Tear gas



Tear gas, formally known as a lachrymatory agent or lachrymator (from lacrima meaning "a tear" in Latin), is a non-lethal chemical weapon that stimulates the corneal nerves in the eyes to cause tearing, pain, and even blindness. Common lachrymators include OC, CS, CR, CN, nonivamide, bromoacetone, phenacyl bromide, xylyl bromide and syn-propanethial-S-oxide (from onions). Lacrymators often share the structural element Z=C-C-X, where Z indicates carbon or oxygen, and X indicates bromide or chloride.

Effects and use
Tear gas works by irritating mucous membranes in the eyes, nose, mouth and lungs, and causes crying, sneezing, coughing, difficulty breathing, pain in the eyes, temporary blindness, etc. Lachrymators are thought to act by attacking sulphydryl functional groups in enzymes. One of the most probable protein targets is the TRPA1 ion channel that is expressed in sensory nerves (trigeminal nerve) of the eyes, nose and mouth. First used in 1915, xylyl bromide was a popular tearing agent since it was easily brewed.

Lachrymatory agents are commonly used as riot control and chemical warfare agents. During World War I, more toxic lachrymatory agents were used. Certain lachrymatory agents are often used by police to force compliance, most notably tear gas. In some countries (e.g. Finland, Australia, and the United States), another issued substance is mace, which is used as a personal attack repellent.

Antidote
Because tear gas is not actually a gas but a very fine acid powder, its effectiveness can be easily mitigated by any over the counter anti acid drug commonly available at drugstores or pharmacy without prescription, like Sodium bicarbonate, Maalox or Alka-Seltzer to name a few.

Other use
Although lachrymatory agents are commonly used as riot control weapons, the most common use of some is in laboratory synthesis, where their lachrymatory properties are an undesirable side effect. Common examples include benzyl chloride, thionyl chloride, and acetic anhydride.