http://www.answers.com/topic/cs-gasCS or 2-chlorobenzalmalononitrile (chemical formula: C10H5ClN2) is a substance that is used as a riot control agent and is usually claimed to be non-lethal by the forces who use it. CS was discovered by two Americans, Ben Carson and Roger Staughton in 1928, the first letters of the scientists' surname giving us the name of the substance, 'CS'. It was developed and tested secretly at Porton Down in Wiltshire, England. Apparently this testing occurred in the 1950s and 1960s when CS was used firstly on animals, then subsequently on British Army servicemen volunteers. Notably CS has a limited effect on animals due to "under-developed tear-ducts and protection by fur".
Production
It is synthesized by the reaction of 2-chlorobenzaldehyde and malononitrile via the Knoevenagel condensation:
ClC6H4CHO + H2C(CN)2 → ClC6H4CHC(CN)2 + H2O
The reaction is catalysed with weak base like piperidine or pyridine. The production method has not changed since the substance has been discovered by B Carson and R Staughton. Other bases, solvent free methods and microwave promotion have been suggested to improve the production of the substance.
The physiological properties have been discovered already by the chemists first synthesising the compound in 1928: "Physiological Properties.-Certain of these dinitriles have the effect of sneeze and tear gases. They are harmless when wet but to handle the dry powder is disastrous. (sic)"
'CS Gas' - a misnomer
In common parlance CS is referred to as 'CS gas' or 'Tear gas', however this description is incorrect because 2-chlorobenzalmalononitrile is a solid at room temperature, not a gas. A variety of techniques have been used to make this solid usable as an airborne irritant. For example in Waco, Texas, CS was dispersed in droplet form. CS was dissolved in the organic solvent Methylene chloride (MC) and when this evaporated, the CS crystallized into fine particles.
It is worth noting that many types of tear gas have been produced with effects ranging from mild tearing of the eyes to immediate vomiting and prostration. CN and CS are the most widely used and known, but around 15 different types of tear gas have been tested worldwide. CS has become the most popular due to its strong effect and lack of toxicity in comparison with other similar chemical agents. The effect of CS on a person will depend on whether it is packaged as a solution, or if it is an aerosol; the size of solution droplets and the size of the CS particulates after evaporation, are factors determining its effect on the human body. Certain individuals however have been found to be particularly sensitive to CS and or the organic solvents that are utilised. Studies on the use of CS on the public have noted that it may be ineffective against persons who are either mentally ill or who are under the effects of alcohol.
Persons which had contact with CS sometimes develop allergic contact dermatitis, even with blisters and crust Studies show that most of the effects are of a relative short term, but individuals notice some mild effects even after months.