Improved ester interchange catalysts

Mixed alkoxide/aryloxide clusters are long-lived and milder than previously reported ester interchange catalysts. They completely transform difficult substrates in a single synthetic operation with lower catalyst and reagent ester loadings. In addition to superior activities, these mixed clusters are kinetically less basic toward enolizable esters.     

Solvent effect on the rate of decomposition of peroxy compounds

Solvent effect on the rate of decomposition of peroxy compounds was described by multiparameter equations based on the linear Gibbs energy relationship. In the decomposition of dialkyl peroxides, the determining factors are the cohesion energy density of solvents and their ability to electrophilic solvation, which accelerate the process. In the case of hydroperoxides, the nonspecific solvation factor should additionally be taken into account.Translated from Zhurnal Organicheskoi Khimii, Vol. 40, No. 10, 2004, pp. 1459–1463.Original Russian Text Copyright © 2004 by Midyana, Makitra, Palchikova.     

Solvent effect on the rate of cycloaddition of isoprene to maleic anhydride

The solvent effect on the rate of the reaction of isoprene with maleic anhydride was studied; the total effect of the solvent polarity and cohesion energy density was revealed.     

Solvent effect on the rate of the Mannich reaction of butyraldehyde with formaldehyde

The Mannich reaction of formaldehyde with butyraldehyde and diethylamine in hydrophilic solvents ensuring homogeneity of the medium follows the kinetic relations typical of an irreversible second-order reaction. The rate constants are determined by the ability of solvents to undergo self-association and their electrophilic solvation power; additional inclusion of the solvent polarity via multiparameter Koppel’-Pal’m equation is necessary to obtain a satisfactory quantitative correlation.     

Organic syntheses without solvent: Base-catalysed ester interchange

Ester interchange of methyl or ethyl carboxylic esters by primary or secondary alcohols is carried out effectively when solid-liquid phase transfer catalysis (PTC) is achieved in the absence of added organic solvent. Vinyl and isopropenyl acetates undergo ester interchange, even in the absence of PTC catalyst, with primary alcohols and phenols.     

Solvent effects on ester alcoholysis at functionalized polyethylene surfaces

The effects of solvent on the accessibility and reactivity of an ester-bound fluorophore at a functionalized polyethylene-solvent interface have been studied. Fluorophore-labeled polyethylene surfaces were prepared by blending together a small amount of a pyrene esterterminated ethylene oligomer and a host linear low density polyethylene in solution. Films cast from such solutions were then studied by fluorescence spectroscopy to show that a significant number of the entrapped pyrene groups were at the polyethylene-solvent interface and capable of reaction with soluble reagents. Subsequently, transesterification of these ester-bound pyrenes using various sodium alkoxides in alcohol, alcohol-toluene, or alcohol-tetrahydrofuran solvent mixtures was studied by fluorescence and UV-visible spectroscopic analysis of the supernatant. The extent of alcoholysis of such esters was found to be significantly affected by the solvent chosen and by the structure of the alcohol. © 1995 John Wiley & Sons, Inc.     

Kinetics of free radical polymerization—XXXI. Solvent effect on the polymerization rate of ethyl acrylate

The free radical polymerization of ethyl acrylate was investigated in benzene and dimethyl formamide solutions at 50°. The effects of initiator and monomer concentration were studied over a wide range. The overall rate of polymerization was proportional to (initiator concentration)^{$\text{1}\text{2}$} but not to the concentration of the monomer. We attempted to interpret this solvent effect on the basis of (i) the diffusion theory, (ii) the theory of charge transfer complexes and (iii) the theory of hot radicals. Our experimental results could only be explained quantitatively in terms of hot radicals.     

Solvent effects on the rate of thermolysis of lauroyl peroxide

Thermolysis of lauroyl peroxide in various organic solvents was studied. It was shown that the primary homolytic dissociation of the peroxide group is accompanied by secondary reactions of chain-induced decomposition. The reaction medium affects the rate of both the primary homolytic dissociation and secondary induced decomposition processes. Correlation equations between the rate constants of the reactions in study and the physicochemical parameters of the solvents were proposed.     

Solvent effect on rate and mechanism of oxidation of chromium(III) by periodate

Summary The kinetics of chromium(III) oxidation by periodate were studied in various EtOH–H₂O solvent mixtures covering the 0.0 to 58.0 wt% EtOH range, at five different temperatures in the 15–35°C range. The rate of reaction increases with increasing EtOH content. Thermodynamic activation parameters have been calculated and an appropriate mechanism is suggested.     

Solvent effect on the rate and direction of furfural transformations during hydrogenation over the Pd/C catalyst

Russian Chemical Bulletin - The rate and directions of transformations during the liquid-phase hydrogenation of furfural with molecular hydrogen in the presence of the 5%Pd/C catalyst (at 423 K, 3...     

Solvent effect on complexation reactions

The inclusion complexation of aromatic amines with cucurbit[6]uril (CB[6]) capped with alkali metal cations was studied spectrophotometrically. We showed that CB[6] capped with alkali metal cations forms a 1:1 inclusion complex with the aromatic amine guests (neutral organic molecules), independent of the length of guest molecules. The effects of salts on the inclusion constants of CB[6] in the presence of different alkali salts were examined and it was found that the inclusion constants increased in the order of alkali cation Cs⁺ < Na⁺ < K⁺, suggesting the interaction of amine guests with the capped alkali metal cation. Further, the structures of the inclusion complexation of aromatic amines with CB[6] were characterized by ¹H NMR measurements. Based on the results, the inclusion abilities of CB[6] capped with alkali metal cations are discussed.     

The effect of direct interchange reactions on the MWD of condensation polymers

In this theoretical study, a relationship has been developed for the transient molecular-weight distribution (MWD) of a condensation polymer undergoing a direct interchange reaction. Direct interchange is one of several reactions which can take place in condensation polymers in the melt. When compared to the more well-known reactions of polycondensation, degradation, and interchange of an end-group with a condensation linkage, direct interchange has a more complex statistical effect on the MWD and is less commonly observed. However, these types of reactions can be quite important in some polymeric systems, such as in the reaction of poly (butylene terephthalate) with polycarbonate. The MWD relationship was developed from the species balance: The rate of accumulation of chains of a given molecular weight is equal to their rate of generation minus their rate of consumption. For this reaction, development of the generation term is quite complex; it is approached here by describing five probability situations which are determined by each possible combination of reactant and product chains. Example distributions computed from these equations show that different transient paths are followed under direct and end-group interchange, but that both reactions lead to the equilibrium most-probable distribution.     

Solvent effect on the kinetics of Beckmann rearrangement

The rate constants for the Beckmann rearrangement of cyclohexanone oxime p-toluenesulfonate in 11 solvents are satisfactorily described by a three-parameter linear correlation including polarizability, electrophilicity, and molar volume of the solvent. The first two factors favor the reaction, whereas increase of the solvent molar volume makes the reaction slower, presumably due to steric hindrances to solvation.     

Solvent effect on the reactivity of trichloromethylperoxy radicals

The solvent effect on the rate of reaction of organic reductants with trichloromethylperoxy radicals can be adequaetly described by multiparameter linear equations. The major factor affecting the reaction rate is the solvent cohesion, enhancing the cage effect.     

Solvent isotope effect on the fluorescence of azoalkanes

A study of fluorescence quantum yields and fluorescence lifetimes of the cyclic azoalkanes I and II reveals a striking dependence of Φ_F and τ_F on solvent and on isotopic substitution (OH å OD). A mechanism involving specific deactivation of the fluorescent state from a hydrogen bonded complex is proposed to rationalize the data. The observation that the quantum yield for decomposition of I does not correlate with the variation of fluorescence parameters with solvent and isotopic change leads to the conclusion that the state responsible for photoreaction proceeds the fluorescent state.     

Solvent effect on the reactivity of arylsulfanyl radicals

The rate of reaction of p-aminophenylsulfanyl radicals with styrenes decreases as a result of solvation of the initial reactants. The determining factor in the reaction with styrene is specific solvation, and in the reaction with α-methylstyrene, nonspecific solvation.