90476-18-9Relevant articles and documents
The mechanism of hydrolysis of aryl ether derivatives of 3-hydroxymethyltriazenes
Carvalho, Emilia,Francisco, Ana Paula,Iley, Jim,Rosa, Eduarda
, p. 2056 - 2063 (2007/10/03)
1-Aryl-3-aryloxymethyl-3-methyltriazenes hydrolyse to the corresponding anilines and phenols by specific-acid-catalysed, general-acid-catalysed and pH-independent mechanisms. All compounds studied exhibit specific- and general acid catalysis, though for 5a general acid catalysis was not observed below a pH of approximately 4, while for compounds 5e,f, such catalysis was absent above a pH of approximately 5. The pH-independent pathway is observed only for those compounds, 5d-f, that contain good aryloxy nucleo-fugic groups. The specific-acid-catalysed pathway is supported by a solvent deuterium isotope effect (SDIE) of 0.64, consistent with a mechanism involving protonation of the substrate followed by rate-determining unimolecular decomposition of the protonated species. The kH+ values gave rise to a Hammett p value of -0.93, reflecting the competing effect of the substituents on the protonation of the substrate and the cleavage of the aryl ether. Correlation of k H+ with the pKa of the phenol leaving group affords a β1g of 0.3. Decomposi tion of the protonated intermediate proceeds via a triazenyliminium ion that can be trapped by methanol. The general-acid-catalysed process exhibits an SDIE of 1.43 and Hammett p values of 0.49, 0.84 and 1.0 for reactions catalysed by chloroacetic, formic and acetic acids, respectively. Correlation of KA with the pKa of the acid gave Bronsted a values that diminish from 0.6 for O-aryl systems that are poor nucleofuges (5a, b) to 0.2 for the best nucleofuge (5f), reflecting the different extents of proton transfer required to expel each phenol. Compounds containing powerful nucleofuges exhibit a pH-independent reaction that has an SDIE of 1.1, a Hammett p value of 3.4 and a Bronsted β1g value of 1.4. These imply a mechanism involving displacement of the aryloxide leaving group to form a triazenyliminium ion intermediate that again was trapped as a methyl ether. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005).
Kinetic Study of the Solvolysis Reactions of 1-Aryl-3-acetoxymethyl-3-alkyltriazenes: Evidence for Iminium Ion Intermediates and the SN1 Mechanism
Hemens, Chantal Marie,Vaughan, Keith
, p. 11 - 16 (2007/10/02)
The first-order rate constants of the reactions of acetoxymethyltriazenes with nucleophiles have been measured.Acetoxymethyltriazenes undergo hydrolysis in phosphate buffer to give the corresponding arylamines, presumably via the hydroxymethyl- and monomethyl-triazenes.The acetoxymethyltriazenes undergo solvolysis in alcohols and in mixtures of alcohols and other solvents; the rate of solvolysis has been correlated with the Grunwald-Winstein parameter (Y) for solvent ionising power, thus supporting the hypothesis of an SN1 mechanism and the intermediate formation of iminium ions during the solvolysis.The hypothesis is further supported by the non-common-ion effect; the presence of lithium chloride in the solvent greatly increases the rate of reaction, whereas lithium acetate causes a slight decrease in rate, attributable to a common-ion effect.Reaction of the acetoxymethyltriazene with sodium azide in aqueous acetone affords the α-azidomethyltriazene (a new type of triazene not previously reported) and provides supporting evidence for the iminium ion hypothesis.On the other hand, the acetoxymethyltriazene did not react with neat ethanethiol, providing further evidence for an SN1 mechanism; and SN2 reaction would be expected to proceed more quickly in the thiol than in the alcohol.It is shown that hydroxymethyltriazenes do not react via iminium ions and that functionalisation to a derivative such as the acetate is necessary for iminium ion generation.The implications of these results for the metabolism of xenobiotic N-alkyl compounds are discussed.
