Quasi-magical acid is a superacid formed by the mixture of chlorosulfonic acid and antimony pentachloride. It is formed, like magic acid, by a coordination bond of the chlorine atom with antimony, in a Lewis acid-base reaction. It has less strength than magical acid, but greater than sulfuric acid, fluorosulfonic acid or chlorosulfonic acid alone. There have been very few studies on reactions with this superacid in organic compounds, but it is known that it also protonates hydrocarbons, although only tertiary, secondary and some that can form conjugated carbocations, such as benzyl. The acidity function of Hammett for this acid is 19.8, quite higher (in this scale) than fluorosulfonic acid, which is 15. The chemical species present in this acid are structurally similar to those in magical acid, only with chlorine atoms instead of fluorine.
wiki
