The Oxorhenium(VII)-Catalyzed Direct Condensation of Phosphoric Acid with an Alcohol

摘要

Phosphoric acid monoesters are among the most important substances in materials and medicinal chemistry as well as in many other fields. Many phosphoric acid monoesters are currently synthesized on an industrial scale and are used in everyday life.[1]-[4] From the perspective of green chemistry, the direct catalytic condensation of equimolar amounts of phosphoric acid and alcohols is attractive for the synthesis of phosphoric acid monoesters, especially for industrial-scale syntheses, since the reaction produces only water as a by-product.[5] Although various methods for the direct catalytic condensation of carboxylic acids with equimolar amounts of alcohols have been reported,[6], [7] there is no successful method for the synthesis of phosphoric acid monoesters by the direct catalytic condensation of phosphoric acid and an equimolar amount of alcohols.[8], [9] The esterification of phosphoric acid is much more difficult than that of carboxylic acids due to its stronger acidity.[10] We describe here the use of oxorhenium(VII) complexes[11], [12] as extremely active catalysts for the direct condensation of phosphoric acid with nearly equimolar amounts of alcohols to give the corresponding phosphoric acid monoesters. Since the present reaction could be easily applicable on a large scale and rhenium salts are believed to exhibit low toxicity,[13] it should be a useful method for the environmentally and industrially important synthesis of phosphoric acid monoesters. To the best of our knowledge, this is the first direct catalytic condensation of a nearly equimolar mixture of phosphoric acid and alcohols for the selective synthesis of phosphoric acid monoesters.