Copper benzoate

Description

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.

Chemical Properties

Blue, crystalline powder; odorless.Slightly soluble in cold water, acids, and alcohol.

Physical properties

Copper (II) benzoates exists in at least two structural forms , depending on the degree of hydration. As for copper (II) acetate , the benzoate adopts a "Chinese lantern" structure, 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 . A hydrated form is also known, wherein each Cu (II) center is bound to four water ligands and benzoate .

Uses

Cupric benzoate monohydrate (cas# 533-01-7) is used as a catalyst in the preparation of positive resist compositions comprising sulfonium compounds as acid diffusion inhibitors for high resolution and minimal line edge roughness.

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 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 yello). Emission from potassium does not complicate the emission spectrum.

Purification Methods

Recrystallise it from hot water. Its solubility in EtOH/*C6H6 (90%) at 25o is 0.1%. [Crawford & Stewart J Chem Soc 228, 289 1953, Beilstein 9 H 84, 9 I 60, 9 III 376, 9 IV 280.]