Acetaminophen is chemically known as N-(4-Hydroxyphenyl)acetamide and is marketed as paracetamol, a class of acet*anilide antipyretic analgesics. It was first synthesized by Morse in 1878 and first used clinically by VonMering in 1893. In the United States, it became an over-the-counter drug in 1955, and China began to produce Chemicalbook in the late 1950s. Its appearance is white crystalline or crystalline powder, melting point 168 ~ 172ºC, odorless, slightly bitter, easily soluble in hot water or ethanol, dissolved in ac*etone, almost insoluble in cold water and pe*troleum ether. It is stable below 45 ° C, but if it is exposed to humid air, it will hydrolyze into aminophenol, and then further oxidize, and the color gradually becomes pink, brown, and finally black, so it should be kept in a cold and dry place.