Stereochemical studies. XI. Equilibria between δ-hydroxy-acids and δ-lactones in aqueous tetrahydrofuran. Relative stabilities of isomeric δ-lactones

1982 ◽  
Vol 60 (20) ◽  
pp. 2546-2553 ◽  
Author(s):  
John T. Edward ◽  
Ellen Cooke ◽  
Themistocles C. Paradellis
Keyword(s):  
Conformational Analysis ◽  
Hydroxy Acid ◽  
Equilibrium Constants ◽  
Methyl Groups ◽  
Hydroxy Acids ◽  
Relative Stabilities ◽  
Experimental Values ◽  
Hydrolysis Of

The equilibrium constants K′ for the hydrolysis of 13 δ-lactones to hydroxy-acids in 54% (mol/mol) aqueous tetrahydrofuran at 25 °C have been determined. The equilibrium constants for the isomerization of the five δ-lactones into their epimers, and for the isomerization of their hydroxy-acids into their epimers, have been calculated by the methods of conformational analysis. These calculated values are consistent with the experimental values of K′. Addition of methyl groups to a hydroxy-acid decreases K′ (the Thorpe–Ingold effect).

Some phase relationships between basic bismuth chlorides in aqueous solutions at 25 °C

1987 ◽  
Vol 65 (12) ◽  
pp. 2824-2829 ◽  
Author(s):  
Peter Taylor ◽  
Vincent J. Lopata
Keyword(s):  
Aqueous Solutions ◽  
Equilibrium Constants ◽  
Natural Occurrence ◽  
Chloride Solutions ◽  
Gibbs Energies ◽  
Activity Ratios ◽  
Aqueous Chloride ◽  
The Stability ◽  
Experimental Values ◽  
Phase Relationships

Observations are reported on the interconversion of solid α-Bi2O3, Bi12O17Cl2, BiOCl, and a daubréeite-like phase tentatively identified as Bi2O2(OH)Cl, in aqueous chloride solutions at 25 °C. Equilibrium constants, K, for these interconversions are expressed as anion activity ratios, {Cl−}/{OH−}. Experimental values of K for equilibrium between Bi2O3 and each of the chlorides are 100.56 ± 0.20 for Bi12O17Cl2, 101.5 ± 0.4 for Bi2O2(OH)Cl, and 103.13 ± 0.04 for BiOCl; the fatter two represent metastable equilibria. These equilibrium constants yielded the following estimates of Gibbs energies of formation: Bi12O17Cl2, −3141 ± 6 kJ mol−1;"Bi2O2(OH)Cl", −696 ± 4 kJ mol−1; BiOCl, −321.5 ± 1.3 kJ mol−1. Phase relationships among these solids are discussed, with reference to natural occurrence, other bismuth oxychlorides, and the stability of other basic salts of bismuth.

scholarly journals Effect of Cationic/Anionic Mixed Micelles on Reaction Kinetics of Alkaline Hydrolysis of Crystal Violet

2019 ◽  
Vol 31 (3) ◽  
pp. 651-655
Author(s):  
Qidist Yilma ◽  
Dunkana Negussa ◽  
Y. Dominic Ravichandran
Keyword(s):  
Crystal Violet ◽  
Alkaline Hydrolysis ◽  
Mixed Micelles ◽  
Sodium Dodecyl ◽  
Binding Constants ◽  
Regression Parameters ◽  
Experimental Values ◽  
Kinetics Of ◽  
Hydrolysis Of ◽  
Good Agreement

Kinetics of alkaline hydrolysis of crystal violet, a triphenylmethane dye in the micellar environment of cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfonate (SDS) and binary mixtures of these surfactants was studied. The regression parameters, together with rate constants and binding constants were obtained by analyzing the rate surfactant profiles using cooperativity model. It was observed that the reaction was catalyzed by both surfactants. The catalytic factor increased by 10 times in SDS and 38 times in CTAB indicating that binding of crystal violet to the micellar surface is stronger in pure CTAB than SDS but the strength drastically reduced in the mixtures of the surfactants. Reduction of binding constant became more important as the mole fraction of CTAB was improved in the mixture. The kinetic data were investigated using Piszkiewicz model and Raghavan-Srinivasan model. The data obtained from the models were in good agreement with the experimental values.

scholarly journals Studies in vitro on shuttle systems of mouse spermatozoa

1982 ◽  
Vol 208 (2) ◽  
pp. 413-417 ◽  
Author(s):  
C Burgos ◽  
C E Coronel ◽  
N M G de Burgos ◽  
L E Rovai ◽  
A Blanco
Keyword(s):  
Hydroxy Acid ◽  
Redox Couple ◽  
Hydroxy Acids ◽  
Mouse Sperm ◽  
External Phase ◽  
Branched Chain ◽  
Glycerol 3 Phosphate Dehydrogenase ◽  
Shuttle System ◽  
Reducing Equivalents

Observations on systems reconstituted in vitro with different starting substrates (2-hydroxy-acids, 2-oxo-acids or leucine) indicate that a branched-chain 2-hydroxy-acid/2-oxo-acid shuttle for the transfer of reducing equivalents from cytosol to mitochondria may be operational in mouse sperm. Evidence is presented suggesting that the 2-oxo-acids produced by intramitochondrial oxidation of 2-hydroxy-acids ingressed from the cytosol can recycle back into the external phase. Observations in vitro demonstrate that, in addition to the branched-chain 2-hydroxy-acid/2-oxo-acid shuttle, the malate/aspartate system is also active in mouse sperm. On the contrary, the lactate/pyruvate redox couple does not appear to function as part of a shuttle system in mouse sperm mitochondria. The glycerol 3-phosphate shuttle probably is not functionally significant in mouse spermatozoa, since the activity of the ‘soluble’ glycerol 3-phosphate dehydrogenase is very low.

Base hydrolysis of trans-Halogenoamminebis(dimethylglyoximato) (III). Complexes

1969 ◽  
Vol 22 (12) ◽  
pp. 2569 ◽  
Author(s):  
SC Chan ◽  
PY Leung
Keyword(s):  
Equilibrium Constants ◽  
Base Hydrolysis ◽  
Hydroxide Ion ◽  
First Order ◽  
Rate Determining Step ◽  
Rapid Formation ◽  
Pseudo First Order ◽  
Conjugate Bases ◽  
Hydrolysis Of ◽  
Conjugate Base

The disappearance of trans-[Co(LH)2(NH3)X] (LH = dimethylglyoximate ion, X = chloride or bromide) has been studied in aqueous solutions over a range of alkali concentrations at various temperatures. The kinetics were done with excess of hydroxide ion at a constant ionic strength so that pseudo first-order rate constants were obtained in all the runs. The results were interpreted in terms of the rapid formation of a pre- equilibrium species which then reacts in a rate-determining step to give products. The relatively large equilibrium constants support a conjugate-base pre-equilibrium, in which the proton is lost from oxygen, while the relatively low reactivities of the conjugate-bases are consistent with the absence of electropositive electromeric effects. The similarity in the reactivities of the chloro and the bromo conjugate-bases suggests the possibility of an SN2CB mechanism.

Network Scission Processes in Peroxide Cured Methylvinyl Silicone Rubber

1967 ◽  
Vol 40 (2) ◽  
pp. 629-634
Author(s):  
D. K. Thomas
Keyword(s):  
Silicone Rubber ◽  
Elevated Temperatures ◽  
Main Chain ◽  
Methyl Groups ◽  
Chain Polymer ◽  
Filled Rubber ◽  
Oxidative Reactions ◽  
Silica Filler ◽  
Silicone Rubbers ◽  
Hydrolysis Of

Abstract In what appeared to be a complex system it transpires that network scission in methylvinyl silicone rubbers at temperatures below 250° C is due largely to hydrolytic reactions in the main chain polymer. At temperatures of 250° C and above there are indications that a significant amount of scission arises from oxidative reactions in the crosslinks, and that this reaction is catalyzed by acidic residues in the rubber. There is no indication that acidic byproducts of the vulcanization reaction catalyze the hydrolysis of siloxane bonds in the polymer. In conventional heat aging tests in which the rubber remains in an unstrained condition the effects of hydrolysis will only be observed if the concentration of water in the system is allowed to rise. Under these circumstances softening will occur because of a shift in the position of equilibrium in the reaction ∼Si—O—Si—O∼ + H2O→∼Si—OH+ HO—Si—O∼ On aging the material in a well ventilated situation the effects of hydrolysis are not seen and the silicone rubber becomes brittle after long exposure at high temperature. This embrittlement must result from additional crosslinking caused by oxidative reactions in the methyl groups of the main chain polymer. When the rubber is used in compression or tension, hydrolytic scission will affect performance, and in applications of this sort it is important to dry the rubber before use and prevent access of moisture to the component during use. With filled rubber the silica filler is a further source of moisture and drying needs to be carried out at elevated temperatures immediately before use. In order to improve the confined heat aging performance of silicone rubber an alternative filler to fine silica is needed which does not have the same affinity for water. It may be, however, that ability to reinforce silicone rubber and affinity for water are inseparable.

Hydrolysis of trioxaadamantane ortho esters. I. Dialkoxycarbocation – ortho ester equilibrium and acidity function

1984 ◽  
Vol 62 (6) ◽  
pp. 1068-1073 ◽  
Author(s):  
Robert A. McClelland ◽  
Patrick W. K. Lam
Keyword(s):  
Acid Concentration ◽  
Intramolecular Interaction ◽  
Uv Spectroscopy ◽  
Equilibrium Constants ◽  
Hydrolysis Product ◽  
Acidity Function ◽  
Ortho Ester ◽  
Aromatic Substituent ◽  
Ortho Esters ◽  
Hydrolysis Of

3-Aryl-2,4,10-trioxaadamantane ortho esters (T) undergo a rapid equilibration with a ring-opened dioxan-2-ylium ion (DH+) prior to hydrolysis to product (a 1,3,5-cyclohexanetriol monobenzoate). The cation is stable in concentrated H2SO4 solutions where it has been characterized by nmr spectroscopy. It is observed using uv spectroscopy in dilute acids, and the ratio [DH+]/[T] at equilibrium has been measured as a function of acidity. Reversibility of the ring opening is established by the pattern of plots of cation absorbance versus acid concentration and by the observation that solutions containing cation on neutralization or dilution yield ortho ester, not hydrolysis product. Equilibrium constants for the reaction [Formula: see text] have been measured by obtaining the acidity function HT for this system. The effects of the aromatic substituent and the steepness of the acidity function plot versus acid concentration are interpreted in terms of a strong intramolecular interaction in the cation between the cationic center and the hydroxyl oxygen.

Studies of the activity of chymotrypsin

1970 ◽  
Vol 257 (813) ◽  
pp. 89-104 ◽  
Keyword(s):  
Equilibrium Constants ◽  
Hydrolytic Enzyme ◽  
Enzyme Activation ◽  
Ethyl Esters ◽  
Activation Mechanism ◽  
Relaxation Techniques ◽  
Kinetic Measurements ◽  
Ph Values ◽  
Solution Studies ◽  
Hydrolysis Of

Physical and chemical studies of chymotrypsin in solution and kinetic measurements of individual steps in reactions catalysed by this hydrolytic enzyme are reported. The solution studies also provide a basis for correlation of individual reaction steps with structural information obtained by Drs Blow and Hartley and discussed at this Discussion. The rate and equilibrium constants pertaining to the three-step mechanism shown below have been determined for the chymotrypsin catalysed hydrolysis of three specific ester substrates—the ethyl esters of V-acetyl-L-tyrosine, N -acetyl-L-tryptophan, and N -acetyl-L-phenylalanine—at selected pH values with use of both flow and relaxation techniques. iV-acetyl-L-phenylalanine—at selected pH values with use of both flow and relaxation techniques. / * E + S ^ 4 E S -y » EP 2 ,---► E + P 2 , * 2 3 £ 3 4 where E is enzyme, S is substrate, ES is a complex, EP 2 is an intermediate compound, and the products P 1 and P 2 are, respectively, an alcohol or amine and an acid. The hydrolysis of chymotrypsin specific substrates is shown to be considerably more complex than is indicated by this previously proposed mechanism. In addition to the steps shown, there exist a number of ionization and conformational equilibria which account for the bell-shaped pH-rate profiles observed for chymotrypsin catalysed reactions. A catalytically active enzyme conformation, which is in pH dependent equilibrium with a catalytically inactive conformation, is shown to have its origin in the enzyme activation mechanism. In the chymotrypsin catalysed hydrolysis of an amide substrate, furylacryloyltryptophanamide, there has been detected an additional intermediate which differs from the intermediate EP 2 observed in ester hydrolysis.

Sign in / Sign up

Export Citation Format

Share Document