Phosphorus(III) Chloride-Zinc(II) Chloride

PCl3-ZnCl2
(PCl3)

[7719-12-2]  · Cl3P  · Phosphorus(III) Chloride-Zinc(II) Chloride  · (MW 137.32) (ZnCl2)

[7646-85-7]  · Cl2Zn  · Phosphorus(III) Chloride-Zinc(II) Chloride  · (MW 136.29)

(preparation of aminodiphosphonic acids,1 trialkylphosphines,2 and arylphosphonic acids;3 conversion of alcohols to alkyl chlorides4)

Physical Data: see entries for Phosphorus(III) Chloride and Zinc Chloride.

Handling, Storage, and Precautions: freshly fused ZnCl2 is used in most cases.

Phosphorylation.

PCl3 and ZnCl2 can be used to prepare phosphonic acids and trisubstituted phosphines. Aminodiphosphonic acids can be formed by the reaction of nitriles and PCl3 in the presence of a Lewis acid. In particular, HCN can be converted to (aminomethylene)diphosphonic acid by reaction of PCl3 and ZnCl2 (eq 1).1 A proton source such as HCl is required.

Arylphosphonic acids and diarylphosphonic acids can also be obtained by reacting diazonium salts with PCl3.5 Although diazonium tetrafluoroborates are most often used, because of their stability and ease of isolation, diazonium chlorozincates (zinc chloride double salts of diazonium chlorides) can be used to prepare the arylphosphonic acids. Thus diazonium chlorozincate is reacted with PCl3 in the presence of CuI to afford the arylphosphonium salt. Arylphosphonic acids are formed after aqueous workup (eq 2).3 Use of diazonium chlorozincates does not offer any advantages over use of the tetrafluoroborate salts.

Tertiary phosphines can be prepared by the Friedel-Crafts reaction of aromatic compounds with PCl3 in the presence of ZnCl2. When 3 equiv of aromatic compound are utilized, triarylphosphines are produced.6 However, if 1 equiv of aromatic compound is used, the aryldichlorophosphine is formed. These aryldichlorophosphines can be hydrolyzed to give arylphosphonous acids, or reacted with 2 equiv of Grignard reagent to give unsymmetrical trisubstituted phosphines (eq 3).2

Chlorination.

Conversion of an alcohol to an alkyl chloride can also be accomplished with PCl3 and ZnCl2. Although this transformation is usually attained from simple alcohols with a number of reagents including POCl3, conversion of O,O-diethyl S-(hydroxymethyl) phosphorodithioate to the chloromethyl phosphorodithioate is not successful when POCl3 is used, and only dehydration occurs. Conversion of the hydroxymethyl to the chloromethyl phosphorodithioate can be accomplished in good yield (eq 4) by reaction of the alcohol with PCl3 followed by addition of a catalytic amount of anhydrous ZnCl2.4 Other Lewis acid catalysts such as SnCl4 are not as effective. Use of PCl5 in inert solvents also gives chlorinated products.

Related Reagents.

Phosphorus(V) Chloride; Phosphorus Oxychloride.


1. (a) Redmore, D. In Topics in Phosphorus Chemistry; Griffith, E. J.; Grayson, M., Eds.; Wiley: New York, 1976; Vol. 8, pp 533. (b) Somer, K. Ger. Patent 2 203 366, 1973 (CA 1973, 79, 105 406w).
2. Constable, A. G.; Langrick, C. R.; Shabanzadeh, B.; Shaw, B. L. ICA 1982, 65, L151.
3. Freedman, L. D.; Doak, G. O. JACS 1953, 75, 4905.
4. Corkins, H. G.; Storace, L.; Weinberger, D.; Osgood, E.; Lowery, S. PS 1981, 10, 133.
5. Doak, G. O.; Freedman, L. D. JACS 1951, 73, 5658.
6. Smith, D. J. H. In Comprehensive Organic Chemistry; Barton, D. H. R.; Ollis, W. D., Eds.; Pergamon: Oxford, 1979; Vol. 2, p 1135.

Suzanne M. Ruder

Virginia Commonwealth University, Richmond, VA, USA



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