A method of phosphorodiamidite production comprising the steps of reacting
a phosphorus trihalide with a dialkyl amine in a polar solvent to form an
intermediate compound. This intermediate compound is then subsequently
reacted with an hydroxylalkyl compound and a dialkyl amine in the
presence of a non-polar cosolvent. Following filtration to remove the
solid by-product the two solvents form separate layers. This is
advantageous as the upper, non-polar solvent, layer contains the
high-purity phosphorodiamidite product.