PROCESS FOR THE ALKOXYCARBONYLATION OF OLEFINS IN A MEDIUM HAVING A LOW BRNSTED ACID CONCENTRATION

Process comprising the following process steps: a) Introducing an ethylenically unsaturated compound; b) adding a ligand-metal complex comprising Pd and a bidentate phosphine ligand, or adding a bidentate phosphine ligand and a compound which comprises Pd; c) adding an alcohol; d) supplying CO; e) heating the reaction mixture, the ethylenically unsaturated compound being reacted to form an ester, where the reaction mixture is admixed with less than 0.1 mol%, based on the amount of substance of the ethylenically unsaturated compound, of Br?nsted acids having an acid strength of pKa ? 3, characterized in that the phosphine ligand is substituted on at least one phosphorus atom by at least one heteroaryl radical.