Reexamination of the Mechanisms of Decomposition of Simple .alpha.-Acetoxynitrosamines in the Physiological pH Range

Evidence for the Formation of α-Hydroxydialkylnitrosamines in the pH-Independent Solvolysis of α-(Acyloxy)dialkylnitrosamines

“…The kinetic data for the acetate esters 5a and 4a (Figure , parts B and C, respectively) were presented as part of the previous study, and the kinetic data for the acetate ester 6a , Figure A, also shows the biphasic dependence indicated for the rate law of eq 1 over the limited range studied. Fits to the rate law of eq 1, using values for the rate constants summarized in Table , are indicated by the solid lines in Figure .…”

“…We previously studied the pH dependence of the buffer-independent decay of some simple α-(acyloxy)dialkylnitrosamines and observed that in the range of pH = 3−13, the rate law of eq 1 was obeyed . It was concluded that the pH-independent term, k 1 , involved rate-limiting formation of N -nitrosiminium ions, as in eq 2, on the basis of the near-zero values of Δ S ⧧ , structure−activity relations, and the trapping of putative N -nitrosiminium ions after the rate-limiting step by azide ion to yield adducts such as in eq 2. , Others 16a have previously characterized the reaction chemistry of 6a and obtained qualitatively similar evidence for the involvement of an N -nitrosiminium ion. It was also concluded, in accord with earlier suggestions, that the pH-dependent term, k OH , involves hydroxide ion attack at the carbonyl group.…”

“…The mechanism of solvolytic decay of simple α-(acyloxy)dialkylnitrosamines was recently reexamined . In the pH range between pH = 3−13 it is dominated by the two-term rate law of eq 1.…”

α-(Acyloxy)dialkylnitrosamines: Effects of Structure on the Formation of N-Nitrosiminium Ions and a Predicted Change in Mechanism

“…This had been the basis of the hypothesis that there was anchimeric assistance by the nitroso group of decomposition, possibly analogous to what had been observed in the case of β-(sulfatooxy)nitrosamines . It was concluded that the dominant mechanism involved the formation of nitrosiminium ions ( D ) in, or prior to, the rate-limiting step, as in eq 3. − The onset of a carbonyl attack mechanism with electron-withdrawing substituents R N and R C (C, eq 1) was predicted .…”

Failure to Isolate the First N-Nitrosiminium Cation

“…The synthesis of the SbCl 6 salt of the first N-nitrosiminium ion, 1 , was reported, along with limited physical characterization . The purported isolation of this cation was claimed as evidence of the pervasive intermediacy of N -nitrosiminium ions in the decomposition of carcinogenic α-acetoxy- N -nitrosamines. , We had need of the ion, 1 , as a precusor to various α-substituted nitrosamines in which we have an ongoing interest. We report here that the method briefly described 1 in fact gives the SbCl 6 salt of the simple iminium ion 2 , and that the limited physical data originally reported indicate that the salt of 2 was also the product in the initial 1 report.…”