Top: Chlorine gas in an ampoule (M. Oelen/Wikimedia Commons). Bottom: Salt mounds at Morton Salt, Newark, Calif. (Oleg Alexandrov/Wikimedia Commons).
As an anion, chlorine is rather ordinary. Sodium grabs all the press from NaCl as the dietary culprit in hypertension, while silver’s the key to AgCl’s action in photography. Arguably, chloride plays a more important role in the antitumor drug cisplatin, Pt(NH3)2Cl2, although its function there is to get lost (that is, hydrolyze) so that platinum has room to bind to DNA. Sadly the -1 oxidation state of chlorine is often glossed over as the necessary counterion to an exotic metal ion or complex cation, the necessary yin to complement the yang.
Conversely molecular chlorine, Cl2, has held a starring role in history, both for its benefits to human health and for its detrimental effects on the environment. Carl Wilhem Scheele, a Swedish pharmacist, first described the greenish yellow gas in 1774 after dropping hydrochloric acid onto manganese dioxide. Sir Humphry Davy recognized the gas as an element in 1810 and named it based on the Greek word for its color, khloros.
Chlorine was by this time already in use. In the small town of Javelle, France, chlorine added to alkaline water created Veau Javelle (“bleach” in English, NaOCl in chemspeak) that was used in the fabric industry in the late-18th century.
The mid-19th century saw one of the most dramatic improvements in human health: Bleach began to be used as a disinfectant in hospitals, and chlorination of the water supply in London during a cholera outbreak in 1850 saved many lives. Chlorine continues to be the disinfectant of choice in the food industry, in swimming pools, and in the drinking water supply in most developed countries.
It’s Elemental: Chlorine
Chemical & Engineering News, September 8, 2003