Para-substituent effect upon the oxygenation reaction of the benzyl radical in solution

Tokumura, Kunihiro; Nosaka, Hideyo; Ozaki, Tomomi

doi:10.1016/0009-2614(90)85210-4

Cited by 15 publications

(9 citation statements)

References 8 publications

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“…The rate constants for the combination of O 2 with benzyl, p-fluorobenzyl, and p-methylbenzyl radicals in liquid hexane were also identical, but smaller values were found for other substituted benzyl radicals. 24 The enhancement of k 1 beyond the k 1,∞ ET value in the case of p-fluorobenzyl radicals, which was observed in the present work, qualitatively resembles that of benzyl radicals (see Figure 4). Quantitatively, however, its onset is observed to occur earlier for p-fluorobenzyl radicals (already at ∼5 bar) than for benzyl radicals (∼10 bar).…”

Section: Effect Of Fluorine-substitution Of Benzyl-type Radicals On Ksupporting

confidence: 78%

Pressure and Temperature Dependence of the Recombination ofp-Fluorobenzyl Radicals

et al. 2006

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The rate constants of the recombination reaction of p-fluorobenzyl radicals, p-F-C6H4CH2 + p-F-C6H4CH2 (+M) --> C14H12F2 (+M), have been measured over the pressure range 0.2-800 bar and the temperature range 255-420 K. Helium, argon, and CO2 were employed as bath gases (M). At pressures below 0.9 bar in Ar and CO2, and 40 bar in He, the rate constant k1 showed no dependence on the pressure and the nature of the bath gas, clearly indicating that it had reached the limiting high-pressure value of the energy-transfer (ET) mechanism (k(1,infinity)ET). A value of k(1,infinity)ET(T) = (4.3 +/- 0.5) x 10(-11) (T/300 K)(-0.2) cm3 molecule(-1) s(-1) was determined. At pressures above about 5 bar, the k1 values in Ar and CO2 were found to gradually increase in a pressure range where according to energy-transfer mechanism, they should remain at the constant value k(1,infinity)ET. The enhancement of the recombination rate constant beyond the value k(1,infinity)ET increased in the order He < Ar < CO2, and it became more pronounced with decreasing temperature. The dependences of k1 on pressure, temperature, and the bath gas were similar to previous observations in the recombination of benzyl radicals. The effect of fluorine-substitution of the benzyl ring on k1 values is discussed. The present results confirm the significant role of radical complexes in the recombination kinetics of benzyl-type radicals in the gas-liquid transition range. The observations on a rate enhancement beyond the experimental value of k(1,infinity)ET at elevated densities up to the onset of diffusion-control are consistently explained by the kinetic contribution of a "radical-complex" mechanism which is solely based on standard van der Waals interaction between radicals and bath gases.

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Section: Effect Of Fluorine-substitution Of Benzyl-type Radicals On Ksupporting

confidence: 78%

Pressure and Temperature Dependence of the Recombination ofp-Fluorobenzyl Radicals

et al. 2006

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“…Singh and coworkers reported that the radical constants for para substituted toluenes were in the order of NH 2 > NO 2 supporting the hypothesis that the formation of the benzylic radical is favoured in the presence of an amino substituent. 33,34 Scheme 5 Synthesis of 10j. In the presence of an additional aromatic ring, as in the case of 12a, the yield of SO 2 during photolysis is significantly higher when compared with 4a (Table 2).…”

Section: Resultsmentioning

confidence: 99%

Benzosulfones as photochemically activated sulfur dioxide (SO₂) donors

Malwal

Chakrapani

2015

Org. Biomol. Chem.

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Sulfur dioxide (SO2) is a gaseous environmental pollutant which is routinely used in industry as a preservative and antimicrobial. Recent data suggests that SO2 may have value as a therapeutic agent. However, due to its gaseous nature, localizing SO2 generation is challenging. Herein, various 1,3-dihydrobenzo[c]thiophene 2,2-dioxides (benzosulfones) were prepared as candidates for photochemically activated sulfur dioxide (SO2) generation. These compounds were found to be stable in buffer but were photolysed upon irradiation with UV light to generate SO2. Our data indicates that photolysis of benzosulfones depends on substituents, and that the presence of electron donating groups results in an enhanced yield of SO2.

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“…It is well-established that the rate constant for reaction of the benzyl radical with O 2 is in the range of 3.0 × 10 9 M -1 s -1 . Since this is at least 1 order of magnitude faster than the recombination rate constant of two benzyl radicals (3−20) × 10 8 M -1 s -1 , ,27b benzylperoxy radical formation is more favorable than benzyl radical coupling.…”

Section: Resultsmentioning

confidence: 99%

Photochemistry of Substituted Benzyldiphenylphosphine Oxides

Zhao¹,

Neckers²

2000

J. Org. Chem.

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Photochemical reactions (lambda irr = 254 nm) of substituted benzyldiphenylphosphine oxides 1a-e have been investigated in benzene and acetonitrile. alpha-Cleavage from the singlet excited state is proposed as the primary process, and products formed both before and after escape of the primary intermediates from the solvent cage result. Radicals 2 and 3 are observed by nanosecond flash photolysis following excitation of 1a at 266 nm in acetonitrile. Acetone sensitization of 1a,b fails to improve the efficiency of product formation. The quantum yields of disappearance of 1a,b are unaffected by O2, and mechanisms for product formation from 1a in the presence of oxygen are proposed.

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Para-substituent effect upon the oxygenation reaction of the benzyl radical in solution

Cited by 15 publications

References 8 publications

Pressure and Temperature Dependence of the Recombination ofp-Fluorobenzyl Radicals

Pressure and Temperature Dependence of the Recombination ofp-Fluorobenzyl Radicals

Benzosulfones as photochemically activated sulfur dioxide (SO₂) donors

Photochemistry of Substituted Benzyldiphenylphosphine Oxides

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Para-substituent effect upon the oxygenation reaction of the benzyl radical in solution

Cited by 15 publications

References 8 publications

Pressure and Temperature Dependence of the Recombination ofp-Fluorobenzyl Radicals

Pressure and Temperature Dependence of the Recombination ofp-Fluorobenzyl Radicals

Benzosulfones as photochemically activated sulfur dioxide (SO2) donors

Photochemistry of Substituted Benzyldiphenylphosphine Oxides

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Product

Resources

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Benzosulfones as photochemically activated sulfur dioxide (SO₂) donors