Hydrogen Peroxide-Ammonium Heptamolybdate1

H2O2-(NH4)6Mo7O24.4H2O
(H2O2)

[7722-84-1]  · H2O2  · Hydrogen Peroxide-Ammonium Heptamolybdate  · (MW 34.02) ((NH4)6Mo7O24)

[12027-67-7]  · H24Mo7N6O24  · Hydrogen Peroxide-Ammonium Heptamolybdate  · (MW 1163.88) ((NH4)6Mo7O24.4H2O)

[12054-85-2]  · H32Mo7N6O28  · Hydrogen Peroxide-Ammonium Heptamolybdate  · (MW 1235.96)

(epoxidation;2 oxidation of secondary alcohols to ketones;2,3 oxidation of aldehydes to acids;2 chemoselection between epoxidation and alcohol oxidation2,4)

Physical Data: (NH4)6Mo7O24.4H2O: dec 190 °C; d 2.498 g cm-3.

Solubility: (NH4)6Mo7O24.4H2O: sol H2O (43 g/100 mL); insol alcohol.

Form Supplied in: (NH4)6Mo7O24.4H2O: colorless or slightly greenish or yellowish crystals; widely available.

Handling, Storage, and Precautions: (NH4)6Mo7O24.4H2O: commercially available ammonium heptamolybdate tetrahydrate can be used and stored at rt under air. For H2O2, see Hydrogen Peroxide.

Epoxidation.

Molybdenum complexes are among the best catalysts for epoxidations with peroxides.1 The hydrogen peroxide-molybdate system is superior to others because of its accessibility, low cost, and easy handling. The epoxidation with hydrogen peroxide-molybdate requires tetraalkylammonium salts2,5 or anion exchange polymers6 for enhancement of the affinity between substrates and oxidizing agents (peroxomolybdates). Monosubstituted alkenes fail to react and disubstituted alkenes react very slowly. Competition experiments reveal high chemoselectivity for the reaction of tri- vs. disubstituted alkenes (eq 1).2 Alkene geometry is retained in the product. A primary allylic alcohol activates and directs the epoxidation to the neighboring double bond (eqs 2 and 3).2

Oxidation of Alcohols.7

Oxidation of secondary alcohols to ketones with hydrogen peroxide-heptamolybdate is accelerated by the addition of Potassium Carbonate.2,3 The oxidation of a secondary alcohol chemoselectively occurs in the presence of a primary alcohol (eq 4).2-5

Steric factors play an important role in these oxidations: the more hindered alcohol is oxidized more rapidly.2 This steric effect has been exploited for selective oxidations of steroids (eq 5).2,3 Primary alcohols are oxidized to carboxylic acids at higher temperatures but the major products are the self-condensed esters. Aldehydes are oxidized to carboxylic acids by this reagent (eq 6).2

Chemoselection Between the Epoxidation and the Alcohol Oxidation.

By controlling pH, the chemoselectivity of the oxidation of unsaturated alcohols can be directed to produce either epoxides or ketones.2 In the absence of potassium carbonate, epoxidation is observed, while in the presence of this base oxidation takes place preferentially (eq 7).4


1. (a) Mimoun, H. In The Chemistry of Peroxides; Patai, S., Ed.; Wiley: New York, 1982; pp 463-482. (b) Mimoun, H. PAC 1981, 53, 2389. (c) Sheldon, R. A.; Kochi, J. K. Metal Catalyzed Oxidations of Organic Compounds; Academic: New York, 1981; pp 48-97. (d) Sharpless, K. B.; Verhoeven, T. R. Aldrichim. Acta 1979, 12, 63.
2. Trost, B. M.; Masuyama, Y. Isr. J. Chem. 1984, 24, 134.
3. Trost, B. M.; Masuyama, Y. TL 1984, 25, 173.
4. Paquette, L. A.; Sauer, D. R.; Cleary, D. G.; Kinsella, M. A.; Blackwell, C. M.; Anderson, L. G. JACS 1992, 114, 7375.
5. Ishii, Y.; Yamawaki, K.; Ura, T.; Yamada, H.; Yoshida, T.; Ogawa, M. JOC 1988, 53, 3587.
6. (a) Srinivasan, S.; Ford, W. T. New J. Chem. 1991, 15, 693. (b) Srinivasan, S.; Ford, W. T. Polym. Mater. Sci. Eng. 1991, 64, 355.
7. For some alternative approaches with molybdenum complexes, see: (a) Jacobson, S. E.; Muccigrosso, D. A.; Mares, F. JOC 1979, 44, 921. (b) Tomioka, H.; Takai, K.; Oshima, K.; Nozaki, H.; Toriomi, K. TL 1980, 21, 4843. (c) Masuyama, Y.; Takahashi, M.; Kurusu, Y. TL 1984, 25, 4417.

Yoshiro Masuyama

Sophia University, Tokyo, Japan



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