Iodine is a
nonmetallic halogen element in Group 17 of periodic table; atomic number 53;
atomic mass 126.9; melting point ca 114 C; boiling point ca 184 C; specific
gravity 4.93 g/cm3; oxidation states: 7,5,1,-1; [Kr] 4d10 5s2 5p5. Iodine is a
nearly black poisonous, corrosive solid at room temperature and readily sublimes
to a deep violet vapour, the colour of which is responsible for its name from
Greek. It is insoluble in water, soluble in common solvents. Iodine is required
in small amounts in human body for the function of the thyroid gland. Iodine
forms many important compounds of iodine such as iodine(V)oxide, potassium
iodide, iodine trichloride and iodoform of an Iodine containing organic
The related name, iodate indicates any salt of iodic acid containing the IO3-
radical; KIO3 (potassium iodate) and NaIO3 (sodium iodate) are the most
important salts. Whereas, iodide indicates any compound of iodine with a more
electropositive element or group such as such as CH3CH2I or any binary compound
of iodine which may contain the I- radical and which may be considered to be
derived from hydriodic acid (HI); KI and NaI are examples.
Dietary iodine is
reduced to iodide, absorbed in the intestines, and later taken up from the
bloodstream by the thyroid gland for incorporation into thyroid hormones. Iodine
is applied in the treatment of thyrotoxic crisis to produce
a thyroid gland of firm texture suitable for operation, it avoids the increased vascularity and friability of the
gland with increased risk of haemorrhage. Iodine has powerful bactericidal activity.
It is used is used for disinfecting skin and for the treatment of minor
wounds and abrasions. Iodine has been used in the purification of drinking water
in case of amoebicidal and bactericidal emergencies. Iodine is used as a component in germicides and disinfectants with
surfactants to carry iodine. Iodine is used in the treatment of herpes simplex, keratoscleritis and
preventing the development of goitre.
Inorganic iodide compounds are soluble in
water and hygroscopic except a few inorganic iodides such as copper iodide.
Their refractive indexes and specific gravities are higher than the
corresponding chlorine and bromine analogues. The important iodides commercially
are potassium iodide (KI), sodium iodide (NaI), hydrogen iodide (HI), and
Potassium and sodium Iodide are used in photography and as
analytical reagents. They are used in the measurement of the energy of gamma
rays, by measuring the amplitude of pulses of light generated by electrons which
are excited by the gamma rays. They are used as nutrition supplements to prevent
goitre and other iodine deficiency in human body. They are used in organic
synthesis as well. Potassium iodide has been used as a mucolytic agent.
Potassium iodide is used as a heat stabilizer and a catalyst in synthetic fiber
Hydriodic acid is the aqueous pale yellow solution of gas
hydrogen iodide; the solution of 59% hydrogen iodide has constant-boiling. It is
a strong acid and reducing agent used as raw materials for pharmaceuticals.
analytical reagent as well as in organic synthesis and making iodine salts.
Inorganic iodate compounds, prepared generally by the oxidation of iodine with
iodic acid or by electrolytic oxidation of iodide solutions, are stable
oxidizers at room temperature though they lose oxygen at higher temperatures.
Iodic acid (hydrogen iodate), a white crystalline powder, is a strong inorganic acid; highly
corrosive oxidizing agent; decomposes at 110 C. It is used as a reducing agent
in organic synthesis. Metallic iodates are explosive or flammable when contact with organic
combustible materials. The important iodates commercially are potassium iodate
and calcium iodate; white, odorless crystaline powder soluble in water,
insoluble in alcohol. They are used as analytical reagents and in the
manufacture of disinfectants, antiseptics, deodorants, medicines and other
iodine compounds as well as oxidation of sulphur dyes. They are used in baking
ingredient conditioner and as animal feed and food supplement for the treatment
of their deficiency.
Organic iodines are very useful reagents as they have lower
heat of formation than chlorine or bromine analogues. Aliphatic Iodides are used
as alkylating agents in synthetic organic chemistry. Iodoform is a simple
structural compound; greenish yellow hexagonal solid with a strong, penetrating
odor; containing about 96 per cent of iodine; melting point 119 C; soluble in
chloroform and ether and somewhat in alcohol and water: used as a topical
anti-infective, applied to the skin. Iodoacetic acid is used in biochemical
research; it alkylates free thiol groups but not disulfide bridges. methyl
iodide, also called iodomethane, is a colorless liquid that turns brown on
exposure to light; used in microscopy and in testing for pyridine. It is
irritating to skin and mucous membranes and is a suspected carcinogen. Ethylene
diamine dihydroiodide is used in animal feeds to prevent deficiency of iodine.
Iodine organic compounds are useful in dye industry for the high bright colors
as well as pharmaceutical industry. They are important for the production of
X-ray contrast media and for the formulating antiseptics.