Sodium Perborate


[10486-00-7]  · BH8NaO7  · Sodium Perborate  · (MW 153.88)

(oxidizing agent for a variety of functional groups)

Physical Data: mp 60 °C (dec.); bulk density 0.74-0.82 g cm-3.

Solubility: sol water (~23 g L-1 at 20 °C, ~37 g L-1 at 30 °C; pH of 1% solution ~10.4); sol acetic acid, lower alcohols.

Form Supplied in: colorless, crystalline, odorless, free-flowing powder; widely available; 96% minimum sodium perborate tetrahydrate; 10% minimum available oxygen.

Handling, Storage, and Precautions: safe when handled correctly. It should be stored in a cool, dry place (below 40 °C) protected from direct heat and humidity.

Sodium perborate tetrahydrate, NaBO3.4H2O, has the 1,4-diboratetraoxane structure (1). This structure is disrupted in polar protic solvents such as water, alcohols, and carboxylic acids, and various types of oxidizing species can be generated, from the perhydroxyl anion to protonated perboric acid, depending on the pH. The reagent is most commonly used in acetic acid at temperatures between ambient and 60 °C; peracetic acid is produced at appreciable rates at higher temperatures. Detailed mechanisms for the various perborate oxidations have yet to be established. In most of its applications, sodium perborate is recommended as a cheap, safe, and convenient alternative to oxidants such as Hydrogen Peroxide, Peracetic Acid and m-Chloroperbenzoic Acid, especially for large scale operations.

Functional Group Oxidations.

Sulfur and Selenium.

Thiols (RSH) and selenols (RSeH) are smoothly oxidized in high yield to disulfides (RSSR) and diselenides (RSeSeR).1 Many sulfides, including a range of heterocyclic sulfur compounds, have been oxidized cleanly to sulfones with excess reagent (eq 1).2-5 Conversion of sulfides into sulfoxides also proceeds in high yield when 1 equiv of oxidant is used, although in most cases small amounts of sulfones are also formed.2,6 Chiral sulfoxides are obtained from appropriate precursors (eq 2).7 Oxidation at sulfur and selenium is faster than at most other functional groups and hence it is not usually necessary to protect amino, hydroxyl, or alkenic centers. In the presence of Acetic Anhydride, sodium perborate is an effective reagent for the preparation of a,b-unsaturated carbonyl compounds by oxidative deselenylation of a-phenylselenocarbonyl derivatives (eq 3).8


Oxidation of p-deficient azines (substituted pyridines, pyrazines, and quinolines; isoquinoline) with sodium perborate in acetic acid gives good yields of the corresponding N-oxides.5,9 The reactions of anilines are particularly interesting. Depending on the reaction conditions, they can be converted into the corresponding azo,10-12 azoxy,13 or nitro2,14 compounds (eq 4). The latter transformation is particularly useful for anilines which contain powerful electron-withdrawing groups in the ortho or para positions (eq 5).2 Excellent yields are obtained of products which are very difficult, or impossible, to prepare by standard aromatic substitution reactions. Primary aliphatic amines are oxidised to C-nitroso compounds15 (isolated in good yield as the dimers), while oximes give moderate yields of the corresponding nitro compounds.16 N,N-Dialkylhydrazones are cleaved to the ketones in good to excellent yield.2,17

Alkenes and Alkynes.

Most types of alkenes react rather sluggishly with sodium perborate in acetic acid and this process is of little use for epoxidation. A mixture of the perborate with acetic anhydride, however, apparently generates peroxybis(diacetoxyborane), (AcO)2B-O-O-B(OAc)2, which does epoxidize alkenes in good yield (eq 6).18 Use of the same reagent system with Sulfuric Acid catalysis gives 1,2-diol monoacetates (eq 7). Similar types of products are obtained from a series of a-substituted styrenes with perborate in acetic acid (eq 8),19 while terminal alkynes give 1-acetoxyalkan-2-ones with added Mercury(II) Acetate as catalyst.20 Epoxidation of a,b-unsaturated ketones can be effected in excellent yield either under phase-transfer conditions21 or simply by using sodium perborate in a two phase water-THF system (eq 9).22 Epoxidation of quinones has been described,23 but in most cases yields are low.

Alcohols, Aldehydes, Ketones, Phenols, and Nitriles.

Simple alcohols react only very slowly with sodium perborate and, as indicated below, aqueous alcohol serves as a very suitable solvent for the hydration of nitriles. Benzylic alcohols are oxidized to aldehydes, ketones, and/or carboxylic acids only at temperatures higher than 60 °C.24 a-Hydroxy acids are oxidized to ketones or carboxylic acids, 1,2-diols are cleaved to acids and ketones, and a-diketones also give carboxylic acids.25 Room temperature Baeyer-Villiger oxidation of ketones proceeds smoothly (eq 10),2 while perborate/acetic acid at 45-50 °C is an excellent reagent for the high yield oxidation of a wide range of aromatic aldehydes to the corresponding carboxylic acids.5,26 Hydroquinones and certain highly substituted phenols are oxidized in good yield to quinones.2 The phenol oxidations may involve initial electrophilic hydroxylation of the electron-rich rings.11,27 Although not formally an oxidation, the hydration of nitriles by perborate is a clean and high yielding reaction.5,28,29 Interestingly, there is no reaction when acetic acid is used as solvent, but use of water, aqueous methanol, or a water-dioxane system gives excellent results.

Boron, Iodine, Phosphorus.

Trialkyl- and triarylboranes are efficiently converted into alcohols and phenols on treatment at room temperature with sodium perborate in a water-THF system.30,31 Oxidation at boron is even faster than oxidation at sulfur (eq 11), and the perborate oxidation is as good as, or better than, the conventional peroxide/base procedure. It is particularly useful for the clean, high yield conversion of alkenylboranes into aldehydes and ketones.32 Iodoarenes are readily oxidised by sodium perborate. Use of acetic acid as solvent gives good yields of (diacetoxyiodo)arenes (eq 12),5 while (dichloroiodo)arenes, ArICl2, are obtained in 60-98% yield when hydrochloric acid is used.33 Sodium perborate has been recommended as a viable alternative to hydrogen peroxide for the large scale oxidative decomposition of toxic organophosphorus ester wastes.34-36

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33. Koyuncu, D.; McKillop, A.; McLaren, L. JCR(S) 1990, 21.
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Alexander McKillop

University of East Anglia, Norwich, UK

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