Chromium(II) Perchlorate1


[13931-95-8]  · Cl2CrO8  · Chromium(II) Perchlorate  · (MW 250.91)

(used to reduce aliphatic halides;2,5,6 reductive dimerization of carbonyl compounds;8 reduction of cations and peroxides9,10)

Physical Data: no data available due to instability in pure solid form.

Form Supplied in: not available commercially; must be prepared before use as an aqueous solution.

Preparative Methods: by the reaction of high purity grade chromium powder with dilute HClO4 or by reducing chromium(III) perchlorate with amalgamated Zn in dilute HClO4 under an inert atmosphere.2 Solutions can be standardized3a by quenching an aliquot in standard dilute FeCl3 solution and titrating the FeII produced to FeIII (1,10-phenanthroline end point) with 0.01 M CeIV. In kinetic measurements the disappearance of CrII can be followed spectrometrically at 750 nm.3b

Handling, Storage, and Precautions: greater than 1 M solutions of Cr(ClO4)2 must be prepared at ice-bath temperature, since the reaction mixture decomposes exothermically at room temperature. Dilute solutions may be safely stored at room temperature. Chromium salts are carcinogenic and should be handled with care. Perchlorates are explosive and thus should be handled appropriately behind a safety shield.

Chromium(II) as a Reducing Agent.

Chromium(II) complexes between Cr(ClO4)2 and 1,2-Diaminoethane react with alkyl halides to give alkanes by the mechanism shown in eqs 1-3.4

If the intermediate radical has an isomerization pathway available, structurally rearranged products can be obtained.4c For example, reduction of halides of the types RC&tbond;C(CH2)nX (n = 4 or 5) with CrII in aqueous DMF containing ethylenediamine afforded substituted methylenecycloalkanes (eq 4).5 Geminal, vicinal, and 1,3-dihalides can be reduced by CrII to generate carbenes, alkenes, and cyclopropanes, respectively.6

Reduction of a-haloacetonitriles,7a a-haloacetamides,7b and a-haloacetic acids7c,7d with CrII gives products derived from intermediate radicals.

Carbonyl Reductions.

Aromatic aldehydes, a,b-unsaturated aldehydes, and some a,b-unsaturated ketones undergo a one-electron reductive coupling to give bimolecular products, whereas aliphatic aldehydes and ketones, aromatic ketones, and esters are unreactive.8

Reduction of Organic Cations.

In aqueous or in acidic ethanolic media, organic cations such as tropylium,9a cyclopropenium,9b N-methylacridinium,9c 2,4,6-triphenylpyrylium,9c and flavylium9c are reduced with Cr(ClO4)2 to the corresponding radicals or dimers.

Reduction of Organic Peroxides.

Organic peroxides, hydroperoxides, peroxy esters, and peroxy acids undergo reduction with Cr2+ to generate alkoxy radicals and organochromium(III) species.6e,10

Miscellaneous Reduction.

The addition of Cr(ClO4)2 to aqueous or methanolic solutions of mitomycin C led to efficient reductive activation of the C-1 and C-10 positions, generating nucleophilic substitution products.11

1. For reviews on chromium(II) reductions, see (a) Hanson, J. R.; Premuzic, E. AG(E) 1968, 7, 247. (b) Kochi, J. K. Record. Chem. Prog. 1966, 27, 207.
2. (a) Lux, H.; Illman, G. CB 1958, 91, 2143. (b) Gould, E. S.; Taube, H. JACS 1964, 86, 1318. (c) Cohen, H.; Meyerstein, D. IC 1974, 13, 2434. (d) House, H. O.; Kinloch, E. F. JOC 1974, 39, 1173.
3. (a) Castro, C. E.; Kray, W. C., Jr. JACS 1963, 85, 2768. (b) Davis, D. D.; Bigelow, W. B. JACS 1970, 92, 5127.
4. (a) Hanson, J. R. S 1974, 1. (b) Ho, T.-L. S 1979, 1. (c) Kochi, J. K.; Powers, J. W. JACS 1970, 92, 137.
5. Crandall, J. K.; Michaely, W. J. JOC 1984, 49, 4244.
6. (a) Castro, C. E.; Kray, W. C.; Jr. JACS 1966, 88, 4447. (b) Julian, P. L.; Cole, W.; Magnani, A.; Meyer, E. W. JACS 1945, 67, 1728. (c) Kray, W.; Castro, C. JACS 1964, 86, 4603. (d) Singleton, D. M.; Kochi, J. K. JACS 1967, 89, 6547. (e) Kochi, J.; Mocadlo, P. JOC 1965, 30, 1134.
7. (a) Kupferschmidt, W. C.; Jordon, R. B. JACS 1984, 106, 991. (b) Sevcik, P.; Kresak, J. CCC 1976, 41, 2198. (c) Kita, P.; Jordon, R. B. IC 1985, 24, 2701. (d) Sevcik, P.; Tkac, J. CCC 1981, 46, 1554.
8. Conant, J. B.; Cutter, H. B. JACS 1926, 48, 1016.
9. (a) Bowie, W. T.; Feldman, M. JPC 1967, 71, 3693. (b) Komatsu, K.; Oshida, M.; Okamoto, K. TL 1974, 4487 and references cited therein. (c) Bowie, W. T.; Feldman, M. JACS 1977, 99, 4721.
10. (a) Samuni, A.; Meisel, D.; Czapski, G. JCS(D) 1972, 1273. (b) Kochi, J. K.; Davis, D. D. JACS 1964, 86, 5264. (c) Hyde, M. R.; Espenson, J. H. JACS 1976, 98, 4463.
11. (a) Hong, Y. P.; Kohn, H. JOC 1991, 56, 6479. (b) Hong, Y. P.; Kohn, H. JACS 1991, 113, 4634.

Palaniappa Nanjappan

Bristol-Myers Squibb Company, Princeton, NJ, USA

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