PH3

PH3, or phosphine, is the simplest phosphine compound. It is a colorless, highly toxic, flammable gas with a distinctive odor. It is poorly soluble in water and is ordinarily encountered as a gas at room temperature and pressure. As a reactive phosphorus hydride, it readily participates in redox and combustion processes.

Structure and properties: PH3 has a trigonal pyramidal molecular geometry with phosphorus at the apex and three hydrogen atoms at the base. A lone pair on phosphorus gives the molecule its pyramidal shape. The P–H bonds are covalent, and the molecule is able to act as a weak Lewis base and as a reducing agent in certain reactions. PH3 is miscible with many organic solvents and is highly reactive toward oxygen, chlorine, and other oxidizers, especially when heated.

Preparation and handling: In laboratory settings, phosphine is commonly generated from calcium phosphide by hydrolysis: Ca3P2 + 6 H2O → 3 Ca(OH)2 + 2 PH3. It can also be produced by other phosphorus-containing reagents under controlled conditions. Because of its high toxicity and flammability, PH3 is handled with appropriate ventilation, gas-detection equipment, and procedures designed to prevent ignition and exposure. It is typically stored and used as a compressed gas or in solution under strict safety controls.

Applications: Phosphine is used as a fumigant to control pests in stored grains and other products. In the field of materials science, PH3 serves as a phosphorus source in chemical vapor deposition processes for the growth of III–V semiconductors and related compounds. It is also a precursor in the synthesis of organophosphorus and coordination compounds.

Safety: PH3 is highly toxic, capable of causing severe health effects and death at elevated concentrations. It is also flammable and can form phosphorus oxides upon combustion. Proper engineering controls, monitoring, and protective equipment are required when handling this gas.