Calcium hypochlorite is an inorganic compound with chemical formula Ca(ClO)2, also written as Ca(OCl)2. It is a white solid, although commercial samples appear yellow. It strongly smells of chlorine, owing to its slow decomposition in moist air. This compound is relatively stable as a solid and solution and has greater available chlorine than sodium hypochlorite.[1] "Pure" samples have 99.2% active chlorine. Given common industrial purity, an active chlorine content of 65-70% is typical.[2] It is the main active ingredient of commercial products called bleaching powder, [a] used for water treatment and as a bleaching agent.[3] History Charles Tennant and Charles Macintosh developed an industrial process in the late 18th century for the manufacture of chloride of lime, patenting it in 1799.[4] Tennant's process is essentially still used today, [4][3] and became of military importance during World War I, because calcium hypochlorite was the active ingredient in trench disinfectant.[4] Uses Sanitation Calcium hypochlorite is commonly used to sanitize public swimming pools and disinfect drinking water. Generally the commercial substances are sold with a purity of 65% to 73% with other chemicals present, such as calcium chloride and calcium carbonate, resulting from the manufacturing process. In solution, calcium hypochlorite could be used as a general purpose sanitizer, [5] but due to calcium residue (making the water harder), sodium hypochlorite (bleach) is usually preferred. Organic chemistry Calcium hypochlorite is a general oxidizing agent and therefore finds some use in organic chemistry.[6] For instance the compound is used to cleave glycols, α-hydroxy carboxylic acids and keto acids to yield fragmented aldehydes or carboxylic acids.[7] Calcium hypochlorite can also be used in the haloform reaction to manufacture chloroform.[8] Calcium hypochlorite can be used to oxidize thiol and sulfide byproducts in organic synthesis and thereby reduce their odour and make them safe to dispose of.[9] The reagent used in organic chemistry is similar to the sanitizer at ~70% purity.[10]