In this paper, (1) alkaline methanolysis, (2) acid methanolysis, (3) alkaline hydro-lysis, (4) aminolysis of (+)-(R)-(R)-mixed anhydride 1 of O-ethyl phenylphosphonothioic:and O-ethyl O-phenylphosphorothioic acid, (5) its reactions with KSH and (6) with PCl_5have been studied. The cleavage of P-O-P bonds in all the reactions studied has beenfound. In reactions (1)-(4), attacks of nucleophiles occur to the phosphorus atoms of phos-phonyl groups forming the products with inversion of configuration, while the configurationof the phosphorus atoms of phosphoryl groups which are not attacked is retained. Inreaction (5), the uncleophile -SH attacks the phosphorus atom of the phosphonyl group,but a racemic product results because of the formation of ph(EtO)P(S)~- which loseschirality; the configuration of the phosphorus atom of the phosphoryl group which is notattacked is still retained. In reaction (6), both the phosphonyl and phosphoryl groups arechlorinated giving as products (-)-(R)-thiophophonyl chloride 1 (3) alkaline hydro-lysis, (4) aminolysis of (+) - (R) - (R) -mixed anhydride 1 of O-ethyl phenylphosphonothioic: The reactions with KSH and (6) with PCl_5have been studied. The cleavage of POP bonds in all the reactions studied has been washed. In reactions (1) - (4), attacks of nucleophiles occur to the phosphorus atoms of phos-phonyl groups forming the products with inversion of configuration, while the configuration of the phosphorus atoms of phosphoryl groups which are not attacked is retained. Inreaction (5), the uncleophile -SH attacks the phosphorus atom of the phosphonyl group, but a racemic product result because of the formation of ph (EtO) P (S) ~ - which loses chirality; the configuration of the phosphorus atom of the phosphoryl group which is notattacked is still retained. the phosphonyl and phosphoryl groups arechlorinated giving as products (-) - (R) -thioph ophonyl chloride 1