Phosphorus trichloride is a colourless, fuming liquid with a sharp characteristic odour that may resemble the hydrogen chloride. From a chemical point of view, it is an inorganic acid chloride. Its reaction with water is immediate and very rapid, it is accompanied by a strong exothermic effect and the release of gaseous hydrogen chloride. Therefore, its transport and storage should be carried out in sealed containers, protected from moisture or water.
Since phosphorus trichloride is characterized by strong caustic properties, the packaging should be made of a suitable material, preferably a specified quality of steel. This substance may cause burns in contact with the skin, therefore personal protective equipment is important when working with phosphorus trichloride. Due to the high vapor pressure, phosphorus trichloride should also be protected against high temperatures.
Phosphorus trichloride is produced directly from phosphorus and chlorine. Thanks to the production technology used, it is characterized by high purity manifested by, among others, very low content of impurities in the form of phosphorus compounds in the fifth oxidation state (i.e., phosphorus oxychloride or PCl5). This is an undeniable superiority and market advantage of this product, especially when it is used to synthesise substances with the required very high purity. In this case the low content of elemental sulphur and heavy metals such as arsenic, iron, lead, nickel, chromium and others are also important.
PCl3 is a high-quality intermediate/raw material. Thanks to high reactivity of phosphorus-chlorine bonds, it has become an excellent substrate for phosphoric and chlorinated chemicals, widely used in chemical and pharmaceutical industries. Its reactivity allows the use of PCl3 for the synthesis of, inter alia, active substances (API – Active Pharmaceutical Ingredient).
Phosphorus trichloride is most commonly used as:
a phosphorous introducing agent to the substrate molecule through the formation of phosphites as well as their subsequent reaction – to form e.g. phosphonates (including hydroxyphosphonates and aminophosphonates), which are inhibitors of many enzymes, acting as transition-state mimetics;
chlorination reagent, used in substitution reactions of hydroxyl groups with a chlorine atom;
activator in coupling reactions, converting carboxylic or sulfonic / sulfinic acids into their chlorides (more reactive derivatives), conjugated to various nucleophiles (e.g., alcohols to form esters or amines to form amides);
a substrate for the synthesis of catalysts, where it acts as a building block for ligands.
The above-described processes are used, inter alia, for the synthesis of drugs based on sulphonamide derivatives (phosphorus trichloride converts sulphonic acids into amides, e.g. chlorthalidone – a diuretic, sulfadiazine – bacteriostatic).
Phosphorus trichloride is also a key substrate in the synthesis of bisphosphonates using the method of von Bayer and Hoffmann. Bisphosphonates are used as bone diseases therapeutic agents (e.g., osteoporosis), inhibiting bone resorption and increasing its mass, e.g. alendronate, risedronate, and etidronate.