from first principles PP-I-1

OY-III-4Carbonylation of Dimethyl Ether on Rh/Cs 2 HPW 12 O 40 :Mechanism of the Reaction in the Presence of Methyl Iodide PromoterKazantsev M.S. 1 , Luzgin M.V. 1,2 , Volkova G.G. 1 , Stepanov A.G. 1,21 Boreskov Institute of Catalysis SB RAS, Novosibirsk, Russia2 Department of Natural Sciences, Novosibirsk State University, Novosibirsk, Russiakazantsev@catalysis.ruCarbonylation of methanol and dimethyl ether (DME) is considered to be the main way toproduce acetic acid and methyl acetate at industrial level. In recent years, the Rh–containingcesium salts of tungstophosphoric heteropoly acid (HPA) have been shown to be effectiveheterogeneous catalysts for halide-free carbonylation of dimetyl ether to methyl acetate [1].We have demonstrated recently that Rh/Cs 2 HPW 12 O 40 works as a bi-functional catalyst,where the activation of DME and CO occurs at different surface centers, Brønsted acid sitesof HPA and rhodium. The interaction between reaction intermediates, Rh-carbonyl andmethoxy-group, gives surface acetate, the immediate precursor of methyl acetate [2].In this paper we report that the use of methyl iodide promoter leads to a noticeableacceleration of the DME carbonylation on Rh/Cs 2 HPW 12 O 40 by opening a new reactionpathway. Using 13 C solid-state NMR, the main peculiarities of the reaction mechanism havebeen established. Methyl iodide forms rhodium-methyl intermediate, Rh-CH 3 . Carbonmonoxide, existing on the surface of Rh/HPA as rhodium carbonyls, is embedded intoRh-CH 3 bond, Rh-acetyl being produced. Then the migration of acetyl group from rhodium toBrønsted acid site of HPA results in the formation of surface acetate group and hydrogeniodide. The acetate reacts with DME molecule producing target product, methyl acetate.Dimethyl ether is activated at Brønsted acid sites of HPA with the formation of surfacemethoxy-group, from which reactive methyl iodide is restored through the interaction withHI. The latter process provides the involvement of DME into the catalytic cycle. All thestages described above occur at 100 °C, thus providing the decrease of the temperaturerequired for the carbonylation in comparison with halide-free system ( 150 °C).Acknowledgements: This work was supported in part by Zamaraev International CharitableScientific Foundation.References:[1] G.G. Volkova, L.M. Plyasova, A.N. Salanov, G.N. Kustova, T.M. Yurieva, V.A. Likholobov,Catal. Lett. 80 (2002) 3.[2] M.V. Luzgin, M.S. Kazantsev, G.G. Volkova, W. Wang, A.G. Stepanov, J. Catal. 277 (2011) 72.97