Acid-catalysed chlorine transfer from N-chloramines to iodide ion: experimental evidence for a predicted change in mechanism.
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 H(2)O at 25 degrees C and I = 0.5 (NaClO(4)). 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 (k(H)/k(D) = 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.
Calvo
Paula
P
Departamento de Química Física, Facultad de Química, Universidad de Santiago de Compostela, , 15782 Santiago de Compostela, Spain.
Crugeiras
Juan
J
Ríos
Ana
A
D000143:Acids / Q000737:chemistry*; D002384:Catalysis; D002700:Chloramines / Q000737:chemistry*; D002713:Chlorine / Q000737:chemistry*; D007454:Iodides / Q000737:chemistry*; D007477:Ions / Q000737:chemistry; D015394:Molecular Structure; D014867:Water / Q000737:chemistry
D000143:Acids; D002700:Chloramines; D007454:Iodides; D007477:Ions; D014867:Water; D002713:Chlorine