Sodium perborate
Sodium perborate (SPB) is used in the detergent industry as a bleaching agent. The crystalline reagent is available inexpensively as a hydrate with the general formula NaBO3 • n H2O (n: 1-4). Indeed, the compound itself is a dimer:
The reagent offers low toxicity and a long shelf life. SPB is a useful reagent in organic synthesis as a substitute for the unstable, highly concentrated hydrogen peroxide solutions that can pose a significant explosion hazard and are not commercially available.
Sodium perborate is soluble in water and releases hydrogen peroxide, but it is not merely a mixture of hydrogen peroxide and sodium borate. NMR and Raman spectroscopy indicate that in dilute solution, an equilibrium exists that still contains peroxoborate anions. These peroxoborate species are able to deliver the hydroperoxide anion at a lower pH than when H2O2 is used:
A. McKillop, W. R. Sanderson, Tetrahedron, 1995, 51,
6145-6166.
DOI
SPB is activated toward nucleophilic oxidation, and also buffers the reaction medium.
For oxidations of organoboranes, Kabalka notes that H2O2 sometimes requires quite harsh conditions that are incompatible with many functional groups, while SPB offers an interesting mild alternative. He assumes that the mild nature of the oxidant is a result of having borate as a leaving group as compared to hydroxide, which is formed in hydrogen peroxide oxidations:
G. W. Kabalka, T. M. Shoup, N. M. Goudgaon, J. Org. Chem., 1989,
54, 5930-5933.
Mixing sodium perborate with acetic acid generates even more powerful oxidation species. As McKillop states in his review (Tetrahedron, 1995, 51, 6145-6166. DOI), the situation is more complex than a simple conversion of a carboxylic acid to the corresponding peracid might suggest. It is possible that the intermediate peracetoxyboron species might act directly on organic substrates.
For applications in organic synthesis see the following reviews:
J. Muzart, Synthesis, 1995, 1325-1347.
DOI
A. McKillop, W. R. Sanderson, J. Chem. Soc., Perkin Transactions 1,
2000, 471-476.
DOI
Recent Literature
Several primary aromatic amines were converted to their corresponding nitro
compounds in good yields with sodium perborate tetrahydrate (SPB) in micellar
media in the presence of a catalytic amount of tungstophosphoric acid (H3PW·nH2O).
H. Firouzabadi, N. Iranpoor, K. Amani, Green Chemistry,
2001, 3, 131-132.
Sodium perborate in acetic acid is an effective reagent for the oxidation of
aromatic aldehydes to carboxylic acids, iodoarenes to (diacetoxyiodo)arenes,
azines to N-oxides, and various sulphur heterocycles to S,S-dioxides.
Nitriles undergo smooth oxidative hydration to amides when aqueous methanol is
employed as solvent.
A. McKillop, D. Kemp, Tetrahedron, 1989,
45, 3299-3306.
A. McKillop, D. Kemp, Tetrahedron, 1989,
45, 3299-3306.
A. McKillop, D. Kemp, Tetrahedron, 1989,
45, 3299-3306.
A. McKillop, D. Kemp, Tetrahedron, 1989,
45, 3299-3306.
Sodium perborate efficiently oxidizes a wide variety of functionally
substituted organoboranes. The product yields exceed those obtained using
standard oxidation procedures.
G. W. Kabalka, T. M. Shoup, N. M. Goudgaon, J. Org. Chem., 1989,
54, 5930-5933.
G. W. Kabalka, T. M. Shoup, N. M. Goudgaon, J. Org. Chem., 1989,
54, 5930-5933.
A convenient oxidation of oximes to nitro compounds uses sodium perborate in
glacial acetic acid as oxidizing agent.
G. A. Olah, P. Ramaiah, C.-S. Lee, G. K. Surya Prakash, Synlett,
1992, 337-339.
