scholarly journals Spin-trapping with 2-methyl-2-nitrosopropane: photochemistry of carbonyl-containing compounds. Methyl radical formation from dimethyl sulfoxide

1982 ◽  
Vol 60 (12) ◽  
pp. 1486-1492 ◽  
Author(s):  
Ionel Rosenthal ◽  
Magdi M. Mossoba ◽  
Peter Riesz
Keyword(s):  
Dimethyl Sulfoxide ◽  
Hydroxyl Radicals ◽  
Hydrogen Abstraction ◽  
Spin Trapping ◽  
Photochemical Reactions ◽  
Methyl Radicals ◽  
Methyl Radical ◽  
Initial Compound ◽  
Acyl Radical ◽  
Benzyl Radical

The photochemical reactions of several carbonyl-containing compounds investigated by spin-trapping with 2-methyl-2-nitrosopropane revealed different modes of scission depending on the structure of the initial compound. Thus, in photo-Fries rearrangements, the acyl radical was detected. 1,3-Diphenyl-2-propanone decarbonylated to yield the benzyl radical. Finally, valerophenone yielded the radicals expected by γ-hydrogen abstraction. In a dark reaction, dimethyl sulfoxide reacts with NaOH to generate methyl radicals. The latter result suggests the need for caution in the use of dimethyl sulfoxide with 2-methyl-2-nitrosopropane for the detection of hydroxyl radicals.

Reactions of free radicals with aromatic compounds in the gaseous phase. I. Kinetics of the reaction of methyl radicals with toluene

1964 ◽  
Vol 17 (12) ◽  
pp. 1329 ◽  
Author(s):  
MFR Mulcahy ◽  
DJ Williams ◽  
JR Wilmshurst
Keyword(s):  
Flow System ◽  
Methyl Radicals ◽  
Methyl Radical ◽  
Hydrogen Atoms ◽  
Methyl Group ◽  
Benzyl Radical ◽  
Toluene Molecule ◽  
Benzyl Radicals ◽  
Butyl Peroxide ◽  
Kinetics Of

The kinetics of abstraction of hydrogen atoms from the methyl group of the toluene molecule by methyl radicals at 430-540�K have been determined. The methyl radicals were produced by pyrolysis of di-t-butyl peroxide in a stirred-flow system. The kinetics ,agree substantially with those obtained by previous authors using photolytic methods for generating the methyl radicals. At toluene and methyl-radical concentrations of about 5 x 10-7 and 10-11 mole cm-3 respectively the benzyl radicals resulting from the abstraction disappear almost entirely by combination with methyl radicals at the methylenic position. In this respect the benzyl radical behaves differently from the iso-electronic phenoxy radical, which previous work has shown to combine with a methyl radical mainly at ring positions. The investigation illustrates the application of stirred-flow technique to the study of the kinetics of free-radical reactions.

Reactions of free radicals with aromatic compounds in the gaseous phase. II. Kinetics of the reaction of methyl radicals with phenol

1965 ◽  
Vol 18 (1) ◽  
pp. 20 ◽  
Author(s):  
MFR Mulcahy ◽  
DJ Williams
Keyword(s):  
Free Radicals ◽  
Gaseous Phase ◽  
Hydrogen Abstraction ◽  
High Reactivity ◽  
Phenoxy Radical ◽  
Methyl Radicals ◽  
Methyl Radical ◽  
Kinetics Of Formation ◽  
Phenolic Substances ◽  
Kinetics Of

Knowledge of the reactivity of phenols towards simple free radicals is needed to throw light on the behaviour of the phenolic substances involved in the pyrolysis of coal and other organic materials. In the present investigation the reaction between methyl radicals and phenol vapour has been studied a t total pressures from 0.5 to 3 cmHg and temperatures from 445 to 547°K, the concentrations of methyl radicals and phenol being varied from 2 × 10-12 to 4 × 10-11 and 1 × 10-8 to 8 × 10-7 mole cm-3 respectively. The main products identified by gas chromatography were methane and o- and p-cresol, together with a little anisole and 2,4- and 2,6-dimethylphenol. The cresols are produced via hydrogen abstraction Diagram followed by combination of a methyl radical at a ring position of the phenoxy radical either ortho or para to the oxygen atom, e.g. in the case of the para position: Diagram The kinetics can be explained by postulating (a) that the keto forms of the cresols (methylcyclohexadienones) formed initially by reaction (6) have a finite lifetime in the gaseous phase and (b) that these molecules, which contain a tertiary hydrogen atom α to a system of a carbonyl bond and two carbon-carbon double bonds, partly undergo hydrogen abstraction by methyl radicals before they are able to enolize: CH3· + (HCH3 = C6H4 = O → CH4 + CH3C6H4O· The mechanism is consistent with the kinetics of formation of methane, the distribu- tion of the free electron in the phenoxy radical, the formation of o- and p-cresols as major products, the kinetics of formation of the cresols, and the high reactivity of the intermediate product towards methyl radicals.

Methyl Radicals in Solid Acetonitrile: Decay or No Decay

1974 ◽  
Vol 52 (11) ◽  
pp. 2171-2174 ◽  
Author(s):  
Frederick Peter Sargent ◽  
Marshall Grant Bailey ◽  
Edward Michael Gardy
Keyword(s):  
Thermal Stability ◽  
Hydrogen Abstraction ◽  
Low Energy ◽  
Quantum Mechanical ◽  
Methyl Radicals ◽  
Methyl Radical ◽  
Cyanide Ion ◽  
Abstraction Reaction ◽  
Hydrogen Abstraction Reaction ◽  
Thermal Stability Of

A comparison of both the e.s.r. spectra and the thermal stability of the radicals produced in γ radiolysis and 185 nm photolysis of acetonitrile shows that the former are not free methyl radicals. The initial species formed by γ radiolysis can be converted by photobleaching into a methyl radical weakly associated with a cyanide ion. The methyl radical of this CH3---CN−pair decays via hydrogen abstraction, whereas the free methyl radicals produced by 185 nm photolysis of acetonitrile are quite stable at 77 K. We ascribe the low energy of activation for the hydrogen abstraction reaction in the γ irradiated samples not primarily to quantum mechanical tunnelling but to perturbation by the cyanide ion.

A Reinvestigation of the Deceptively Simple Reaction of Toluene with ●OH, and the Fate of the Benzyl Radical. I. a Combined Thermodynamic and Kinetic Study on the Competition Between ●OH Addition and Hydrogen Abstraction Reactions.

2019 ◽  
Author(s):  
Zoi Salta ◽  
Agnie M. Kosmas ◽  
Marc E. Segovia ◽  
Martina Kieninger ◽  
Oscar Ventura ◽  
...  
Keyword(s):  
Density Functional ◽  
Room Temperature ◽  
Hydrogen Abstraction ◽  
Reaction Rates ◽  
Composite Model ◽  
Alternative Mechanism ◽  
Radical Intermediate ◽  
Experimental Conditions ◽  
Methyl Group ◽  
Benzyl Radical

This work reports density functional and composite model chemistry calculations performed on the reactions of toluene with the hydroxyl radical. Both experimentally observed H-abstraction from the methyl group and possible additions to the phenyl ring were investigated. Reaction enthalpies and heights of the barriers suggest that H-abstraction is more favorable than ●OH addition to the ring. The calculated reaction rates at room temperature and the radical-intermediate product fractions support this view. This is somehow contradictory with the fact that, under most experimental conditions, cresols are observed in a larger concentration than benzaldehyde. Since the accepted mechanism for benzaldehyde formation involves H-abstraction, a contradiction arises that begs for an explanation. In this first part of our work we give the evidences that support the preference of hydrogen abstraction over ●OH addition and suggest an alternative mechanism which shows that cresols can actually arise also from the former reaction and not only from the latter.

A Reinvestigation of the Deceptively Simple Reaction of Toluene with ●OH, and the Fate of the Benzyl Radical. I. a Combined Thermodynamic and Kinetic Study on the Competition Between ●OH Addition and Hydrogen Abstraction Reactions.

2019 ◽  
Author(s):  
Zoi Salta ◽  
Agnie M. Kosmas ◽  
Marc E. Segovia ◽  
Martina Kieninger ◽  
Oscar Ventura ◽  
...  
Keyword(s):  
Density Functional ◽  
Room Temperature ◽  
Hydrogen Abstraction ◽  
Reaction Rates ◽  
Composite Model ◽  
Alternative Mechanism ◽  
Radical Intermediate ◽  
Experimental Conditions ◽  
Methyl Group ◽  
Benzyl Radical

This work reports density functional and composite model chemistry calculations performed on the reactions of toluene with the hydroxyl radical. Both experimentally observed H-abstraction from the methyl group and possible additions to the phenyl ring were investigated. Reaction enthalpies and heights of the barriers suggest that H-abstraction is more favorable than ●OH addition to the ring. The calculated reaction rates at room temperature and the radical-intermediate product fractions support this view. This is somehow contradictory with the fact that, under most experimental conditions, cresols are observed in a larger concentration than benzaldehyde. Since the accepted mechanism for benzaldehyde formation involves H-abstraction, a contradiction arises that begs for an explanation. In this first part of our work we give the evidences that support the preference of hydrogen abstraction over ●OH addition and suggest an alternative mechanism which shows that cresols can actually arise also from the former reaction and not only from the latter.

Enhancement of hydroxyl radical generation by phenols and their reaction intermediates during ozonation

1998 ◽  
Vol 38 (6) ◽  
pp. 147-154 ◽  
Author(s):  
Hideo Utsumi ◽  
Sang-Kuk Han ◽  
Kazuhiro Ichikawa
Keyword(s):  
Hydroxyl Radical ◽  
Hydroxyl Radicals ◽  
Spin Trapping ◽  
Active Species ◽  
Generation Rate ◽  
Peak Height Ratio ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Phenol Derivatives ◽  
Semiquinone Radicals

Generation of hydroxyl radicals, one of the major active species in ozonation of water was directly observed with a spin-trapping/electron spin resonance (ESR) technique using 5,5-dimethyl-1-pyrrolineN-oxide (DMPO) as a spin-trapping reagent. Hydroxyl radical were trapped with DMPO as a stable radical, DMPO-OH. Eighty μM of ozone produced 1.08 X 10-6M of DMPO-OH, indicating that 1.4% of •OH is trapped with DMPO. Generation rate of DMPO-OH was determined by ESR/stopped-flow measurement. Phenol derivatives increased the amount and generation rate of DMPO-OH, indicating that phenol derivatives enhance •OH generation during ozonation of water. Ozonation of 2,3-, 2,5-, 2,6-dichlorophenol gave an ESR spectra of triplet lines whose peak height ratio were 1:2:1. ESR parameters of the triplet lines agreed with those of the corresponding dichloro-psemiquinone radical. Ozonation of 2,4,5- and 2,4,6-trichlorophenol gave the same spectra as those of 2,5- and 2,6-dichlorophenol, respectively, indicating that a chlorine group in p-position is substituted with a hydroxy group during ozonation. Amounts of the radical increased in an ozone-concentration dependent manner and were inhibited by addition of hydroxyl radical scavengers. These results suggest that p-semiquinone radicals are generated from the chlorophenols by hydroxyl radicals during ozonation. The p-semiquinone radicals were at least partly responsible for enhancements of DMPO-OH generation.

Hydrogen abstraction by methyl radicals in glasses

1984 ◽  
Vol 78 ◽  
pp. 175 ◽  
Author(s):  
Takahisa Doba ◽  
Keith U. Ingold ◽  
Willem Siebrand ◽  
Timothy A. Wildman
Keyword(s):  
Hydrogen Abstraction ◽  
Methyl Radicals
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