isoprene

Isoprene, also known as 2-methyl-1,3-butadiene, is an unsaturated hydrocarbon with the formula C5H8 and the structural formula CH2=C(CH3)-CH=CH2. It is a colorless, highly volatile liquid at room temperature with a boiling point around 34°C. It is insoluble in water and miscible with many organic solvents. Isoprene polymerizes readily by free-radical mechanisms to give polyisoprene, the main constituent of natural rubber. Its cis- and trans-polyisoprenes have differing properties; natural rubber is predominantly cis-1,4-polyisoprene.

Occurrence and biosynthesis: Isoprene is emitted in large quantities by many plants, particularly tropical and subtropical trees, and contributes to the global atmospheric volatile organic compound burden. In plants, isoprene is produced in chloroplasts via the methylerythritol phosphate (MEP) pathway from DMAPP, and isoprene synthase catalyzes its formation. Minor anthropogenic sources include industrial processes and fossil fuel combustion.

Industrial use and production: Isoprene is a key monomer for synthetic rubber and various elastomers and specialty polymers. Most commercial isoprene is produced from fossil-fuel–derived feedstocks and is polymerized by addition polymerization to form polyisoprene. It can be copolymerized with other monomers to tailor material properties.

Safety and environment: Isoprene is highly flammable and poses health risks if inhaled; long-term exposure can cause respiratory irritation. In the atmosphere, it reacts with oxidants and contributes to ozone and secondary organic aerosols formation.