Organobromine compound
Overview
 
Organobromine compounds are organic compound
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...

s that contain carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

 bonded
Chemical bond
A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms. The bond is caused by the electromagnetic force attraction between opposite charges, either between electrons and nuclei, or as the result of a dipole attraction...

 to bromine
Bromine
Bromine ") is a chemical element with the symbol Br, an atomic number of 35, and an atomic mass of 79.904. It is in the halogen element group. The element was isolated independently by two chemists, Carl Jacob Löwig and Antoine Jerome Balard, in 1825–1826...

. The most pervasive is the naturally produced bromomethane. One prominent application is the use of polybrominated diphenyl ethers as fire-retardants. A variety of minor organobromine compounds are found in nature, but none are biosynthesized or required by mammals. Organobromine compounds have fallen under increased scrutiny for their environmental impact.
Most organobromine compounds, like most organohalide compounds, are relatively nonpolar.
Encyclopedia
Organobromine compounds are organic compound
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...

s that contain carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

 bonded
Chemical bond
A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms. The bond is caused by the electromagnetic force attraction between opposite charges, either between electrons and nuclei, or as the result of a dipole attraction...

 to bromine
Bromine
Bromine ") is a chemical element with the symbol Br, an atomic number of 35, and an atomic mass of 79.904. It is in the halogen element group. The element was isolated independently by two chemists, Carl Jacob Löwig and Antoine Jerome Balard, in 1825–1826...

. The most pervasive is the naturally produced bromomethane. One prominent application is the use of polybrominated diphenyl ethers as fire-retardants. A variety of minor organobromine compounds are found in nature, but none are biosynthesized or required by mammals. Organobromine compounds have fallen under increased scrutiny for their environmental impact.

General properties

Most organobromine compounds, like most organohalide compounds, are relatively nonpolar. Bromine is more electronegative than carbon (2.8 vs 2.5). Consequently, the carbon in a carbon–bromine bond is electrophilic, i.e. alkyl bromides are alkylating agents.

Carbon–halogen
Halogen
The halogens or halogen elements are a series of nonmetal elements from Group 17 IUPAC Style of the periodic table, comprising fluorine , chlorine , bromine , iodine , and astatine...

 bond strengths, or bond dissociation energies are of 115, 83.7, 72.1, and 57.6 kcal/mol for bonded to fluorine
Carbon–fluorine bond
The carbon–fluorine bond is a bond between carbon and fluorine that is a component of all organofluorine compounds. It is the strongest single bond in organic chemistry—and relatively short—due to its partial ionic character. The bond also strengthens and shortens as more fluorines are...

, chlorine, bromine, or iodine, respectively.

The reactivity of organobromine compounds resembles but is intermediate between the reactivity of organochlorine and organoiodine compound
Organoiodine compound
Organoiodine compounds are organic compounds that contain one or more carbon–iodine bonds. They occur widely in organic chemistry, but are relatively rare in nature...

s. For many applications, organobromides represent a compromise of reactivity and cost. The principal reactions for organobromides include dehydrobromination
Dehydrohalogenation
Dehydrohalogenation is an organic reaction from which an alkene is obtained from an alkyl halide . It is also called a β-Elimination reaction and is a type of elimination reaction....

, Grignard reaction
Grignard reaction
The Grignard reaction is an organometallic chemical reaction in which alkyl- or aryl-magnesium halides add to a carbonyl group in an aldehyde or ketone. This reaction is an important tool for the formation of carbon–carbon bonds...

s, reductive coupling
Wurtz reaction
The Wurtz reaction, named after Charles-Adolphe Wurtz, is a coupling reaction in organic chemistry, organometallic chemistry and recently inorganic main group polymers, whereby two alkyl halides are reacted with sodium to form a new carbon-carbon bond:...

, and nucleophilic substitution
Nucleophilic substitution
In organic and inorganic chemistry, nucleophilic substitution is a fundamental class of reactions in which an electron nucleophile selectively bonds with or attacks the positive or partially positive charge of an atom or a group of atoms called the leaving group; the positive or partially positive...

.

From bromine

Alkenes reliably add bromine without catalysis to give the vicinal
Vicinal (chemistry)
In chemistry vicinal stands for any two functional groups bonded to two adjacent carbon atoms. For example the molecule 2,3-dibromobutane carries two vicinal bromine atoms and 1,3-dibromobutane does not....

 dibromides:
RCH=CH2 + Br2 → RCHBrCH2Br

Aromatic compounds undergo bromination simultaneously with evolution of hydrogen bromide. The reaction details following the usual patterns of electrophilic aromatic substitution
Electrophilic aromatic substitution
Electrophilic aromatic substitution EAS is an organic reaction in which an atom, usually hydrogen, appended to an aromatic system is replaced by an electrophile...

:
RC6H5 + Br2 → RC6H4Br + HBr

A prominent application of this reaction is the production of tetrabromobisphenol-A from bisphenol-A.

Free-radical substitution with bromine is commonly used to prepare organobromine compounds. Carbonyl-containing, benzylic, allylic substrates are especially prone to this reactions. For example, the commercially significant bromoacetic acid
Bromoacetic acid
Bromoacetic acid is the chemical compound with the formula CH2BrCO2H. This colorless solid is a relatively strong alkylating agent. Bromoacetic acid and its esters are widely used building blocks in organic synthesis, for example in pharmaceutical chemistry....

 is generated directly from acetic acid and bromine in the presence of phosphorus tribromide
Phosphorus tribromide
Phosphorus tribromide is a colourless liquid with the formula PBr3. It fumes in air due to hydrolysis and has a penetrating odour. It is widely used in the laboratory for the conversion of alcohols to alkyl bromides.-Preparation:...

 catalyst:
CH3CO2H + Br2 → BrCH2CO2H + HBr

Bromine also converts fluoroform
Fluoroform
Fluoroform is the chemical compound with the formula CHF3. It is one of the "haloforms", a class of compounds with the formula CHX3 . Fluoroform is used in diverse niche applications and is produced as a by-product of the manufacture of Teflon...

 to bromotrifluoromethane
Bromotrifluoromethane
Bromotrifluoromethane is an organic halide with the chemical formula CBrF3. Alternative names are Halon 1301, R13B1, Halon 13B1 and BTM.- Table of physical properties :- Uses :...

.

From hydrogen bromide

Hydrogen bromide adds across double bonds to give alkyl bromides, following the Markovnikov rule:
RCH=CH2 + HBr → RCHBrCH3

Under free radical conditions, the direction of the addition can be reversed. Free-radical addition is used commercially for the synthesis of 1-bromoalkanes, precursors to tertiary amines and quaternary ammonium salts. 2-Phenethyl bromide
2-Phenylethylbromide
2-Phenylethylbromide is an organobromide that can be produced by the action of bromine and red phosphorus on 2-phenylethanol.It is moderately toxic by ingestion.When reacted with hydrazine, phenelzine is produced....

 (C6H5CH2CH2Br) is produced via this route from styrene.

Hydrogen bromide can also be used to convert alcohols to alkyl bromides. This reaction is employed in the industrial synthesis of allyl bromide
Allyl bromide
Allyl bromide is an organic halide. Its refractive index is 1.4697 . Allyl bromide is an alkylating agent used in synthesis of polymers, pharmaceuticals, allyls and other organic compounds. Physically, allyl bromide is a clear liquid with an intense, acrid, and persistent smell...

:
HOCH2CH=CH2 + HBr → BrCH2CH=CH2 + H2O

Methyl bromide, another fumigant, is generated from methanol and hydrogen bromide.

From bromide salts

Bromide ions, as provided by salts like sodium bromide
Sodium bromide
Sodium bromide is an inorganic compound with the formula NaBr. It is a high-melting white, crystalline solid that resembles sodium chloride. It is a widely used source of the bromide ion and has many applications.-Synthesis, structure, reactions:...

, function as a nucleophiles in the formation of organobromine compounds by displacement.

Industrially significant organobromine compounds


Fire-retardants

Organobromine compounds are widely used as fire-retardants. The most prominent member is tetrabromobisphenol-A (4,4'-(1-methylethylidene)bis-(2,6-di-bromophenol, see figure). It and tetrabromophthalic anhydride are precursors to polymers wherein the backbone features covalent carbon-bromine bonds. Other fire retardants, such as hexabromocyclododecane and the bromodiphenyl ethers, are additives and are not chemically attached to the material they protect. The use of organobromine fire-retardants is growing but is also controversial because they are persistent pollutants.

Fumigants and biocides

Ethylene bromide, obtained by addition of bromine to ethylene, was once of commercial significance as a component of leaded gasoline. It was also a popular fumigant in agriculture, displacing 1,2-dibromo-3-chloropropane ("DBCB"). Both applications are declining owing to environmental and health considerations. Methyl bromide is also an effective fumigant, but its production and use are controlled by the Montreal Protocol
Montreal Protocol
The Montreal Protocol on Substances That Deplete the Ozone Layer is an international treaty designed to protect the ozone layer by phasing out the production of numerous substances believed to be responsible for ozone depletion...

. Growing in use are organobromine biocides used in water treatment. Representative agents include bromoform
Bromoform
Bromoform is a pale yellowish liquid with a sweet odor similar to chloroform, a halomethane or haloform. Its refractive index is 1.595 . Bromoform is produced naturally by phytoplankton and seaweeds in the ocean and this is thought to be the predominant source to the environment...

 and dibromodimethylhydantoin
DBDMH
DBDMH is an organic compound derived from the heterocycle called dimethylhydantoin. This white crystalline compound with a slight bromine odor is widely used as a disinfectant used for drinking water purification, recreational water treatment, as a bleaching agent in pulp and paper mills, and for...

 (“DBDMH”).

Dyes

Many dyes contain carbon-bromine bonds. The naturally occurring Tyrian purple
Tyrian purple
Tyrian purple , also known as royal purple, imperial purple or imperial dye, is a purple-red natural dye, which is extracted from sea snails, and which was possibly first produced by the ancient Phoenicians...

 (6,6’-dibromoindigo) was a valued dye before the development of the synthetic dye industry in the late 19th century. Several brominated anthroquinone derivatives are used commercially. Bromothymol blue
Bromothymol blue
Bromothymol blue is a chemical indicator for weak acids and bases. The chemical is also used for observing photosynthetic activities or respiratory indicators .Bromothymol blue acts as a weak acid in solution...

 is a popular indicator in analytical chemistry
Analytical chemistry
Analytical chemistry is the study of the separation, identification, and quantification of the chemical components of natural and artificial materials. Qualitative analysis gives an indication of the identity of the chemical species in the sample and quantitative analysis determines the amount of...

.

Pharmaceuticals

Commercially available organobromine pharmaceuticals include the vasodialator nicergoline
Nicergoline
Nicergoline is an ergot derivative used to treat senile dementia and other disorders with vascular origins. It has been found to increase mental agility and enhance clarity and perception. It decreases vascular resistance and increases arterial blood flow in the brain, improving the utilization of...

, the sedative brotizolam
Brotizolam
Brotizolam is a sedative-hypnotic thienodiazepine drug which is a benzodiazepine analog. It possesses anxiolytic, anticonvulsant, hypnotic, sedative and skeletal muscle relaxant properties, and is considered to be similar in effect to short-acting benzodiazepines such as triazolam...

, and the anticancer agent pipobroman
Pipobroman
Pipobroman is an alkylating agent....

. Otherwise, organobromine compounds are rarely pharmaceutically useful, in contrast to the situation for organofluorine compounds
Organofluorine chemistry
Organofluorine chemistry describes the chemistry of organofluorine compounds, organic compounds that contain the carbon–fluorine bond. Organofluorine compounds find diverse applications ranging from oil- and water-repellents to pharmaceuticals, refrigerants and reagents in catalysis...

. Several drugs are produced as the bromide (or equivalents, hydrobromide) salts, but in such cases bromide serves as an innocuous counterion of no biological significance.

Organobromine compounds in nature

Organobromine compounds are the most common organohalides in nature. Even though the concentration of bromide is only 0.3% of that for chloride in sea water, organobromine compounds are more prevalent in marine organisms than organochlorine derivatives. Their abundance reflects the easy oxidation of bromide to the equivalent of Br+, a potent electrophile. The enzyme bromoperoxidase
Bromoperoxidase
Bromoperoxidases are enzymes that catalyse the bromination of hydrocarbons. The enzymes accomplish this reaction via the following reaction:Related chloroperoxidase enzymes effect chlorination....

 catalyzes this reaction. The oceans are estimated to release 1–2 million tons of bromomethane annually. Some edible algae contain 80% by weight bromoform (CHBr3). Some of these organobromine compounds are employed in a form of interspecies "chemical warfare." Only one organobromine compound is found in humans.


In addition to conventional brominated natural products, a variety of organobromine compounds result from the biodegradation of fire-retardants. Metabolites include methoxylated and hydroxylated aryl bromides as well as brominated dioxin derivatives. Such compounds are considered persistent organic pollutant
Persistent organic pollutant
thumb|right|275px|State parties to the Stockholm Convention on Persistent Organic PollutantsPersistent organic pollutants are organic compounds that are resistant to environmental degradation through chemical, biological, and photolytic processes...

s and have been found in mammals.

Safety

Alkyl bromine compounds are often alkylating agents and the brominated aromatic derivatives are implicated as hormone disruptors. Of the commonly produced compounds, ethylene dibromide is of greatest concern as it is both highly toxic and highly carcinogenic.
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