Rodrigo Manoel da Silva Justo, Gustavo Fernandes Souza Andrade and Giovanni Wilson Amarante* Pages 209 - 216 ( 8 )
Background: In this work, we aimed to synthesize gold nanoparticles stabilized with Nacetyl- L-cysteine and study their catalytic activity towards the benzaldehyde oxidation as well as the formation of imines.
Methods: N-acetyl-L-cysteine stabilized gold nanoparticles were prepared and the catalyst was characterized via spectroscopic techniques such as UV-VIS spectrophotometry and SERS. Gold nanoparticles dimensions were evaluated through DLS and SEM. After having the catalytic system set, the oxidation of benzaldehyde and the one-pot reaction for the synthesis of imines were proceeded. All the products were characterized via NMR spectroscopy.
Results: Regarding the nanoparticles dimensions, a diameter of approximately 25 nm was achieved. Firstly, gold nanoparticles were effective towards the benzaldehyde oxidation, with a conversion of 97%. Furthermore, we investigated a one-pot formation of imines and it was noticed through NMR analysis a carboxylic acid as intermediate. Finally, a substrate scope with different aldehydes and amines was created and products were obtained with up 99%.
Conclusion: N-acetyl-L-cysteine modified gold nanoparticles are effective support-free catalyst for the chemoselective aldehyde oxidation/amine coupling to imine under mild conditions. Aromatic aldehydes were consumed to form benzoic acids and went under an amine coupling reaction giving a wide range of imines. This consists the first example in which there is a support-free catalyst capable of synthesize imines from aldehydes through carboxylic acids with good to excellent yields.
Gold nanoparticles, catalysis, imines, N-acetyl-L-cysteine, benzoic acid, benzaldehyde.
Chemistry Department, Federal University of Juiz de Fora, Juiz de Fora, Chemistry Department, Federal University of Juiz de Fora, Juiz de Fora, Chemistry Department, Federal University of Juiz de Fora, Juiz de Fora