p-Nitrobenzenesulfonyl Peroxide1

[6209-72-9]  · C12H8N2O10S2  · p-Nitrobenzenesulfonyl Peroxide  · (MW 404.36)

(oxygen electrophile for addition to unsaturated compounds;1 preparation of a-nosyloxy ketones and esters;3 addition to 1-alkoxy-1-silyloxy-1,3-dienes;6 addition to enols3 to give tricarbonyl esters and amides;3 addition to amines to give N-nosyloxyamines1)

Alternate Name: p-NBSP.

Physical Data: mp 128 °C (dec); decomposition at the melting point is exothermic; typical preparations with mp >124 °C are generally satisfactory.

Solubility: sol (>1 g 100 mL-1) ethyl acetate, acetone, acetonitrile; slightly sol dichloromethane, ether, chloroform; insol pentane, water.

Form Supplied in: off-white or pale yellow powder; typical impurities are p-nitrobenzenesulfonic acid and water.

Analysis of Reagent Purity: purity is determined by iodometric titration. A weighed quantity (~70 mg) of the peroxide is dissolved in ethyl acetate (20 mL) and treated with glacial acetic acid (10 mL) and 10% potassium iodide (10 mL). The solution is titrated to a starch endpoint with standardized thiosulfate (~0.01 N).

Preparative Method: prepared by the addition of p-nitrobenzenesulfonyl chloride (20 g) in chloroform (40 mL) to a -20 °C solution of Potassium Carbonate (15.6 g) and 30% Hydrogen Peroxide in 2:1 water-ethanol (360 mL).2 The mixture is agitated in a chilled Waring Blender cup at full power for 1.5 min. The mixture is filtered on a large Buchner funnel and the oily solid is washed copiously several times with water. A good washing protocol is to suspend the solid in water and stir in the Waring Blender at medium power for 1 min and refilter. The faintly yellow solid is dried by passing air through the solid on the filter, and then in vacuo at room temperature. It is prudent to use plastic implements when manipulating the peroxide.

Purification: the crude peroxide is dissolved in reagent grade acetone (360 mL), the solution is cooled to -78 °C, and a vigorous stream of air is directed onto the surface of the stirred solution. When the volume has been reduced to 180 mL, the mixture is filtered and air is passed through the solid until it is completely dry. Purities of >97% normally result if care is taken to completely dry the peroxide when it is first isolated. Yields of 40-50% of purified product are normal. An alternate method of purification which delivers material suitable for most purposes (>95% purity) is to suspend the peroxide in acetone (150 mL) and stir at -78 °C for 1.5-2 h. Filtration and air drying give acceptable product. It is even more crucial that the crude product be quite dry before using this procedure as the major impurity seems to be water that is not easily removed by this method of purification.

Handling, Storage, and Precautions: can be stored for long periods of time at -20 °C without loss of purity and can be handled in the laboratory using normal laboratory procedures and precautions. Plastic spatulas are recommended for transfer. Vigorous reaction occurs with neat or concentrated solutions of good electron donors such as amines, alkenes, or alkoxides, but p-NBSP is relatively stable towards oxygen, water, acids, and a variety of common solvents such as acetone, ethyl acetate, dichloromethane, and acetonitrile. Because p-NBSP can decompose exothermically (but not explosively), personal protection in the form of eye protection, gloves, etc. is necessary when handling the peroxide.

Electrophilic Addition.

p-Nitrobenzenesulfonyl peroxide is a pseudohalogen reagent whose reactivity is comparable to that of chlorine. It provides a source of electrophilic oxygen for attachment of the p-nitrobenzenesulfonyloxy (nosyloxy) group to electron donors. Subsequent chemistry depends on the donor function and the reactions that the p-nitrobenzenesulfonate adduct undergoes.3

Enol Derivatives.

Electrophilic addition of p-NBSP to compounds with electron-rich double bonds provides a smooth method for the electrophilic attachment of the nosylate group. Reaction with enol derivatives of ketones (R1,R2 = alkyl, aryl) gives 2-nosyloxy ketones in generally high yields (60-90%) (eq 1).4 These are excellent precursors for a-amino ketones, a-hydroxy acetals, and a-hydroxy ketones.3 Reaction with ketene silyl acetals (X = Me3SiO, R1 = alkoxy, R2 = alkyl, aryl) gives 2-nosyloxy esters, also in excellent yields (65-90%);5 these are easily converted in high yields to amino acids and their N-substituted derivatives.3 Reactions with other nucleophiles give other 2-substituted esters.3

Silyloxy dienes.

Silyl enol ether derivatives of unsaturated esters (1-alkoxy-1-trimethylsilyloxy-1,3-dienes) react with p-NBSP to give both 2-nosyloxy and 4-nosyloxy unsaturated esters.6 Replacement of the nosyloxy group by nucleophiles yields 4-substituted 2,3-unsaturated esters.3

Enols.

Compounds with naturally high enol contents react directly with p-NBSP to give a-nosyloxy carbonyl compounds. b-Keto esters7 and b-keto amides8 react readily to give the corresponding 2-nosyloxy b-keto esters and amides (eq 2). These derivatives undergo reductive elimination to give tricarbonyl esters and tricarbonyl amides in high yields. They can also be reduced to 3-hydroxy-2-nosyloxy esters, which are convertible to many densely functionalized products.3

Amines.

Amines react with p-NBSP at -78 °C to give N-[(p-nitrobenzene)sulfonyl]oxy amines (eq 3).1 These adducts undergo facile base-promoted eliminations to imines.9 In the absence of base, they undergo ionization-rearrangement reactions which yield skeletally rearranged iminium ions. These adducts are also effective reagents for the preparation of N-substituted lactams from cyclic ketones and acetals.3


1. (a) Hoffman, R. V. In Advances in Oxygenated Processes; Baumstark, A. L., Ed.; Jai Press: Greenwich, CT, 1991; Vol. 3, pp 43-70. (b) Hoffman, R. V. OPP 1986, 18, 179. (c) Hoffman, R. V. In The Chemistry of Peroxides; Patai, S., Ed; Wiley: New York, 1983; pp 259-278.
2. Dannley, R. L.; Corbett, G. E. JOC 1966, 31, 153.
3. Hoffman, R. V. T 1991, 47, 1109.
4. Hoffman, R. V.; Carr, C. S.; Jankowski, B. C. JOC 1985, 50, 5148.
5. Hoffman, R. V.; Kim, H.-O. JOC 1988, 53, 3855.
6. Hoffman, R. V.; Kim, H.-O. JOC 1991, 56, 1014.
7. Hoffman, R. V.; Wilson, A. L.; Kim, H.-O. JOC 1990, 55, 1267.
8. Hoffman, R. V.; Huizenga, D. J. JOC 1991, 56, 6435.
9. Hoffman, R. V.; Bartsch, R. A.; Cho, B. R. ACR 1989, 22, 211.

Robert V. Hoffman

New Mexico State University, Las Cruces, NM, USA



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