Organic Syntheses Using Sodium Hypochlorite Pentahydrate (NaOCl·5H<sub>2</sub>O) Crystals

Sodium hypochlorite pentahydrate (NaOCl·5H2O) has recently become commercially available and is one of the promising oxidants for environmentally benign organic syntheses, because the postoxidation waste is “table salt”(NaCl). NaOCl·5H2O has succeeded in overcoming many disadvantages of the conventional aqueous solution of sodium hypochlorite (aq. NaOCl, the concentration is up to 13%). NaOCl·5H2O contains 44% NaOCl and minimal amounts of sodium hydroxide and NaCl. The aq. NaOCl is prepared from NaOCl·5H2O and water, and has a lower pH value (ca. 11) than that of the conventional aq. NaOCl (ca. 13). NaOCl·5H2O is more stable than the conventional aq. NaOCl below 7 °C. This review summarizes the organic synthetic reactions using NaOCl·5H2O. The oxidation of primary or secondary alcohols (including sterically-hindered alcohols) can be efficiently carried out by using NaOCl·5H2O in the presence of TEMPO (2,2,6,6-tetramethylpiperidin-1-oxyl) and tetrabutylammonium hydrogen sulfate as catalysts without pH adjustment. Even in the absence of catalysts, NaOCl·5H2O selectively oxidizes allylic, benzylic, and secondary alcohols using acetonitrile as the solvent. Aliphatic primary alcohols are hard to oxidize under this reaction condition. NaOCl·5H2O is applicable to glycol cleavage, and this reagent can easily cleave trans-cyclic glycols which are difficult to react with conventional “glycol cleavage” reagents. The oxidation of sulfides with an equimolar amount of NaOCl·5H2O in aqueous acetonitrile selectively produces the corresponding sulfoxides in high yields under a catalyst-free condition. Sulfones are efficiently obtained by the oxidation of sulfides with 2.4 eq. of aqueous NaOCl prepared from NaOCl·5H2O in toluene. This reaction is also catalyst-free. The reaction of disulfides or thiols with NaOCl·5H2O in acetic acid produces sulfonyl chloride. The reaction of NaOCl·5H2O with NaBr in acetic acid gives HOBr, and the resulting HOBr reacted with disulfides or thiols to afford the corresponding sulfonyl bromides. N-Sulfonyloxaziridines (Davis’ oxaziridines) can be synthesized by reacting the corresponding N-sulfonylimines with aqueous NaOCl in acetonitrile without any catalyst. The reaction of phenols with NaOCl·5H2O in the presence of water causes oxidative dearomatization. (Diacetoxyiodo)arenes can be easily prepared from the reaction of iodoarenes with NaOCl·5H2O in acetic acid.