[7486-26-2] · BrNaO2 · Sodium Bromite · (MW 134.89)
(selective oxidant; oxidizes secondary in preference to primary alcohols, and a,o-diols to lactones; sulfides oxidized to sulfoxides; can be used for Hofmann degradation)
Solubility: sol H2O (28 g/100 mL at 0 °C; 91 g/100 mL at 100 °C); insol most organic solvents.
Form Supplied in: aqueous solution.
Analysis of Reagent Purity: titration with Na3AsO3.
Preparative Methods: the commercial reagent is concentrated under reduced pressure below -30 °C to produce the trihydrate. Anhydrous material is obtained by crystallization from aqueous 2N NaOH followed by drying (20 °C/5 mmHg).
Purification: crystallization as above.
Handling, Storage, and Precautions: refrigerate, thermally labile; handle in a fume hood.
Sodium bromite oxidizes a range of secondary alcohols to the corresponding ketones (eq 1) in aqueous acetic acid.2 If the reagent is used in the presence of Alumina, other solvents can be used, in particular dichloromethane, thereby simplifying product isolation (eq 2).3 Selective oxidation of a primary-secondary diol results in the formation of the hydroxy ketone (eq 3),2 whereas oxidation of a primary alcohol produces the ester rather than the corresponding aldehyde (eq 4).4 Following this pattern of reactivity, a,o-diols give good yields of lactones (eq 5).4
A catalytic quantity of metals and metal salts (such as Cu, Cu2+, Fe3+, Al3+) has been reported to improve the oxidation of various types of alcohols to ketones, lactones, and diones.5 Sodium bromite has been used as the stoichiometric oxidant in oxidations of alcohols catalyzed by N-oxyl compounds such as (1), conditions which allow for the oxidation of primary alcohols to aldehydes (eqs 6 and 7) or acids depending on the conditions (eq 8).6 Primary alcohols are oxidized in preference to secondary alcohols (eq 9).
The oxidation of sulfides to sulfoxides with sodium bromite is often highly selective, with little or no sulfone being produced, and it is possible to avoid oxidation of other potentially reactive functional groups (eqs 10 and 11).2 This oxidation can be performed very effectively in the presence of
wet Montmorillonite K10 (eq 12).7
Sodium bromite has been used for a number of other oxidations, including the generation of nitrile oxides for dipolar cycloadditions (eq 13),8 the conversion of alkenes to a-bromo ketones (eq 14),9 the preparation of N-bromoamides (eq 15),10 and the Hofmann degradation (eq 16).11
University of Salford, UK