Cevasco, G. and Thea, S. and Vigo, D. and Williams, A. and Zaman, F. (2006) Catalysis and inhibition of ester hydrolysis in the presence of resorcinarene hosts functionalized with dimethylamino groups. Journal of Physical Organic Chemistry, 19 (10). pp. 630-636. ISSN 0894-3230.
|The full text of this publication is not available from this repository. (Contact us about this Publication)|
Complexation and catalysis of two calixresorcinarene (RES) derivatives with nucleophilic N,N-dimethylamino functions attached to their upper rims in the hydrolysis of carboxylate and sulfonate esters of 4-nitrophenol and 2,4-dinitrophenol have been investigated. Rate constants obey the complexation equation: k(obs) = k(b) x K-s + k(c) [Host] / K-s + [Host] Values of the dissociation constant (K-s) of the complexes are within the range exhibited by other systems such as cyclodextrins-ester complexes. The reactions of sulfonate esters only exhibit inhibition by the macrocyclic hosts. The reactions of the carboxylate esters exhibit catalysis and inhibition depending on the pH of the system. It is proposed that the dimethylamino function in RES3 and RES5 behaves as a nucleophile to form a reactive acylammonium species which subsequently decomposes and regenerates the catalytic amine. In the reaction of substituted phenyl acetates with RES3 the effective charge on the leaving oxygen in the complexed state (+0.88) is slightly more positive than that in the free ester (+0.70). The effective charge on the leaving oxygen in the transition structure is substantially more positive (+0.04 units) than in a model intramolecular reaction of tertiary dimethylamines with aryl esters (-0.53 units). The influence of the host on the reaction in the complex includes an electronic component which is ascribed to solvation of the transition structure of the rate-limiting step by water molecules located within the cavity of the host. It is suggested that this solvation is stronger than that occurring in the transition state for the model intramolecular reaction.
|Additional information:||Cevasco, Giorgio Thea, Sergio Vigo, Daniele Williams, Andrew Zaman, Flora 27 JOHN WILEY & SONS LTD 142PQ|
|Divisions:||Faculties > Science Technology and Medical Studies > School of Physical Sciences|
|Depositing User:||Maggie Francis|
|Date Deposited:||05 Sep 2008 14:26|
|Last Modified:||14 Jan 2010 14:42|
|Resource URI:||http://kar.kent.ac.uk/id/eprint/11011 (The current URI for this page, for reference purposes)|
- Depositors only (login required):