Despite its importance and wide use as oxidizing agent, aqueous H₂O₂ has disadvantages. It easily decomposes, and when the substrates are not water-soluble, biphasic reaction mixtures are required. Thus, oxidizing agents that are anhydrous and soluble in organic solvents are desired. To this purpose, several H₂O₂ adducts of phosphine oxides, for example [tBu₃PO• H₂O₂]2₂and [Ph₃PO• H₂O₂]₂ H₂O₂, have been synthesized and characterized. These adducts represent an extension to the adducts previously reported by the Bluemel group, and display comparable physical properties.
Furthermore, di(hydroperoxy)alkane adducts, R₃PO•(HOO)₂CR'R" (R, R', R" = alkyl, aryl), were synthesized and fully characterized. These adducts can be constructed using a wide variety of alkanes and phosphine oxides. All di(hydroperoxy)alkane adducts are structurally well defined as proven by single crystal X-ray analysis, and they contain two active oxygen atoms per assembly.
These adducts of the type R₃PO•(HOO)₂CR'R" are highly soluble in organic solvents, allowing for oxidation reactions to occur in one phase. Moreover, there are many beneficial features to be harvested from their well-defined molecular structure and relatively anhydrous character. For example, selective and fast oxidation of dialkylsulfides to corresponding sulfoxides can be accomplished, without overoxidation to sulfones, because the solid oxidizing agents can easily be administered stoichiometrically. The adducts can also successfully oxidize substrates sensitive to hydrolysis, such as Ph₂P-PPh₂, without cleaving the P-P bond.
The R₃PO•(HOO)₂CR'R" adducts are robust and practically no decomposition is found after storing the solids for 100 days at 4 °C. At room temperature, the adducts slowly decompose over time, via the release of oxygen gas. When exposed to higher temperatures or mechanical stress such as hammering or grinding, no sudden release of energy and/or oxygen was observed, attesting to the stability of the adducts. In the presence of catalytic amounts of acid, adducts with di(hydroperoxy)cycloalkane moieties decompose by undergoing a Baeyer-Villiger oxidation, and the di(hydroperoxy)cycloalkanes are transformed into the corresponding lactones.
The R₃PO•(HOO)₂CR'R" adducts are stable, solid, stoichiometric and soluble materials, and can serve as an excellent complement to aqueous H₂O₂ as oxidizing agents
