A synthetic method for tetraalkylmonothiopyrophosphates has been worked out as follows:Tetraalkylmonothiopyrophosphates(2,R=C₂H₅,i-C₄H₉) were synthesized from the reaction of two moles of the corresponding dialkyl phosphonates with one mole of sulfur in carbon tetrachloride in the presence of excess triethylamine.The yields ranged from 65 to 80%.The method can be modified for the synthesis of unsymmetrical diethyl dialkyl monothiopyrophoshpates(6,R=alkyl=i-C₃H₇,i-C₄H₉,sec-C₄H₉).The reaction mechanism was briefly discussed.