Mustard gas

Mustard gas (HD) is a chemical compound that was first used as a chemical weapon in World War I. In pure form, it is a colorless, odorless, viscous liquid at room temperature and causes blistering of the skin. The name comes from impure mustard gas, which is usually yellow-brown in color and has an odor resembling mustard, garlic or horseradish. It is otherwise not related to mustard in any way.

Chemistry

Chemically, it is a thioether with the formula C4H8Cl2S. Its structure can be described as 1,1-thio-bis-, (ClCH2CH2)2S, 2,2′-dichlorodiethyl sulfide or bis-(2-chloroethyl)-sulfide. Mustard gas can be synthesized by reacting sulfur dichloride (SCl2) with two moles of ethylene (C2H4).

Related Topics:
Thioether - C - H - Cl - S

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Although the compound is commonly known as "mustard gas", it is a viscous liquid at normal temperatures. The pure compound has a melting point of 14°C (57°F) and decomposes before boiling at 218°C (423°F).

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The compound readily eliminates chloride ion by intramolecular nucleophilic substitution to form a cyclic sulfonium ion. This very reactive intermediate is particularly detrimental to cellular health as it has a strong tendency to bond to the guanine nitrogen in DNA strands. This leads to either immediate cellular death or, as recent research has found, cancer. Mustard gas is not very soluble in water but is very soluble in fat, contributing to its rapid absorption into the skin.

Related Topics:
Guanine - DNA - Cancer

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In the wider sense, compounds with the structural element BCH2CH2X, where X is any leaving group and B is a Lewis base are known as mustards. Such compounds can form cyclic onium ions that readily react with nucleophiles. Examples are bis-(2-chloroethyl)ether or the (2-haloethyl)amines.

Related Topics:
Leaving group - Lewis base - Nucleophile

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