| Popis: |
The effect of the carboxylic acids RCO 2 H (RC 2 H 5 , C 6 H 5 , m -ClC 6 H 4 , p -NO 2 C 6 H 4 and o -HOC 6 H 4 ) on the hydroformylation of hex-1-ene catalysed by Rh(acac) (CO) (PPh 3 ) ( 1 ) have been studied. The decrease of the rate of hydroformylation compared with a carboxylic acid-free system was observed. The inhibiting influence of carboxylic acids is stronger in reactions proceeding in the presence of free phosphine ( e.g. ( 1 )/[RCO 2 H+PPh 3 ]) where not only the reaction rate, but also hex-1-ene conversion decrease. The inhibiting effect of carboxylic acids may be explained by partial elimination of catalytically active forms of the general formula HRh(CO) x (PPh 3 ) y by the reaction of HRh(CO) x (PPh 3 ) y in the presence of RCO 2 H/PPh 3 and H 2 /CO to give Rh(RCO 2 ) (CO) (PPh 3 ) 2 . The equilibrium of this reaction depends mainly on the concentrations of the H + ions and that of free phosphine. Several new rhodium complexes were formed in the reaction of ( 1 ) with RCO 2 H, e.g. , [Rh(RCO 2 ) (CO) (PPh 3 )] 2 , [Rh(RCO 2 ) (CO) 2 (PPh 3 )], [Rh(RCO 2 ) (CO) (PPh 3 ) 2 ], [Rh(RCO 2 ) (CO) 2 ] 2 , have been isolated and used as hydroformylation reaction catalysts. The structures of Rh(acac) (HOC 6 H 4 CO 2 ) 2 (PPh 3 ) (H 2 O) and [Rh(HOC 6 H 4 CO 2 ) (COD)] 2 have been determined by X-ray diffraction studies. |
