Methods for preparing phosphonium salts by reacting a primary phosphine or a secondary phosphine with an ester compound selected from the group consisting of: a phosphate triester; a phosphonate diester; a sulfate diester; and a sulfonate ester; to form a phosphonium salt of formula VII wherein each of RQ, RX, RY, and RZ is independently hydrocarbyl and X− is a phosphate, phosphonate, sulfate, or sulfonate are provided herein. These phosphonium salts may find utility in a wide range of applications, including as surfactants, as polar solvents (ionic liquids), as antimicrobial agents, and as a component of spinning finish in polyamide fiber processing.