◽  
Methyl Group ◽  
First Order ◽  
Ortho Substituent

First-order rate constants have been measured for the pyrolysis of 15 phenyl azides in decalin solution. The rate for phenyl azide is increased only slightly by all para and many ortho substituents; in these cases Eact and ΔSact values are related linearly. ��� The very large rate increases when the ortho substituent is phenylazo, nitro, acetyl or benzoyl cannot be from steric or normal electronic effects and therefore identify a specific involvement of these groups in the transition state. This rate enhancement is reduced to scarcely significant levels by a 6-chloro or 6-methyl group in 2- nitrophenyl azide, but not by a 6-nitro group. These results raise doubts about recent claims1 to establish mechanism by measuring polar effects on rates of pyrolysis of azides in which steric effects might also operate.

Derivation of rate constants for steps in the free-radical chain decomposition of paraffins

1962 ◽  
Vol 268 (1332) ◽  
pp. 36-45 ◽  
Keyword(s):  
Nitric Oxide ◽  
Free Radical ◽  
Rate Constants ◽  
High Pressures ◽  
Radical Mechanism ◽  
Methyl Radicals ◽  
Saturated Hydrocarbons ◽  
Radical Chain ◽  
Free Radical Mechanism ◽  
Standard Values

The Rice-Herzfeld free-radical mechanism for the thermal decomposition of saturated hydrocarbons, including both the uninhibited reaction and that partially inhibited by nitric oxide, involves the rate constants of various individual steps. If standard values are assumed for the rate constants of H -abstraction from n -pentane by methyl radicals, alkyl radical recombination, and addition of methyl to nitric oxide, then those of all the steps for a series of paraffins can be found. The method depends on measurements of the rate constant in the region where the chain reaction is of the first order, the inhibitory action of nitric oxide as a function of paraffin pressure, and the acceleration of paraffin decomposition rate produced by high pressures of nitric oxide. Values are derived for propane, three pentanes ( neo -, iso - and normal pentane) and three octanes ( normal octane, 2:3:4-trimethyl pentane and 2:2:4-trimethyl pentane), and the variations of the several rate constants with structure are discussed.

The Cerium(IV)-Induced Decomposition of Peroxymonosulfate: Acid Dependence and Peroxydisulfate Formation

1990 ◽  
Vol 43 (2) ◽  
pp. 321 ◽  
Author(s):  
C Marsh ◽  
Z Zhang ◽  
JO Edwards
Keyword(s):  
Free Radical ◽  
Redox System ◽  
Chain Mechanism ◽  
Radical Chain ◽  
Rate Law ◽  
Radical Chain Mechanism ◽  
Induced Decomposition ◽  
Acid Dependence

An improved rate law for the CeIV-induced decomposition of HOOSO3- in aqueous H2SO4 has been established by study of the rate as a function of acidity. In aqueous HClO4 the rate is much faster but a rate law could not be obtained. Peroxydisulfate, by a variant of the AsIII and FeII analysis of the redox system, has been shown to be formed in the amount of half of the CeIV lost. A free-radical chain mechanism is postulated.

Rate constants for abstraction of bromine from bromotrichloromethane by butyl, cyclopropylmethyl, and phenyl radicals in solution

1988 ◽  
Vol 66 (1) ◽  
pp. 11-16 ◽  
Author(s):  
Lukose Mathew ◽  
John Warkentin
Keyword(s):  
Free Radicals ◽  
Temperature Dependence ◽  
Rate Constant ◽  
Rate Constants ◽  
Radical Chain ◽  
Dichloromethane Solution ◽  
Chain Decomposition ◽  
Product Yields ◽  
Product Composition ◽  
Diffusion Controlled

The radical chain decomposition of cyclopropylmethyl (1-hydroxy-1-methylethyl)-diazene [Formula: see text] at 253–341 K in hexafluorobenzene or in dichloromethane solution containing bromotrichloromethane affords cyclopropylmethyl bromide, 4-bromo-1-butene, 1-bromo-5,5,5-trichloro-2-pentene, and 3,5-dibromo-1,1,1-trichloropentane from the cyclopropylmethyl portion of 1. Other major products are nitrogen, acetone, and chloroform. The rate constant for formation of cyclopropylmethyl bromide by attack of cyclopropylmethyl free radicals from 1 at bromine of BrCCl3[Formula: see text] was calculated from the product composition using the known rate constant for rearrangement of cyclopropylmethyl radicals to 3-buten-1-yl radicals. At 25 °C,[Formula: see text] and the temperature dependence is given by [Formula: see text], where θ = 2.3RT kcal/mol−1. Non-chain decomposition of (CH3)2C(OH)N=N—R (2, R = Bu, and 3, R = Ph) in the presence of excess 1,1,3,3-tetramethylisoindolin-2-yloxyl (4) and bromotrichloromethane afforded BuBr and PhBr, respectively, in yields determined by the relative concentrations of 4 and BrCCl3. Rate constants for coupling (kc) of Bu• and Ph• with 4 were assumed to be proportional to rate constants for diffusion controlled reactions, kd, which were estimated from measured viscosities. Values of [Formula: see text] and[Formula: see text], calculated from kc and product yields for reactions at 80 °C, are 0.26 × 109 and 1.55 × 109 M−1 s−1, respectively. The relative radical reactivities toward BrCCl3 at 80 °C are Ph, 6; cpm, 5; Bu, 1.

THE EFFECT OF HYALURONIDASE AND CORTISOL ON THE INACTIVATION OF VASOPRESSINS BY RAT KIDNEY SLICES

1962 ◽  
Vol 24 (4) ◽  
pp. 415-424 ◽  
Author(s):  
M. W. SMITH
Keyword(s):  
Arginine Vasopressin ◽  
Rate Constants ◽  
Rat Kidney ◽  
Sodium Succinate ◽  
Initial Concentration ◽  
First Order ◽  
Kidney Slices ◽  
Lysine Vasopressin ◽  
Normal Rat ◽  
Testicular Hyaluronidase

SUMMARY 1. Rat kidney slices inactivated 8-arginine vasopressin 1·23 times as fast as 8-lysine vasopressin and 2·14 times as fast as 2-phenylalanine-8-lysine vasopressin. The rate of inactivation became dependent upon the initial concentration of these peptides when this reached 8–11 μg./ml. There was a positive correlation between the apparent first-order rate constants of these vasopressins and their pressor potency per mg. peptide. 2. 8-Arginine vasopressin was not inactivated by hyaluronidase but rat kidney slices inactivated 8-arginine vasopressin 1·25 times as fast when testicular hyaluronidase was present. 3. Slices of rat kidney taken 7 days after bilateral adrenalectomy inactivated 8-arginine vasopressin at the same rate as those taken from normal animals. Cortisol sodium succinate did not affect the rate of 8-arginine vasopressin inactivation by normal rat kidney slices, but there was no increased rate of inactivation when hyaluronidase, 8-arginine vasopressin and cortisol sodium succinate were incubated together with normal rat kidney slices.

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