title: One-pot synthesis of imines from nitroaromatics and alcohols by tandem photocatalytic and catalytic reactions on Degussa (Evonik) P25 titanium dioxide.
abstract: Photoirradiation (λ > 300 nm) of Degussa (Evonik) P25 TiO2, a mixture of anatase and rutile particles, in alcohols containing nitroaromatics at room temperature produces the corresponding imines with very high yields (80-96%). Other commercially available anatase or rutile TiO2 particles, however, exhibit very low yields (<30%). The imine formation involves two step reactions on the TiO2 surface: (i) photocatalytic oxidation of alcohols (aldehyde formation) and reduction of nitrobenzene (aniline formation) and (ii) condensation of the formed aldehyde and aniline on the Lewis acid sites (imine formation). The respective anatase and rutile particles were isolated from P25 TiO2 by the H2O2/NH3 and HF treatments to clarify the activity of these two step reactions. Photocatalysis experiments revealed that the active sites for photocatalytic reactions on P25 TiO2 are the rutile particles, promoting efficient reduction of nitrobenzene on the surface defects. In contrast, catalysis experiments showed that the anatase particles isolated from P25 TiO2 exhibit very high activity for condensation of aldehyde and aniline, because the number of Lewis acid sites on the particles (73 μmol g(-1)) is much higher than that of other commercially available anatase or rutile particles (<15 μmol g(-1)). The P25 TiO2 particles therefore successfully promote tandem photocatalytic and catalytic reactions on the respective rutile and anatase particles, thus producing imines with very high yields.
authors.affiliation: Research Center for Solar Energy Chemistry, and Division of Chemical Engineering, Graduate School of Engineering Science, and §Institute for NanoScience Design, Osaka University , Toyonaka 560-8531, Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Hirakawa
authors.forename: Miyu
authors.initials: M
authors.lastname: Katayama
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Shiraishi
authors.forename: Hirokatsu
authors.initials: H
authors.lastname: Sakamoto
authors.forename: Kunlei
authors.initials: K
authors.lastname: Wang
authors.forename: Bunsho
authors.initials: B
authors.lastname: Ohtani
authors.forename: Satoshi
authors.initials: S
authors.lastname: Ichikawa
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Tanaka
authors.forename: Takayuki
authors.initials: T
authors.lastname: Hirai
keywords: Degussa (Evonik) P25; catalysis; imines; photocatalysis; titanium dioxide