What Is Phosphorus Pentachloride?
Phosphorus pentachloride is an inorganic compound with the formula PCl5. It is a widely used reagent in the synthesis of various substances, similar to phosphorus trichloride and phosphoryl chloride.
It has a molar mass of 208.2 g/mol, sublimates at 160°C, has a specific gravity of 2.1, and a CAS number of 10026-13-8. In its gaseous form, phosphorus pentachloride exhibits a trigonal bipyramidal structure. Upon loss of a chloride ion, it forms a tetrahedral cation, and with an additional chloride ion, an octahedral anion.
Uses of Phosphorus Pentachloride
Phosphorus pentachloride is utilized in the manufacture of pharmaceuticals, dyes, and other chlorides. Its strong reactivity makes it an effective chlorinating agent for both organic and inorganic compounds.
1. Synthesis of Organic Compounds
It is employed to produce carboxylic acid chlorides from carboxylic acids and alkyl chlorides from alcohols. While efficient, byproducts like trichloride phosphate can complicate purification, leading to the preference for alternatives like thionyl chloride in laboratory settings. Phosphorus pentachloride is also used to prepare the Vilsmeier-Haack reagent, aiding in the synthesis of aromatic ketones and aldehydes.
2. Synthesis of Inorganic Compounds
It can chlorinate inorganic substances, including metals, and form adducts with metal chlorides. For example, it reacts with lithium fluoride to produce lithium hexafluorophosphate, a key electrolyte in lithium-ion batteries.
Properties of Phosphorus Pentachloride
A white or pale yellow crystalline solid, phosphorus pentachloride fumes in moist air due to its high hygroscopicity. It is produced from phosphorus trichloride and chlorine gas, and is extremely reactive, especially with water, producing hydrogen chloride and phosphoric acid.
Other Information on Phosphorus Pentachloride
Hazards of Phosphorus Pentachloride
Phosphorus pentachloride is acutely toxic, corrosive, and severely irritating to skin and eyes. It poses explosion risks when reacting with water. Proper protective gear, including eyewear and rubber gloves, is essential for handling. It is regulated under various safety and health legislations, emphasizing the need for careful risk assessment and handling precautions.