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Camphorsulfonic acid, sometimes abbreviated CSA or 10-CSA is an organosulfur compound. Like typical sulfonic acids, it is a relatively strong acid that is a colorless solid at room temperature and is soluble in water and a wide variety of organic substances.
This compound is commercially available. It can be prepared by sulfonation of camphor with sulfuric acid and acetic anhydride:
Although this reaction appears to be a sulfonation of an unactivated methyl group, the actual mechanism is believed to involve a retro-semipinacol rearrangement, deprotonation next to the tertiary carbocation to form an alkene, sulfonation of the alkene intermediate, and finally, semipinacol rearrangement to re-establish the ketone function.
In organic synthesis, CSA and its derivatives can be used as resolving agents for chiral amines and other cations. The synthesis of osanetant was an example of this. 3-bromocamphor-8-sulfonic acid was used in the synthesis of enantiopure devazepide.