Cv. Costa et al., ON THE YIELD OF INTERMEDIATES FORMED IN THE PHOTOREDUCTION OF BENZOPHENONE, Journal of photochemistry and photobiology. A, Chemistry, 99(1), 1996, pp. 51-56
The production of intermediates (light absorbing transients, LAT) has
been examined in the photoreduction of benzophenone by different hydro
gen donors in inert solvents (acetonitrile and benzene). For 2-propano
l in acetonitrile, a branching ratio of 0.3 for the coupling reaction
between dimethyl- and diphenylketyl radicals was extracted by computer
model simulations considering inner filter effects and the quenching
of triplet benzophenone by LAT. Experimental evidence is presented tha
t indicates that LAT could be an efficient H-donor. Steady-state quant
um yields for LAT production, Phi(LAT), and benzophenone conversion, -
Phi(Ph2CO), were determined for the donors 2-propanol, n- and c-hexane
, benzhydrol and tetrahydrofuran. The relative quantum yield, -Phi(LAT
)/Phi(Ph2CO), which indicates the differential partitioning of the pro
ducts, shows that 2-propanol and tetrahydrofuran are nearly ten times
more efficient than alkanes. From the analysis of the mechanism we der
ived an upper limit for the rate constant for the coupling reaction of
two diphenylketyl radicals to yield LAT: k(6d) less than or equal to
5 x 10(5) M(-1) s(-1).