4-Piperidinecarboxylic acid, 4-((1-oxopropyl)phenylamino)-1-(2-(2-thienyl)ethyl)-, methyl ester, ethanedioate 73005-06-8 Methyl 4-((1-oxopropyl)phenylamino)-1-(2-(2-thienyl)ethyl)-4-piperidinecarboxylate ethanedioate Thiofentanil oxalate