2-acetoxybenzoic acid 2-(acetyloxy)benzoic acid salicylic acid acetate acetylsalicylic acid aspirin C9H8O4 MW: 180.15 odorless crystals (6 polymorphs) pKa = 3.48 LD50 (mice) = 1.1 g/kg In 1950, Aspirin was listed in the Guinness Book of World Records as the best-selling pain-reliever in history.