World production exceeds one-third of a million tonnes.[7] Phosphorus trichloride is prepared industrially by the reaction of chlorine with white phosphorus, using phosphorus trichloride as the solvent. In this continuous process PCl3 is removed as it is formed in order to avoid the formation of PCl5.
P4 + 6 Cl2 → 4 PCl3
Structure and spectroscopy
It has a trigonal pyramidal shape. Its 31PNMR spectrum exhibits a singlet around +220 ppm with reference to a phosphoric acid standard.[citation needed]
Reactions
The phosphorus in PCl3 is often considered to have the +3 oxidation state and the chlorine atoms are considered to be in the −1 oxidation state. Most of its reactivity is consistent with this description.[8]
Triphenylphosphine is produced industrially by the reaction between phosphorus trichloride, chlorobenzene, and sodium:[13]
PCl3 + 3 PhCl + 6 Na → PPh3 + 6 NaCl, where Ph = C6H5
Under controlled conditions or especially with bulky R groups, similar reactions afford less substituted derivatives such as chlorodiisopropylphosphine.
Conversion of alcohols to alkyl chlorides
Phosphorus trichloride is commonly used to convert primary and secondary alcohols to the corresponding chlorides.[14] As discussed above, the reaction of alcohols with phosphorus trichloride is sensitive to conditions. The mechanism for the ROH →RCl conversion involves the reaction of HCl with phosphite esters:
P(OR)3 + HCl ⇌ HP(OR)+3Cl−
HP(OR)+3Cl− → RCl + HOP(OR)2.
HOP(OR)2 + HCl ⇌ H2OP(OR)+2Cl−
H2OP(OR)+2Cl− → RCl + (HO)2P(OR)
(HO)2P(OR) + HCl ⇌ H(HO)2P(OR)+Cl−
H(HO)2P(OR)+Cl− → RCl + (HO)3P
The first step proceeds with nearly ideal stereochemistry but the final step far less so owing to an SN1 pathway.
Redox reactions
Phosphorus trichloride undergoes a variety of redox reactions:[13]
3PCl3 + 2 CrO3 → 3POCl3 + Cr2O3
PCl3 + SO3 → POCl3 + SO2
3 PCl3 + SO2 → 2POCl3 + PSCl3
PCl3 as a nucleophile
Phosphorus trichloride has a lone pair, and therefore can act as a Lewis base,[15] e.g., forming a 1:1 adduct Br3B-PCl3. Metal complexes such as Ni(PCl3)4 are known, again demonstrating the ligand properties of PCl3.
This Lewis basicity is exploited in the Kinnear–Perren reaction to prepare alkylphosphonyl dichlorides (RP(O)Cl2) and alkylphosphonate esters (RP(O)(OR')2). Alkylation of phosphorus trichloride is effected in the presence of aluminium trichloride give the alkyltrichlorophosphonium salts, which are versatile intermediates:[16]
PCl3 + RCl + AlCl3 → RPCl+ 3 + AlCl− 4
The RPCl+ 3 product can then be decomposed with water to produce an alkylphosphonic dichloride RP(=O)Cl2.
^Gay-Lussac; Thénard (27 May 1808). "Extrait de plusieurs notes sur les métaux de la potasse et de la soude, lues à l'Institut depuis le 12 janvier jusqu'au 16 mai" [Extracts from several notes on the metals potassium and sodium, read at the Institute from the 12th of January to the 16th of May]. Gazette Nationale, Ou le Moniteur Universel (in French). 40 (148): 581–582. From p. 582: "Seulement ils ont rapporté qu'en traitant le mercure doux par le phosphure, dans l'espérance d'avoir de l'acide muriatique bien sec, il ont trouvé une liqueur nouvelle très limpide, sans couleur, répandant de fortes vapeurs, s'enflammant spontanément lorsqu'on en imbibe le papier joseph; laquelle ne paraît être qu'une combinaison de phosphore, d'oxigène et d'acide muriatique, et par conséquent analogue à cette qu'on obtient en traitant le soufre par le gas acide muriatique oxigèné." (Only they reported that by treating calomel with phosphorus, in the hope of obtaining very dry hydrogen chloride, they found a new, very clear liquid, colorless, giving off strong vapors, spontaneously igniting when one soaks filter paper in it; which seems to be only a compound of phosphorus, oxygen, and hydrochloric acid, and thus analogous to what one obtains by treating sulfur with chlorine gas.)
^Gerrard, W.; Isaacs, M. J. D.; Machell, G.; Smith, K. B.; Wyvill, P. L. (1953). "394. Interaction of phosphorus trichloride with alcohols and with hydroxy-esters". Journal of the Chemical Society (Resumed): 1920. doi:10.1039/JR9530001920.
^ abCorbridge, D. E. C. (1995). Phosphorus: An Outline of its Chemistry, Biochemistry, and Technology (5th ed.). Amsterdam: Elsevier. ISBN0-444-89307-5.
^Brown, Geoffrey W. (1971). "Displacement of Hydroxyl Groups". The Hydroxyl Group (1971). PATai's Chemistry of Functional Groups. pp. 593–639. doi:10.1002/9780470771259.ch11. ISBN9780470771259.
^R. R. Holmes (1960). "An examination of the basic nature of the trihalides of phosphorus, arsenic and antimony". Journal of Inorganic and Nuclear Chemistry. 12 (3–4): 266–275. doi:10.1016/0022-1902(60)80372-7.
