Bromide

A bromide ion is a bromine atom with charge of −1.

Compounds with bromine in formal oxidation state −1 are called bromides, and each individual chemical in this class can be called a bromide, as well. The class name can include ionic compounds such as caesium bromide or covalent compounds such as sulfur dibromide.

Natural occurrence

Bromide is present in typical seawater (35 PSU) with a concentration of around 65 mg/l, which is around 0.2% of all dissolved salts. Seafoods generally have high levels of bromide, while foods derived from land have variable amounts.

Chemistry

One can test for a bromide ion by adding dilute nitric acid (HNO₃), then silver nitrate (AgNO₃). A cream precipitate forms that disappears in concentrated ammonia solution.

Medical uses

Bromide compounds, especially potassium bromide, were frequently used as sedatives in the 19th and early 20th century. This gave the word "bromide" its colloquial connotation of a boring cliché, a bit of conventional wisdom overused as a sedative.

The bromide ion is antiepileptic, and bromide salts are still used as such, particularly in veterinary medicine.

Chronic toxicity from bromide can result in bromism, a syndrome with multiple neurological symptoms. Bromide toxicity can also cause a type of skin eruption. See potassium bromide.

Lithium bromide was used as a sedative beginning in the early 1900s, but it fell into disfavor in the 1940s when some heart patients died after using it as a salt substitute. [ [http://www.webmd.com/content/Article/87/99356.htm?pagenumber=1 Bipolar disorder] ] Like lithium carbonate and lithium chloride it was used as treatment for Bipolar disorder.

In biology

Bromide is needed by eosinophils (white blood cells of the granulocyte class, specialised for dealing with multicellular parasites), which use it to generate antiparasitic brominating compounds by the action of eosinophil peroxidase, an enzyme which preferentially uses bromide. [ [http://www.jbc.org/cgi/content/abstract/264/10/5660 Eosinophils preferentially use bromide to generate halogenating agents - Mayeno et al. 264 (10): 5660 - Journal of Biological Chemistry ] ] . Despite this use by the body, bromide is not known to be strictly necessary for life, as its functions may generally be replaced (though in some cases not as well) by chloride.

Bromide salts are also sometimes used in hot tubs and spas as mild germicidal agents, using the action of an added oxidizing agent to generate "in situ" hypobromite, in a similar fashion to the peroxidase in eosinophils.

History

In some cases, bromide is available in a liquid form at pharmacies. It has been rumoured (in particular by British troops during world War II, who believed it was regularly added to their tea) that bromide can reduce incidence of erections for males (see anaphrodisiac), and this was actually its initial pharmacological use. However, such an action is common to all effective sedatives and not known to be especially particular to bromide.

References