Benzene

Benzene is a colorless, flammable liquid made of flat, six-sided molecules. Six carbon atoms form a ring, and each one holds a single hydrogen atom. The electrons in the ring's bonds are shared evenly all the way around, which makes benzene unusually stable. Michael Faraday first isolated it in 1825, and August Kekulé proposed the ring shape in 1865.

Nobody builds benzene atom by atom. Its carbon and hydrogen come from crude oil. In a refinery, a process called catalytic reforming reshapes the chain molecules in naphtha into rings over a platinum catalyst, releasing hydrogen. Benzene also comes out of the steam crackers that make ethylene, and from coal tar when coal is baked into coke. It is then separated from similar ring molecules by extraction and distillation.

Benzene is the ring at the heart of styrene, which leads to polystyrene and ABS. Joined with propylene, it becomes cumene, which splits into phenol and acetone. Benzene is a known carcinogen, so factories handle it in closed systems, and it's no longer used as an everyday solvent.