Synthesis of phosphorus trichloride

Preparation of phosphorus trichloride

According to many literature references the synthesis of phosphorus trichloride offers experimental difficulty. Particularly, in many sources for the preparation of PCl3 yellow phosphorus is used. The following synthesis, based on Inorganic Syntheses (Volume II, 145, 1946) proceeds smoothly, gives good yields from red phosphorus and chlorine.

Preparation of phosphorus trichloride

Preparation of phosphorus trichloride

The apparatus is assembled as shown below:

A glass apparatus for the preparation of phosphorus trichloride

A glass apparatus for the preparation of phosphorus trichloride

All parts of apparatus must be DRY! Chlorine tank (instead of gas cylinder a regular chlorine generator could be used) which stands on the top of the platform scales. The chlorine tank is connected to sulfuric acid safety trap and Drechsel bottle which indicates the rate of flow of the chlorine gas. The gas tube is connected to an inlet tube which extends to within 0.5 cm of the bottom of the reaction flask. It is important that the inlet tube and condenser should be of large diameter to avoid plugging and flooding. According to authors inlet tube of 2.5 cm. i.d. is recommended. Finally the reaction flask is connected to a condenser (condensing tube having an internal diameter of 2.5) protected from moisture with phosphorus pentoxide. The length of condenser according authors is 130 cm, however 2 or 3 condenser connected in parallel cold be used. If the separate parts of apparatus are not connected with ground-glass or PTFE joints then special litharge-glycerin cement should be used as it is resistant to the attack of chlorine and phosphorus trichloride. The side arm of the flask is closed with a glass rod plug held in position by rubber tubing or with an ordinary cork, which will withstand the attack of cold phosphorus trichloride.

Before synthesis phosphorus must be dried for several days in a thin layer in a vacuum desiccator over concentrated sulfuric acid. 200 g of dry red phosphorus are placed in the reaction flask. 250 ml of phosphorus trichloride is added to make a mobile suspension. The reaction flask is started to heat  and when it is boiling vigorously the addition of the chlorine is started. The gas tank is balanced so the amount of chlorine used in the chlorination reaction is known. It is very important to keep the phosphorus trichloride boiling vigorously at all times to prevent the formation of phosphorus pentachloride, which will plug the inlet tube. For the experiment 463 g of chlorine gas is required.  After the addition of the chlorine, the flask is disconnected and phosphorus trichloride is then distilled collecting fraction boiling at 75° C. The yield is about 94 % of the theoretical. Phosphorus trichloride is a clear colorless liquid with boiling point 75.9° C and a specific gravity of 1.574 g/cm3.

Inorganic Syntheses, Vol 2, 145, 1946

IUPAC Name

trichlorophosphane

InChI

InChI=1S/Cl3P/c1-4(2)3

InChI Key

FAIAAWCVCHQXDN-UHFFFAOYSA-N

Canonical SMILES

P(Cl)(Cl)Cl

MeSH Synonyms

phosphorous trichloride, phosphorus chloride, phosphorus chloride (PCl3), phosphorus chloride, (32)P-labelled, phosphorus trichloride, trichlorophosphine

Depositor-Supplied Synonyms

PHOSPHORUS TRICHLORIDE, Phosphorous trichloride, Trichlorophosphine, Phosphorus chloride, trichlorophosphane, Phosphorous chloride, Phosphorus(III) chloride, PCl3, Phosphorus chloride (PCl3), Phosphine, trichloro-, Fosfortrichloride, Phosphortrichlorid, Trojchlorek fosforu, Phosphorus chloride (Cl6P2), 7719-12-2, Fosforo(tricloruro di), Phosphore(trichlorure de), Fosfortrichloride [Dutch], Phosphortrichlorid [German], Trojchlorek fosforu [Polish], Phosphorus trichloride solution, HSDB 1031, Fosforo(tricloruro di) [Italian], FAIAAWCVCHQXDN-UHFFFAOYSA-N, Phosphore(trichlorure de) [French], EINECS 231-749-3, UN1809, 11082-95-4, trichloridophosphorus, Phosphorustrichloride, Chloride of phosphorus, phosphorus tri-chloride, phosphorous tri-chloride, Phosphorus(III)chloride, AC1L2NEH, AC1Q3VHP, [PCl3], UNII-M97C0A6S8U, phosphorus (III) trichloride, 276812_ALDRICH, 310115_ALDRICH, 320463_ALDRICH, M97C0A6S8U, CHEBI:30334, CTK1C4729, 157791_SIAL, 320463_SIAL, AKOS015904450, UN 1809, AN-21834, BP-31000, KB-59623, LS-109038, Phosphorus trichloride [UN1809] [Poison], P1611, Phosphorus trichloride [UN1809] [Poison], 3B4-1783, I14-17279

Removed Synonyms

CID24387, phosphorus chloride, (32)P-labelled, C043693, 37231-52-0

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6 comments

  1. Azide

    Any other possible routes that do not use elemental Phosphorus? (It’s already hard enough for the average home chemist to get, besides from Matchboxes & flare striking pads [Red P] and White P, which unless you have Willy Pete artillery rounds sitting around, then you’re out of luck!)

      1. emmanuel ross

        For us who can’t decipher german what exactly does this Ebay listing say. Is it actually possible to receive it thru the mail?

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