Terephthaloyl chloride

Terephthaloyl chloride (TCL, 1,4-benzenedicarbonyl chloride) is the acid chloride of terephthalic acid and is one of two monomers used to make Kevlar, the other being p-phenylenediamine, which is also used in some hair sprays. Its CAS reference number is 100-20-9 and its chemical formula is 8422.

TCL is used as a key component in performance polymers and aramid fibers, where it imparts flame resistance, chemical resistance, temperature stability, light weight, and very high strength. TCL is also an effective water scavenger, used to stabilize isocyanates and urethane prepolymers.

TCL is a clear, water-white liquid above its freezing point and a white crystalline solid at room temperature, soluble in organic solvents. Its melting point is 81.5-83 °C, its boiling point is 265 °C. It is corrosive.

TCL is used for making various copolymers and aramid polymers such as Twaron and kevlar: