Phosphorus-Based Anionic Surface-Active Agents and Their Role in Agrochemical Formulations

Phosphorus-based anionic surfactants prepared by reacting an alcohol or an ethoxylate with tetraphosphoric acid (TPA) or with phosphorus pentoxide (P₂O₅) are complex in structure, yielding differing compositions of mono- and diprotic species of alkyl phosphates. When surfactants prepared from TPA-based product and P₂O₅-based product are compared, it is seen that whilst the free alcohol content is essentially the same, the monoester content has been considerably increased at the expense of the “diprotic” or polyphosphate species. The properties exhibited by these surface-active agents can be directly attributed to these structural differences and are particularly emphasized in the formulation of agrochemicals. Phosphates prepared using P₂O₅ can be of significant advantage in the formulation of emulsifiable concentrates and suspension concentrates where the influence of the diprotic species assists emulsion stability and dispersion rheology, whereas the TPA route is preferable in circumstances involving high electrolyte conditions such as fertilizer solutions.