Polyphosphoric acid is a colorless, transparent and viscous liquid, which is corrosive and belongs to the second-class inorganic acid corrosive substance. Polyphosphoric acid is a kind of protonic acid, which can dissolve many low molecular and high molecular organic compounds. In organic synthesis, it is used as water loss agent, cyclizer, acylating agent, catalyst or solvent for condensation, cyclization, rearrangement, substitution and other reactions. Polyphosphoric acid esters (PPE) are sometimes used to increase the solubility of polyphosphate in organic solvents. In addition, polyphosphoric acid is also used as a substitute and analytical reagent for orthophosphate.