Silica Gel-Supported Polyphosphoric Acid (PPA/SiO₂) as an Efficient and Reusable Catalyst for Conversion of Carbonyl Compounds into Oxathioacetals and Dithioacetals

Abstract

A simple and efficient method for the conversion of carbonyl compounds to oxathioacetals and dithioacetals by using polyphosphoric acid supported on silica gel (PPA/SiO₂) as an acid catalyst have been developed. PPA/SiO₂ is easily recovered from the reaction mixture and reused without a decrease in catalytic ­activity.

Key words

oxathioacetals - dithioacetals - protecting groups - polyphsphoric acid - silica gel

References

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18

The Preparation of PPA/SiO ₂ : PPA (2.1 g) was charged in the round-bottom flask, and CHCl₃ (100 mL) was added. After the mixture was stirred at 50 ºC for 1 h, SiO₂ [Wakogel C-200 (Wako Pure Chemical Ind. Ltd.), 4.9 g] was added to the solution, and the mixture was stirred for another 1 h. The CHCl₃ was removed with rotary evaporator and the resulting solid was dried in vacuo at r.t. for 3 h.

19

Used PPA/SiO₂ was regenerated as follows: PPA/SiO₂ was recovered by filtration from the reaction mixture, and then it was put in the 50 mL round-bottom flask and dried in vacuo at 100 °C for 2 h.