Simultaneous production of p-tolualdehyde and hydrogen peroxide in photocatalytic oxygenation of p-xylene and reduction of oxygen with 9-mesityl-10-methylacridinium ion derivatives

Abstract

Photooxygenation of p-xylene by oxygen occurs efficiently under photoirradiation of 9-mesityl-2,7,10-trimethylacridinium ion (Me(2)Acr(+)-Mes) to yield p-tolualdehyde and hydrogen peroxide, which is initiated via photoinduced electron transfer of Me(2)Acr(+)-Mes to produce the electron-transfer state.

Solar Synthesis: Prospects in Visible Light Photocatalysis

“…This type of bond construction commonly relies on acid catalysts, such as 6 , that direct bond formation to the most substituted carbon of the alkene to yield the Markovnikov product. However, in Nicewicz's work, the cyclization process is promoted via photooxidation by a mesityl-substituted acridinium salt 7 originally reported by Fukuzumi (65, 66). This organic photocatalyst has many of the same properties as ruthenium and iridium complexes, including strong visible light absorption and a long excited-state lifetime, but its photoexcited state is sufficiently oxidizing to react with trisubstituted aliphatic alkenes (66, 67).…”

“…However, in Nicewicz's work, the cyclization process is promoted via photooxidation by a mesityl-substituted acridinium salt 7 originally reported by Fukuzumi (65, 66). This organic photocatalyst has many of the same properties as ruthenium and iridium complexes, including strong visible light absorption and a long excited-state lifetime, but its photoexcited state is sufficiently oxidizing to react with trisubstituted aliphatic alkenes (66, 67). The resulting alkene radical cations can undergo nucleophilic attack by a tethered alcohol; however, due to the polarization of the radical cation, the regioselectivity complements that of acid-catalyzed reactions and results in the exclusive formation of the anti-Markovnikov addition product.…”

Formation of a long-lived electron-transfer state in mesoporous silica-alumina composites enhances photocatalytic oxygenation reactivity

“…The photocatalytic activity was accelerated by the addition of Brønsted acid such as trifluoroacetic acid (TFA) to the photocatalytic oxygenation system (21). The conversion of p-xylene oxygenation was limited to a 44% yield by 80 min photoirradiation (380 nm < λ < 500 nm) of an O 2 -saturated MeCN solution containing p-xylene (4.0 mM) and Acr þ -Mes (0.20 mM).…”

“…Another serious problem for electron donor-acceptor organic molecules, including Acr þ -Mes, is instability under photoirradiation (20). The degradation of Acr þ -Mes also results from intermolecular oxidation of Acr þ -Mes by the ETstate under photoirradiation (21).…”

Direct Synthesis of Secondary Benzylic Alcohols Enabled by Photoredox/Ni Dual-Catalyzed Cross-Coupling

“…Although 4CzIPN ( E * 1/2 = 1.35 V vs SCE) 11 proved to be a viable catalyst, the Ir catalyst 1 provided superior yields (entries 1–2). MesAcr (mesitylacridinium) has a sufficiently high oxidation potential ( E * 1/2 = 2.2 V vs SCE), 12 but it did not give any desired product 6a (entry 4), likely because of its inability to reduce the putative Ni(I) ( E red > -1.1 V) 5a intermediate (Scheme 1, 2d ). Other organophotocatalysts such as Eosin Y were also ineffective under these reaction conditions (entry 3), most likely because of their low redox potential ( E * 1/2 = 0.79 V vs SCE).…”