Copper benzoate

Copper benzoate is the chemical compound with the formula Cu(C6H5CO2)2. This coordination complex is derived from the cupric ion and the conjugate base of benzoic acid. Because copper emits blue in a flame, this salt has found some use as a source of blue light in fireworks.[2]

Copper benzoate
Names
IUPAC name
copper dibenzoate
Other names
cupric benzoate
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.007.776
UNII
  • InChI=1S/2C7H6O2.Cu/c2*8-7(9)6-4-2-1-3-5-6;/h2*1-5H,(H,8,9);/q;;+2/p-2 checkY
    Key: YEOCHZFPBYUXMC-UHFFFAOYSA-L checkY
  • InChI=1/2C7H6O2.Cu/c2*8-7(9)6-4-2-1-3-5-6;/h2*1-5H,(H,8,9);/q;;+2/p-2
    Key: YEOCHZFPBYUXMC-NUQVWONBAX
  • [Cu+2].[O-]C(=O)c1ccccc1.[O-]C(=O)c1ccccc1
  • Chinese lantern structure: c0ccccc0[C-](O[Cu+2]123)O[Cu+2](O[C-](O1)c0ccccc0)(O[C-](O2)c0ccccc0)O[C-](O3)c0ccccc0
Properties
C14H10CuO4
Molar mass 305.7728 g/mol
Appearance blue solid
Density 1.197g/cm3
Boiling point 249.3 °C (480.7 °F; 522.5 K) at 760mmHg
Hazards
Flash point 111.4 °C (232.5 °F; 384.5 K)
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 cations
 sodium benzoate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Preparation

In laboratory, copper benzoate can be made by combining aqueous solutions of potassium benzoate with copper sulfate. Copper benzoate precipitates as a pale blue solid:

2 C6H5COOK + CuSO4 → Cu(C6H5COO)2 + K2SO4

The primary use of this compound is in production of blue flame in fireworks. Copper benzoate made from sodium benzoate for use in fireworks may result in strong yellow dilution of the flame unless the precipitate is carefully washed to remove sodium ion (which emits brightly yellow). Emission from potassium does not complicate the emission spectrum.

Structure

Copper(II) benzoates exists in at least two structural forms, depending on the degree of hydration. As of copper(II) acetate, the benzoate adopts a "Chinese lantern" structure,[3] wherein a pair of copper centers are linked by four bridging carboxylate ligands. Typically one site on each copper center is occupied by water, which can be replaced by other ligands.[4] A hydrated form is also known, wherein each Cu(II) centre is bound to four water ligands and benzoate.[5]

References
  1. NIOSH Pocket Guide to Chemical Hazards. "#0150". National Institute for Occupational Safety and Health (NIOSH).
  2. "Wouter's Practical Pyrotechnics page". Archived from the original on 2007-01-07.
  3. Wells, A.F. (1984) Structural Inorganic Chemistry, Oxford: Clarendon Press. ISBN 0-19-855370-6.
  4. T. Kawata, H. Uekusa, S. Ohba, T. Furukawa, T. Tokii, Y. Muto, M. Kato "Magneto-structural correlation in dimeric copper(II) benzoates" Acta Crystallogr. 1992, vol. B48, pp. 253-261. doi:10.1107/S0108768191012697
  5. Koizumi, H.; Osaki, K.; Watanabé, T. "Crystal Structure of Cupric Benzoate Trihydrate Cu(C6H5COO)2.3H2O" Journal of the Physical Society of Japan 1963, Volume 18, pp. 117.
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