Iodine [Monograph #5034, Merck Index, Ed. 12.1]

CAS Registry number:

[7553-56-2]

Literature references:

I; at. wt 126.9045; at. no. 53; valences 1 to 7 (usually monovalent); elemental state: I₂. A halogen. Abundance in igneous rocks: 3x10^-5% by wt; in seawater 5x10^-8% by wt. Natural isotope: 127 (100%); isotopes range in mass number from 117 to 139; radioactive tracer elements: 124, 125, 128, 131, 132. Discovered in 1811 by Courtois. Classed among the rarer elements. Extracted from Chilean nitrate-bearing earth (caliche) and from seaweed. Prepn of ultra-pure iodine for research purposes according to the equation 2KI + CuSO₄·5H₂O → CuI + K₂SO₄ + ½ I₂ + 5H₂O: Schmeisser in Handbook of Preparative Inorganic Chemistry, Vol. 1, G. Brauer, Ed. (Academic Press, New York, 2nd ed., 1963) p 275. Reviews: MTP Int. Rev. Sci.: Inorg. Chem., Ser. One, Vol. 3, V. Gutmann, Ed. (Butterworths, London, 1972); Downs, Adams, "Chlorine, Bromine, Iodine and Astatine" in Comprehensive Inorganic Chemistry vol. 2, J. C. Bailar, Jr. et al., Eds. (Pergamon Press, Oxford, 1973) p 1107-1594; C. J. Mazac in Kirk-Othmer Encyclopedia of Chemical Technology vol. 13 (Wiley-Interscience, New York, 3rd ed., 1981) pp 649-677.

Properties:

Bluish-black scales or plates; diatomic; metallic luster; characteristic odor; sharp, acrid taste; violet corrosive vapor.

Vapor pressure (solid):

0.030 mm (0°C); 0.305 mm (25°C); 2.154 mm (50°C); 26.78 mm (90°C).

Heat capacity at constant pressure (25°C)

13.011 cal/mole/°C: Shirley, Giauque, J. Am. Chem. Soc. 81, 4778 (1959).

Total soly in water (25°C):

0.0013 moles/l with negligible formation of HOI (6.4x10^-6 moles/l); freely sol in aq solns of HI or iodides.

Soly in organic solvents (g I₂/100 g soln, 25°C):

benzene 14.09; CS₂ 16.47; ethanol 21.43; ethyl ether 25.20; cyclohexane 2.719; CCl₄ (35°C) 2.603: Hildebrand, Jenks, J. Am. Chem Soc. 42, 2180 (1920); Hildebrand et al., ibid. 72, 1017 (1950); sol in chloroform, glacial acetic acid, glycerol oils.

Miscellaneous:

Solutions of iodine in aq solns of inorganic iodides are brown or deep brown, depending on the concentration of the iodine. Solvents contg nitrogen atoms, such as pyridine, amines, or quinoline dissolve iodine to form brown solns. Chloroform, carbon tetrachloride, carbon disulfide, and especially phosphorus trichloride give violet solns. The violet color is also given by fluorinated amines. The soly in water is also increased by alkali bromides, but decreased by sulfates and nitrates. Less reactive than bromine; E°_(aq) ½ I₂/I^- 0.535 V dissociation energy (25°C): 36.115 kcal. Iodine stains may be removed with sodium thiosulfate soln or ammoniated alc. Incompat: alkaloids, starch, tannins.

Melting point:

113.60°C

Boiling point:

185.24°C

Density:

4.93 (solid, 25°C)

Caution:

Potential symptoms of overexposure are irritation of eyes and nose; lacrimation; headache; tight chest; skin burns, rash; cutaneous hypersensitivity. See NIOSH Pocket Guide to Chemical Hazards (DHHS/NIOSH 90-117, 1990) p 128. Ingestion of large quantities causes abdominal pain, vomiting and diarrhea due to the highly corrosive action of iodine on the GI tract. See Clinical Toxicology of Commercial Products, R. E. Gosselin et al., Eds. (Williams Wilkins, Baltimore, 5th ed., 1984) Sect. III, pp 213-214.