Polar and steric effects in the stability of silver complexes of primary amines

Abstract

The complex-formation constants of alkylamines NRH₂ with Ag^I have been determined at 25 °C and I= 0.1 mol dm^–3, the background salt being mainly [NRH₃][NO₃]. The pK_a, logK₁, and logβ₂ valuee are: R = Me, 10.64, 3.06, 6.78; Et, 10.66, 3.44; 7.34; Prⁱ, 10.62, 3.64, 7.77; Bu^t, 10.66, 3.69, 7.87; Bu⁸, 10.56, 3.65, 7.77; cyclopropyl, 9.06, 3.10, 6.43; cyclopentyl, 10.63, 3.61, 7.83; and cyclohexyl, 10.62, 3.72, 8.02. It is shown that these variations of pK_a and logK can be readily understood in terms of Taft's (1957) equation relating formation and rate constants to polar and steric effects. Correlations from this equation suggest that Ag⁺ is much less susceptible to steric hindrance than is the proton.