Benzenesulfonic acid, from benzene preparation

It then appears analogous to benzenesulfonic acid (as methylcarbonic acid). The remarkable preparation of propionic acid by action of carbon dioxide on cthylsodium, which has very recently been discovered by WanMyn, can then be understood in the same way as the formation of benzenesulfonic acid from benzene and sulfuric acid anhydride. 

The benzylideneanilines of Table IX are prepared by refluxing a mixture of 0.010 mole each of the appropriate para-substituted benzaldehyde and aniline in 150 ml of benzene containing 0.1 gm of benzenesulfonic acid for 2-4 hr. A Dean-Stark trap is used to collect the water and then the solvent is removed under reduced pressure. The residue is recrystallized from hexane or other... 

In Summary Nitration of benzene requires the generation of the nitronium ion, N02, which functions as the active electrophile. The nitronium ion is formed by the loss of water from protonated nitric acid. Sulfonation is achieved with fuming sulfuric acid, in which sulfur trioxide, SO3, is the electrophile. Sulfonation is reversed by hot aqueous acid. Benzenesulfonic acids are used in the preparation of detergents, dyes, compounds containing leaving groups, and sulfa drugs. 

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