15950-66-0Relevant articles and documents
Catalysis and inhibition of ester hydrolysis in the presence of resorcinarene hosts functionalized with dimethylamino groups
Cevasco, Giorgio,Thea, Sergio,Vigo, Daniele,Williams, Andrew,Zaman, Flora
, p. 630 - 636 (2008/02/08)
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: kobs = kb × Ks + k c[Host]/Ks + [Host] Values of the dissociation constant (Ks) 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. Copyright
Reactions within Association Complexes: The Reaction of Imidazole with Substituted Phenyl Acetates in the Presence of Detergents in Aqueous Solution
Pirinccioglu, Necmettin,Zaman, Flora,Williams, Andrew
, p. 2537 - 2543 (2007/10/03)
The bimolecular rate constants for reaction of imidazole with phenyl acetates complexed with sodium dodecyl sulfate (SDS) or cetyltrimethylammonium bromide (CTAB) micelles obey Bronsted equations with βlg similar to that of the reaction in aqueous solution. The dissociation constants of ester (KS) and the hypothetical dissociation constant (KTS) of the transition state of the micelle complexes obey Hansch equations with similar sensitivities (p) to π (-0.66 and -0.589 for KS and -0.735 and -0.495 for KTS, respectively). The slopes also indicate that the microsolvation environments associated with the transition state and the complexed ester have aqueous character. The relative values of KTS and KS indicate that the transition state of the reaction of imidazole with ester is more weakly complexed to both micelles than is the reactant ester. Log KTS values are linear functions of log KS for reactions with both CTAB and SDS; the slopes are, respectively, -0.893 and -1.19 consistent with a slightly more "water-like" medium for the transition state than for the site of binding of ester with CTAB-micelle and slightly less for the SDS-micelle. The results for ester and transition state are consistent with the location of the phenyl residue in a hydrophobic region that possesses water molecules. It is concluded that the acetyl group in the complexed transition state is located in an aqueous part of the Stern region, whereas the phenyl residue is in a part of the Stern region that possesses alkane components. The derived kinetic and complexation parameters in these experiments refer to micelles with Stern regions that have been maintained at constant ionic compositions.
Photochemistry of halogenated benzene derivatives. Part VI. Photoreactions of tetra- and pentachlorophenols in water-acetonitrile mixtures
Choudhry, Ghulam Ghaus,Wielen, Frans W. M. van der,Webster, G. R. Barrie,Hutzinger, Otto
, p. 469 - 475 (2007/10/02)
Laboratory photochemical studies of aqueous acetonitrile solution of some polychlorinated phenols (PCPs) such as 2,3,4,5-tetrachlorophenol (2,3,4,5-Cl4-Pn)(1), 2,3,4,6-Cl4-Pn(2), 2,3,5,6-Cl4-Pn(3), and pentachlorophenol (Cl5-Pn)(4) at λ>285 nm have been carried out for 6 and 24 h exposure times.All the investigated PCPs underwent reductive dechlorination.This process was dependent not only upon the position of OH group but also upon the relative positions of the Cl substituents on the benzene ring.The Cl4-Pn 2 (and 3) and Cl5-Pn (4) also yielded photoproducts of molecular formulae C8H4Cl3NO(M+.=235) and C8H3Cl4NO(M+.=269), respectively.Furthermore, phenol 3 is unique amongst the investigated PCPs; in addition to the above mentioned photoproducts, it yielded hexa-, hepta-, and octachlorodihydroxybiphenyl(s) as well as heptachlorohydroxydiphenyl ether.
