Graphitic carbon nitride catalysed photoacetalization of aldehydes/ketones under ambient conditions

Abstract

Graphitic-C3N4 is shown for the first time to catalyse photoacetalization of aldehydes/ketones with alcohols to acetals in high yields using visible light under ambient conditions; transient charge separation over the material is effective to catalyse the reaction in the absence of Lewis or Brønsted acids, giving a new green alternative catalyst.

Surface-Doped Graphitic Carbon Nitride Catalyzed Photooxidation of Olefins and Dienes: Chemical Evidence for Electron Transfer and Singlet Oxygen Mechanisms

“…2 ) through an electron transfer mechanism, as shown in Scheme 6. The formation of superoxide anion O• − 2 and not a hydroxyl radical has been also recently documented [20]. We must note here that control experiments either with the CD-C 3 N 4 in dark (entry 10) or without the photocatalyst under irradiation conditions (entry 11) did not show any detectable oxidation products (entry 10) or small traces observed by 1 H NMR and GC analysis (entry 11).…”

“…p-Methoxy-acetophenone 4c is most probably produced from the cleavage of dioxetane 4d via the intermediacy of superoxide anion (O•2) through an electron transfer mechanism, as shown in Scheme 6. The formation of superoxide anion O•2and not a hydroxyl radical has been also recently documented [20]. We must note here that control experiments either with the CD-C3N4 in dark (entry 10) or without the photocatalyst under irradiation conditions (entry 11) did not show any detectable oxidation products (entry 10) or small traces observed by 1 H NMR and GC analysis For comparison reasons, apart from CD-C 3 N 4 , four sensitizers were utilized in the above reaction (entries 1-4).…”

“…Although many studies concern the photochemical activity and spectroscopic data analysis of g-C 3 N 4 as well as modification of its surface [19], applications to organic transformations are limited. For example, graphitic C 3 N 4 as well as its surface-doped-materials, catalyze a few reactions; a) photoacetalization of aldehydes/ketones [20] b) the Friedel-Crafts reaction of benzene [21] c) oxidation of alcohols using transition metal doped g-C 3 N 4 [22][23][24][25] d) oxidation of sulfides to sulfoxides using oxidized g-C 3 N 4 (CNO). In addition, selective oxidations of benzylic C-H bonds utilizing mesoporous g-C 3 N 4 with N-OH co catalysts have been reported [26][27][28][29].…”

Phosphorylated Polyacrylonitrile Fibers as an Efficient and Greener Acetalization Catalyst

“…The electronic nature of the substituents has a significant effect on the reaction activity. Generally, the reaction activity of the aldehydes with electron‐withdrawing groups is lower than that of those with electron‐donating and halogen groups . With regard to the nitro‐substituted aldehydes, high yields (96–98 %) were achieved when the reaction time was prolonged to 3.5 h ( 3 b – 3 d ).…”

“…However, in the case of p ‐methoxybenzaldehyde ( 3 g ) and p ‐dimethylaminobenzaldehyde ( 3 h ), low yields were obtained, and similar results could be seen in the literature . It should be also mentioned that the p ‐hydroxybenzaldehyde presents a moderate yield of 60 % ( 3 j ), which is much higher than that of some reported literature in which no product was obtained . The lower yields for p ‐substituted benzaldehydes could be attributed to the formation of carbenium intermediates and hydrogen‐bonding interactions.…”