Perchloric Acid and Its Salts: Very Powerful Catalysts in Organic Chemistry

The use of perchloric acid has evolved significantly in several applications such as esterification reactions, cationic polymerization, isomerization, and rearrangement. Metal perchlorates are powerful and selective catalysts that can usually be employed under mild reaction conditions, at relatively low temperatures, and several functional groups are generally well tolerated. The lithium and magnesium perchlorates are dangerous if heated over their decomposition temperatures (300-500 °C) in the presence of oxidizable materials or under highly acidic conditions. The introduction of the perchlorate salt is supposed to increase the acidity of the Lewis acid to promote the abstraction of the acetoxy group from the donor. Several rare earth perchlorates has been tested, and the use of 30 mol % of hydrated La(ClO4) 3, Ce(ClO4)3, or Pr(ClO4) 3, in the presence of K2CO3 has been found to be most effective.