20267-19-0Relevant academic research and scientific papers
A mild and efficient chemoselective protection of primary alcohols as pivaloyl esters using La(NO3)3·6H2O as a catalyst under solvent-free conditions
Prabhakar,Suryakiran,Venkateswarlu
, p. 732 - 733 (2007)
Primary alcohols are selectively and efficiently protected as their pivaloyl esters with pivaloyl chloride in the presence of catalytic amounts of La(NO3)3·6H2O at room temperature under solvent-free conditions in excellent yields. Copyright
Kinetics and quantitative structure-activity relationships for pseudomonas sp. Lipase-catalyzed hydrolysis of both monoesters and diesters of ethylene glycol
Chiou, Shyh-Ying,Cheng, Yu-Ru,Lu, Chun-Ping,Lin, Yan-Fu,Lin, Long-Yau,Lin, Gialih
, p. 201 - 207 (2007/10/03)
The goal of this work is to study kinetics and quantitative structure-activity relationships for steady states of Pseudomonas sp. lipase-catalyzed hydrolysis of both diesters and monoesters of ethylene glycol. Based on the steady-state kinetics of the enzyme-catalyzed hydrolysis of the diesters of ethylene glycol, the diesters and the monoesters react simultaneously as soon as monoester has started to build up in the reaction medium. In other words, the apparent Km values of the diesters are the Km values of the diesters (KmA) plus the Km values of the monoesters (KmB), and all Vmax values are about the same. Moreover, the pH-stat titration curve of the enzyme-catalyzed hydrolysis of the diesters of ethylene glycol is initially hyperbolic, then there is a sharp falloff in the hydrolysis rate. The abrupt stoppage of the reaction (relaxation stage) may be due to the existence of two phases in the reaction medium, that is, the product (ethylene glycol) and the substrates (the diesters of ethylene glycol) are not miscible. Furthermore, quantitative structure-activity relationships for varied acyl groups of mono- and diesters of ethylene glycol are studied. The fact that both pKmA and pK mB values are linearly correlated with the hydrophobicity constant (π) but not with the electronic substituent constants (σ*) indicates that the affinity of these substrates for the enzyme depends only on the hydrophobicitv of substrates. Copyright
Alkyl Group Effects on the Rate Constants and Equilibrium Constants for Formation of Cyclic Tetrahedral Intermediates
Santry, Linda J.,Azer, Salwa,McClelland, Robert A.
, p. 2909 - 2914 (2007/10/02)
2-Hydroxy-2-alkyl-1,3-dioxolanes T are the cyclic intermediates of the degenerate intramolecular ester interchange reactions of ethylene glycol monoalkanoates A, in which alkanoyl groups transfer from one end of ethylene glycol to the other.This study reports equilibrium constants for the cyclization AT to the tetrahedral intermediate stage with 10 alkanoate derivatives.These equiilibrium constants, which when written as / are all large (1 E7-1 E9) in favor of the ring opened form, were obtained as the ratio of rate constants for equilibration occuring with H+ catalysis.Rate constants for the ring opening of T were directly measured through a study of kinetics of the hydrolysis of 2-methoxy-2-alkyl-1,3-dioxolane ortho esters.These hydrolysis proceed via T, and under acid conditions the breakdown of this intermediate is rate-limiting.Rate constants in the ring-closing direction were obtained by preparing HOCH2CD2OOCR and, with the use of 1H NMR spectroscopy, measuring the kinetics of isomerization to an equilibrium mixture with RCOOCH2CD2OH.The reaction under investigation is an intramolecular analogue of H+-catalyzed alkanoate ester hydrolysis, whose rate constant define the steric substituent parameter Es.The ring-closure rate constant for A -> T do show an excellent correlation with Es.However, the rate constants for ring-opening T -> A and the overall equilibrium constant are badly correlated, showing quite different behavior for series with α and β branching in the alkyl group.Thus, for this system the Es parameter does not correlate free energy differencies between the acyl derivative and tetrahedral intermediate.It is only the free energy differences between the acyl form and the transition state leading to the intermediate that fit Es.
