Calcium Hypochlorite1


[7778-54-3]  · CaCl2O2  · Calcium Hypochlorite  · (MW 142.99)

(oxidizing agent for the conversion of alcohols to aldehydes,2 ketones,3 carboxylic acids,4 esters,3 and methyl esters;5 aldehydes to acids6 and t-butyl esters;5 ethers to esters,3 and thioethers to sulfoxides;7 for the C-C bond cleavage of 1,2-dioxygenated compounds;8 for the chlorination of benzenoid compounds;1 for the conversion of alkenes to chlorohydrins9)

Alternate Names: calcium oxychloride; hypochlorous acid, calcium salt; B-K powder.

Physical Data: mp 100 °C; specific gravity 2.35.

Solubility: insol organic solvents; slightly sol H2O (with decomposition); very sol H2O with a few drops of HOAc; aqueous solutions of acetic acid, acetonitrile, acetone, MeOH, and t-butanol, and biphasic solutions of H2O with EtOAc, CH2Cl2, ether, benzene, and CCl4 are used for oxidations.

Form Supplied in: white or light yellow granular solid with strong chlorine odor; widely available.

Purification: composition is generally 60-70% Ca(OCl)2 [Ca(OCl)2, 65%; NaCl, 15%; H2O, 10%; Ca(OH)2, 4%; CaCO3, 3%; CaClO3, 1.5%; CaCl2, 1%].10

Handling, Storage, and Precautions: commercially available Ca(OCl)2 (65%) is easy to handle and may be stored in a desiccator without substantial decomposition.11 Anhydrous Ca(OCl)2 must be stored in a brown bottle kept away from sunlight and moisture. It explodes when in direct contact with organic material, especially lubrication oils. This reagent should be handled in a fume hood.

General Conditions of Use.

Ca(OCl)2 is an inexpensive and broad-based reagent for the oxidation of a variety of functional groups.1-9 Its advantage over Sodium Hypochlorite (NaOCl) is its relative stability at ambient temperature11 and its ease of handling as a solid. NaOCl is commercially available in dilute aqueous solutions (usually about 3-5%) that deteriorate rather rapidly. Thus the solution must be frequently titrated to define the quantity of oxidant present. In addition, because of the low concentration of NaOCl in solution an excessive volume of solvent is usually present.12 The major difficulty encountered with the use of Ca(OCl)2 is that of solubility. It is insoluble in most common organic solvents and forms a cloudy solution in water. However, complete solubility in water is attained by the addition of a few drops of acetic acid, giving a final oxidizing solution that is clear and light yellow. Aqueous organic biphasic solutions are also useful media in which to carry out the oxidations.

Oxidation of Alcohols, Ethers, Thioethers, and Aldehydes.

Ca(OCl)2 efficiently oxidizes primary alcohols to esters3 (eq 1), where both the acid and alcohol portion of the ester are derived from the alcohol. In the presence of Molecular Sieves and with excess MeOH, methyl esters5 are obtained (eq 2), while with t-butanol, carboxylic acids4 are generated (eq 3). A variety of substituted methyl benzoates are thus easily prepared from the corresponding benzyl alcohols by the former method, and t-butyl esters are available from aldehydes.5 Aldehydes, which are easily oxidized to carboxylic acids6 with Ca(OCl)2 (eq 4), are themselves available in remarkably high yield from primary alcohols, in less than 15 min, when a catalytic amount of 4-(benzoyloxy)-2,2,6,6-tetramethylpiperidin-1-oxyl is added (eq 5).2 (Ruthenium(III) Chloride has also been used to catalyze this reaction.13)

Secondary alcohols afford ketones3 in high yield in aqueous media (eq 6), or in organic media (CH2Cl2, CCl4, Et2O, EtOAc) with a catalytic amount of hypochlorite resin (IRA 900)14 using a triphasic system (liquid-solid-solid) (eq 7). Acyclic and cyclic ethers give esters (eq 8)3 and lactones (eq 9),3 respectively, although the yields are lower than for the oxidation of the other groups. A variety of alkyl and aryl-alkyl thioethers can be selectively oxidized to sulfoxides (eq 10)7 in yields exceeding 70% however, dibenzyl sulfide is inefficiently converted to dibenzyl sulfoxide (25%).

Carbon-Carbon Bond Cleavage Reactions.

a-Diols, a-diones, a-hydroxy ketones, and a-hydroxy and a-keto acids8 are oxidatively cleaved with Ca(OCl)2 (eqs 11 and 12). The yields are good to excellent and the products obtained (aldehydes, ketones, acids) depend on the oxidation state of the carbon atoms bearing the original oxygen groups. In an interesting two-step high-yield preparation of piperonal, the glycol obtained from electrochemical oxidation of isosafrole is converted to piperonal in near quantitive yield by glycol cleavage15 when treated with Ca(OCl)2 in benzene/H2O (eq 13).

Chlorination of Benzenoid Compounds.

As depicted in eq 14, if the glycol of isosafrole is oxidized in MeCN/CH2Cl2/H2O at ambient temperature, ring chlorination15 takes place instead of C-C bond cleavage to afford 1-[2-chloro-4,5-(methylenedioxy)phenyl]propane-1,2-diol (85%). Ca(OCl)2 can thus be used for chlorination of aromatics (benzene, naphthalene).1 While chlorobenzene, nitrobenzene, and 4-nitrotoluene do not react, good results are obtained when the substrate has strong electron-donating substituents (eqs 15-17).1 Activated rings having oxidizable substituents will undergo chlorination and oxidation, depending on the reactivities of the groups and the number of equivalents of Ca(OCl)2 used (eqs 18 and 19).

Conversion of Alkenes to Chlorohydrins.

Ca(OCl)2 converts mono-, di-, tri-, and tetrasubstituted, cyclic, and acyclic alkenes to the corresponding chlorohydrins9 in good yield (eqs 20-23). The reactions are carried out under mild conditions and the expected regiochemistry is obtained.

1. Nwaukwa, S. O.; Keehn, P. M. SC 1989, 19, 799.
2. Inokuchi, T.; Matsumoto, S.; Nishiyama, T.; Torii, S. JOC 1990, 55, 462.
3. Nwaukwa, S. O.; Keehn, P. M. TL 1982, 23, 35.
4. Kabalka, G. W.; Chatla, N.; Wadgaonkar, P. P.; Deshpande, S. M. SC 1990, 20, 1617.
5. McDonald, C. E.; Nice, L. E.; Shaw, A. W.; Nestor, N. B. TL 1993, 34, 2741.
6. Nwaukwa, S. O.; Keehn, P. M. TL 1982, 23, 3131.
7. Weber, J. V.; Schneider, M.; Salami, B.; Paquer, D. RTC 1986, 105, 99.
8. Nwaukwa, S. O.; Keehn, P. M. TL 1982, 23, 3135.
9. Nwaukwa, S. O. Int. J. Chem. 1990, 1, 37.
10. Fisher Scientific Chemical Division, 1 Reagent Lane, Fair Lawn NJ 07410.
11. There was no change in concentration of oxidant for Ca(OCl)2 when titrations were carried out over a period of 212 months. See Vogel, A. I. A Textbook of Quantitative Inorganic Analysis, 3rd ed.; Wiley: New York, 1961.
12. Stevens, R. V.; Chapman, K. T.; Weller, H. N. JOC 1980, 45, 2030.
13. Genet, J. P.; Pons, D.; Jugé, S. SC 1989, 19, 1721.
14. Schneider, M.; Weber, J-V.; Faller, P. JOC 1982, 47, 364.
15. Torii, S.; Uneyama, K.; Ueda, K. JOC 1984, 49, 1830.

Philip M. Keehn

Brandeis University, Waltham, MA, USA

Stephan O. Nwaukwa

Ondo State University, Ado-Ekiti, Nigeria

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