Pyridinium p-toluenesulfonate (PPTS) is an organic salt formed from pyridine and p-toluenesulfonic acid. It is a white to off-white crystalline solid with the CAS number 24057-28-1. It is known for its mild acidity and is soluble in polar organic solvents. PPTS is a versatile and mild acid catalyst widely used in organic synthesis. Its primary application is as a highly effective and selective reagent for the deprotection of tetrahydropyranyl (THP) ethers to regenerate alcohols under mild conditions. It is also employed in other acid-catalyzed transformations, such as the cleavage of acetals, ketals, and silyl ethers, where its mild nature minimizes side reactions like rearrangements or eliminations. It serves as a convenient, non-hygroscopic, and easy-to-handle alternative to p-toluenesulfonic acid (TsOH) in many reactions. Due to its specific reactivity profile, PPTS is a staple reagent in synthetic chemistry laboratories, particularly in multistep synthesis for the protection and deprotection of functional groups. It is valued for its operational simplicity and high selectivity.