An improved process is provided for the recovery of catalyst components from oligomeric impurities which are formed during the industrial preparation of 2,5-dihydrofuran by the catalytic isomerization of vinyl oxirane followed by an essential separation of the oligomeric by-products which otherwise cause deactivation of the catalyst. The catalyst components consist essentially of (a) an onium iodide and (b) a Lewis acid selected from the group consisting of the chloride, bromide or iodide of the metals zinc, tin, cobalt and bismuth, preferably zinc, where the catalyst optionally includes a donor ligand. This separation is carried out by the steps of extracting the initial product mixture containing zinc, cobalt or bismuth halides as Lewis acids with hydrocarbons or chlorinated hydrocarbons containing from 5 to 14 carbon atoms in order to form two separate phases on standing, separating off the extraction solvent phase which contains the dissolved catalyst and then recovering the separated catalyst by distilling off the extraction solvent. The recovery of tin iodide requires the presence of a special onium halide component such as phosphazenium or phosphazanium halides, preferably the iodides, having a high molecular weight and especially those which contain from 16 to 72 carbon atoms while remaining soluble in the extracting agent.