Most common mineral acids solutions (HCl, H2SO4, HNO3, H3PO4, etc.) are prepared in water. Infact, system is acidic only in aqueous medium.
However, in few cases, it isn't advisable/viable to perform reaction is aqueous medium. This can be due to poor solubility of reactant in water. This situation arises especially, if reactant is highly non-polar in nature.
There also exist a possibility that, reactant is not stable in aqueous medium. In such event, use of water has to be avoided.
For such reaction, solid camphorsulfonic acid is added in reaction, when acid is required to initiate/catalyst the reaction.
The major advantage that camphorsulfonic acid offers is that, it is solid and hence it is easy to weight. Also, they don't required water addition for the reaction.
