N-arylnitreniurn ions

Aryl Nitrenium Ions in Aqueous Solution

“…82,83 A critical evaluation of Scribner's conclusions showed that he had neglected to consider that acyl transfer to generate the hydroxamic acid (33, Scheme 4.9) was a dominant reaction of these compounds under these conditions. 54 Underwood showed that no 18 …”

“…88 The study by Novak and coworkers of hydrolysis of esters of hydroxamic acids 18,89-96 has been reviewed. 54 The pH-independent hydrolysis rate constants of 38a-f in 5 vol% CH 3 CN-H 2 O (Schemes 4.12 and 4.13) correlated with s þ with r þ À4.5 at 25 C. 18 This is less negative than r þ for NÀ ÀO bond cleavage of similar esters in less polar solvents, 87,88 but the trend is in the expected direction and the magnitude of the effect is consistent with rate limiting formation of a nitrenium ion. 18 The hydrolysis products of 38a-d and 39 are summarized in Scheme 4.12.…”

“…The regioselectivity of these reactions has been reviewed elsewhere. 54,55 The lifetimes of 64n and 64o are about 0.6 and 0.2 ms, respectively, if k az % 5 Â 10 9 M À1 s À1 . These are remarkably long lifetimes compared to the 4-phenylcumyl cation and the 1-(4-biphenylyl)ethyl cation that have estimated lifetimes of about 0.5 and 0.1 ns, respectively, in 1:1 TFE-H 2 O based on linear free energy correlations.…”

“…[32][33][34][35][36][37] Their results have been reviewed. 38,[53][54][55] In the absence of nucleophiles, the lifetimes of 77b-f were governed by rearrangement (k m ) and thermal reversion to 76 (k sc ). 32,34,35 The ions 77a and 77g appeared to be too shortlived to be detected, but products consistent with nitrenium ions were detected.…”

“…16,38,[48][49][50][51][52][53][54][55][56] Our previous review covered the literature on aqueous solution chemistry of nitrenium ions up to the late 1990s. 54 The current review summarizes studies described earlier and concentrates on more recent developments. This review focuses on aqueous solution chemistry, but studies in other solvents (particularly alcohols) are discussed where appropriate.…”