Basicité et structure de phosphoramides aliphatiques: dosage protométrique en solvants non-aqueux

Abstract

Brönsted basicities (as half-neutralization potentials) have been determined at 25 °C by potentiometric titrations in nitromethane or in the mixture sulfolane/benzene 98:2 p/p for 19 aliphatic phosphoramides OPXYZ, with X, Y, or Z = Me; OEt; NMe2; NEt2; NHEt; N(CH2)n (n = 3 or 4); or X + Y = —NMe—(CH2)2—NMe—. Almost all of these weak bases give an homohydrogen bonding. Those with an Me or N(CH2)3 substituent are not stable in acidic medium, which is confirmed by back-titration and measure of E vs. time at the equivalent point. After comparing the results obtained in the two solvents, the effect of the nature of the substituents X, Y, Z on half-neutralization potentials and instability in acidic medium is analyzed.

Oligodeoxynucleoside phosphoramidates (P-NH2): synthesis and thermal stability of duplexes with DNA and RNA targets

“…Consequently, the modification P-NH 2 is not protonated between pH 5.45 and 7. This result is in accord with the known low basicity of phosphoric amide diesters (18,33,34). In contrast, the stability of the 'parent' duplex d(Tp) 11 dT-9 increases with increasing NaCl concentration as expected.…”

On the Lewis Basicity of Phosphoramides: A Critical Examination of Their Donor Number through Comparison of Enthalpies of Adduct Formation with SbCl5and BF3

“…A revised value of 209.2 kJ mol À 1 (50 kcal mol À 1 ) was proposed by Cataldo, on the basis of several corrections, in particular a hypothetical ring opening of aziridinyl groups during the calorimetric measurements. Indeed, it is known that the strained aziridine and azetidine cycles are not stable under acidic conditions, [28,29] and possible secondary reactions during the calorimetric measurements would have remained unnoticed.…”