Polyphosphoric Acid–PPA

Physical characteristics:

Appearance: olorless viscous liquid, easy to deliquesce.

Polyphosphoric acid (PPA) has strong dehydration, low nucleophilicity and moderate acidity. Unlike sulfonic acid, polyphosphoric acid generally does not oxidize the reactants and is soluble in organic solvents. Although its acidity is weaker than sulfonic acid, its dehydration is equivalent to 100% sulfonic acid, so it is widely used in laboratories. .

Application of Polyphosphoric Acid:

Polyphosphoric acid is a protonic acid, which can dissolve a variety of low molecular and high molecular organic compounds. Used as a catalyst or solvent for condensation, cyclization, rearrangement, substitution and other reactions. Used as a compound cyclizing agent and acylating agent in organic synthesis. Also used as a substitute for orthophosphoric acid and analytical reagents.

Catalyze intramolecular cyclization reaction

Polyphosphoric acid can catalyze the intramolecular cyclization of carboxylic acid, ester, ketone, aldehyde, alcohol, alkene and hydrazone compounds, such as the synthesis of quinone (formula 1) under PPA catalysis. Many quinoline and quinoline derivatives are synthesized under PPA catalysis, such as N-ethoxyformylethyl spirotetrahydroquinoline cyclization under the catalysis of excess PPA, the yield is about 60%

Catalyze the intermolecular cyclization reaction

Polyphosphoric acid is generally used for intramolecular reactions, but it can also catalyze the intermolecular cyclization reaction. For example, the reaction of catalytic synthesis of thiophene and other substances and catalytic acylation reaction, the earliest application of PPA catalyzed acylation reaction is the reaction of cyclohexene and acetic acid. PPA can catalyze the reaction of a carbonyl group with a thiol to a sulfur heterocycle (Formula 3), and the reaction of phenylenediamine to form benzimidazole.

Catalytic molecular rearrangement and isomerization:

Polyphosphoric acid has the characteristics of low nucleophilicity, good solubility, moderate acidity and weak oxidizability. In addition to catalyzing cyclization reactions within or between molecules, it is also molecular rearrangement And isomerization efficient catalyst. For example, in the rearrangement of some amino acids (formula 4) and the Beckmann rearrangement of oxime (formula 5) , PPA acts as a catalyst.