ISSN:
0021-8383
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Vinylogous Acyl Compounds. XIX. Vinylogous Acyl Group Migration in 2-Aminophenol. A Contribution to the Isomerization Mechanism of Mixed Diacyl Derivatives of 2-AminophenolStarting 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 3 ⇌ 4. 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 for studying 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 constants 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 nonkinetic 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.
Additional Material:
6 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/prac.19803220114
