Chromium hexacarbonyl

Chromium hexacarbonyl, also known by its chemical formula Cr(CO)₆, is a chemical compound consisting of one chromium atom and six carbon monoxide molecules. This compound is a notable example of a metal carbonyl, which are complexes that feature transition metals bonded to carbon monoxide ligands. Chromium hexacarbonyl is important in both industrial applications and research within organometallic chemistry.

Properties

Chromium hexacarbonyl is a colorless, volatile, and crystalline solid at room temperature. It has a melting point of 130°C and sublimes upon heating. This compound is soluble in organic solvents such as benzene, toluene, and alcohols, but it is insoluble in water. It is notable for its octahedral molecular geometry and is a diamagnetic substance due to the absence of unpaired electrons.

Synthesis

The synthesis of chromium hexacarbonyl is typically achieved through the direct reaction of chromium metal with carbon monoxide at high temperatures and pressures. This process requires a finely divided chromium powder to increase the surface area for the reaction:

\[ \text{Cr} + 6 \text{CO} \rightarrow \text{Cr(CO)}_6 \]

Alternative methods involve the reduction of chromium compounds, such as chromium(III) chloride, in the presence of carbon monoxide under similar conditions.

Applications

Chromium hexacarbonyl is used as a catalyst and a reagent in organic synthesis, particularly in processes involving the homologation of aldehydes and the preparation of alcohols, acids, and hydrocarbons. Its ability to undergo transformation into other organometallic compounds makes it a valuable starting material in the synthesis of complex organochromium compounds.

Safety and Environmental Concerns

Chromium hexacarbonyl is highly toxic and poses significant health risks upon exposure. It is a potent irritant to the skin, eyes, and respiratory system. Inhalation of its vapors can lead to severe lung damage and pulmonary edema. Due to its toxicity, handling of chromium hexacarbonyl requires strict safety precautions, including the use of appropriate personal protective equipment and ventilation controls.

Environmental exposure to chromium hexacarbonyl can occur through industrial emissions. It is important to monitor and control its release into the environment to prevent contamination of air and water sources. Regulatory guidelines and safety protocols are in place to manage its use and disposal.

Regulation

The handling and use of chromium hexacarbonyl are subject to regulation under various chemical safety standards and guidelines, including those set by the OSHA, the EPA, and international bodies such as the European Chemicals Agency (ECHA).

See Also

• Metal carbonyl
• Organometallic chemistry
• Transition metal