Issue 18, 2010

Acid-catalysed chlorine transfer from N-chloramines to iodide ion: experimental evidence for a predicted change in mechanism

Abstract

Rate constants for acid catalysis of the reactions of N-chlorodimethylamine (1), N-chloro-2,2,2-trifluoroethylamine (2) and N,N-dichlorotaurine (3) with iodide ion were determined in H2O at 25 °C and I = 0.5 (NaClO4). The failure to detect significant catalysis by general acids of chlorine transfer from 1 to the nucleophile, together with the observed inverse solvent deuterium isotope effect on the hydronium ion-catalysed reaction (kH/kD = 0.37), indicates that this process occurs by protonation of 1 in a fast equilibrium step, followed by rate determining chlorine transfer to iodide ion. The appearance of general acid catalysis for the reactions of 2 and 3 shows that increasing the leaving group ability leads to a change to a concerted mechanism, which is suggested to be enforced by the absence of a significant lifetime of the protonated chloramine intermediate in the presence of iodide ion.

Graphical abstract: Acid-catalysed chlorine transfer from N-chloramines to iodide ion: experimental evidence for a predicted change in mechanism

Supplementary files

Article information

Article type
Paper
Submitted
08 Apr 2010
Accepted
18 Jun 2010
First published
22 Jul 2010

Org. Biomol. Chem., 2010,8, 4137-4142

Acid-catalysed chlorine transfer from N-chloramines to iodide ion: experimental evidence for a predicted change in mechanism

P. Calvo, J. Crugeiras and A. Ríos, Org. Biomol. Chem., 2010, 8, 4137 DOI: 10.1039/C004976J

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