2-[(Di-methyl-phenyl-phosphanyl-idene)aza-nium-yl]-5-methyl-benzene-sulfonate benzene monosolvate.

The title compound, C15H18NO3PS·C6H6, is a rare example of a crystallographically characterized exocyclic phosphiniminium-arene-sulfonate zwitterion, which crystallises as its benzene solvate. The crystal structure shows that the N atom is protonated and that the iminium H atom forms both intra- and inter-molecular hydrogen bonds to the single-bonded sulfonate O atom in an R 2 (2)(4) graph-set motif. The dihedral angle between the aromatic rings in the main molecule is 89.49 (8)°.