Copper(I) bromide
Copper bromide is the chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

 with the formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....

 CuBr. This diamagnetic solid adopts a polymeric structure akin to that for zinc sulfide
Zinc sulfide
Zinc sulfide is a inorganic compound with the formula ZnS. ZnS is the main form of zinc in nature, where it mainly occurs as the mineral sphalerite...

. The compound is widely used in the synthesis
Organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...

 of organic compounds.

Preparation, basic properties, structure

The pure solid is colourless, although samples are often colored due to the presence of copper(II) impurities (see picture). The copper(I) ion also oxidizes easily in air. It is commonly prepared by the reduction of cupric salts with sulfite
Sulfites are compounds that contain the sulfite ion SO. The sulfite ion is the conjugate base of bisulfite. Although the acid itself is elusive, its salts are widely used.-Structure:...

 in the presence of bromide. For example, the reduction of copper(II) bromide
Copper(II) bromide
Copper bromide is a chemical compound. It is used in photographic processing as an intensifier and as a brominating agent in organic synthesis....

 with sulfite yields copper(I) bromide and hydrogen bromide
Hydrogen bromide
Hydrogen bromide is the diatomic molecule HBr. HBr is a gas at standard conditions. Hydrobromic acid forms upon dissolving HBr in water. Conversely, HBr can be liberated from hydrobromic acid solutions with the addition of a dehydration agent, but not by distillation. Hydrogen bromide and...

2 CuBr2 + H2O + SO32− → 2 CuBr + SO42− + 2 HBr

CuBr is insoluble in most solvents due to its polymeric structure, which features four-coordinated, tetrahedral Cu centers interconnected by bromide ligands (ZnS structure). Upon treatment with Lewis bases, CuBr converts to molecular adduct
An adduct is a product of a direct addition of two or more distinct molecules, resulting in a single reaction product containing all atoms of all components. The resultant is considered a distinct molecular species...

s. For example with dimethyl sulfide
Dimethyl sulfide
Dimethyl sulfide or methylthiomethane is an organosulfur compound with the formula 2S. Dimethyl sulfide is a water-insoluble flammable liquid that boils at and has a characteristic disagreeable odor. It is a component of the smell produced from cooking of certain vegetables, notably maize,...

, the colorless complex is formed:
CuBr + S(CH3)2 → CuBr(S(CH3)2)

In this coordination complex, the copper is two-coordinate, with a linear geometry. Other soft ligands afford related complexes. For example triphenylphosphine
Triphenylphosphine is a common organophosphorus compound with the formula P3 - often abbreviated to PPh3 or Ph3P. It is widely used in the synthesis of organic and organometallic compounds. PPh3 exists as relatively air stable, colorless crystals at room temperature...

 gives CuBr(P(C6H5)3), although this species has a more complex structure.

Applications in organic chemistry

In the Sandmeyer reaction
Sandmeyer reaction
The Sandmeyer reaction is a chemical reaction used to synthesize aryl halides from aryl diazonium salts. It is named after the Swiss chemist Traugott Sandmeyer....

, CuBr is employed to convert diazonium salts into the corresponding aryl
In the context of organic molecules, aryl refers to any functional group or substituent derived from an aromatic ring, be it phenyl, naphthyl, thienyl, indolyl, etc....

ArN2+ + CuBr → ArBr + N2 + Cu+

The aforementioned complex CuBr(S(CH3)2) is widely used to generate organocopper reagents. Related CuBr complexes are catalysts for Atom Transfer Radical Polymerization
ATRP (chemistry)
Atom transfer radical polymerization is an example of a living polymerization or a controlled/living radical polymerization . Like its counter part, ATRA or atom transfer radical addition, it is a means of forming carbon-carbon bond through transition metal catalyst...

and Cu-catalyzed Cross-Dehydrogenative Couplings (CDC).

External links

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