Chromyl Chloride1

[14977-61-8]  · Cl2CrO2  · Chromyl Chloride  · (MW 154.92)

(reagent for converting alkenes to aldehydes, oxiranes, ketones, chlorohydrins, a-chloro ketones, vicinal chloroacetates, and a-hydroxy ketones, and for oxidizing alkylaromatics to alcohols, aldehydes, and ketones)

Alternate Names: dichlorodioxochromium; Etard reagent.

Physical Data: mp -96.5 °C; bp 117 °C; d 1.911 g cm-3.

Solubility: sol CCl4, CH2Cl2, ether.

Form Supplied in: dark red liquid.

Preparative Methods: prepared from Chromium(VI) Oxide and Titanium(IV) Chloride.2-4

Handling, Storage, and Precautions: cancer suspect agent; all chromium(VI) reagents must be handled with care; the mutagenicity of CrVI compounds is well documented.5 This reagent should be handled in a fume hood.

Oxidation of Alkenes to Aldehydes, Oxiranes, Ketones, Chlorohydrins, a-Chloro Ketones, Vicinal Chloroacetates, and a-Hydroxy Ketones.

The products from the chromyl chloride oxidation of alkenes depend on the structure of the alkene and the experimental conditions. Oxidation of terminal aliphatic alkenes and alkenylaromatics with chromyl chloride in dichloromethane, followed by reductive workup with Zinc dust or Sulfur Dioxide, affords the corresponding aldehydes (eqs 1 and 2).6-9 a-Chloro Ketones are the only products if propanone replaces dichloromethane as the solvent (eq 3).10,11 Reductive zinc dust workup affords the corresponding ketones. The initially formed chlorohydrin and oxirane products may also be isolated.10,12,13 Epoxidation is stereospecific, yielding an oxirane with the same geometry as the starting alkene. Oxiranes are also the intermediates leading to vicinal chloroacetates when the oxidation is performed in 2:1 dichloromethane-acetyl chloride (eq 4).14 Chromyl chloride reacts regiospecifically with O-silylated enolates in dichloromethane at -78 °C to afford a-hydroxy ketones (eq 5).15

Oxidation of Alkylaromatics to Aldehydes, Ketones, and Alcohols.

Chromyl chloride oxidizes methylbenzenes to the corresponding aldehydes (Etard reaction).16,17 The ultrasonic-mediated chromyl chloride oxidation of diphenylmethane, indan, and triphenylmethane affords diphenyl ketone (99%), 1-indanone (80%), and triphenylmethanol (99%), respectively.2 These yields are higher than those obtained by previous procedures.

Other Applications.

Chromyl chloride oxidizes phenols to quinones and coupling products.18 Chromyl chloride is used to prepare Di-t-butyl Chromate,2 t-butyl chromate-tripyridine,19 and 2,4-(2,4-dimethylpentyl) chromate,2,20 which are useful oxidants.

1. (a) Wiberg, K. B. In Oxidation in Organic Chemistry; Wiberg, K. B., Ed.; Academic: New York, 1965; Part A, pp 131-135. (b) Freeman, F. In Organic Synthesis By Oxidation With Metal Compounds; Mijs, W. J.; de Jonge, C. R. H. I., Eds.; Plenum: New York, 1986; Chapter 2. (c) Lee, D. G. The Oxidation of Organic Compounds by Permanganate Ion and Hexavalent Chromium; Open Court: La Salle, IL, 1980. (d) Stewart, R. Oxidation Mechanisms: Applications to Organic Chemistry; Benjamin: New York, 1964. (e) Cainelli, G.; Cardillo, G. Chromium Oxidations in Organic Chemistry; Springer: Berlin, 1984. (f) Freeman, F. Rev. React. Species Chem. React., 1973, 1, 37. (g) Hartford, W. H.; Darrin, M. CR 1958, 58, 1.
2. Luzzio, F. A.; Moore, W. J. JOC 1993, 58, 512.
3. Udy, M. J. Chromium, Chemistry of Chromium and Its Compounds; Rheinhold: New York, 1956; Vol. 1, pp 191-192.
4. Sisler, H. H. In Inorganic Synthesis; Fernelius, W. C., Ed.; McGraw-Hill: New York, 1946; Vol. 2, pp 205-207.
5. Cupo, D. Y.; Wetterhahn, K. E. Cancer Res. 1985, 45, 1146 and references cited therein.
6. Freeman, F.; Cameron, P. J.; DuBois, R. H. JOC 1968, 33, 3970.
7. Freeman, F.; DuBois, R. H.; Yamachicka, N. J. T 1969, 25, 3441.
8. Freeman, F.; DuBois, R. H.; McLaughlin, T. G. OSC 1988, 6, 1028.
9. Jones, T. H.; Blum, M. S.; Fales, H. M. TL 1980, 21, 1701.
10. Sharpless, K. B.; Teranishi, A. Y.; JOC 1973, 38, 185.
11. Sharpless, K. B.; Teranishi, A. Y.; Backvall, J.-E. JACS 1977, 99, 3120.
12. Sharpless, K. B.; Flood, T. C. JACS 1971, 93, 2316.
13. Bachelor, F. W.; Cheriyan, U. O. CJC 1976, 54, 3383.
14. Backvall, J. E.; Young, M. W.; Sharpless, K. B. TL 1977, 3523.
15. Lee, T. V.; Toczek, J. TL 1982, 23, 2917.
16. Wheeler, O. H. CJC 1958, 36, 667.
17. Wheeler, O. H. CJC 1958, 36, 949.
18. Strickson, J. A.; Leigh, M. T 1968, 24, 5145.
19. Sharpless, K. B.; Akashi, K. JACS 1975, 97, 5927.
20. Corey, E. J.; Barrette, E.-P.; Magriotis, P. TL 1985, 26, 5855.

Fillmore Freeman

University of California, Irvine, CA, USA

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