US Patent 7030230 Process of purifying phosphoramidites

A process of purifying phosphoramidite precursors useful in inter alia synthesis of oligonucleotides comprises dissolving a crude phosphoramidite in a polar phase, adding a basic compound to the polar phase, adding a portion of water to the polar phase, contacting the polar phase with a first apolar phase to extract impurity into the apolar phase, separating the first apolar phase from the polar phase, adding a second aliquot of water to the polar phase, and contacting the polar phase with a second apolar phase, whereby the phosphoramidite partitions into the second apolar phase.