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:
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.
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.
Sodium perborate (SPB), a principal component of washing powders, can be used as an inexpensive and eco-friendly oxidant in the palladium-catalyzed C-H acyloxylation of alkenes in excellent regio- and stereochemistry. The reactions used anhydrides as acyloxy sources. The method enables the conversion of both terminal and internal alkenes, and allows even benzylic C-H oxidation.
L. T. Pilarski, P. G. Janson , K. J. Szabó, J. Org. Chem., 2011, 76, 1503-1506.
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.
A catalytic enantio- and diastereoselective addition of alkyl 1,1-diboron reagents to aryl and vinyl aldehydes provides 1,2-hydroxyboronates promoted by a readily available chiral monodentate phosphoramidite-copper complex. Products contain two contiguous stereogenic centers and are obtained in good yield, good d.r., and high e.r. The 1,2-hydroxyboronate products can be transformed into versatile derivatives.
M. V. Joannou, B. S. Moyer, S. J. Meek, J. Am. Chem. Soc., 2015, 137, 6176-6179.
Bidentate Oxazoline-substituted imidazolium salts based on [2.2]paracyclophane with planar and central chirality can be used as ligand in Cu(I)-catalyzed asymmetric β-boration of α,β-unsaturated esters, giving the desired products in high enantioselectivities and yields.
Z. Niu, J. Chen, Z. Chen, M. Ma, C. Song, Y. Ma, J. Org. Chem., 2015, 80, 602-608.
A Rh-catalyzed hydroboration of α, β-unsaturated carbonyl compounds with pinacolborane proceeds with high levels of regio-, diastereo-, and enantioselectivities to provide products with two vicinal stereocenters. Through the appropriate choice of substrate geometry (E or Z) and ligand enantiomer, all possible diastereoisomers are readily accessible.
T.-T. Gao, W.-W. Zhang, X. Sun, H.-X. Lu, B.-J. Li, J. Am. Chem. Soc., 2019, 141, 4670-4677.
A transition-metal-free coupling of aldehydes and ketones with geminal bis(boron) building blocks provides homologated carbonyl compounds upon oxidation. Aldehydes with an enolizable stereogenic center undergo this reaction with complete retention of stereochemistry.
T. C. Stephens, G. Pattison, Org. Lett., 2017, 19, 3498-3501.
A copper(I)-catalyzed asymmetric borylative propargylation of simple ketones offers broad substrate scope, good tolerance of functional groups, high diastereo- and enantioselectivities, and reaction robustness. The borylative product can also serve as a cross-coupling partner in Pd-catalyzed Suzuki-Miyaura reactions.
X.-C. Gan, L. Yin, Org. Lett., 2019, 21, 931-936.
Hydroboration of 1-alkynyl-1-boronate esters and in situ transmetalation furnishes 1-alkenyl-1,1-borozinc heterobimetallic intermediates. Reaction with aldehydes and in situ cyclopropanation generates B(pin) substituted cyclopropyl carbinols with excellent diastereoselectivities. Oxidation provides trisubstituted α-hydroxycyclopropyl carbinols, that allow access to both cis- and trans-2,3-disubstituted cyclobutanones via a facile pinacol-type rearrangement.
M. M. Hussain, H. Li, N. Hussain, M. Ureña, P. J. Carroll, P. J. Walsh, J. Am. Chem. Soc., 2009, 131, 6516-6524.