Chlorine is a halogen (along with fluorine, bromine, iodine, astatine): highly reactive, never found in nature except in compounds, which halogens can form with all metal elements and most non-metals.
As Bayer puts it, "Chlorine is an important basic substance in the chemical industry and is absolutely indispensable in the manufacture of plastics and medicines...", and it's also a major component of public health infrastructure, via water purification. I've recently read Steven Johnson's How We Got To Now: Six Innovations That Made The Modern World, which includes the story of John Leal's introduction of chloride of lime (Ca(ClO)2) into the Jersey City reservoir in 1908 (the first [American] chlorination of a public water supply)... and I have explored CFCs and organochloride pesticides in other connections, and lately I've been thinking about the inevitability of unanticipated consequences in technological evolution.
It didn't take much Google exploration to find a Chlorine Product Tree which summarizes industrial pathways for chlorine (see also The Element of Surprise for a simpler presentation). I'd like to find a chronological treatment of the 20th century development of chlorine chemistry to augment the Product Tree.
I generally seek summaries of technological history when I'm exploring a topic, and was delighted to find Robert Baldwin's "History of the Chlorine Industry" (Journal of Chemical Education, 1927), from which I gleaned the utterly serendipitous facts that (1) the Canadian product Javex (called Clorox in the US) was named after Berthollet's work with bleach (eau de Javel in French) on the Quai de Javelle in Paris, 1789 (a year fraught with other things in Paris...), and (2) that the first American commercial production of liquid chlorine by electrolysis was at Rumford Falls ME in 1909 (or perhaps 1892 or 1893), for bleaching in the paper industry. Electrolysis of NaCl brine remains the primary method of chlorine production, worldwide; a mercury-cell process has been a significant source of environmental contamination.
Inorganic mercury can be metabolized to highly toxic methyl-mercury (CH3)2Hg by anaerobic bacteria and this substance is bio-accumulated in the marine food chain. (Ayres 1996:6) [Japan's Minamata incident is the most famous instance, and involved acetaldehyde production, not chlorine, but led directly to the decline in mercury cell use in chlorine production]...and there's a photographic history connection: Fox-Talbot's 1835 experiments used AgCl.
The Germans first used chlorine gas as a weapon in WW I on 22 April 1915, at the start of the Second Battle of Ypres. The British retaliated at Loos on 24 September 1915, but a change of wind brought the gas back over British lines. Phosgene (also a chlorine product, COCl2) proved to be a more tractable weapon, and mustard gas (C4H8Cl2S) was even more effective. The still more fearsome Lewisite (C2H2AsCl3) was developed but not deployed in WW I.
SO: paper and textile bleaching, water purification, warfare... The final sentence of Baldwin 1927: "Chlorine is indispensable today, and the measure of its use is an index of the comparative civilization of a country."
[a section here on the interwar history of chlorocarbon development]
After WW I, surplus production of chlorine provoked a hunt for possible uses ("important means of upgrading the value of industrial chlorine") . A glance at this 1914 summary of chlorine production is instructive, and the tale of chlorocarbon chemistry unreels through the 1920s and 1930s with the development of a host of synthetic (i.e., manmade, not naturally occurring) creations, to the point of ubiquity. Extracts from Gramse and Diamond 1968:
There is hardly a consumer product that has not required chlorine and/or alkalai at some stage of its manufacture (1)... the use of chlorine in producing organic chemicals constitutes the largest single end-use category for chlorine. Production of C1 and C2 chlorinated hydrocarbons accounts for the largest proportion of chlorine consumption. (4)1,2-Dichloroethane (ethylene dichloride) [is] the largest volume chlorinated organic [and] ...most goes into the manufacture of vinyl chloride ...used for making polymers and copolymers for films, fibers, foams, rubbers, etc.
...Substantial quantities of chlorine are consumed in the manufacture of non-chlorine containing end products such as alcohols and glycols... (5)
...widely used chlorine-containing insecticides include: chlordan, aldrin, dieldrin, toxaphene... (6)
Ayres:
Chlorinated hydrocarbon solvents have been employed widely since the 1920s. They were crucial at the beginning of the century as rapid industrialization prompted the need for fast and effective non-fllammable solvents... carbon tetrachloride and chloroform... most extensively used chlorinated solvents today are methylene (di)chloride CH2Cl2, perchloroethylene (PERC, tetrachloroethylene), trichloroethylene (TRI, TCE)... (III:4)\\CFCs banned from production in 1996 (Montreal Protocol); 1,1,1 trichloroethane [methyl chloroform] too, as greenhouse gas?\\
By 2006, major uses of chlorine in the US were
manufacturing of vinyl chloride to make PVC plastics (36%), manufacturing of other organic compounds (41%), manufacturing of inorganic chemicals (15%), water treatment (4%), and pulp and paper bleaching (1%)There was one producer in Maine: Holtra-Chem in Orrington, which supplied chlorine to the pulp and paper industry using the mercury cell process, and dumped 6-12 tons of Hg into the lower Penobscot... The plant was opened in 1967 and closed in 2000 (see 2008 Compliance Order for details).Dow Chemical produced about 30% of the total (Freeport TX, Plaquemine LA); between them, TX and LA produced more than 2/3 of the total (mostly because of ready access to brine, a major input). [Chlorinetoxological.pdf]
Unintended consequences abound, and a significant number of the synthetic chlorocarbon chemicals have proved to have profound environmental consequences, and have been banned or severely restricted. One thinks of carbon tetrachloride, of DDT and other -icides (insect, herb, germ, fung), of PCBs, of BHC, of tetraethyl lead, of freon... but also of such positive (or at least ubiquitous) inventions as chloroform, chloramphenicol, polyvinyl chloride (PCV)...
Consider the case of CFCs:
[a pointer to the Midgley story belongs about here; include a link to MidgleyEthyl.pdf (Industrial and Engineering Chemistry, May 1939)]The ozone layer has protected the Earth from UV radiation for something like 2 billion of Earth's 4.6 billion year existence. The layer developed as a consequence of terrestrial oxygen production (by plant respiration) and has always been dynamic: incoming UV breaks atmospheric O2 into O, and O and O2 combine into O3, which acts as a UV shield. Only with the synthesis of CFCs (in the 1930s) and their widespread use as refrigerants and propellants did the stratospheric ozone layer come under attack from terrestrial material.
...chlorine is only transported into the stratosphere in the first place by virtue of the great stability (i.e., persistence) of chlorofluorocarbons in the presence of atmospheric oxygen and OH- radicals. Whereas most organic chemicals are rapidly oxidized, this is not true of CFCs. These are compounds used widely as refrigerants, foam blowing agents and solvents (and formerly as aerosol propellants) precisely because of this stability. (Ayres 1996:3)The scope of the CFCproblem was identified by James Lovelock in the 1970s (his electron capture detector was the critical measurement device) and further analyzed by Rowland and Molina 1974 (Nobel Prize in Chemistry, 1995). An ozone "hole" was first noted over the Antarctic in 1985. NASA's webpage on the Antarctic ozone hole and the independent site The Ozone Hole summarize current data, which include (thanks to the phasing out of CFCs) "positive indications that the ozone layer is on track to recovery towards the middle of the century" according to UN Under-Secretary-General and United Nations Environment Programme Executive Director Achim Steiner.Ayers adds that "a 1% decrease in stratospheric ozone... results in an increase of the order of 1% of UV reaching ground level. This, in turn, is a major cause of skin cancer in humans, genetic damage, and possible immune system suppression. (III:9)
Some organo-chlorines are persistent, toxic, and bioaccumulative. Among these are
(I keep seeing India as a manufacturer of organochlorines...)
- DDT was first synthesized in 1874, but not realized as an insecticide until 1939. Ayers estimates 3.7 MMT was produced worldwide between 1944 and 1996.
- Lindane is produced from hexachlorocyclohexane (HCH) and was used as an insecticide and seed treatment, but is now widely banned as a neurotoxin.
- Hexachlorobenzene (HCB) was used as a fungicide until being withdrawn in the early 1980s.
- The aldrins
- chlordane and heptachlor
- pentachlorophenol replaced creosote as a wood preservative
- 2,4,5-T "Agent Orange" broadleaf defoliant
- PCBs: mostly used in transformers and capacitors Monsanto ended non-electrical use in 1971, and ceased US production in 1977
- dioxins: formed in all sorts of combustion processes. 2,3,7,8 TCDD especially toxic/carcinogenic, present as contaminant in Agent Orange
It's so easy to fall into four-legs-good-two-legs-bad thinking when tempted by apparent villainy and corporate mendacity and venality as candidate explanations for observed disasters (after all, blame has to be assigned somewhere...), and it's much more of an effort to try to understand what really happened in the longer run. We know, for example, that
Greenpeace and some other environmental groups have called for the chlorine industry to be phased out. However, chlorine industry supporters say that "banning chlorine would mean that millions of people in the third world would die from want of disinfected water".And consider this recent Reuters news item: Dow Chemical to exit century-old chlorine business, and another story specific to the Plaquemine LA operations. The Bottom Line, for what it's worth:
the plant closings are "...a continuation of Dow's shift to 'downstream high-margin products and technologies' rather than cyclical commodity products."