Title: Chlorine
CAS Registry Number: 7782-50-5
Literature References: Cl; at. wt 35.4527; at. no. 17; valences 1, 3, 5, 7. A halogen; Group VIIA (17). Does not occur as elemental state, Cl2, in nature. Abundance in igneous rock (95% of earth's crust): 0.031% by wt; in seawater: 1.9% by wt (primarily as NaCl). Naturally occurring stable isotopes (mass numbers): 35 (75.77%), 37 (24.23%); known artificial radioactive isotopes: 31-34, 36 (longest-lived known isotope, T½ 3.0 ´ 105 yrs; b-, EC decay), 38-46, 48. Discovered in 1774 by C. W. Scheele; recognized as an element in 1810 by H. Davy. Commercial sources: seawater, ocean derived mineral deposits, brines from lakes, wells and springs. Industrial prepn from brine in electrolytic cells. Lab prepn from MnO2 and HCl: Schmeisser in Handbook of Preparative Inorganic Chemistry vol. 1, G. Brauer, Ed. (Academic Press, New York, 2nd ed., 1963) p 272. Cosmogenic production and determn of 36Cl for geological dating: H. E. Gove, Philos. Trans. R. Soc. London Ser. A 323, 103 (1987); M. G. Zreda et al., Earth Planet. Sci. Lett. 105, 94 (1991). Reviews: Ciba Review vol. 12, no. 139 (Aug. 1960); ACS Monograph Series no. 154, entitled "Chlorine," J. S. Sconce, Ed. (Reinhold, New York, 1962) 901 pp; MTP Int. Rev. Sci.: Inorg. Chem., Ser. One vol. 3, V. Gutmann, Ed. (Butterworths, London, 1972); A. J. Downs, C. J. Adams, "Chlorine, Bromine, Iodine and Astatine" in Comprehensive Inorganic Chemistry vol. 2, J. C. Bailar, Jr. et al., Eds. (Pergamon Press, Oxford, 1973) pp 1107-1594; Chemistry of the Elements, N. N. Greenwood, A. Earnshaw, Eds. (Pergamon Press, New York, 1984) pp 920-1041; L. C. Curlin, T. V. Bommaraju in Kirk-Othmer Encyclopedia of Chemical Technology vol. 1 (Wiley-Interscience, New York, 4th ed., 1994) pp 938-1025. Review of potential human health and environmental adverse effects of chlorine and its compounds: E. Delzell et al., Regul. Toxicol. Pharmacol. 2, S1-S1056 (1994).
Properties: Greenish-yellow, diatomic gas; suffocating odor. mp -101.00°. bp -34.05°. d20 at 6.864 atm 1.4085 (liq); d-35 at 0.9949 atm 1.5649 (liq). d (relative to air) 2.48. Heat capacity at constant pressure (gas, 25°) 8.11 cal/mole/°C. Vapor pressure data: Giauque, Powell, J. Am. Chem. Soc. 61, 1970 (1939). Critical temp 144°; critical pressure 76.1 atm; critical density 0.573. Sol in water (25°) with formation of aqueous Cl2 (0.062 moles/l), HOCl (0.030 moles/l) and Cl- (0.030 moles/l); total soly: 0.092 moles/l. More sol in alkalies. Oxidizing agent. Very reactive; E0 (aq) ½Cl2/Cl- 1.356 V; dissociation energy (25°): 57.978 kcal. Forms halides with all elements except the rare gases helium, neon and argon. Noncombustible in air; most combustible materials will burn in chlorine. Forms explosive mixtures with flammable gases and vapors. Reacts explosively or forms explosive compounds with many common chemicals, especially acetylene, turpentine, ether, ammonia gas, fuel gas, hydrocarbons, hydrogen and finely divided metals. LC50 (1 hr) in rats, mice (ppm): 293, 137 (K. C. Back et al., Reclassification of Materials Listed as Transportation Health Hazards (TSA-20-72-3; PB 214-270, 1972) pp A-182-183).
Melting point: mp -101.00°
Boiling point: bp -34.05°
Density: d20 at 6.864 atm 1.4085 (liq); d-35 at 0.9949 atm 1.5649 (liq); d (relative to air) 2.48
Toxicity data: LC50 (1 hr) in rats, mice (ppm): 293, 137 (K. C. Back et al., Reclassification of Materials Listed as Transportation Health Hazards (TSA-20-72-3; PB 214-270, 1972) pp A-182-183)
CAUTION: Potential symptoms of overexposure are burning of eyes, nose and mouth; lacrimation, rhinorrhea; coughing, choking and substernal pain; nausea, vomiting; headache, dizziness; syncope; pulmonary edema; pneumonia; hypoxemia; dermatitis; direct contact with liquid may cause frostbite. See NIOSH Pocket Guide to Chemical Hazards (DHHS/NIOSH 97-140, 1997) p 58. See also Patty's Industrial Hygiene and Toxicology vol. 2F, G. D. Clayton, F. E. Clayton, Eds. (Wiley-Interscience, New York, 4th ed., 1994) pp 4483-4505.
Use: Manuf of organic and inorganic chemicals. As oxidizing and bleaching agent in pulp and paper industry, and for textiles. As disinfectant for water purification, industrial waste, sewage, swimming pools. In the extraction and refining of metals. 36Cl for determining geological age of natural samples such as meteorites, surface rocks, polar ice and ground water. Has been used as a military poison gas under the name bertholite.

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