Nomenclature
CAS number: 7553-56-2
Description and references
I; at. wt 126.90447; at. no. 53; valences 1,
1, 3, 5, 7. A halogen; Group VIIA (17). Does not exist as elemental
state, I, in nature. Occurs as diatomic molecule, I2.
Abundance in igneous rocks: 3×105% by wt; in seawater:
5×108% by wt. Naturally occurring stable isotope (mass
number): 127 (100%); known artificial radioactive isotopes: 108
to 141; commonly used radioactive tracer elements: 123 (T 13.27 hrs, EC decay), 125 (T 59.408 days, EC decay),
129 (T 1.57×107 years, β decay),
131 (T 8.02070 days, β decay). Discovered
in 1811 by Courtois. Classed among the rarer elements. Trace element
essential to animal and plant life. Extracted commercially from natural
subterranean brines, and Chilean nitrate-bearing earth (caliche);
formerly from seaweed. Reviews: 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) p 1107-1573; Chemistry of the
Elements N. N. Greenwood, A. Earnshaw, Eds. (Pergamin
Press, New York, 1984) pp 920-1041; A. Lauterbach, G. Ober in Kirk-Othmer Encyclopedia of Chemical Technology vol. 14 (Wiley-Interscience, New York, 4th ed., 1995)
pp 709-737. Review of geochemistry: R. Fuge, C. C. Johnson, Environ. Geochem. Health 8, 31-54
(1986); of human toxicity: Iodine Toxicity (PB89-183016, 1989) 107 pp; of metabolism and nutritional deficiency:
J. T. Dunn in Contemporary Endocrinology:
Diseases of the Thyroid, L. E. Braverman, Ed. (Humana
Press Inc., Totowa, NJ, 1997) pp 349-360; of toxicology and human
exposure: Toxicological Profile for Iodine (PB2004-104399, 2004) 580 pp.
Properties
Bluish-black scales or plates; diatomic; metallic
luster; characteristic odor; sharp acrid taste. Readily sublimes
at rm temp, forming violet corrosive vapor. mp 113.60°. bp 185.24°. d (solid, 25°) 4.93, d (liq 120°) 3.960. Vapor pressure (solid): 0.030 mm
(0°); 0.305 mm (25°); 2.154 mm (50°); 26.78 mm (90°). Heat capacity
at constant pressure (25°) 13.011 cal/mole/°C: Shirley, Giauque, J. Am. Chem. Soc. 81, 4778 (1959).
Total soly in water (25°) 0.0013 moles/l with negligible formation
of HOI (6.4×106 moles/l); freely sol in aq solns of HI
or iodides. Soly in organic solvents (g I2/100 g soln,
25°): benzene 14.09; CS2 16.47; ethanol 21.43; ethyl ether
25.20; cyclohexane 2.719; heptane 1.702; CCl4 (35°) 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. Solutions of iodine
in aq solns of inorganic iodides are brown or deep brown, depending
on the concn of the iodine. Solvents contg nitrogen atoms, such as
pyridine, amines, or quinoline form brown solns. Aliphatic hydrocarbons,
chloroform, carbon tetrachloride, carbon disulfide, phosphorus trichloride
and fluorinated amines give violet solns. Aromatic hydrocarbons give
pink or reddish-brown solns. Alcohols and ethers give deep brown
solns. Soly in water is increased by alkali bromides, but decreased
by sulfates and nitrates. Less reactive than bromine; E° (aq) I2/I 0.535 V dissociation energy (25°): 36.115
kcal. Iodine stains may be removed with sodium thiosulfate soln or
ammoniated alc.Caution
Potential symptoms of overexposure
are irritation of eyes, skin, and nose; lacrimation; headache; tight
chest; skin burns, rash; cutaneous hypersensitivity. See NIOSH Pocket Guide to Chemical Hazards (DHHS/NIOSH 97-140, 1997) p 172. 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.Use
Manuf of organic and inorganic chemicals, pharmaceuticals,
radiopaque contrast agents, animal feed supplements, disinfectants,
stabilizers, inks, colorants, photographic chemicals. Catalyst in
the alkylation and condensation of aromatic amines; in sulfations
and sulfonations; for prodn of synthetic rubber. Microbicide for
drinking water and swimming pools. Artificial radioisotopes as tracers
in biological, biochemical and chemical research; in medical imaging.
Iodometric standard in analytical chemistry.
Therapeutic Category
Antihyperthyroid; anti-infective (topical).
Therapeutic Category (Veterinary)
Internally for goiter, hypothyroidism,
in iodine deficiency. Topically as antiseptic, disinfectant, counterirritant
and to promote absorption.
Keywords
Antihyperthyroid; Antiseptic/Disinfectant; Halogens/Halogen Containing Compounds