Acid-base properties of phosphine oxides in nitromethane

Abstract

1. The acid-base properties of the phosphine oxides were studied by the method of potentiometric titration in nitromethane. The titration curve has two potential jumps at the points of 50% and 100% neutralization, which is due to the formation of complexes of the BHB+ type at the first stages of protonation. 2. A linear correlation was obtained between the values of pK a (CH3NO2) and the σσϕ constants of the substituents at the phosphorus atom, which permitted a calculation of the σϕ constants of the -CH2OR and -CH2COOH groups. 3. Aminomethylphosphine oxides are titrated as nitrogen bases. Substantial differences in the values of pK a (CH3+NO2) of different degrees of protonation of the molecules of these compounds are probably due to the formation of intramolecular hydrogen bonds (of the type N+-H ... N) and the inductive effect of the protonated dialkylaminomethyl group.