Copper (I) Bromide

Cuprous Bromide or Copper (I) Bromide is a pale, crystalline powder with a faint green hue. It does not form a crystalline hydrate.  It is used as a precursor for lasers and light-emitting diodes.  It is also used as a catalyst for organic synthesis.

Despite being an ionic compound, it is only sparingly soluble in pure water.  This is unlike Copper (II) Bromide (cupric bromide) which is highly soluble in water.  However, Copper (I) Bromide is readily soluble in dilute acidic or alkaline solutions, such as those containing ammonium hydroxide, hydrochloric acid, or hydrobromic acid.  Copper (I) Bromide is also insoluble in most organic solvents, so it is coordinated with organic ligands such as bipyridine and N,N,N’,N”,N”-pentamethyldiethylenetriamine (PMDETA) to solubilize it.

Copper (I) Bromide is a widely recognized catalyst. It plays a crucial role in the Sandmeyer reaction, facilitating the conversion of an aryl diazonium salt into a reactive radical. This radical subsequently abstracts the bromide ion from the copper complex, resulting in the formation of a Bromide-carbon bond on the aromatic ring at the carbon atom previously bonded to the amine group. This process provides enhanced regiochemical control compared to direct halogenation. Furthermore, Cuprous Bromide finds applications in click chemistry, specifically in the interaction between azides and alkynes, as well as in atom transfer radical polymerization.

Copper (I) Bromide is also used to create Copper Bromide lasers, which are used for dermatology treatments.  Such lasers emit in the yellow region of light, which is absorbed better by hemoglobin than melanin.  In addition, compared to other yellow-emitting lasers, Copper (I) Bromide lasers are more powerful.

References

1. Nanda, A. K., & Matyjaszewski, K. (2003). Effect of [PMDETA]/[Cu(I)] Ratio, Monomer, Solvent, Counterion, Ligand, and Alkyl Bromide on the Activation Rate Constants in Atom Transfer Radical Polymerization.(opens in new tab) Macromolecules, 36(5), 1487–1493. https://doi.org/10.1021/MA0340107
2. Akhtar, R., Zahoor, A. F., Rasool, N., Ahmad, M., & Ali, K. G. (2021). Recent trends in the chemistry of Sandmeyer reaction: a review.(opens in new tab) Molecular Diversity, 26(3), 1837. https://doi.org/10.1007/S11030-021-10295-3
3. Liang, L., Ruiz, J., & Astruc, D. (2011). The efficient copper(I) (hexabenzyl)tren catalyst and dendritic analogues for green “click” reactions between azides and alkynes in organic solvent and in water: Positive dendritic effects and monometallic mechanism.(opens in new tab) Advanced Synthesis and Catalysis, 353(18), 3434–3450. https://doi.org/10.1002/ADSC.201100449
4. Kazaryan, M. A., Petrash, G. G., & Trofimov, A. N. (1980). Comparison of the characteristics of copper, copper chloride, and copper bromide vapor lasers.(opens in new tab) Soviet Journal of Quantum Electronics, 10(3), 328. https://doi.org/10.1070/QE1980V010N03ABEH009984
5. McCoy, S., Hanna, M., Anderson, P., McLennan, G., & Repacholi, M. (1996). An evaluation of the copper-bromide laser for treating telangiectasia.(opens in new tab) Dermatologic Surgery, 22(6), 551–557. https://doi.org/10.1111/J.1524-4725.1996.TB00373.X