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The promotional effect of low concentrations of water on the catalytic activity in the Co-catalysed methoxycarbonylation of oct-1-ene to straight and branched chain C 9 methylesters has been demonstrated. Under rigorously anhydrous conditions, only moderate octene conversions are noted. The controlled addition of water leads to enhanced octene conversions, by factors of up to 2.5, ester product selectivity remaining unchanged. Addition of dry pyridine to the anhydrous system results in the known promotional effects on both activity and selectivity towards linear esters. Further addition of water leads to enhanced oct-1-ene conversions, particularly at low pyridine loadings, whilst maintaining the improved product selectivity associated with the presence of pyridine. The role of water, which influences the rate as strongly as pyridine, has been attributed to increasing the effective concentration of HCo(CO) 4 , thereby enhancing the hydride mechanistic pathway for methoxycarbonylation. Certain amide/water compositions have also been found to result in significant promotional effects relative to the performance of standard Co-based catalysts. Thus, 4- and 3-amidopyridine ( iso -nicotinamide and nicotinamide, respectively) display enhancements in rate and selectivity approaching that of pyridine itself whereas, in total contrast, 2-amidopyridine (picolinamide) acts as an effective poison of both olefin isomerisation and methoxycarbonylation activity. |
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