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多聚磷酸(Polyphosphoric Acid,簡称PPA)是有机合成中近幾年來發現的新的試剂,在分子內閉环缩合上,有特殊的优點。早在1938年Koebner及Robinson二氏用磷酸与五氧化二磷的混合物为分子內閉环縮合
Polyphosphoric Acid (PPA) is a new reagent found in organic synthesis in recent years. It has special advantages in the intramolecular ring closure. As early as 1938 Koebner and Robinson two with phosphoric acid and phosphorus pentoxide mixture for the closed-loop intramolecular condensation