Potassium bromide (
K Br) is a
salt
Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quant ...
, widely used as an
anticonvulsant
Anticonvulsants (also known as antiepileptic drugs or recently as antiseizure drugs) are a diverse group of pharmacological agents used in the treatment of epileptic seizures. Anticonvulsants are also increasingly being used in the treatment of ...
and a
sedative
A sedative or tranquilliser is a substance that induces sedation by reducing irritability or excitement. They are CNS depressants and interact with brain activity causing its deceleration. Various kinds of sedatives can be distinguished, but ...
in the late 19th and early 20th centuries, with over-the-counter use extending to 1975 in the US. Its action is due to the
bromide ion (
sodium bromide is equally effective). Potassium bromide is used as a veterinary drug, as an antiepileptic medication for dogs.
Under standard conditions, potassium bromide is a white crystalline powder. It is freely soluble in water; it is not soluble in
acetonitrile
Acetonitrile, often abbreviated MeCN (methyl cyanide), is the chemical compound with the formula and structure . This colourless liquid is the simplest organic nitrile ( hydrogen cyanide is a simpler nitrile, but the cyanide anion is not clas ...
. In a dilute aqueous solution, potassium bromide tastes sweet, at higher concentrations it tastes bitter, and tastes salty when the concentration is even higher. These effects are mainly due to the properties of the potassium ion—sodium bromide tastes salty at any concentration. In high concentration, potassium bromide strongly irritates the gastric mucous membrane, causing nausea and sometimes vomiting (a typical effect of all soluble potassium salts).
Chemical properties
Potassium bromide, a typical
ionic salt, 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
Silver bromide (AgBr) is a soft, pale-yellow, water-insoluble salt well known (along with other silver halides) for its unusual sensitivity to light. This property has allowed silver halides to become the basis of modern photographic materials. A ...
for
photographic film
Photographic film is a strip or sheet of transparent film base coated on one side with a gelatin emulsion containing microscopically small light-sensitive silver halide crystals. The sizes and other characteristics of the crystals determine ...
:
:
KBr_ + AgNO3_ -> AgBr_ + KNO3_
Aqueous bromide also forms
complexes when reacted with some metal halides such as
copper(II) bromide
Copper(II) bromide ( Cu Br2) is a chemical compound. It is used in photographic processing as an intensifier and as a brominating agent in organic synthesis.
It is also used in the copper vapor laser, a class of laser where the medium is copper ...
:
:
2 KBr_ + CuBr2_ -> K2 uBr3
Preparation
A traditional method for the manufacture of KBr is the reaction of
potassium carbonate with an iron(
III
III or iii may refer to:
Companies
* Information International, Inc., a computer technology company
* Innovative Interfaces, Inc., a library-software company
* 3i, formerly Investors in Industry, a British investment company
Other uses
* ...
,
II) bromide, , made by treating scrap iron under water with excess
bromine
Bromine is a chemical element with the symbol Br and atomic number 35. It is the third-lightest element in group 17 of the periodic table ( halogens) and is a volatile red-brown liquid at room temperature that evaporates readily to form a simi ...
:
:
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
Epilepsy is a group of non-communicable neurological disorders characterized by recurrent epileptic seizures. Epileptic seizures can vary from brief and nearly undetectable periods to long periods of vigorous shaking due to abnormal electrica ...
. At the time, it was commonly thought that epilepsy was caused by masturbation.
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 as several tons a year (the dose for a given person being a few grams per day).
By the beginning of the 20th century the generic word had become so widely associated with being sedate that
bromide came to mean a dull, sedate person or a boring
platitude uttered by such a person.
There was not a better epilepsy drug until
phenobarbital in 1912. The
British Army
The British Army is the principal land warfare force of the United Kingdom, a part of the British Armed Forces along with the Royal Navy and the Royal Air Force. , the British Army comprises 79,380 regular full-time personnel, 4,090 Gurkha ...
has historically been claimed to lace soldiers'
tea with bromide to quell sexual arousal but that is likely untrue as doing so would also diminish alertness in battle. Several other substances have also been named in
anaphrodisiac myths.
Bromide compounds, especially
sodium bromide, remained in over-the-counter sedatives and headache remedies (such as the original formulation of
Bromo-Seltzer) in the US until 1975, when bromides were outlawed in all over-the-counter medicines, due to chronic toxicity. Bromide's exceedingly long half life in the body made it difficult to dose without side effects. Medical use of bromides in the US was discontinued at this time, as many better and shorter-acting sedatives were known by then.
Potassium bromide is used in veterinary medicine to treat
epilepsy in dogs, either as first-line treatment or in addition to phenobarbital, when 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 them. The use of bromide as a treatment drug for animals means that veterinary medical diagnostic laboratories are able as a matter of routine to measure serum levels of bromide on order of a veterinarian, whereas human medical diagnostic labs in the US do not measure bromide as a routine test.
Potassium bromide is not approved by the US
Food and Drug Administration
The United States Food and Drug Administration (FDA or US FDA) is a federal agency of the Department of Health and Human Services. The FDA is responsible for protecting and promoting public health through the control and supervision of food ...
(FDA) for use in humans to control seizures. In Germany, it is still approved as an antiepileptic drug for humans, particularly children and adolescents. These indications include severe forms of generalized tonic-clonic seizures, early-childhood-related tonic–clonic seizures, and also severe myoclonic seizures during childhood. Adults who have reacted positively to the drug during childhood/adolescence may continue treatment. Potassium bromide tablets are sold under the brand name ''Dibro-Be mono'' (Rx-only). The drug has almost complete bioavailability, but the bromide ion has a relatively long half life of 12 days in the blood,
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.
The therapeutic index (ratio of effectiveness to toxicity) for bromide is small. 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:
*''
Bromism'' These are central nervous system reactions. They may include:
:depression,
:
lethargy
Lethargy is a state of tiredness, sleepiness, weariness, fatigue, sluggishness or lack of energy. It can be accompanied by depression, decreased motivation, or apathy. Lethargy can be a normal response to inadequate sleep, overexertion, overwo ...
,
somnolence
Somnolence (alternatively sleepiness or drowsiness) is a state of strong desire for sleep, or sleeping for unusually long periods (compare hypersomnia). It has distinct meanings and causes. It can refer to the usual state preceding falling asleep ...
(from daytime sleepiness to
coma
A coma is a deep state of prolonged unconsciousness in which a person cannot be awakened, fails to respond normally to painful stimuli, light, or sound, lacks a normal wake-sleep cycle and does not initiate voluntary actions. Coma patients exhi ...
)
:loss of appetite and
cachexia
Cachexia () is a complex syndrome associated with an underlying illness, causing ongoing muscle loss that is not entirely reversed with nutritional supplementation. A range of diseases can cause cachexia, most commonly cancer, congestive heart fa ...
, nausea/emesis with
exicosis (loss of body fluid)
:loss of
reflexes
In biology, a reflex, or reflex action, is an involuntary, unplanned sequence or action and nearly instantaneous response to a stimulus.
Reflexes are found with varying levels of complexity in organisms with a nervous system. A reflex occurs ...
or pathologic reflexes
:
clonic seizures
:
tremor
:
ataxia
Ataxia is a neurological sign consisting of lack of voluntary coordination of muscle movements that can include gait abnormality, speech changes, and abnormalities in eye movements. Ataxia is a clinical manifestation indicating dysfunction of ...
:loss of neural sensitivity
:
paresis
:
cerebral edema with associated headache and
papilledema of the eyes
:
delirium
Delirium (also known as acute confusional state) is an organically caused decline from a previous baseline of mental function that develops over a short period of time, typically hours to days. Delirium is a syndrome encompassing disturbances ...
: confusion, abnormal speech, loss of concentration and memory, aggressiveness
:
psychosis
Psychosis is a condition of the mind that results in difficulties determining what is real and what is not real. Symptoms may include delusions and hallucinations, among other features. Additional symptoms are incoherent speech and behavi ...
*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,
aphthous stomatitis,
bad breath, and
constipation
Constipation is a bowel dysfunction that makes bowel movements infrequent or hard to pass. The stool is often hard and dry. Other symptoms may include abdominal pain, bloating, and feeling as if one has not completely passed the bowel moveme ...
occur.
Optics
Potassium bromide is transparent from the near
ultraviolet
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation ...
to long-wave
infrared
Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...
wavelength
In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats.
It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tr ...
s (0.25-25 µm) and has no significant
optical absorption
In physics, absorption of electromagnetic radiation is how matter (typically electrons bound in atoms) takes up a photon's energy — and so transforms electromagnetic energy into internal energy of the absorber (for example, thermal energy). A ...
lines in its high transmission region.
It is used widely as infrared optical windows and components for general spectroscopy because of its wide spectral range. In
infrared spectroscopy
Infrared spectroscopy (IR spectroscopy or vibrational spectroscopy) is the measurement of the interaction of infrared radiation with matter by absorption, emission, or reflection. It is used to study and identify chemical substances or functi ...
, samples are analyzed by grinding with powdered potassium bromide and pressing into a disc. Alternatively, samples may be analyzed as a liquid film (neat, as a solution, or in a mull with
Nujol
Nujol is a brand of mineral oil by Plough Inc., cas number 8012-95-1, and density 0.838 g/mL at 25 °C, used in infrared spectroscopy. It is a heavy paraffin oil so it is chemically inert and has a relatively uncomplicated IR spectrum, with m ...
) between two polished potassium bromide discs.
Due to its high solubility and
hygroscopic
Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption or adsorption from the surrounding environment, which is usually at normal or room temperature. If water molecules become suspended among the substance' ...
nature it must be kept in a dry environment. The
refractive index
In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium.
The refractive index determines how much the path of light is bent, ...
is about 1.55 at 1.0 µm.
Photography
In addition to manufacture of silver bromide, potassium bromide is used as a restrainer in
black and white
Black-and-white (B&W or B/W) images combine black and white in a continuous spectrum, producing a range of shades of grey.
Media
The history of various visual media began with black and white, and as technology improved, altered to color. ...
developer
Developer may refer to:
Computers
*Software developer, a person or organization who develop programs/applications
* Video game developer, a person or business involved in video game development, the process of designing and creating games
* Web de ...
formulas. It improves differentiation between exposed and unexposed crystals of silver halide, and thus reduces fog.
References
External links
Veterinary use note at Auburn University
{{DEFAULTSORT:Potassium Bromide
Potassium compounds
Bromides
Sedatives
Anticonvulsants
Pesticides
Optical materials
Photographic chemicals
Metal halides
GABAA receptor positive allosteric modulators
Alkali metal bromides
Rock salt crystal structure