[trī¦klȯr·ō′meth·əl ¦klȯr·ə′fȯr‚māt] (organic chemistry) ClCOOCCl3 A toxic, colorless liquid with a boiling point of 127-128°C; soluble in alcohol, ether, and benzene; used in organic synthesis, and as a military poison gas during World War I. Also known as diphosgene.