Removal of Triphenylphosphine Oxide by Precipitation with Zinc Chloride in Polar Solvents

While the use of triphenylphosphine
as a reductant is common in
organic synthesis, the resulting triphenylphosphine oxide (TPPO) waste
can be difficult to separate from the reaction product. While a number
of strategies to precipitate TPPO are available, none have been reported
to work in more polar solvents. We report here that mixing ZnCl2 with TPPO precipitates a TPPO–Zn complex in high yield
in several common polar organic solvents. The solvent compatibility
of this procedure and the reliability of the precipitation in the
presence of polar functional groups were examined to show the utility
and limitations of this method.