Methyl vinyl ketone, MVK, or vinyl methyl ketone (butenone, IUPAC), is a colorless liguid that is soluble in water. It is polar, with a specific gravity of 0.8636, which is lighter than water. It is flammable, with a flammable range of 2.1%-15.6% in air, and the vapor density is 24, which is heavier than air. Boiling point is 177°F(80°C), flash point is 20°F (-6°C), and ignition temperature is 915°F (490°C). MVK is a skin and eye irritant. The four-digit UN identification number is 1251. The NFPA 704 designation is health 4, flammability 3, and reactivity 2. The primary uses are as a monomer for vinyl resins and as an intermediate in steroid and vitamin A synthesis. The structure and molecular formula for MVK are shown in Figure 5.59.