The invention relates to a process for the synthesis of a Ziegler Natta procatalyst, the process comprising first treating magnesium alkoxide with a twice used mixed solvent of TiCl4 and chlorobenzene to form a first stage product, then treating the first stage product with a once used mixed solvent of TiCl4 and chlorobenzene to form a second stage product and finally treating the second stage product with mixed solvent recovered by treatment of effluent from the first treatment with benzoyl chloride so as to convert contaminant of formula TiCl3OR in the effluent to an addition complex which is precipitated, filtered off and hydrolyzed to recover ethyl benzoate and to form Ti(OH)4 as a side product, the product after final treatment being subjected to a plurality of successive washing steps with used as well as recovered hexane.