Copper(II) bromide
Chemical compound
From Wikipedia, the free encyclopedia
Copper(II) bromide (CuBr2) is a chemical compound that forms an unstable tetrahydrate CuBr2·4H2O. It is used in photographic processing as an intensifier and as a brominating agent in organic synthesis.[3]
Anhydrous | |
 Tetrahydrate | |
| Names | |
|---|---|
| Other names
Cupric bromide Copper dibromide | |
| Identifiers | |
3D model (JSmol) |
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| ChemSpider | |
| ECHA InfoCard | 100.029.243 |
| EC Number |
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PubChem CID |
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| UNII | |
CompTox Dashboard (EPA) |
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| Properties | |
| CuBr2 | |
| Molar mass | 223.37 g/mol |
| Appearance | grayish black crystals deliquescent |
| Density | 4.710 g/cm3, solid |
| Melting point | 498 °C (928 °F; 771 K) |
| Boiling point | 900 °C (1,650 °F; 1,170 K) |
| 55.7 g/100 mL (20 °C) | |
| Solubility | Soluble in alcohol, acetone, ammonia, insoluble in benzene, ether, sulfuric acid |
| +685.5·10−6 cm3/mol | |
| Structure | |
| monoclinic | |
| Hazards | |
| GHS labelling:[1] | |
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| Danger | |
| H302, H314, H410 | |
| P260, P264, P264+P265, P270, P273, P280, P301+P317, P301+P330+P331, P302+P361+P354, P304+P340, P305+P354+P338, P316, P317, P321, P330, P363, P391, P405, P501 | |
| NFPA 704 (fire diamond) | |
| NIOSH (US health exposure limits):[2] | |
PEL (Permissible) |
TWA 1 mg/m3 (as Cu) |
REL (Recommended) |
TWA 1 mg/m3 (as Cu) |
IDLH (Immediate danger) |
TWA 100 mg/m3 (as Cu) |
| Related compounds | |
Other anions |
Copper(II) fluoride Copper(II) chloride |
Other cations |
Copper(I) bromide Nickel(II) bromide Zinc bromide Cadmium bromide Mercury(II) bromide |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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It is also used in the copper vapor laser, a class of laser where the medium is copper bromide vapour formed in-situ from hydrogen bromide reacting with the copper discharge tube.[4] Producing yellow or green light, it is used in dermatological applications.
Occurrence
Molecular and crystal structure
In the solid state CuBr2 has a polymeric structure, with CuBr4 planar units connected on opposite sides to form chains. The crystal structure is monoclinic, space group C2/m, with lattice constants a = 714 pm, b = 346 pm, c = 718 pm, e ß = 121° 15'.[7] CuBr2 monomeric units are present in the gas phase at high temperature.[8]
The tetrahydrate, structurally formulated as [CuBr2(H2O)2]·2H2O, has a monoclinic crystal structure and consists of distorted square planar trans-[CuBr2(H2O)2] centres as well as two molecules of water.[9]
Synthesis
Copper(II) bromide can be obtained by combining copper(II) oxide and hydrobromic acid:[10]
- CuO + 2HBr → CuBr2 + H2O.
The tetrahydrate can be produced by recrystallization of solutions of copper(II) bromide at 0 °C. If heated above 18 °C, it releases water to produce the anhydrous form.[9]
Purification
Copper(II) bromide is purified by crystallization twice from water, filtration to remove any CuBr and concentration under vacuum. This product is dehydrated using phosphorus pentoxide.[11]
Usage
Copper(II) bromide lasers produce pulsed yellow and green light and have been studied as a possible treatment for cutaneous lesions.[12] Experiments have also shown copper bromide treatment to be beneficial for skin rejuvenation.[13] It has been widely used in photography as its solution was used as the bleaching step for intensifying collodion and gelatin negatives.[14] Copper(II) bromide has also been proposed as a possible material in humidity indicator cards.[15]
Reactions
Copper(II) bromide in chloroform-ethyl acetate reacts with ketones resulting in the formation of alpha-bromo ketones. The resulting product can be directly used for the preparation of derivatives. This heterogeneous method is reported to be the most selective and direct method of formation of α-bromo ketones.[16]
A CuBr2/LiBr reagent combination can be used in the dibromination of n-pentenyl glycosides (NPGs). This allows for an NPG to serve as a glycosyl acceptor during halonium-promoted couplings. Such reactions give high yields of the dibromides from alkenyl sugars that are resistant to a direct reaction with molecular bromine.[17]