Formation and nucleophilic capture of N-nitrosiminium ions

Abstract

A study of the solvolysis of a series of (N-nitrosomethylamino)arylmethyl esters and azides and the products of nucleophilic trapping of the corresponding N-nitrosiminium ion intermediates in aqueous media, 25°C, ionic strength 1 M is reported. Structure-reactivity data for the forward and reverse reactions have been obtained. In three cases, the rate constants for reactions of the cations with nucleophiles have been measured directly by laser flash photolysis. The data allow a comparison of the degree to which the N-methyl-N-nitroso functionality enhances cation stability from a thermodynamic and kinetic perspective. It has been possible to deduce that the carbon basicity of azide ion is less than 1 kcal/mol greater than that of acetate ion.Key words: nitrosiminium ions, α-acetoxynitrosamines, carbocations, iminium ions, nucleophilicity.

Cyclic α-Acetoxynitrosamines: Mechanisms of Decomposition and Stability of α-Hydroxynitrosamine and Nitrosiminium Ion Reactive Intermediates

“…In summary, both of the cyclic α-acetoxynitrosamines appear, as in other cases, , to decompose predominantly, if not exclusively, through the formation of N -nitrosiminium ion intermediates at physiological pH. They do so with markedly different rate constants, the piperidine derivative being greater than 100 times more reactive than the pyrrolidine derivative, as might have been deduced. , The reason for the differences in propensity of the two compounds to undergo solvolysis is addressed below.…”

“…Finally, the linear Eyring plots give no evidence of curvature that would signify the existence of more than one mechanism with a single rate-controlling step. We cannot rule out that acetate reacts at the nitroso nitrogen, but there is evidence against this in related systems …”

Mechanisms of Decomposition of α-Hydroxydialkylnitrosamines in Aqueous Solution

“…This involved group exchange starting with the R-chloroacetate esters in a mixture of aqueous hydrogen peroxide and acetonitrile, followed by extraction and purification by preparative thin-layer chomatography. Synthesis of the esters was previously published (13). The synthesis of the R-deuterated substrate, [R-2 H]-1a, for the measurement of secondary R-deuterium kinetic isotope effects was carried out as described for the protio compound, starting with deuterated benzaldehyde that was generated by the Neff reaction, as described previously (14).…”

“…1 H NMR (CDCl3): δ 9.96 (1H, s), 7.41-7.21 (5H, m), 2.85 (3H, s). 13 C NMR (CDCl3): δ 134. 6, 134.1, 129.7, 129.6, 129.3, 125.8, 123.7, 95.1, 26.5.…”

“…1 H NMR for (Z)-3 (CDCl3, E/Z ∼ 40): δ 3.72 (3H, s). 13 C NMR for 3 (CDCl3): δ 136.1, 131.5, 129.5, 127.8, 96.0, 27.1. 4 was crystallized from pentane.…”