We don't have synonyms for urethans yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are urethane, urethan and urethanes.
(n) :
Alternative form of urethane. [(organic chemistry, uncountable) A white crystalline organic compound, ethyl-carbamate, NH₂COOC₂H₅, used in the synthesis of other organic compounds.]
(n) :
Alternative form of urethane. [(organic chemistry, uncountable) A white crystalline organic compound, ethyl-carbamate, NH₂COOC₂H₅, used in the synthesis of other organic compounds.]