Comparative pulse radiolysis studies of alkyl- and methoxy-substituted semiquinones formed from quinones and hydroquinones

Roginsky, Vitaly A.; Pisarenko, L. M.; Bors, Wolf; Michel, Christa; Sarán, Manfred

doi:10.1039/a801082j

Cited by 40 publications

(53 citation statements)

References 2 publications

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“…The λ rad values with 2‐propanol (Table 3) and TEA (Table 4) are virtually identical. This is in accordance with the nearly identical spectra of • QH and Q •– for quinones in water (36, 37).…”

Section: Resultssupporting

confidence: 88%

“…In aqueous solution at pH 7 the semiquinone radicals are generally present as radical anions; p K a = 4 for BQ and 5 for Me 4 BQ (36, 37).…”

Section: Discussionmentioning

confidence: 99%

“…For parent BQ the maximum quantum yield of formation of QH 2 is unity (3,6). The semiquinone radical ( • QH/Q •– ), the properties of which have been investigated by radiation chemistry (34–39), plays a key role in the photoreduction of quinones.…”

Section: Introductionmentioning

confidence: 99%

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Photoreduction of p-Benzoquinones: Effects of Alcohols and Amines on the Intermediates and Reactivities in Solution¶

Görner¹

2007

Photochemistry and Photobiology

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The photochemistry of 1,4‐benzoquinone (BQ) and alkyl‐, Cl‐ and related derivatives, e.g. methyl‐, 2,6‐dimethyl‐, chloro‐, 2,5‐dichloro‐1,4‐benzoquinone, duroquinone and chloranil, was studied in nonaqueous solvents by UV–vis spectroscopy using nanosecond laser pulses at 308 nm. The reactivity of the triplet state (3Q*) of the quinones with 2‐propanol in the absence of water is largest for BQ and depends mainly on the quinone structure, whereas the rate constant of electron transfer from amines, such as triethylamine (TEA) or 1,4‐diazabicyclo[2.2.2]octane, is close to the diffusion‐controlled limit for BQ and most derivatives. Photoinduced charge separation after electron transfer from amines to 3Q* and the subsequent charge recombination or neutralization are supported by time‐resolved conductivity measurements. The half‐life of the decay kinetics of the semiquinone radical (•QH/Q•–) depends significantly on the donor and the medium. The photoconversion into the hydroquinones was measured under various conditions, the quantum yield, λirr= 254 nm, increases with increasing 2‐propanol and TEA concentrations. The effects of quenching of 3Q*, the •QH/Q•– radicals and the photoconversion are outlined. The mechanisms of photoreduction of quinones in acetonitrile by 2‐propanol are compared with those by TEA in benzene and acetonitrile, and the specific properties of substitution are discussed.

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Section: Resultssupporting

confidence: 88%

“…In aqueous solution at pH 7 the semiquinone radicals are generally present as radical anions; p K a = 4 for BQ and 5 for Me 4 BQ (36, 37).…”

Section: Discussionmentioning

confidence: 99%

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Photoreduction of p-Benzoquinones: Effects of Alcohols and Amines on the Intermediates and Reactivities in Solution¶

Görner¹

2007

Photochemistry and Photobiology

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“…This is present as anion in the applied pH range of 5-8 due to equilibrium 7 and pK, = 4.2-5 (32)(33)(34). Radical termination and protonation reaction 8 eventually yields QH2.…”

Section: Q + H V + ' * Q -3*q 111mentioning

confidence: 99%

Photoreactions of p-Quinones with Dimethyl Sulfide and Dimethyl Sulfoxide in Aqueous Acetonitrile†

Görner¹

2006

Photochem Photobiol

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The effects of dimethyl sulfide (DMS) and dimethyl sulfoxide (DMSO) on the photoreactions of 1,4-benzoquinone (BQ), 1,4-naphthoquinone (NQ), 9,10-anthraquinone (AQ) and several derivatives in acetonitrile/water were studied. The observed triplet state of the quinones is quenched and the rate constant is close to the diffusion-controlled limit for reactions of most quinones with DMS and lower with DMSO. Semiquinone radical anions (Q*-) produced by electron transfer from sulfur to the triplet quinone were detected. For both DMS and DMSO the yield of Q*- is similar, being generally low for BQ and NQ, substantial for AQ and largest for chloranil. The specific quencher concentrations and the effects of quinone structure and redox potentials on the time-resolved photochemical properties are discussed.

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“…Bors and co-workers 360 investigated the disproportionation of semiquinones (Q •-) when other reactions are hindered (Scheme 72).…”

Section: Pulse Radiolytic Studies On 14-benzoquinonesmentioning

confidence: 99%

Recent advances in 1,4-benzoquinone chemistry

Abraham¹,

Joshi²,

Pardasani³

et al. 2011

J. Braz. Chem. Soc.

166

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As 1,4-benzoquinonas são encontradas em toda a natureza, podendo ser sintetizadas por diversas estratégias. Esta revisão apresenta os desenvolvimentos recentes das metodologias de síntese, das reações de ciclo adição, da química computacional e dos estudos de pulso radiolítico. Destaca ainda a sua significância química e biológica e de seus compostos derivados.1,4-Benzoquinones are ubiquitous in nature and can be synthesized by diverse strategies. Recent developments on their synthetic methodologies, cycloaddition reactions, computational chemistry and pulse radiolytic studies are reported in this review. Their chemical and biological significance as well as their derivates' are also covered.

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Comparative pulse radiolysis studies of alkyl- and methoxy-substituted semiquinones formed from quinones and hydroquinones

Cited by 40 publications

References 2 publications

Photoreduction of p-Benzoquinones: Effects of Alcohols and Amines on the Intermediates and Reactivities in Solution¶

Photoreduction of p-Benzoquinones: Effects of Alcohols and Amines on the Intermediates and Reactivities in Solution¶

Photoreactions of p-Quinones with Dimethyl Sulfide and Dimethyl Sulfoxide in Aqueous Acetonitrile†

Recent advances in 1,4-benzoquinone chemistry

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