74251-93-7Relevant articles and documents
Vinylogous Acyl Compounds. XIX. Vinylogous Acyl Group Migration in 2-Aminophenol. A Contribution to the Isomerization Mechanism of Mixed Diacyl Derivatives of 2-Aminophenol
Fischer, Gerhard W.
, p. 99 - 124 (2007/10/02)
Starting with 2-acylaminophenols 5 and 2-(2-acylvinylamino)-phenols 6 the N-acyl O-acylvinyl derivatives 7 of 2-aminophenol and their N-acylvinyl O-acyl isomers 8 were prepared and characterized.These vinylogous acyl compounds are able to isomerize in the same manner as simple O,N-diacylated 2-aminophenols 3 and 4, which under suitable conditions easily rearrange to give a dynamic equilibrium 34.Contrary to 3 and 4, however, the isomerization of 7 and 8 can be followed directly by spectroscopic methods, so that vinylogs of this type are useful model systems forstudying acyl group migrations in 2-aminophenol.Kinetic measurements show that the mutual rearrangement of 7 and 8 is a reversible general based catalyzed reaction, being first order with respect to substrate and catalyst.The isomerization of the N-acetyl derivatives 7a-h as well as the N-benzoyl derivatives 7i-p results in strictly linear HAMMETT correlations with positive reaction constant ρ.In the case of 7a-h the equilibrium constant K and the forward and reverse velocity constants k1 and k2 (including activation parameters) could be determined.The kinetic investigations and additional non-kinetic experiments indicate that the catalyst acts as proton acceptor and not - as hitherto supposed - as acyl group transferring nucleophile.Based on the findings an isomerization mechanism for mixed diacyl derivatives of 2-aminophenol is suggested.
