Kinetic Studies of the Hydrolyses and Aminolyses of Phosphorus (V) Chlorides And Proton Transfer at Carbon

Phosphorus oxychloride (POCl3) and thiophosphoryl chloride (PSCl3) are useful phosphorylating reagents. However, they are usually used under dry conditions as their reactivity toward water has been perceived as a problem. As part of an on-going program to develop aqueous aminophosphorylation procedures, we have investigated the reactivities of phosphodichloridate and thiophosphodichloridate ions in aqueous solutions as more selective water-soluble alternatives to POCl3 and PSCl3. We report the pH-kobs profiles for the hydrolyses of phosphodichloridate and thiophosphodichloridate ions in aqueous solutions. Both species show broad pH-kobs plateaus that extend to high pHs. The aminolyses of phosphodichloridate and thiophosphodichloridate ions in aqueous amine solutions have also been followed. Good selectivity towards aminolysis over hydrolysis processes has been observed. We have applied our kinetic data towards the optimisation of aqueous aminophosphorylation procedures, which has led to near-quantitative conversion of amino-nucleosides to thiophosphoramidate products. Finally, an additional research project focused upon peri-dimethylamino substituent effects on proton transfer at carbon in α-naphthylacetate esters. Rate constants for the exchange of hydrogen for deuterium at the α-CH2 positions of naphthalen-1-yl-acetic acid tert-butyl ester and 8-(N,N-dimethylamino-naphthalen-1-yl)-acetic acid tert-butyl ester have been determined in potassium deuteroxide solutions.