Copper(II) bromide

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.[2]

Copper (II) bromide

Anhydrous

Tetrahydrate
Names
Other names
Cupric bromide
Copper dibromide
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.029.243
EC Number
  • 232-167-2
UNII
  • InChI=1S/2BrH.Cu/h2*1H;/q;;+2/p-2 checkY
    Key: QTMDXZNDVAMKGV-UHFFFAOYSA-L checkY
  • InChI=1/2BrH.Cu/h2*1H;/q;;+2/p-2
    Key: QTMDXZNDVAMKGV-NUQVWONBAD
  • [Cu+2].[Br-].[Br-]
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, ethyl ether, sulfuric acid
+685.5·10−6 cm3/mol
Structure
monoclinic
Hazards
NFPA 704 (fire diamond)
NFPA 704 four-colored diamond
2
0
0
NIOSH (US health exposure limits):
PEL (Permissible)
 TWA 1 mg/m3 (as Cu)[1]
REL (Recommended)
 TWA 1 mg/m3 (as Cu)[1]
IDLH (Immediate danger)
 TWA 100 mg/m3 (as Cu)[1]
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).
checkY verify (what is checkY☒N ?)
Infobox references

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.[3] Producing yellow or green light, it is used in dermatological applications.

Synthesis

Copper(II) bromide can be obtained by combining copper oxide and hydrobromic acid:[4]

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.[5]

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.[6]

Molecular and crystal structure
Crystal structure of copper(II) bromide

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] It forms bright green-blue solutions in water, and reacts with Aluminium exothermically: 3 CuBr2 + 2 Al forms 2 AlBr3 and 3 Cu.

The tetrahydrate, structurally formulated as [CuBr2(H2O)2]·2H2O, has a monoclinic crystal structure and consists of distorted square planartrans-[CuBr2(H2O)2] centres as well as two molecules of water.[5]

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.[9]

Dibromination of NPGs, n-pentenyl glycosides, using CuBr2/LiBr reagent combination was performed in order for an NPG to serve as a glycosyl acceptor during halonium-promoted couplings. Such reaction gives high yield of the dibromides from alkenyl sugars that are resistant to a direct reaction with molecular bromine.[10]

Usage

Copper(II) bromide lasers produce pulsed yellow and green light and have been studied as a possible treatment for cutaneous lesions.[11] Experiments have also shown copper bromide treatment to be beneficial for skin rejuvenation.[12] It has been widely used in photography as its solution was used as the bleaching step for intensifying collodion and gelatin negatives.[13] Copper(II)bromide has also been proposed as a possible material in humidity indicator cards.[14]

Safety

Copper(II) bromide is harmful if swallowed. It affects the central nervous system, brain, eyes, liver, and kidneys. It causes irritation to skin, eyes, and respiratory tract.

Natural occurrence

Pure copper(II) bromide is as yet (2020) unknown among minerals. However, barlowite, Cu4BrF(OH)6, contains both copper and bromide.[15][16]

See also

Copper(I) bromide

References
  1. NIOSH Pocket Guide to Chemical Hazards. "#0150". National Institute for Occupational Safety and Health (NIOSH).
  2. Huang, Jianhui; Macdonald, Simon J. F.; Harrity, Joseph P. A. (2009). "A cycloaddition route to novel triazole boronic esters". Chem. Commun. (4): 436–438. doi:10.1039/b817052e. PMID 19137177.
  3. Livingstone, E. S.; Maitland, A. (1991). "A high power, segmented metal, copper bromide laser". Measurement Science and Technology. 2 (11): 1119. Bibcode:1991MeScT...2.1119L. doi:10.1088/0957-0233/2/11/022. ISSN 0957-0233. S2CID 250801465.
  4. Breitinger, D. K.; Herrmann, W. A., eds. (1999). Synthetic methods of Organometallic and Inorganic Chemistry. New York: Thieme Medical Publishers. ISBN 0-86577-662-8.
  5. Kenji Waizumi; Hideki Masuda; Hitoshi Ohtaki (1992). "X-ray structural studies of FeBr2·4H2O, CoBr2·4H2O, NiCl2·4H2O and CuBr2·4H2O. cis/trans selectivity in transition metal(II) dihalide tetrahydrate". Inorganica Chimica Acta. 192 (2): 173–181. doi:10.1016/S0020-1693(00)80756-2.
  6. Hope et al. J Chem Soc 5226 1960, Glemser & Sauer in Handbook of Preparative Inorganic Chemistry (Ed.Brauer) Academic Press Vol II p 1009 1965.
  7. Helmholz, Lindsay (1947). "The Crystal Structure of Anhydrous Cupric Bromide". J. Am. Chem. Soc. 69 (4): 886–889. doi:10.1021/ja01196a046.
  8. Conry, Rebecca R. (2006). "Copper: Inorganic & Coordination Chemistry". Encyclopedia of Inorganic Chemistry (2nd ed.). John Wiley & Sons. doi:10.1002/0470862106.ia052. ISBN 978-0-470-86210-0.
  9. King, L. Carroll; Ostrum, G. Kenneth (1964). "Selective Bromination with Copper(II) Bromide". J. Org. Chem. 29 (12): 3459–3461. doi:10.1021/jo01035a003.
  10. Rodebaugh, Robert; Debenham, John S.; Fraser-Reid, Burt J.; Snyder, James P. (1999). "Bromination of Alkenyl Glycosides with Copper(II) Bromide and Lithium Bromide: Synthesis, Mechanism, and DFT Calculations". J. Org. Chem. 64 (5): 1758–1761. doi:10.1021/jo9718509. PMID 11674253.
  11. McCoy, S.; Hanna, M.; Anderson, P.; McLennan, G.; Repacholi, M. (June 1996). "An evaluation of the copper-bromide laser for treating telangiectasia". Dermatol. Surg. 22 (6): 551–7. doi:10.1111/j.1524-4725.1996.tb00373.x. ISSN 1076-0512. PMID 8646471. S2CID 22626280.
  12. Davis P., Town G., Haywards H. A practical comparison of IPLs and the Copper Bromide Laser for photorejuvenation, acne and the treatment of vascular&pigmented lesions.
  13. Diane Heppner The Focal Encyclopedia of Photography, Inc. Elsevier 20074th edition
  14. George McKedy US Patent Application Publication, Pub.No.: US2010/0252779 A1
  15. "Verification".
  16. "List of Minerals". 21 March 2011.
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