acetanilides

Acetanilides are a class of chemical compounds defined by the amide structure N-phenylacetamide. In this family the amide nitrogen is bound to a phenyl ring (Ar-NH-CO-CH3), and many derivatives carry substituents on the aryl ring. The core compound is acetanilide itself, with various substitutions giving a range of analogues.

Preparation and properties: Acetanilides are typically prepared by acetylation of aniline with acetyl chloride or acetic anhydride. They are usually white crystalline solids with limited water solubility and melting points in the general range of 110–125 °C, depending on substitutions. The amide nitrogen is not strongly basic, reflecting amide chemistry, and the compounds tend to be more soluble in organic solvents than in water.

History and uses: In the late 19th and early 20th centuries, acetanilide and several of its derivatives were used as analgesics and antipyretics. Acetanilide itself was later withdrawn in many markets due to safety concerns, notably the risk of methemoglobinemia associated with some metabolites. Some acetanilide derivatives have been investigated as pharmaceuticals or synthetic intermediates. Parallels exist with related acetylated aniline derivatives, such as acetaminophen, which is structurally related but prepared via different routes and used as a widely used analgesic and antipyretic.

Safety and notes: Because of potential hematologic toxicity, acetanilides are viewed with caution and are largely of historical or synthetic interest today. They are primarily discussed in the context of amidide chemistry and as substrates in organic synthesis rather than as current medicines.