Phosphorus Trichloride

Phosphorus trichloride ($PCl_3$) is the most important of the phosphorus trihalides.

Preparation

It is prepared simply by passing dry chlorine gas over heated white phosphorus:

An alternative route uses thionyl chloride reacting with white phosphorus:

Properties

$PCl_3$ is a colourless, oily liquid that is moisture-sensitive: it hydrolyses readily in the presence of water to give phosphorous acid and hydrochloric acid:

It is also reactive toward organic compounds bearing an $-OH$ group, such as acetic acid and ethanol, converting them into their chloro derivatives:

$3C_2H_5OH + PCl_3 \rightarrow 3C_2H_5Cl + H_3PO_3$ …