Phosphorus oxychloride is a colourless liquid with the formula POCl3. It hydrolyses in moist air releasing phosphoric acid and fumes of hydrogen chloride. It is mainly used to make phosphate esters.

Reactions with water

POCl3 reacts with water to give hydrogen chloride and phosphoric acid:

O=PCl3 + 3 H2O → O=P(OH)3 + 3 HCl

Uses

Phosphorus oxychloride is an important intermediate in the production of triarylphosphate esters (e.g., triphenyl phosphate and tricresyl phosphate), which have been used as flame retardants and plasticizers for PVC. It is acutely toxic to the eyes, throat, and respiratory tract. Phosphorus oxychloride is also used in nuclear reprocessing, as chlorinating agent, especially to replace oxygen in organic compounds, as solvent in cryoscopy and the semiconductor industry.

Hazards

Phosphorus oxychloride has a strong oxidizing and liposoluble effects; besides burning the digestive tract, it can also cause acute necrosis and autolysis in the liver when absorbed through the digestive tracts. Additionally, besides burning the skin, when completely absorbed through the skin, 3% can cause death in animals. When phosphorus oxychloride is inhaled and comes in contact with the moist respiratory tract mucosa, it will break down into phosphoric acid and hydrogen chloride, and it will irritate and corrode the mucosa. When humans contact at a concentration of 70mg/m3, they will usually exhibit symptoms after a 2-6h latency period, including respiratory tract mucosa irritation and eye pain. Serious cases include a choking sensation, cyanosis, pulmonary edema, heart failure, anemia, liver damage, and proteinuria.

Warnings and Precautions

Phosphorus oxychloride is often used in industrial production; there are many details to take note of when using phosphorus oxychloride to prevent safety concerns and accidents:

1. Phosphorus oxychloride preparation: As many factories use water jet vacuums to store phosphorus oxychloride, great attention must be paid to the switch order to prevent accidents. The buffer vacuum tank must be frequently inspected to prevent the water from being sucked into storage containers and causing accidents.

2. Phosphorus oxychloride with hydrogen chloride: take care to not add an excess of phosphorus chloride. If there is an excess, slowly drop in water to hydrolyze the phosphorus chloride, and then remove the produced phosphoric acid.

3. Slowly place any materials containing phosphorus oxychloride into a hydrolysis kettle containing cold water and mix continuously. Avoid adding water to the material.

4. Whenever using systems containing phosphorus oxychloride, take care to measure the water content in all the components to prevent an excess of water from causing an explosion.

5. Frequently inspect reactors for cracks and imperfections to prevent water from leaking in and coming in contact with the phosphorus oxychloride.

6. When adding phosphorus oxychloride to a reactor, remain observant and stop adding material immediately if there are any abnormal occurrences. Only continue adding material after investigating the cause of these occurrences.

7. Phosphorus oxychloride reacts slowly with water when at a lower temperature. Thus, drop in slowly to prevent sudden intense reactions.

8. Phosphorus oxychloride can be used in combination with dichloroethane and toluene solutions, but not with alcohol and ammonia solutions.