Several
catalysis systems, WO
3![dot operator](http://www.sciencedirect.com/scidirimg/entities/22c5.gif)
H
2O/H
2O
2–H
2O–H
3O
+/Q
+A
−/H
3PO
4/H
2SO
4/solvent (Q
+A
− = Arquad 2HT®, [CH
3(
n-C
8H
17)
3N]
+Cl
−; [CH
3(
n-C
8H
17)
3N]
+![Click to view the MathML source](http://www.sciencedirect.com/cache/MiamiImageURL/B6WHJ-4P0VD7W-2-1D/0?wchp=dGLbVlz-zSkWA)
, [CH
3(
n-C
8H
17)
3N]
+H
2![Click to view the MathML source](http://www.sciencedirect.com/cache/MiamiImageURL/B6WHJ-4P0VD7W-2-1T/0?wchp=dGLbVlz-zSkWA)
; solvent: CHCl
3 or toluene) were used to selectively and efficiently convert olefins to their corresponding epoxides at room temperature. With cyclooctene and using Arquad 2HT® as the
phase-transfer agent, there is a synergy when both phosphate and sulfate anions are present in the reaction medium compared with systems using either one or the other. The importance of the tungsten(VI) source is, as found previously, underlined by the strong activity increase when WO
3![dot operator](http://www.sciencedirect.com/scidirimg/entities/22c5.gif)
H
2O is used instead of Na
2WO
4![dot operator](http://www.sciencedirect.com/scidirimg/entities/22c5.gif)
2H
2O, even at room temperature. The influence of the
phase-transfer agent Q
+A
− has been evaluated for the system WO
3![dot operator](http://www.sciencedirect.com/scidirimg/entities/22c5.gif)
H
2O/H
2O
2–H
2O–H
3O
+/Q
+A
−/toluene. With Q
+A
− (Q
+ = [CH
3(
n-C
8H
17)
3N]
+ and A
− = Cl
−,
![Click to view the MathML source](http://www.sciencedirect.com/cache/MiamiImageURL/B6WHJ-4P0VD7W-2-26/0?wchp=dGLbVlz-zSkWA)
, and H
2![Click to view the MathML source](http://www.sciencedirect.com/cache/MiamiImageURL/B6WHJ-4P0VD7W-2-2K/0?wchp=dGLbVlz-zSkWA)
), the best results for the conversion of cyclooctene at room temperature are obtained with [CH
3(
n-C
8H
17)
3N]
+H
2![Click to view the MathML source](http://www.sciencedirect.com/cache/MiamiImageURL/B6WHJ-4P0VD7W-2-30/0?wchp=dGLbVlz-zSkWA)
.
31P NMR experiments show the transfer in the organic
phase of the [PO
4{W
2O
2(
μ-O
2)
2(O
2)
2}
2]
3− and [HPO
4{W
2O
2(
μ-O
2)
2(O
2)
2}]
2− complexes with H
3PO
4 and H
2![Click to view the MathML source](http://www.sciencedirect.com/cache/MiamiImageURL/B6WHJ-4P0VD7W-2-3C/0?wchp=dGLbVlz-zSkWA)
, whereas only [PO
4{W
2O
2(
μ-O
2)
2(O
2)
2}
2]
3− can be identified with the addition of H
3PO
4/
![Click to view the MathML source](http://www.sciencedirect.com/cache/MiamiImageURL/B6WHJ-4P0VD7W-2-3S/0?wchp=dGLbVlz-zSkWA)
or H
2![Click to view the MathML source](http://www.sciencedirect.com/cache/MiamiImageURL/B6WHJ-4P0VD7W-2-3X/0?wchp=dGLbVlz-zSkWA)
/H
2SO
4. Moreover, acid-sensitive epoxides can be prepared using buffers generated by the addition of sodium hydrogenocarbonate or, preferably, disodium hydrogenophosphate, leading to high selectivities toward the corresponding epoxides. The data show that disodium hydrogenophosphate gives the best results even if the reaction time has to be increased to obtain high conversions. The WO
3![dot operator](http://www.sciencedirect.com/scidirimg/entities/22c5.gif)
H
2O/H
2O
2–H
2O/[CH
3(
n-C
8H
17)
3N]
+H
2![Click to view the MathML source](http://www.sciencedirect.com/cache/MiamiImageURL/B6WHJ-4P0VD7W-2-3Y/0?wchp=dGLbVlz-zSkWA)
/toluene
catalysis system can be reused in 5 consecutive runs with no loss in activity.