potassium bromide

Potassium bromide
Identifiers
CAS number	7758-02-3 Y
PubChem	253877
RTECS number	TS7650000
Properties
Molecular formula	KBr
Molar mass	119.002 g/mol
Appearance	white solid
Density	2.75 g/cm3
Melting point	734 °C, 1007 K, 1353 °F
Boiling point	1435 °C, 1708 K, 2615 °F
Solubility in water	53.5 g/100 ml (0 °C) 102 g/100 mL (100 °C)
Solubility in glycerol	21.7 g/100 mL
Solubility in ethanol	4.76 g/100 mL (80 °C)
Structure
Crystal structure	Sodium chloride
Coordination geometry	octahedral
Dipole moment	10.41 D (gas)
Hazards
MSDS	MSDS at Oxford University
EU Index	Not listed
Related compounds
Other anions	Potassium fluoride Potassium chloride Potassium iodide
Other cations	Lithium bromide Sodium bromide Rubidium bromide Caesium bromide
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Potassium bromide (KBr) is a salt, widely used as an anticonvulsant and a sedative in the late 19th and early 20th centuries. Its action is due to the bromide ion (sodium bromide is equally effective). Potassium bromide is presently used as a veterinary drug, as an antiepileptic medication for dogs and cats.

Under standard conditions, potassium bromide is a white crystalline powder. It is freely soluble in water. In a dilute aqueous solution, potassium bromide tastes sweet, at higher concentration it tastes bitter, and when most concentrated it tastes salty to humans (these effects are due mainly to potassium ion; sodium bromide merely tastes salty at all concentrations). In high concentration potassium bromide strongly irritates the gastric mucous membrane, leading to nausea and sometimes vomiting (again this effect is typical of all soluble potassium salts).

Chemical properties

Potassium bromide is a typical ionic salt which is fully dissociated and near pH 7 in aqueous solution. It serves as a source of bromide ions- this reaction is important for the manufacture of silver bromide for photographic film:

KBr(aq) + AgNO₃(aq) → AgBr(s) + KNO₃(aq)

Aqueous bromide Br^- will also form complexes when reacted with some metal halides such as copper(II) bromide:

2 KBr(aq) + CuBr₂(aq) → K₂[CuBr₄](aq)

Preparation

A traditional method for the manufacture of KBr is the reaction of potassium carbonate with a bromide of iron, Fe₃Br₈, made by treating scrap iron under water with excess bromine:^{[citation needed]}

4 K₂CO₃ + Fe₃Br₈ → 8 KBr + Fe₃O₄ + 4 CO₂

Applications

Medical and Veterinary

The anticonvulsant properties of potassium bromide were first noted by Sir Charles Locock at a meeting of the Royal Medical and Chirurgical Society in 1857. Bromide can be regarded as the first effective medication for epilepsy. At the time, it was commonly thought that epilepsy was caused by masturbation.^[1] Locock noted that bromide calmed sexual excitement and thought this was responsible for his success in treating seizures. In the latter half of the 19th century, potassium bromide was used for the calming of seizure and nervous disorders on an enormous scale, with the use by single hospitals being as much a several tons a year (the dose for a given person being a few grams per day). ^[2].

There would not be a better drug for epilepsy until phenobarbital in 1912. It was often said the British Army laced the soldiers' tea with bromide to quell sexual arousal, however because doing so would also diminish alertness in battle it is likely to be an urban legend and similar stories were also told about a number of substances.^[3]

Potassium bromide is used to treat epilepsy in dogs, either as first-line treatment or in addition to phenobarbital when the seizures are not adequately controlled with phenobarbital alone. Use of bromide in cats is limited because it carries a substantial risk of causing lung inflammation (pneumonitis) in this species.

Potassium bromide is not approved by the US Food and Drug Administration (FDA) for use in humans to control seizures. In Germany it continues to be approved for use as an antiepileptic drug for humans, particularly children and adolescents. These indications include severe forms of generalized tonic-clonic seizures, early-childhood-related Grand-Mal-seizures, and also severe myoclonic seizures during childhood. Adults who have reacted positively to the drug during childhood/adolescence may continue treatment. KBr is sold under the brand name Dibro-Be mono (RX-only). When used for proper indications it shows promising results.^{[citation needed]} The drug has almost complete bioavailability, but the bromide ion has a relatively long half-life of 12 days in the blood ^[4], making bromide salts difficult to adjust and dose. Bromide is not known to interfere with the absorption or excretion of any other anticonvulsant, though it does have strong interactions with chloride in the body, the normal body uptake and excretion of which strongly influences bromide's excretion. ^[5].

The therapeutic index (ratio of effectiveness to toxicity) is very small for bromide. As with other antiepileptics, sometimes even therapeutic doses (3 to 5 grams per day, taking 6 to 8 weeks to reach stable levels) may give rise to intoxication. Often indistinguishable from 'expected' side-effects, these include:

• Loss of appetite, nausea/emesis, lethargy, propensity to sleep during the daytime, depression, loss of concentration and memory, confusion, headache, and

• Bromism (central reactions reaching from somnolence to coma, cachexia, exicosis, loss of reflexes or pathologic reflexes, clonic seizures, tremor, ataxia, loss of neural sensitivity, paresis, papillar edema of the eyes, abnormal speech, cerebral edema, delirium, aggressiveness, psychoses)

• Acne-form dermatitis and other forms of skin disease may also be seen, as well as mucous hypersecretion in the lungs. Asthma and rhinitis may worsen. Rarely, tongue disorder, aphten, bad breath, and obstipation occur.

Optics

KBr is transparent from the near ultraviolet to long wave infrared wavelengths (0.25-25 µm). KBr has no significant optical absorption lines in its high transmission region. It is used for optical windows and prisms. It must be kept in a dry environment due to high solubility and hygroscopic nature. The refractive index is about 1.55 at 1.0 µm.

In infrared spectroscopy, samples are analyzed by grinding with KBr powder, and pressing into a disc. Alternatively, the samples may be analyzed as a liquid film (neat, as a solution, or in a mull with Nujol) between two polished KBr discs.^[6]

References

1. ^ Goodman and Gilman, The Biological Basis of Therapeutics, Fourth Edition, Chapter 10 (Hypnotics and Sedatives), p. 121, The MacMillan Co., London, 1970.
2. ^ Goodman and Gilman, op, cite, p 121
3. ^ Barbara Mikkelson (2 Auust 2007). "The Saltpeter Principle". Snopes.com. http://www.snopes.com/military/saltpeter.asp. 
4. ^ Goodman and Gilman, op cite, p 121
5. ^ Goodman and Gillman, op. cite, pg. 122
6. ^ W. Reusch. "Infrared Spectroscopy". VirtualText of Organic Chemistry. http://www.cem.msu.edu/~reusch/VirtualText/Spectrpy/InfraRed/infrared.htm. Retrieved 2007-12-18. 

External links

• Broken link - Veterinary use note at Auburn University
• Pesticide information