Triphenylmethyl Hydroperoxide1


[4198-93-0]  · C19H16O2  · Triphenylmethyl Hydroperoxide  · (MW 276.35)

(oxidant useful for enantioselective metal-catalyzed epoxidation of allylic alcohols2 and enantioselective oxidation of sulfides to sulfoxides3)

Alternate Names: trityl hydroperoxide, THP.

Physical Data: mp 87.5-88.5 °C; d 1.27 g cm-3.

Solubility: insol H2O; sol most organic solvents.

Form Supplied in: commercially available as white, crystalline solid, 95+%.

Analysis of Reagent Purity: iodometric titration7 (see t-Butyl Hydroperoxide).

Preparative Methods: has been prepared in several ways.4 The following method involves the acid-catalyzed reaction of triphenylmethanol with 30% Hydrogen Peroxide in acetic acid.5 Triphenylmethanol (5.2 g, 20 mmol) is dissolved in 60 mL of glacial acetic acid, and ether (20 mL) is added to prevent solidification of the acetic acid at ice bath temperatures. Concentrated H2SO4 (4 drops, 0.08 mL) and 10 mL of 30% H2O2 are added to this solution. The solution is stirred at 0 °C for 3.5 h and then neutralized with aqueous NaOH. Care must be taken to keep the solution cold during the neutralization. The mixture is then extracted twice with ether, and the ether extracts are combined, washed sequentially with 5% NaHCO3 and water, and then dried over anhydrous MgSO4. The ether is removed in vacuo and the hydroperoxide is recrystallized from pentane. The yield of white solid is 5 g (91%), mp 84-86 °C. This compound consistently shows an assay purity of 99% by iodometric titration.

Purification: purified by recrystallization from ether, petroleum ether, pentane, pentane-ether, or CHCl3-pentane.6

Handling, Storage, and Precautions: an unusually stable hydroperoxide which is relatively resistant (but still susceptible) to induced explosive decomposition. Like most alkyl hydroperoxides, it should be stored cold (ca. 0 °C) in the absence of light in a container such as a polyethylene bottle that is unlikely to shatter if there is pressure buildup. Exposing the pure hydroperoxide or concentrated solutions to heat, acid, reducing materials, or transition metal salts should be avoided. Upon completion of reactions, steps should be taken to safely destroy any remaining reagent. This can usually be done safely by exposing the reaction mixture to a mild reducing agent such as aqueous sodium sulfite, dimethyl sulfide, or triphenylphosphine. The reagent should always be handled in a fume hood.

Enantioselective Epoxidation of Allylic Alcohols.

THP can be used in place of t-butyl hydroperoxide (TBHP) as the oxidant in the Sharpless asymmetric epoxidation of allylic alcohols to give scalemic epoxy alcohols.2 Usually, THP has been used for mechanistic studies and not for synthetic advantage. In one case, however, use of THP with a nontartrate ligand resulted in a reversal of enantioselectivity (eq 1).8 With tartrate ligands, enantioselectivity is not reversed going from TBHP to THP.

Enantioselective Oxidation of Sulfides to Sulfoxides.

THP has also been used in the titanium-tartrate catalyzed asymmetric oxidation of prostereogenic sulfides to give scalemic sulfoxides.3 Unlike Cumyl Hydroperoxide (which gives improved results over TBHP), THP gives poor asymmetric induction (eq 2).9

1. (a) Patai, S. The Chemistry of Hydroxy, Ether and Peroxide Groups; Wiley: New York, 1993. (b) Patai, S. The Chemistry of Peroxides; Wiley: New York, 1983. (c) Swern, D. Organic Peroxides; Wiley: New York, 1970; Vol. I. (d) Swern, D. Organic Peroxides; Wiley: New York, 1971; Vol. II. (e) Swern, D. Organic Peroxides; Wiley: New York, 1972; Vol. III; (f) Kirk-Othmer Encyclopedia of Chemical Technology; 3rd Ed.; Wiley: New York, 1982; Vol. 17, pp 27-90. (g) Davie, A. G. Organic Peroxides; Butterworths: London, 1961. (h) Hawkins, E. G. E. Organic Peroxides; Spon: London, 1961. (i) Tobolsky, A. V.; Mesrobian, R. B. Organic Peroxides; Interscience: New York, 1954.
2. Woodward, S. S.; Finn, M. G.; Sharpless, K. B. JACS 1991, 113, 106.
3. Zhao, S. H.; Samuel, O.; Kagan, H. B. T 1987, 43, 5135.
4. (a) Wieland, H.; Maier, J. CB 1931, 64B, 1205. (b) Hüttel, R.; Ross, H. CB 1956, 89, 2644. (c) Davies, A. G.; Feld, R. JCS 1956, 4669.
5. (a) Bissing, D. E.; Matuszak, C. A.; McEwen, W. E. JACS 1964, 86, 3824. (b) Criegee, R.; Dietrich, H. LA 1948, 560, 135.
6. Richardson, W. H.; Hodge, V. F. JOC 1970, 35, 4012.
7. (a) Siggia, S.; Hanna, J. G. Quantitative Organic Analysis via Functional Groups, 4th ed.; Wiley: New York, 1979; pp 325-372. (b) Johnson, R. M.; Siddiqi The Determination of Organic Peroxides; Pergamon: London, 1970. (c) Swern, D. Organic Peroxides; Wiley: New York, 1971, Vol. II. (d) Kirk-Othmer Encyclopedia of Chemical Technology, 3rd Ed.; Wiley: New York, 1982; Vol. 17, pp 27-90.
8. Hawkins, J. M.; Sharpless, K. B. TL 1987, 28, 2825.
9. For examples of other catalysts used with THP to enantioselectively oxidize aryl methyl sulfides to the corresponding sulfoxides, see: (a) Sasaki, C.; Nakajima, K.; Kojima, M.; Fujita, J. BCJ 1991, 64, 1318. (b) Nakajima, K.; Sasaki, C.; Kojima, M.; Aoyama, T.; Ohba, S.; Saito, Y.; Fujita, J. CL 1987, 2189.

Bryant E. Rossiter&dead;

Brigham Young University, Provo, UT, USA

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