General Description
Odorless white solid. Sinks and mixes with water.
Reactivity Profile
Bromine trifluoride rapidly attacks the following salts: barium chloride, cadmium chloride, calcium chloride, cesium chloride, lithium chloride, silver chloride, rubidium chloride, potassium bromide, potassium chloride, POTASSIUM IODIDE(7681-11-0), rhodium tetrabromide, sodium bromide, sodium chloride, and sodium iodide [Mellor 2, Supp. 1:164, 165. 1956].
Air & Water Reactions
Water soluble.
Health Hazard
May irritate eyes or open cuts.
Chemical Properties
Potassium iodide is a white crystals, granules, or powder; strong, bitter, saline taste. becomes yellowish when exposed to bright light due to photochemical decomposition liberating traces of free iodine. Soluble in water, alcohol, acetone, and glycerol. slightly soluble in ether and ammonia. It may be prepared bythe reaction of iodine with hot potassiumhydroxide solution followed by separation from the iodate (which isalso formed) by fractional crystallization. In solution it has the interestingproperty of dissolving iodine to formthe triiodide ion I3-, which is brown. Potassium iodide is widely used as ananalytical reagent, in photography,and also as an additive to table salt toprevent goitre and other disordersdue to iodine deficiency.
Occurrence
Potassium iodide is found in seaweed. Some important applications of this compound involve its use in pharmaceuticals and as a source of iodine in food,especially in animal and poultry feed. Potassium iodide is added to table salt to provide iodine in human food.
Another major use is in making photographic emulsions. In analytical chemistry, potassium iodide is used in iodometric titration with starch indicator to analyze dissolved oxygen, dissolved chlorine, sulfide, and other analytes in water.
Application
Potassium iodide was first used as the primary halide in Talbot’s calotype process, then in the albumen on glass process followed by the wet collodion process. It was also used as a secondary halide in silver bromide gelatin emulsions, animal feeds, catalysts, photographic chemicals, and for sanitation. Potassium iodide is produced by reaction of potassium hydroxide with iodine. The product is purified by crystallization from water. Potassium iodide is ionic compound which iodine ions and silver ions can form yellow precipitate silver iodide (when exposes to light, it can decompose, it can be used to make high-speed photographic film), silver nitrate can be used to verify the presence of iodine ions.
Preparation
Potassium iodide is made by absorption of iodine in potassium hydroxide:
I2 + 6KOH → 5KI + KIO3 + 3H2O
Most potassium iodate, KIO3 , is separated from the product mixture by crystallization and filtration. Remaining iodates are removed by evaporation of the solution and other processes, such as carbon reduction or thermal decompostion at 600oC to iodide:
2KIO3 → 2KI + 3O2
Another method of preparation that does not involve the formation of iodate is by treating iron turnings with iodine solution. The product, ferrosoferric iodide, Fe3I8?16H2O, is boiled with 15 wt% potassium carbonate solution:
Fe3I8.16H2O + 4K2CO3 → 8 KI + 4CO2 + Fe3O4 + 16H2O
A similar method is used to prepare potassium bromide, discussed earlier (see Potassium Bromide.)
Potassium iodide can be prepared by reacting hydriodic acid with potassium bicarbonate:
HI + KHCO3 → KI + CO2 + H2O
It is purified by melting in dry hydrogen.
Potassium iodide also may be obtained by various electrolytic processes.
Brand name
Iosat (Anbex); Thyro-Block (Medpointe); Thyrosafe
(R R Registrations); Thyroshield (Fleming).
Flammability and Explosibility
Nonflammable
Pharmacokinetics
Potassium Iodide is a metal halide composed of potassium and iodide with thyroid protecting and expectorant properties. Potassium iodide can block absorption of radioactive iodine by the thyroid gland through flooding the thyroid with non-radioactive iodine and preventing intake of radioactive molecules, thereby protecting the thyroid from cancer causing radiation. In addition, this agent acts as an expectorant by increasing secretion of respiratory fluids resulting in decreased mucus viscosity.
Clinical Use
Potassium iodide is used to treat the cutaneous lymphatic
form of sporotrichosis, although newer agents
are also effective in this disorder and may be better tolerated tolerated.
The drug is also used for erythema nodosum and
nodular vasculitis.
Purification Methods
Crystallise it from distilled water (0.5mL/g) by filtering the near-boiling solution and cooling. To minimise oxidation to iodine, the process can be carried out under N2 and the salt is dried under a vacuum over P2O5 at 70-100o. Before drying, the crystals can be washed with EtOH or with acetone followed by pet ether. It has also been recrystallised from water/ethanol. After 2 recrystallisations, ACS/USP grade had Li and Sb at <0.02 and <0.01 ppm respectively. [Lingane & Kolthoff Inorg Synth I 163 1939.]
