Chlorine. Cl; at. wt 35.453; at. no. 17; valences I to 7; elemental state: C12. A halogen. Abundance in igneous rock (95% of earth's crust): 0.031% by wt; in Seawater: 1.9% by wt (primarily as NaCl). Natural isotopes: 35 (75.53%); 37 (24.47%); seven radioactive isotopes and two Isomers are known; radioactive tracer elements: 36Cl (T 3.08 x l05 yrs; b-, EC); 30Cl (T 37.29 min; b-); formed in atm by bombardment with cosmic rays. Discovered in 1774 by Scheele; recognized as an element in 1810 by Davy. Produced on a large scale by electrolysis from fused chlorides. The industrial product is about 99.3% pure. Contaminants are traces of bromide, hexachloroethane, hexachlorobenzene, and water. Purification: Fyc, Beaver, J. Am. Chem. Soc. 63, 1268 (1941); A. Klemeuc, Die Behandlung und Reindarstellung von Gasen (Vienna, 2nd ed., 1948) pp 153. 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. Manuf: Faith, Keyes & Clark's Industrial Chemicals. F. A. Lowenheim, M. K. Moran, Eds. (wiley-Interscience. New York, 4th ed. 1975) pp 244-253. Reviews: Ciba Review vol. 12, no.139 (Aug 1960); Chlorine, J. S. Sconce, Ed., ACS. Monograph Series no. 154 (Reinhold, New York, 1962) 901 pp; MTP Int. Rev. Sci.: Inorg. Chem., Ser. One, vol. 3, V. Gutmann, Ed. (Butterworths, London, 1972); Downs, C 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.

Greenish yellow, diatomic gas; suffocating odor. mp is -101.00. bp -34.05. d20 at 6.864 atm 1.4085 (liq.); d-35 at 0.9949 atm 1 5649 (liq.). Critical temp 144; critical pressure 76.1 atm. Heat capacity at constant pressure (gas, 25) 8.11 cal/mole/C. Marketed in the form of gas over liquid compressed into steel cylinders. Caution: Never heat cylinders. Vapor pressure data: Giauque, Powell, J. Am. Chem. Soc. 61, 1970 (1939). 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. See Chlorinated Lime and Sodium Hypochlorite Soln. Acts as an electron-acceptor in forming complexes with many donor species: Bent, Chem. Rev. 68, 587 (1968). Very reactive; E (aq) Cl2/Cl- 1.356 V; dissociation energy (25): 57.978 kcal; combines readily with all elements except the rare gases (xenon excluded) and nitrogen. Forms explosive mixtures with hydrogen; many finely divided metals will burn in an atm of chlorine. Oxides are strong oxidizing agents and explosive. Monatomic chlorine is unstable under ordinary conditions, however, it can be formed as a result of thermal or optical dissociation, by an electrical discharge or as an intermediate during chemical reactions. Dangerous to inhale: K. C. Back et al., Reclassification of Materials Listed as Transportation Health Hazards (TSA-20-72-3; PB 214-270). LC50 (One hr), inhalation by rats, mice: 293 ppm. 137 ppm.

Caulion: A powerful irritant. Can cause fatal pulmonary edema. Threshold odor detection: 0.2-0.4 ppm. cf. Patty's Industrial Hygiene and Toxicology vol. 2B, G. D. Clayton, F. E. Clayton. Eds. (Wiley-lnterscience. New York, 3rd ed., 1981) pp 2954-2965

USE: Largely for manuf chlorinated lime which is used in bleaching all kinds of fabrics; for purifying water; disinfecting; detinning and dezincing iron; manuf synthetic rubber and plastics. chlorinated hydrocarbons. and a large number of other chemicals. It is an indispensable reagent in synthetic chemistry. Has been used as a military poison gas under the name bertholite. 36Cl is considered an extinct nuclide and provides a method of determining the geological age of meteors.
Ref.: 2095, pp 323-324.
The Merck Index - Eleventh Edition.
Copyright 1989 by Merck & Co., Inc.