Photoreduction of benzophenone in benzene. I. Mechanism of secondary reactions

Dedinas, Jonas

doi:10.1021/j100672a002

Cited by 33 publications

(13 citation statements)

References 3 publications

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“…These data were obtained primarily to elucidate the reaction mechanism; a further discussion of interpretation is presented in the following section. The minor products were m -cyclohexylnonafluorobenzophenone (4), dicyclohexyloctafluorobenzophenones (5), decafluorobenzhydrol (6), and bicyclohexyl (7). It is interesting that there was no eicosafluorobenzopinacol (8) formed in this reaction and that the quantum yield of bicyclohexyl was very low, <0.001.…”

Section: Oh (C6f5)2c-c6humentioning

confidence: 95%

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Kinetics and mechanism of decafluorobenzophenone photochemical reactions in cyclohexane, benzene, and alkyl aromatics

Dedinas¹,

Regan²

1972

J. Phys. Chem.

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The photochemistry of decafluorobenzophenone was investigated in degassed solutions of cyclohexane, benzene, toluene, and p-xylene using 366-nm irradiation. In cyclohexane the primary photochemical step is hydrogen abstraction by triplet decafluorobenzophenone, 3( , *), with a rate constant of 7.5 X 10® M-1 sec-1. The primary radicals formed undergo two types of radical-radical reactions, (a) combination and (b) an aromatic substitution reaction. At high concentrations (C) and at low light intensities (/a), aromatic substitution of decafluorobenzophenone by cyclohexyl radical is also observed. Thus, the quantum yield ( ) is dependent on C and Ia. In cyclohexane using C = 0.01 M and by extrapolating /a to =°, = 0.41 for decafluorobenzophenone disappearance, the major products of which are cyclohexyldi(pentafluoro)phenylcarbinol (24%) and o-and p-cyclohexylnonafluorobenzophenone (22 and 54%). Benzene quenches the triplet state with a rate constant fcq of 1.6 X 108 M-1 sec-1, There is no conversion of decafluorobenzophenone to products in pure benzene. In toluene and p-xylene, = 0.055 and 0.096, respectively, indicating that both hydrogen abstraction and direct quenching by the aromatic ring is taking place. The rates of hydrogen abstraction from cyclohexane and quenching by benzene are much higher than those obtained in the photochemistry of benzophenone. These higher rates must be due to the inductive effect of fluorine substitution, which increases the charge polarization of the 3( , *) state. The quenching mechanism by benzene thus can be explained by a charge-transfer complex or an exciplex between the ketone in the 8( , *) state and-benzene.

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Section: Oh (C6f5)2c-c6humentioning

confidence: 95%

“…The light source (1000-W xenon-mercury arc lamp), actinometry, and preparations of degassed samples for irradiation have been previously described. 7 Monochromatic light, 366 nm, was used. Cylindrical spectrophotometer cells matte of either Pyrex or quartz were attached to degassing tubes and were used as reactors.…”

Section: Methodsmentioning

confidence: 99%

Kinetics and mechanism of decafluorobenzophenone photochemical reactions in cyclohexane, benzene, and alkyl aromatics

Dedinas¹,

Regan²

1972

J. Phys. Chem.

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“…As semilogarithmic plots of benzophenone concentration, [BP], evaluated from the absorbance at 256 nm in Figure 5 against time gave a straight line, the quantum yield, (_ ), was calcuated from its slope by using eq 13. The results are summarized in Table I. The independence of (-ß ) against IQ at 30 °C ascertains that the hydrogen abstraction by benzophenone triplet in poly(vinyl alcohol) proceeds as a one-photon process, different from the case in PMMA.2,13 The values of (-ß ) for T < Tg are /a = fca[PVA]/(fe0 + *a[PVA]) = 1 -r0-1 Jo"/p(f) dt (14) which can be calculated from integration of phosphorescence decay curves. Values of /a are also given in Table I.…”

Section: Kinetics For Nonexponential Decay Ofmentioning

confidence: 99%

Photochemistry in polymer solids. 8. Mechanism of photoreaction of benzophenone in poly(vinyl alcohol)

Horie¹,

Ando²,

Mita³

1987

Macromolecules

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“…(4) fiir die Quantenausheute der Benzophenonreduktion in Benzol von Q = 0,005. Das entspricht der bereits hekannten GroBe fur diese Reaktion [17]. Wird Handelsiibliches Benzophenon (Reachim, Vio, Sojuzchimexport) wurde dreimal aus n-Hexan umkristallisiert und bei 40 "C im Vakuum getrocknet.…”

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Photoinduzierte H‐Abstraktionen an Benzylarylethern durch Benzophenon

1978

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Photoinduced H‐Abstraction on Benzyl Aryl Ethers by Benzophenone The triplet state of benzophenone abstracts in benzene of benzyl aryl ether 6 hydrogen atom from the CH2‐group. The formed α‐ether radicals 1 and diphenylhydroxymethyl radicals 8 react to form the three possible reaction products in statistical distribution. Benzaldehydes 2 and phenols 11 are formed in a side reaction. From quantum yield measurements of the benzophenone reduction in dependence upon the concentration of benzyl phenyl ether 6a follows a rate constant of the H‐abstraction of 9.5 ·105 M−1s−1 which is in good agreement with measurements in presence of naphthalene as a quencher. The quenching constant for benzophenone triplet by naphthalene is 2 · 109 M−1s−1. For benzyl phenyl ethers substituted in the benzyl ring the reaction constant for the H‐abstraction reaction was determined, ϱ = −0,68,

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Photoreduction of benzophenone in benzene. I. Mechanism of secondary reactions

Cited by 33 publications

References 3 publications

Kinetics and mechanism of decafluorobenzophenone photochemical reactions in cyclohexane, benzene, and alkyl aromatics

Kinetics and mechanism of decafluorobenzophenone photochemical reactions in cyclohexane, benzene, and alkyl aromatics

Photochemistry in polymer solids. 8. Mechanism of photoreaction of benzophenone in poly(vinyl alcohol)

Photoinduzierte H‐Abstraktionen an Benzylarylethern durch Benzophenon

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