S 2791 (OTTO) Sulphur powder, 99.98% Cas 7704-34-9 - used as a reagent to make the polymer rayon and many organosulfur compounds. S 2791 (OTTO) Sulphur powder, 99.98% Cas 7704-34-9 - used in pharmaceutical skin preparations for the treatment of acne and other conditions. It acts as a keratolytic agent and also kills bacteria, fungi, scabies mites, and other parasites.