Patent ID: 7250538

Claim:
A process for the hydroformylation of an optionally substituted ethylenically unsaturated compound by reaction thereof with carbon monoxide and hydrogen in the presence of a catalyst system comprising: (a) a source of Group VIII metal cations; (b) a diphosphine ligand having the general formula (I): X 1 —R—X 2 (I) wherein X 1 and X 2 each independently represent an optionally substituted cyclic group with at least 5 ring atoms, of which one is a phosphorus atom, and R represents a bivalent optionally substituted cycloalkene bridging group which is connected to each phosphorus atom by a sp 2 hybridized carbon atom; (c) an acid having a pK a <3, measured in an aqueous solution at 18° C., or a salt derived therefrom; and (d) a source of halide anions.