Tear Gases

Name(s)	Structure	Molecular Formula	Chemical Abstracts Service Registry Number
CS, [(2-chlorophenyl)methylene]propanedinitrile, ( o-chlorobenzylidine)malononitrile, 2-chlorobenzalmalononitrile		C ₁₀H ₅ClN ₂	2698-41-1
CN, 2-chloro-1-phenylethanone, 2-chloroacetophenone, a-chloroacetophenone, phenacyl chloride, chloromethyl phenyl ketone		C ₈H ₇ClO	532-27-4
PS, trichloronitromethane, chloropicrin		CCl ₃NO ₂	76-06-2
BA, 1-bromo-2-propanone, bromoacetone		C ₃H ₅BrO	598-31-2
CA, a-bromobenzeneacetonitrile, a-bromophenylacetonitrile, bromobenzylcyanide		C ₈H ₆BrN	5798-79-8
CR, dibenz[ b,f][1,4]oxazepine		C ₁₃H ₉NO	257-07-8

Background and History

Tear gases are usually not lethal unless inhaled in large quantities, and affect people by inhalation and topical contact to mucus membranes and skin. General effects are tearing and sneezing; these agents can cause lung tissue damage and may lead to pulmonary edema (excess liquid in lung tissue). These complications may develop hours to a day after exposure.

Tear gases have been known since the middle of the 19 ^th century. Chloropicrin (PS) was first synthesized from picric acid (2,4,6-trinitrophenol) and calcium hypochlorite ("chloride of lime") in 1848, It was manufactured by this method during World War I, and used both as an irritant and as a lethal chemical during that conflict. Although its toxicity makes chloropicrin a poor riot control agent, it continues to be used as a soil sterilant, a grain disinfectant and an intermediate in synthesis, e.g., of methyl violet.

Although not widely appreciated, the use of tear gases predates the use of lethal chemical warfare agents. Several belligerents in World War I had been using munitions filled with irritants from almost the beginning of hostilities. Ethyl bromoacetate was used in August 1914, chloroacetone in November 1914, and mixtures of xylyl bromide, xylylene bromide, and benzyl bromide in January 1915. Bromobenzylcyanide (CA) was used by both the French and Americans towards the end of World War I. All these compounds are extreme irritants capable of severely limiting the effectiveness of unprotected troops.

During World War I, the tear gas a-chloroacetophenone (CN) was investigated in the United States, but production plants remained unfinished in November 1918. Police in many countries adopted CN, which works primarily as an eye irritant, as a riot control agent between World War I and World War II. During World War II, all belligerents manufactured CN in large quantities.

During the 1950s, one limitation of CN became apparent; determined demonstrators could avoid much of the effect of CN by closing their eyes. o-Chlorobenzylidine malononitrile (CS) was adopted as a CN replacement when it was found to have wider ranging effects. CS tear gas takes effect almost immediately, causing severe burning and involuntary closing of the eyes, copious tearing, extreme burning in the nose, a tendency to breathe through the mouth, extreme burning in the throat, and coughing. In some cases there can be nausea and vomiting. CS also causes a burning sensation on exposed parts of the body. A desirable feature of CS as a riot control agent is that recovery quickly follows when the affected person is no longer exposed to CS; fresh air is a rapid antidote.

CS and CN are both solid materials that are used in riot control as pyrotechnics; a burning pyrotechnic candle disperses a solid aerosol of the agent. Alternatively, as a liquid solution of CN or CS can be dispersed aerosol spray in products such as MACE™. In this application, a 1 percent (CN) to 2 percent (CS) solution in an inert solvent is sprayed through an aerosol nozzle.

Additional toxicity and physical data for CS and CN can be found at the NTP CHEMICAL REPOSITORY:

Physical Properties

The physical properties of CS, CN, and PS are given in the first part of the table; properties of BA, CA, and CR are provided in the second part.

CS

CN

PS

Description
White crystalline solid

White to light yellow powder

Slightly oily liquid with intense odor

Molecular weight
188.62

154.60

164.37

Melting point (ÜC)
95-96

58-59; 54; 56.5

-64; -69.2

Boiling point (ÜC)
310-315

244-245

112

Vapor pressure at 20ÜC (mm Hg)
3.4x10 ^-5

5.4x10 ^-3

16.91

Water solubility (g/L)
1-5 at 16ÜC

<1 at 19ÜC

2.272 at 0ÜC; 1.621 at 25ÜC

Solubility in organic solvents
acetone, dioxane, methylene chloride, ethyl acetate, benzene

alcohol, ether, carbon disulfide, benzene

benzene, ethanol, carbon disulfide, ether

Threshold limit (mg L ^Ç1)
—

3x10 ^-4

1.4x10 ^-2

Concentration in air at 20ÉC
(mg L ^-1)
—

0.105

184

BA

CA

CR

Description
yellowish-brown liquid with a penetrating odor

whitish-yellow crystalline mass, with the odor of sour fruit

a pale yellow crystalline solid with a pepper-like odor

Molecular weight
136.98

196.05

195.22

Melting point (ÜC)
-54; -36.5

25.4; 29

73

Boiling point (ÜC)
136; 137

242

—

Vapor pressure at 20ÜC (mm Hg)
9

0.012

—

Water solubility (g/L)
sparingly soluble

"practically insoluble"

limited solubility

Solubility in organic solvents
alcohol, acetone

alcohol, ether, chloroform, acetone, benzene, glacial acetic acid

—

Threshold limit (mg L ^Ç1)
0.001

1.5 x10 ^-4

—

Concentration in air at 20ÉC
(mg L ^-1)
75

CA

—

Methods for Decontamination

Methods for treatment of persons exposed to modern tear gases a can be found online at the Medical NBC Information Server in Chapter 7 of FM 8-9 the Handbook on the Medical Aspects of NBC Defensive Operations, Part III-Chemical.

Spill procedures for CS and CN can be found at the NOAA CAMEO web site:

References

Tear Gases

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