Abstract: N-Acetyl-para-aminophenyl N'-acetylaminothioalkanoates I are new analgesic compounds with greatly reduced hepatotoxic effects, when taken in overdose, relative to N-acetyl-para-aminophenyl. They are prepared by reacting an N-acetylaminothioalkanoic acid IV with a reactive organic chloride V to form a mixed anhydride II and then reacting the latter with N-acetyl-para-aminophenol. The mixed anhydrides II are new and useful intermediates. Alternatively the derivatives I may be prepared by reacting the acid IV with bis-(4-nitrophenyl) sulfite to form a para-nitrophenyl N-acetylaminothioalkanoic acid ester VIII, reducing the latter to a para-aminophenyl N-acetylaminothioalkanoate VII, and acetylating this product. The esters VII and VIII are new and useful intermediates. Both reactions may pass through S-blocked intermediates, which are also new. Pharmaceutical compositions containing the derivatives I are disclosed, and also analgesic methods using them.