Indeed, No Need for HMPA! A DFT Study Comparing the Lewis Basicity of Phosphoric Acid Triamides

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Abstract
It has been long known that hexamethylphosphoric acid triamide ( HMPA ) may cause genetic defects and cancer. Nevertheless, it is frequently used as highly polar aprotic solvent and as very strong Lewis base in synthetic organic chemistry as well as in other applications. Several attempts of replacing this hazardous compound by alternative strong Lewis bases have been reported in the literature, but the knowledge about these useful compounds and their properties does not receive the deserved attention of potential applicants. In the current computational study, we compare the Brønsted and Lewis basicity of HMPA , the already established replacement compound tripyrrolidino phosphoric acid triamide ( TPPA ) and of two conformationally restricted phosphoric acid triamides. The density functional theory study also includes N , N ′ ‐ dimethyl‐ N , N ′ ‐ propylene urea ( DMPU ) as known Lewis basic additive in a few transformations of lithium organic compounds. The Gibbs free energies of the reactions of these Lewis bases with protons, with lithium cations and with samarium(II) as well as samarium(III) species, were calculated including THF as solvent sphere. The results reveal that TPPA and one of the newly designed phosphoric acid triamides ( HAPO‐2 ) are stronger bases than HMPA in all computed reactions and are excellent substitutes of hazardous HMPA .

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