Chinese Name: Polyphosphoric Acid Foreign Name: Polyphosphoric Acid Abbreviation: PPA Alias: Polyphosphoric Acid, Multiphosphoric Acid Molecular Formula: H?P?O?? Molecular Weight: 337.93 CAS Number: 8017-16-1 EINECS: 232-417-0 Boiling Point: 856°C Density: 2.1 Solubility: Miscible with water Properties: Colorless viscous liquid, hygroscopic. Uses: 1. Polyphosphoric acid (PPA) exhibits strong dehydrating properties, low nucleophilicity, and moderate acidity. Unlike sulfonic acids, PPA generally does not oxidize reactants and is soluble in organic solvents. Although its acidity is weaker than that of sulfonic acids, its dehydrating ability is comparable to 100% sulfonic acid, making it widely used in laboratories. 2. Catalyzing intramolecular cyclization reactions: PPA can catalyze intramolecular cyclization reactions of compounds such as carboxylic acids, esters, ketones, aldehydes, alcohols, alkenes, and hydrazones. For example, it is used in the synthesis of quinones under PPA catalysis. 3. Many quinoline and quinoline derivatives are synthesized under PPA catalysis. For instance, N-ethoxycarbonylethyl spirotetrahydroquinoline cyclizes in the presence of excess PPA with a yield of approximately 60%. 4. In organic synthesis, it is used as a cyclizing and acylating agent for compounds. It also serves as a substitute for orthophosphoric acid and as an analytical reagent.