Process for alkoxycarbonylation of ethylenically unsaturated compounds using benzene-based diphosphine ligands and aluminium triflate

Process comprising the process steps of:

• a) initially charging an ethylenically unsaturated compound,
• b) adding a ligand of formula (I):
• where
• R1 and R3 are each a —(C3-C20)-heteroaryl radical,
• R2 and R4 are each —(C1-C12)-alkyl,
• and a compound comprising Pd;
• c) pretreating aluminium triflate at least twice by applying a vacuum to reduce pressure and the vacuum applied is broken by flooding with inert gas;
• d) adding the pretreated aluminium triflate from c) as a solution, where the ratio of aluminium triflate:ligand is in the range from 2.5 mol:1 mol to 15 mol:1 mol;
• e) adding an alcohol;
• f) feeding in CO;
• g) heating the reaction mixture from a) to f), with conversion of the ethylenically unsaturated compound to an ester.