Perborates, epoxidation with

Epoxidation of alkenes. In combination with acetic anhydride, sodium perborate can effect epoxidation of alkenes at room temperature in 16-24 hours. Sulfuric acid can increase the rate, but lower the yields. 

Sodium perborate oxidation of alcohols by is aided by Aliquat, but also requires the addition of chromium oxide [17]. However, the long reaction times at 60-80°C and the variable yields do not make the procedure particularly attractive. In contrast, direct epoxidation of a,p-unsaturatcd ketones has been conducted with moderate success using sodium perborate catalysed by tetra-n-hexylammonium hydrogen sulphate [18, 19]. 

The formation of peracids as the effective oxidizing species has often been proposed for oxidations with sodium percarbonate in the presence of organic acids or acid anhydrides30-32. It was observed that at room temperature and in dichloromethane as solvent, the addition of acetic anhydride induced the epoxidation by sodium perborate of mono-, di- and trisubstituted alkenes, including a,/i-unsaturated ketones in a slightly exothermic reaction33 (equation 6). 

Savizky, R. M., Suzuki, N. and Bove, J. L. The use of sonochemistry in the asymmetric epoxidation of substituted chalcones with sodium perborate tetrahydrate. Tetrahedron Asymmetry, 1998, 9, 3967-3969. 

Sodium perborate (NaB03 nH20 n = 1-4) is a cheap and widely used industrial chemical. If sulfuric acid is added to a mixture of the perborate and an alkene in acetic anhydride, an exothermic reaction occurs leading to anti addition to the double bond with formation of the corresponding l-hydroxy-2-ace-toxy derivative in moderate yield. Peroxybis(diacetoxy)borane, (AcO)2BOOB(OAc)2, may be the reactive species in this oxidation and it seems likely that the epoxide is an intermediate. 

The epoxidation of alkenes by means of either sodium perborate or sodium percarbonate and acetic anhydride can be enhanced by sonication [46], When sodium perborate was used with sonication, the reaction time could be reduced significantly, but the yield was not significantly improved. With sodium percarbonate both a higher yield and a shorter reaction time were obtained. The mechanistic aspects of these reactions were discussed. 

Several oxidants were tested in an epoxidation reaction in the presence of iminium salt catalysts to determine which offers the best profile in the absence of water [42]. These reactions were carried out at 0 °C with 1-phenylcyclohexene as substrate and (17) and /or (24) as catalysts (5-20 mol%), in dichloromethane as solvent. Most of the systems examined showed either high levels of background epoxidation (alkaline hydrogen peroxide, peracids, persulphates) or very low rates of reaction, even in the presence of 20 mol% of the catalysts (perselenates, percarbonates, perborates and iodosobenzene diacetate). Tetra-N-butylammo-nium Oxone, reported by Trost [43], was also unsuccessful as oxidant. 

Quinone epoxides, for example the epoxide of juglone, have been obtained by reaction with sodium perborate.3... 

Oxidations. Alcohols are oxidized in dichloroethane with catalytic amounts of a dichromate salt using sodium percarbonate as a recycling agent and PTC. - Epoxidations of enones by sodium perborate or NaOCP under PTC conditions give high yields. However, with NaOCl and hexaethylguanidinium chloride, cyclohexenones give 6,6-dichloro-2,3-epoxycyclohexanones. 

Other major industrial applications for hydrogen peroxide include the manufacture of sodium percarbonate and sodium perborate, used as mild bleaches in laundry detergents. It is used in the production of certain organic peroxides such as dibenzoyl peroxide, used in polymerisations and other chemical processes. Hydrogen peroxide is also used in the production of epoxides such as propylene oxide. Reaction with carboxylic acids produces a corresponding peroxy acid. Peracetic acid and meta-chloroperoxybenzoic acid (commonly abbreviated mCPBA) are prepared from acetic acid and /weto-chlorobenzoic acid, respectively. The latter is commonly reacted with alkenes to give the corresponding epoxide. 

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