[en] This work is related to the synthesis of organophosphorus extracting agents used in purification of heavy metals such as uranium. The mono- and di (4-(1,1,3,3- tetramethylbutyl)) phenyl phosphoric acids, respectively MOPPA and DOPPA, are synthesizd by reaction of phosphorus pentoxid with 4(1,1,3,3-tetramethylbuthyl)) phenol. the separation of MOPPA from DOPPA is realised by liquid-liquid extraction. The Characterization, carried out by infrared uv-visible spectrophotometries, ph-metry and mass spectrometry, has confirmed the identity of the synthesized products. This study also showed that the products proportions are comporable to those of the homologous products obtained with 2-ethylbexanol in the same synthesis conditions