Methyl Butyl Ketone. Also known as: 2-Hexanone. CAS Number: 591-78-6. A colorless liquid with a very pungent, acetone-like odor. It is a waste product of wood pulping, coal gasification, and oil shale operations. Was formerly used in paint, paint thinner, and other chemical substances, but its uses have been restricted and it is no longer made in the United States. Chemical formula = C4H9COCH3. Molecular weight = 100.16 g/mol.