Synthesis of Long‐Chain n‐Alkylphosphonic Acids by Phosphonylation of Alkyl Bromides with Red Phosphorus and Superbase under Micellar/Phase Transfer Catalysis

Abstract Long‐chain n ‐Alkylphosphonic acids, AlkP(O)(OH) 2 , are synthesized in up to 91 % yield (mostly 40–60 %) by straightforward phosphonylation of alkyl bromides (AlkBr, Alk=C 4 –C 18 ) with red phosphorus (P n ) in the multiphase KOH/H 2 O/toluene system in the presence of 2–10 mol % of cetyltrimethylammonium bromide (CTAB), acting as a micellar/phase transfer catalyst and as a generator/transporter of superbasic hydroxide anions, the intermediate potassium phosphinates being in situ oxidized/neutralized by nitric acid. The key steps of the phosphonylation mechanism are the P−P bond cleavage of P n polymeric molecules by superbasic − OH anions, dissolved in the CTAB micelles, and phase transfer of polyphosphide anions to the organic phase and their alkylation with AlkBr.