Phosphorus trichloride (PCl) and Phosphorus pentachloride (PCl5) are reactive chemicals used as chlorinating reagents in a chemical laboratory. They are both hazardous and toxic and neither is found in nature. They both react upon contact with water to produce corrosive and toxic hydrogen chloride gas. At room temperature and pressure, phosphorus trichloride is a liquid and phosphorus pentachloride is a solid. Both will chlorinate carboxylic acids to their corresponding acyl chloride derivatives and both will chlorinate alcohols by substituting the hydroxyl group with a chlorine atom to yield an alkyl chloride. The use of thionyl chloride could provide similar results in such cases, except that the byproducts sulfur dioxide and hydrogen chloride are both gases which normally separate from the reaction product mixture.