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Photocatalytic One-pot N-alkylation of Nitroaromatic Compounds Using Pt/TiO2

Amer Hakki ,  Ralf Dillert ,  Detlef Bahnemann 

Leibniz University Hannover, Institute of Technical Chemistry, Callinstrasse 3, Hannover 30167, Germany


N-alkylarylamines are important intermediates in the production of many compounds. However, traditional methods for secondary amine formation are often problematic because of harsh reaction conditions, generally poor yields, and/or low chemical selectivity.

We have employed photo-platinized TiO2 nano-sized particles as a photocatalyst for the one-pot synthesis of N-alkylarylamines from five nitro aromatic compounds (o, m-, p-nitrotoluene, 5-nitro-m-xylene, and p-nitrostyrene) and ethanol through the illumination of Ar-purged suspensions of this catalyst in ethanolic solutions containing the nitro aromatic compounds.

GC/MS analysis of the UV(A)-irradiated mixtures showed a gradual conversion of the nitro aromatic compounds to N-alkylarylamines during illumination time. The produced N-alkylarylamines can be further transferred by prolonged irradiation time into N,N-dialkylarylamines. The products were identified by comparing the molecular ion and mass fragmentation pattern with those reported in the GC/MS library and/or with those of the original compounds that have been synthesized by independent methods. The N-alkylarylamines have also been obtained when p-nitrotoluene react with other alcohols (n-propanol, n-butanol).

The reaction mechanism has been proposed, depending on the detected intermediates, as follows: (1) the nitro aromatic compound is reduced by the photogenerated electrons in the conduction band or with those which were trapped by the Pt deposits on the semiconductor┬┤s surface to an aromatic amine; (2) in the meantime the alcohol is dehydrogenated to an aldehyde consuming the photogenerated holes in the valance band of the illuminated TiO2; (3) the aromatic amine reacts with aldehyde to form a Schiff base; (4) the Schiff base is hydrogenated on the Pt nanoparticles loaded at the surface of TiO2 yielding N-alkylarylamine; (5) the latter react with the produced aldehyde forming N,N-dialkylarylamine.


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Presentation: Oral at E-MRS Fall Meeting 2008, Symposium D, by Amer Hakki
See On-line Journal of E-MRS Fall Meeting 2008

Submitted: 2008-05-30 12:42
Revised:   2009-06-07 00:48