What Is Potassium Bromide?
Potassium bromide, a white crystalline compound, is formed by the combination of potassium and bromine, with a melting point of 734°C and a boiling point of 1,435°C. It is industrially produced by reducing potassium bromate through the reaction of potassium hydroxide and bromine, or by reacting hydrogen bromide with potassium hydroxide.
Crystallization of a saturated aqueous solution of potassium bromide by adding ethanol or another solution results in luminescence due to crystal luminescence.
Uses of Potassium Bromide
Transparent to infrared light, single crystals of potassium bromide are utilized as prisms for infrared spectroscopy. Its effect of suppressing central excitation in the cerebral cortex makes it a valuable raw material for nerve sedatives and antiepileptic drugs in the medical field. Additionally, potassium bromide finds applications in photography as a raw material for silver bromide, in developing solutions, as a chemical reagent, and in soap production.
Properties of Potassium Bromide
While soluble in alcohol and water, potassium bromide is insoluble in ether. It is hygroscopic, deliquescent, and should be stored in dry containers. Its aqueous solution ionizes into potassium and bromide ions, maintaining a neutral pH of 7. Reactions with sulfuric acid liberate bromine, and it forms complex salts when reacted with metal halides, such as copper (II) bromide.
Structure of Potassium Bromide
With the chemical formula KBr, potassium bromide has a molar mass of 119.002 g/mol and a density of 2.75 g/cm3. Its crystal structure mirrors that of sodium chloride, featuring an octahedral coordination structure.
Other Information on Potassium Bromide
1. Synthesis of Potassium Bromide
The traditional synthesis involves the reaction of iron bromide (Fe3Br8) with potassium carbonate, where iron bromide is produced by reacting excess bromine (Br2) with iron scraps in water.
2. Optical Applications of Potassium Bromide
Transparent in the near-ultraviolet to far-infrared regions (0.25-25 μm), potassium bromide is used in prisms or optical windows due to its refractive index of approximately 1.55 at 1.0 μm. It is ideal for infrared spectroscopy as it does not interfere with the measurement area and is used in solid-state NMR to adjust the magic angle during 13C measurement.
3. Applications in Medicine and Veterinary Medicine
As a pioneering therapeutic agent for epilepsy, potassium bromide is currently used in combination with other drugs for treating Dravet syndrome and as an antiepileptic drug for dogs, often as a first-line drug or in conjunction with phenobarbital when it alone is ineffective.
4. Application to Silver Halide Photography
Previously a staple in the developing process of silver halide photography and as a development inhibitor, potassium bromide’s use has declined but remains in specialized applications such as astrophotography. Sodium thiosulfate has largely replaced it as a fixing agent.