in conjunction with both hypochlorites and TEMPO gives carboxylic acids without chlorination side products. The reaction is usually carried out in two steps in the same pot: partial oxidation is effected with TEMPO and hypochlorite, then chlorite is added to complete the oxidation. Only primary alcohol oxidation is observed. In conjunction with Sharpless dihydroxylation, this method can be used to generate enantiopure α-hydroxy acids. (11) A significant limitation of both of the above methods is incompatibility with free amine or alkene functionality, both of which undergo competitive oxidation. The use of bis(acetoxy)iodobenzene (BAIB) as the terminal oxidant avoids this problem. BAIB is unable to oxidize the nitroxide radical directly, and initial formation of oxoammonium is believed to be due to acid-catalyzed disproportionation. BAIB may then oxidize the resulting hydroxylamine to an oxoammonium salt. Although the reaction is conducted under acidic conditions (acetic acid is a byproduct, and is often added to facilitate disproportionation), selectivity for primary alcohol oxidation is substantial. Base-sensitive functional groups, such as epoxides, are tolerated under these conditions. (12) Other two-electron terminal oxidants used with TEMPO include mCPBA (secondary oxidation is favored, although side reactions may occur), N-chlorosuccinimide, and Oxone. Copper(II), both as the free chloride salt and as a complex with bidentate ligands, oxidizes TEMPO to its oxoammonium salt. In these reactions, air serves as the terminal oxidant. It is unclear whether air oxidizes copper(I) to copper(II), or whether alcohol oxidation is partially mediated by copper and air oxidizes the resulting hydroxylamine back to the oxoammonium salt. The former occurs during the Wacker process, but the latter explains why copper complexes and a few other metal complexes are able to oxidize alcohols in conjunction with TEMPO. (13) Comparison with related methods Activated manganese dioxide, which oxidizes allylic and benzylic alcohols, is cheaper than TEMPO and operationally simple to use. Chromium-based reagents such as pyridinium chlorochromate can also be used to convert alcohols to carbonyl compounds; although the stoichiometric generation of chromium wastes is a disadvantage. Oxidations employing dimethyl sulfoxide, such as the Swern and Moffatt reactions, involve no heavy metals and oxidize a wide variety of substrates. Oxoammonium oxidations are preferred to DMSO methods for reactions of diols and acetylenic alcohols. Dess-Martin periodinane is a highly selective, mild oxidant of alcohols, whose primary disadvantages are difficulties with preparation and safety. References Organic oxidation reactions