Tear gas was never something I ever imagined encountering. I’m neither an active protester nor a mischievous rebel who might come in contact with this chemical that acts as a “pacifying” crowd control, yet I still experienced its forceful grasp on my sensory system. Several years ago, my brother completed boot camp on Parris Island and was officially recognized as a United States marine. While touring the island, my brother pointed out an intimidating building with no windows and large steel doors. He told me and my sister that this was where they exposed the marine recruits to CS Gas, chemical name of 2-chlorobenzalmalonitrile (figure 1),
in an attempt to train them on the proper use of gas masks and to provide exposure to the chemical prior to their deployment. I’ve always had an impulse of curiosity mixed with bad decision making. This curiosity drove me to go inside with my sister to see what it would have been like. Even though the chamber had not been used in weeks, I felt a stinging sensation as soon as I first inhaled immediately. As I exhaled, my eyes burned and I began coughing furiously. Finding my way out, I could only wonder how my brother could last a full 5 minutes in that chamber. This experience is akin to drowning, only the substance is transmittable in the air.
As a weird twist of fate would have it, my brother was recently hired assembling tear gas canisters. I asked him about this chemical, for not even tear gas could deter my curiosity, and he explained the process of making it into an aerosol and about the CS gas component. This sparked my interest so I did some more research and I found some interesting chemistry. Tear gas is a term given to a varied group of chemical agents that act as riot deterrents and crowd disruptors. Commonly used by law enforcement, military, and paramilitary, tear gas is a chemical weapon, also referred to as a lachrymatory agent (from lain lacrima, meaning “tear”), that causes severe eye, respiratory, and skin irritation. Many have seen this chemical in Media footage of aggressive protests, however, tear gas is actually a misnomer for there are several different kinds of tear gas that range from being relatively innocuous (if you can call any chemical weapon harmless) to a severe health risk. A common misconception is that tear gas, as the name implies, is a gas, where in actuality it is usually an aerosol. Aerosols are a colloidal suspension of particles dispersed in air or gas. This simply means that individual solid particles of these substances are dispersed through the air that simulate a gaseous expansion. Dust and fog are examples of colloidal suspensions. Because CS gas is in fact a powder, it does not make much of a deterrent, unless one has a shovel. In order to create a better dispersal mechanism, the compound is made into an aerosol.
The most common form of tear gas is CS which contains the chemical listed above. Another type of tear gas is CN (Chloracetophenone) which is commonly referred to as “mace”. CN was created by Allan Litman in 1965. CN, also called Phenacyl chloride, is made using Friedel-Crafts acylation of benzene (figure 2).
This reaction substitutes a carbonyl halide on a benzene. This reaction is called an electrophilic aromatic substitution reaction. Phenacyl chloride is more toxic then CS and can cause permanent eye damage. CR (Dibenzoxazepine) is also severely toxic and has widely been replaced by less harmful agents such as CS gas. OC and PAVA (tediously long names) known as “pepper spray” are also used. OC is a capsaicinoid derived from chili peppers (figure 3). PAVA is a synthetic capsaicinoid. Due to the toxicity of CR and CN, CS is the most widely used tear gas used in crowd control while OC and PAVA are used in personal defense.
CS was developed at Middlebury College by Ben Corson and Roger Stoughton. CS is a cyanocarbon with two cyanide groups attached to a chlorobenzene. CS is highly reactive due to the nitrile groups (cyanide groups) that attacks pain receptors. The gas irritates the mucous membranes of the eyes, nose, throat, and stomach causing most of the symptoms associated with its exposure. In general, the effects of CS gas are temporary; however, those suffering from asthma or other respiratory illnesses can have extended problems after contact with the gas. The gas can be lethal to individuals suffering from asthma that are exposed in certain circumstances. There have even been cases where improper firing of the canisters have led to facial injury and death. CS and OC are the most commonly used crowd control agents used today. Tear gas is highly effective at disrupting riots, but there remains controversy. There are some who argue that these weapons should be banned. The Omega Research Foundation states “less-lethal weapons are presented as more acceptable alternatives to guns. But these weapons augment rather than replace the more lethal weapons.” Regardless on one’s stand, these chemical weapons are dangerous and should be respected as such. My first-hand account gave me a perspective on the potential lethality of substances that are incomprehensibly small.
Layman Chemistry 