1-Hexene, 50 mmols or 7 wt.%, was hydroformylated with (1.77-0.77:1 by motes) H-2-CO in Et benzoate as solvent over 300 ppm Rh as a Rh(acac)(CO)(PPh3) catalyst at 2.0 MPa, 105-175 degrees C, and 10-50% of PPh3, At 105 degrees C and (1.13:1) H-2-CO, the selectivity toward aldehydes was max. at 93%. An Increase in H-2 partial pressure favored, and higher temps. disfavored, n-heptanal. The H-2/CO mote ratio was crucial within the (0.95-1.77):1 range. At the 1.13:1, 10% PPh3 and 175 degrees C, the conversion was max. At the 0.78:1, the selectivity fell from 140 degrees C onwards. The 1.13:1 H-2-CO, 105-120 degrees C and 10% PPh3 were optimum reaction parameters and the n-/iso-heptanal product ratio was 7. The liq. catalyst isolated from the reaction mixt. and recycled (4 times) into successive runs was as active as the fresh catalyst.