PHOTOOXYGENATION OF BIPHENYL AND ITS DERIVATIVES via PHOTOINDUCED ELECTRON TRANSFER: EFFECT OF Mg(CIO₄)₂ ON PHOTOOXYGENATION

Abstract

The 9,10‐dicyanoanthracene (DCA)‐sensitized photooxygenation of biphenyl derivatives in the presence of Mg(CIO4)2 in acetonitrile produces benzoic acid and its derivatives in high yields. In the absence of Mg(CIO4)2, the rates for the consumption of biphenyl derivatives decrease by a factor of 0.5‐0.8, compared with those in the presence of Mg(CIO4)2. In these cases, however, both biphenyls and DCA are oxygenated to give benzoic acids and anthraquinone, respectively, indicating that the addition of Mg(CIO4)2 retards the photooxygenation of DCA. With 4‐methylbiphenyl, the photooxygenation proceeds efficiently without added Mg(CIO4)2, and benzene rings and methyl groups are competitively oxygenated to give benzoic acid, 4‐methylbenzoic acid, 4‐phenylbenzoic acid, and 4‐phenylbenzaldehyde. The addition of Mg(CIO4)2 facilitates the oxidation of benzene rings, giving benzoic acid and 4‐methylbenzoic acid as major products. These photooxygenations are initiated by a one‐electron transfer from biphenyls to the excited singlet DCA and proceed via the radical cations of biphenyls and the radical anion of DCA.

Mechanism of Quenching of Triplet States by Oxygen: Biphenyl Derivatives in Acetonitrile

“…b Calculated using eqs 15 and 16 and the values for the constants in Scheme given in the text. c From ref .…”

Dual Catalysis Strategies in Photochemical Synthesis

“…However, coordination of a Lewis acid to DCA •− is proposed to stabilize the radical anion and decrease the rate of unproductive back-electron transfer. A similar strategy has been applied to a number of other transformations, including the photooxygenation of cyclopropanes, 78,84,163 disiletenes, 164 biphenyls, 165,166 and 1,5-dienes, 167 as well as the addition of methanol to 1,1-diaryl alkenes. 168 Lewis acids can alter the photoelectrochemical properties of photocatalysts by coordination to heteroatom binding sites in much the same way as they can change the redox potential of Lewis basic organic substrates (section 2.2.1).…”

“…However, coordination of a Lewis acid to DCA •– is proposed to stabilize the radical anion and decrease the rate of unproductive back-electron transfer. A similar strategy has been applied to a number of other transformations, including the photooxygenation of cyclopropanes, ,, disiletenes, biphenyls, , and 1,5-dienes, as well as the addition of methanol to 1,1-diaryl alkenes …”

A comparative study of the photochemistry of biphenyl adsorbed on cellulose and silicalite

“…The low formation of hydroxybiphenyls can be attributed to the lower water content of this support, owing to its hydrophobic character. The formed degradation products must involve molecular oxygen [35], which, unlike the cellulose case, is present in silicalite. The degradation products also indicate the presence of a source of hydrogen and carbon (see Scheme 1).…”