US EPA

7947283 

Journal Article 

KINETICS AND MECHANISM OF DECAFLUOROBENZOPHENONE PHOTOCHEMICAL REACTIONS IN CYCLOHEXANE, BENZENE, AND ALKYL AROMATICS 

Dedinas, J; Regan, TH 

1972 

1 

Journal of Physical Chemistry
ISSN: 0022-3654 

76 

26 

3926-3933 

English 

10.1021/j100670a004 

WOS:A1972O359600004 

https://www.scopus.com/inward/record.uri?eid=2-s2.0-0000024004&doi=10.1021%2fj100670a004&partnerID=40&md5=e24cccde25ad726a6f409309df2f1700
Exit
 

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(n,π*), with a rate constant of 7.5 × 106 . 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 (Ia), aromatic substitution of decafluorobenzophenone by cyclohexyl radical is also observed. Thus, the quantum yield (φ) is dependent on C and Ia. In cyclohexane using C = 0.01 M and by extrapolating 7a 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 kq of 1.6 × 108 M-1 sec-1. There is no conversion of decafluorobenzophenone to products in pure benzene. In toluene and p-xylene, φ = 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(n,π*) state. The quenching mechanism by benzene thus can be explained by a charge-transfer complex or an exciplex between the ketone in the 3(n,π*) state and benzene.