What is Methanethiol? Methylmercaptan, also known as methyl mercaptan, is a colorless gas with an extremely unpleasant odor often described as putrid or rotten cabbage. With the chemical formula CH4S, Methylmercaptan consists of a methane backbone bonded to a thiol functional group which gives this compound its unique smell. With a boiling point of only 4°C, Methylmercaptan exists as a gas...