Mustard Gas (bis(2-chloroethyl) sulfide) is a potent cytotoxic and vesicant chemical used as a weapon.

• Formula: $(ClC{H}_{2}C{H}_2{)}_{2}S$.
• Synthesis: Originally prepared from ethylene and sulfur dichloride.
• Properties: It is an oily liquid that causes severe blistering of the skin and mucous membranes upon contact. Its name comes from its mustard-like odor. It acts by alkylating DNA, which halts cell division and leads to cell death.