Para Nitro Toulene Ortho Sulphonic Acid (PNTOSA) is an organic compound. Its chemical name is 4 Nitro Toluene 2 Sulfonic Acid or 1 Methil 4 Nitro Benzene 2 Sulphonic Acid. It is a crystal with a gray or brown color, and its empirical formula is C 7 H7NO5S. PNTOSA is acid used for intermediating dye stuff and the most common commercial name for this product is PNTOSA. If you use Para Nitro Toluene Ortho Sulphonic Acid, you should always keep it away from fire or high temperature because it is easily incendiary.