Phosphorus Oxychloride-Zinc(II) Chloride


[10025-87-3]  · Cl3OP  · Phosphorus Oxychloride-Zinc(II) Chloride  · (MW 153.32) (ZnCl2)

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

(powerful Lewis Acid used in Friedel-Crafts reactions to prepare xanthones,1 benzophenones,2 coumarins,3 and chromanones;4 phosphorylation of alcohols5)

Physical Data: see entries for Phosphorus Oxychloride and Zinc Chloride.

Handling, Storage, and Precautions: in most cases, freshly fused ZnCl2 must be used for the best results. See Phosphorus Oxychloride for potential hazards.

Friedel-Crafts Reactions.

Phosphorus oxychloride and zinc(II) chloride combined are used as a catalyst6 in Friedel-Crafts reactions. Hydroxyxanthones can be prepared by reaction of o-hydroxybenzoic acid and hydroxybenzenes in the presence of POCl3 and ZnCl2 (eq 1).1 Although hydroxybenzophenones are also isolated by this method, they can be converted to xanthones by heating to 200 °C. A variety of hydroxyxanthones7,8 and methoxyxanthones,9 as well as benzophenones,2 can be prepared in this manner.

In a similar fashion, the Friedel-Crafts reaction of phenol and malonic acid in the presence of POCl3 and ZnCl2 gives 4-hydroxycoumarin (eq 2).3 Neither POCl3 nor ZnCl2 are effective alone. Additionally, the use of AlCl3 instead of ZnCl2 is not effective. Other coumarins can also be prepared in a similar manner.10,11

Phosphorus oxychloride and ZnCl2 can also be employed to prepare chromanones from hydroxybenzenes and 3,3-dimethylacrylic acid in one step (eq 3).4

Phosphorylation of Alcohols.

The phosphorylation of alcohols with POCl3 and ZnCl2 can also be accomplished. Simple alcohols,12 as well as fluorinated alcohols (eq 4),5 when added in excess to POCl3 and ZnCl2, form phosphates readily.

Related Reagents.

Phosphorus(III) Chloride; Phosphorus(V) Chloride; Phosphorus Oxychloride.

1. Grover, P. K.; Shah, G. D.; Shah, R. C. JCS 1955, 3982.
2. Lakshminarayanan, K. R.; Kulkarni, A. B. IJC 1973, 11, 705.
3. Shah, V. R.; Bose, J. L.; Shah, R. C. JOC 1960, 25, 677.
4. Iyer, P. R.; Shah, G. D. IJC 1968, 6, 227.
5. Zakharov, L. S.; Pisarenko, V. V.; Godovikov, N. N.; Kabachnik, M. I. IZV 1971, 2503 (CA 1971, 76, 99 026s).
6. Doolan, P. C.; Gore, P. H. CC 1968, 1624.
7. Mucheli, M. V. R.; Kudav, N. A. CI(L) 1985, 31.
8. Grover, P. K.; Shah, G. D.; Shah, R. C. CI(L) 1955, 62.
9. Dalal, S. R.; Shah, R. C. CI(L) 1957, 140.
10. Dallacker, F.; Kratzer, P.; Lipp, M. LA 1961, 643, 97.
11. Jain, M. P.; Nath, B. Indian Chem. J. 1977, 12, 19.
12. Rao, K. V.; Chiranjivi, C. Indian J. Technol. 1976, 14, 401.

Suzanne M. Ruder

Virginia Commonwealth University, Richmond, VA, USA

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