by Phosphorus pentachloride, commonly known as PCl5, is an inorganic compound with the formula PCl5. It is a colorless volatile liquid with a choking odor. PCl5 crystallizes into colorless rhombic crystals below 40°C.
Properties of Pentachloride
The Phosphorus Pentachloride is highly reactive and hygroscopic in nature. It readily absorbs moisture from air and reacts violently with water to form hydrochloric acid and phosphoric acid. PCl5 has a boiling point of 110°C and density of 1.62 g/cm3. It is nonflammable but supports combustion. In terms of molecular structure, PCl5 is considered a slightly distorted trigonal bipyramidal molecular geometry with phosphorus at the center.
Preparation of Pentachloride
PCl5 can be prepared through the direct chlorination of white or red phosphorus. In a typical laboratory preparation, pieces of red phosphorus are added slowly to a flask containing excess chlorine gas at 0-5°C while being shaken vigorously. This results in a direct substitution reaction where chlorine replaces phosphorus-phosphorus bonds with phosphorus-chlorine bonds. The byproduct of this reaction is PCl3 which is separated by fractional distillation as it has a lower boiling point than PCl5.
Uses of Pentachloride
Due to its strong chlorinating ability, PCl5 finds wide application as a chlorinating and chlorosulfonating agent in organic reactions. Some common uses include:
– Preparation of acid chlorides by reaction with carboxylic acids. PCl5 readily replaces the hydroxyl group with a chlorine atom to yield acid chlorides.
– Synthesis of phosphoryl chloride (POCl3) which is used as a phosphorus-based reagent and catalyst.
– Production of alkyl chlorides through chlorination of alkanes and alkylbenzenes. PCl5 adds a chlorine atom to carbon-hydrogen bonds.
– Manufacture of chlorohydrins through chlorination of alcohols. This involves substitution of a hydroxyl group with chlorine.
– Preparation of chlorosulfonic acid which is further used in dye and pharmaceutical industries.
Safety Considerations for Phosphorus Pentachloride
Due to its strong reactivity and toxicity, certain safety precautions must be followed while handling Phosphorus Pentachloride. PCl5 readily hydrolyzes to form hydrochloric acid and emits toxic phosphorus oxides. It causes severe burns to skin, eyes and mucous membranes on contact. Hence, PCl5 must be stored and used in a well-ventilated fume hood while wearing appropriate personal protective equipment like gloves, goggles, and lab coat. Contact with water or moisture must be strictly avoided. In case of exposure, affected areas should be flushed with water immediately and medical attention sought. Its waste must be passed through sodium bicarbonate solution to neutralize before disposal. Proper labeling and documentation is also important from a safety standpoint.
Pentachloride is a colorless liquid with wide industrial usage as a versatile chlorinating and phosphorus-transfer reagent in organic synthesis owing to its high chlorination ability. However, due to its highly reactive and toxic nature, appropriate safety precautions must be followed during handling and use of this compound. With proper care and protection, PCl5 serves as a useful chemical for laboratory preparations and industrial scale production of important intermediates.
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1. Source: Coherent Market Insights, Public sources, Desk research
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