<unk>  is an organosulfur compound used as a short-acting sulfa drug. It is an organic compound. Formerly,  it was a common oral and topical antimicrobial, until less toxic alternatives were discovered. It is still occasionally used, sometimes in combination with sulfabenzamide and sulfacetamide, and in aquariums.
It exists in various forms (polymorphs).  The imide tautomer is dominant, at least in the solid state.  In this tautomer, the proton resides on the ring nitrogen, not the structure shown above.
Sulfathiazole
Trichlormethiazide
Clomethiazole
Pyrazolone
Iproniazide
Ipriflavone
Tiazofurine
Ethambutol