Aqueous-gas phase partitioning and hydrolysis of organic iodides

2003 ◽  
Vol 81 (3) ◽  
pp. 230-243 ◽  
Author(s):  
G A Glowa ◽  
J C Wren
Keyword(s):  
Rate Constants ◽  
Partition Coefficients ◽  
Nuclear Reactor ◽  
Molecular Iodine ◽  
Molecular Structures ◽  
Hydrolysis Rate ◽  
Reactor Accident ◽  
Phase Partitioning ◽  
Temperature Dependences ◽  
Hydrolysis Of

The volatility and decomposition of organic iodides in a reactor containment building are important parameters to consider when assessing the potential consequences of a nuclear reactor accident. However, there are few experimental data available for the volatilities (often reported as partition coefficients) or few rate constants regarding the decomposition (via hydrolysis) of organic iodides. The partition coefficients and hydrolysis rate constants of eight organic iodides, having a range of molecular structures, have been measured in the current studies. This data, and data accumulated in the literature, have been reviewed and discussed to provide guidelines for appropriate organization of organic iodides for the purpose of modelling iodine behaviour under postulated nuclear reactor accident conditions. After assessment of the partition coefficients and their temperature dependences of many classes of organic compounds, it was found that organic iodides could be divided into two categories based upon their volatility relative to molecular iodine. Similarly, hydrolysis rates and their temperature dependences are assigned to the two categories of organic iodides.Key words: organic iodide, hydrolysis, partition coefficient, iodine behaviour model, nuclear reactor safety.

The reduction of I2 by H2O2 in aqueous solution

2001 ◽  
Vol 79 (3) ◽  
pp. 304-311 ◽  
Author(s):  
J M Ball ◽  
J B Hnatiw
Keyword(s):  
Aqueous Solution ◽  
Hydrogen Peroxide ◽  
Nuclear Reactor ◽  
Ph Dependence ◽  
Radiolysis Product ◽  
Molecular Iodine ◽  
Water Radiolysis ◽  
Reactor Accident ◽  
Rate Law ◽  
Accident Conditions

The reduction of I2 by hydrogen peroxide, a primary water radiolysis product, has been identified as a key reaction that would influence iodine volatility in nuclear reactor accident conditions (1–3). Although there have been a number of studies of the reduction of I2, there exists a great degree of controversy regarding the intermediates involved, the effect of buffers, and the general rate law (1–9). Because the rates and the mechanism of this reaction are important in predicting the pH dependence of iodine behaviour in reactor containment building after a postulated reactor accident, we have undertaken a kinetic study of I2 reduction by H2O2 in aqueous solution over a pH range of 6–9. The experiments were performed using stopped-flow instrumentation and monitoring the decay of I–3 spectrophotometrically. The effects of buffer catalysis have been examined by comparison of kinetic data obtained in sodium barbital (5,5-diethylbarbituric acid), disodium citrate, and disodium hydrogen phosphate buffers. The effect of buffers, combined with the complex acid dependence of the rate law, explains many of the discrepancies reported in earlier literature.Key words: hydrogen peroxide, molecular iodine, kinetics, iodine volatility.

Kinetics and mechanism of the hydrolysis of a (5,6)-spirophosphorane. Thermodynamics of the hydrolysis of cyclic five-membered and six-membered phosphonium ions

1991 ◽  
Vol 69 (12) ◽  
pp. 2064-2074 ◽  
Author(s):  
Glenn H. McGall ◽  
Robert A. McClelland
Keyword(s):  
Free Energy ◽  
Transition State ◽  
Rate Constants ◽  
Strong Acid ◽  
Membered Ring ◽  
Phosphate Esters ◽  
Hydrolysis Rate ◽  
Activation Free Energy ◽  
Stabilizing Effect ◽  
Hydrolysis Of

The cyclic five-membered phosphonium ion 2b (2-(2′-hydroxyethoxy)-2-phenyl-1,3,2-dioxaphospholan-2-ylium) derived from ring-opening of the (5,5)-spirophosphorane 1b (5-phenyl-1,4,6,9-tetraoxa-5-phosphaspiro[4,4]nonane) has been observed in neat CF3SO3H and at >85% H2SO4. The cation undergoes hydrolysis in the latter solutions, and an extrapolation has been carried out to obtain an estimate for reactivity in 100% water. Hydrolysis rate constants for phenyltrialkoxyphosphonium ions in water are 107, 100, and 5 × 10−3 s−1 for cyclic five-membered, cyclic six-membered, and acyclic derivatives respectively; these show an excellent correlation with rate constants for a similar series of phosphate esters. An investigation of the hydrolysis of the (5,6)-spirophosphorane 5 (5-phenyl-8,8-dimethyl-1,4,6,10-tetraoxa-5-phosphaspiro[4,5]decane) provides a clue as to the origins of these rate differences. This phosphorane can in principle hydrolyze via two isomeric cyclic phosphonium ions, the six-membered 14 and the five-membered 15. The former is thermodynamically more stable, being the only cation observed under equilibrating conditions of strong acid. However, the hydrolysis of the spirophosphorane, as well as the hydrolysis of fully formed 14, channels through the cyclic five-membered 15. A thermodynamic breakdown reveals that the 9.5 kcal mol−1 difference in activation free energy for the hydrolysis of five- and six-membered cyclic phosphonium ions is due to a combination of a higher free energy (2.5–4.5 kcal mol−1) for the five-membered cation, and a lower free energy (7–5 kcal mol−1) for the pentacoordinate transition state with the five-membered ring. This analysis also shows that a (5,6)-spirophosphorane is 6–8 kcal mol−1 more stable than a (6,6)-spirophosphorane. Thus, a five-membered ring has a significant stabilizing effect on a pentacoordinated phosphorus structure. The accelerated hydrolysis of cyclic phosphonium ions and phosphate esters with five-membered rings is caused by a combination of this stabilizing effect in the transition state and a destabilizing effect in the ground state associated with ring strain. Key words: phosphorane, hydrolysis, phosphate, phosphonium.

Solvent effect as a criterion of solvolysis mechanism. Solvolysis of 3-acyl-1,3-diphenyltriazenes

1981 ◽  
Vol 46 (9) ◽  
pp. 2091-2103 ◽  
Author(s):  
Oldřich Pytela ◽  
Petr Svoboda ◽  
Miroslav Večeřa
Keyword(s):  
Transition State ◽  
Solvent Effect ◽  
Mole Fraction ◽  
Rate Constant ◽  
Rate Constants ◽  
Proton Donor ◽  
Hydrolysis Rate ◽  
Solvent Mixtures ◽  
Solvent Dependence ◽  
Hydrolysis Of

Solvent dependence of hydrolysis rate constants of 3-acetyl-1,3-diphenyltriazene (I) and 3-(N-methylcarbamoyl)-1,3-diphenyltriazene (II) has been followed in the solvent mixtures ethanol-water, methanol-water, dioxane-water, and formamide-water within the mole fraction x = 0.0 to 0.5 at 25, 35 and 45 °C. A criterion has been suggested, based on sign of change of logarithm of the observed rate constant in dependence on change of the solvent composition, for evaluation of the reaction molecularity and, hence, participation of water in the hydrolysis mechanism. It has been found that water takes part as a proton donor in the transition state of hydrolysis of the substrates studied.

Hydrolysis of amides. IV. Dilute acid hydrolysis of amides of the type R2CH-CONH2 and R3C-CONH2

1971 ◽  
Vol 24 (3) ◽  
pp. 471 ◽  
Author(s):  
PD Bolton ◽  
GL Jackson
Keyword(s):  
Free Energy ◽  
Hydrogen Bonding ◽  
Acid Hydrolysis ◽  
Rate Constants ◽  
Hydrolysis Rate ◽  
Dilute Acid ◽  
Dilute Acid Hydrolysis ◽  
Reasonable Explanation ◽  
Hydrolysis Of

Enthalpies and entropies of activation have been derived from rate constants measured over a range of temperature for the dilute acid hydrolysis of isobutyramide, diethylacetamide, α-methylbutyramide, cyclohexaneoarboxamide, cyclopentane-carboxamide, and trimethylacetamide. ��� These data, in combination with data for other amides produced earlier, show the hydrolysis rate constants to be dominated by steric influences but with a perturbing effect which is proportional to the number of α-hydrogens present in the substituent. The "α-hydrogen bonding" concept of hyperconjugation appears to offer a reasonable explanation of these perturbations. ��� Controlled steric changes are shown to be non-additive for this reaction and to exert their influence primarily through the enthalpy component of the observed free energy changes.

Kinetics of alkaline hydrolysis of mono- and dimethyl esters of 2,3- and 3,4-thiophenedicarboxylic acids, cyanothiophenecarboxylic acids and their dihydroanalogues

1987 ◽  
Vol 52 (8) ◽  
pp. 2005-2018
Author(s):  
Milan Struhárik ◽  
Pavel Hrnčiar ◽  
Dušan Loos
Keyword(s):  
Kinetic Parameters ◽  
Alkaline Hydrolysis ◽  
Rate Constants ◽  
Activation Parameters ◽  
Hydrolysis Rate ◽  
Electronic Effects ◽  
Cyclic System ◽  
Kinetics Of ◽  
Hydrolysis Of ◽  
Reactivity Order

Kinetics of alkaline hydrolysis of mono- and dimethyl esters of 2,3- and 3,4-thiophenedicarboxylic acids and their dihydroanalogues have been studied in 70% dioxane. The rate measurements have been carried out by the titrimetric method and the k1, k2 rate constants evaluated by the Frost-Schwemer method. The activation parameters of these reactions have been calculated. The results are compared with kinetic parameters of alkaline hydrolysis of methyl and dimethyl phthalates. The hydrolysis rate is significantly affected by the cyclic system to which the methoxycarbonyl groups are bound, the reactivity order being: Dihydrothiophene > thiophene > benzene. Also measured were the kinetics of alkaline hydrolyses of methyl 4-cyano-3-thiophenecarboxylate and 3-cyano-2-thiophenecarboxylate and of their dihydroanalogues. No meaningful preference of the hydrolysis of the group at the position 2 has been observed in case of 2,3-isomers. However, it has been confirmed that the hyper- and hypo-ortho transfer of electronic effects operates in the thiophene nucleus.

scholarly journals Acidic and alkaline bimolecular hydrolysis of substituted formanilides. Computational analysis and modelling of substitution effects

2017 ◽  
Vol 10 (1) ◽  
pp. 35-40
Author(s):  
Martin Michalík ◽  
Peter Škorňa ◽  
Vladimír Lukeš ◽  
Erik Klein
Keyword(s):  
Alkaline Hydrolysis ◽  
Rate Constants ◽  
Quantum Chemical ◽  
Computational Analysis ◽  
Hydrolysis Rate ◽  
Substitution Effects ◽  
Chemical Methods ◽  
Quantum Chemical Methods ◽  
Hydrolysis Of

Abstract In this article, the study of 67 compounds representing various para-, meta- and ortho- substituted formanilides is presented. These molecules and the products of their acidic and alkaline hydrolysis were studied using DFT quantum chemical methods in order to calculate the reaction enthalpies. These enthalpies are correlated with the hydrolysis rate constants, kH, published for the acid-catalysed acyl cleavage bimolecular (AAC2) mechanism and the modified base-catalysed acyl cleavage bimolecular (BAC2) mechanism. The found linear dependences can be used for the prediction of rate constants of non-synthesised formanilide derivatives.

THE EFFECT ON REACTION RATES CAUSED BY THE SUBSTITUTION OF C14 FOR C12: I. THE ALKALINE HYDROLYSIS OF CARBOXYL-LABELED ETHYL BENZOATE

1949 ◽  
Vol 27b (10) ◽  
pp. 807-812 ◽  
Author(s):  
William H. Stevens ◽  
Richard W. Attree
Keyword(s):  
Alkaline Hydrolysis ◽  
Rate Constants ◽  
Room Temperature ◽  
Reaction Rates ◽  
Ethyl Benzoate ◽  
Hydrolysis Rate ◽  
Rate Of Hydrolysis ◽  
Hydrolysis Of

A study of the alkaline hydrolysis of C14 carboxyl-labeled ethyl benzoate has shown that the substitution of C14 for C12 changes the rate of hydrolysis of the ester. Ester molecules containing C14 hydrolyze at a slower rate than normal ester molecules. The ratio of the hydrolysis rate constants at room temperature has been found to be 0.86 ± 0.016.

scholarly journals Tryptophan Fluorescence and Time-Lag Hydrolysis of Peptide Bonds during Degradation of β-Lactoglobulin by Trypsin

Catalysts ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 1368
Author(s):  
Mikhail M. Vorob’ev
Keyword(s):  
Rate Constants ◽  
Time Lag ◽  
Tryptophan Fluorescence ◽  
Hydrolysis Rate ◽  
Lag Phase ◽  
Peptide Bonds ◽  
Proteolytic Action ◽  
Lag Times ◽  
Β Lactoglobulin ◽  
Hydrolysis Of

The opening of protein globules and corresponding exposure of their internal peptide bonds, the so-called demasking effect, is required for successful hydrolysis of peptide bonds by proteases. Under the proteolytic action of trypsin on β-lactoglobulin (β-LG), the evolution of tryptophan fluorescence spectra showed that the demasking process consists of two stages with different demasking rate constants for each stage. It was found that the ratio of these constants depends on the concentration of trypsin and changes are approximately threefold when the concentration of trypsin changes in the range of 0.3–15 mg/L. Simulation of hydrolysis taking into account the demasking effect demonstrated how the apparent first-order rate constants obtained experimentally are related to the true hydrolysis rate constants and demasking parameters. The lag phase in the kinetic curves corresponding to the hydrolysis of various peptide bonds in β-LG was also analyzed. The increased lag times indicated sites that are hydrolyzed by a two-stage demasking mechanism.

Eds Of Radioactive Particles By Self-Induced Fluorescence

1990 ◽  
Vol 48 (2) ◽  
pp. 238-239
Author(s):  
Gregory L. Finch ◽  
Richard G. Cuddihy
Keyword(s):  
Electron Beam Irradiation ◽  
Nuclear Reactor ◽  
X Rays ◽  
Reactor Accident ◽  
Internal Radiation ◽  
X Ray ◽  
External Sources ◽  
X Irradiation ◽  
Available Information ◽  
Individual Particles

The elemental composition of individual particles is commonly measured by using energydispersive spectroscopic microanalysis (EDS) of samples excited with electron beam irradiation. Similarly, several investigators have characterized particles by using external monochromatic X-irradiation rather than electrons. However, there is little available information describing measurements of particulate characteristic X rays produced not from external sources of radiation, but rather from internal radiation contained within the particle itself. Here, we describe the low-energy (< 20 KeV) characteristic X-ray spectra produced by internal radiation self-excitation of two general types of particulate samples; individual radioactive particles produced during the Chernobyl nuclear reactor accident and radioactive fused aluminosilicate particles (FAP). In addition, we compare these spectra with those generated by conventional EDS.Approximately thirty radioactive particle samples from the Chernobyl accident were on a sample of wood that was near the reactor when the accident occurred. Individual particles still on the wood were microdissected from the bulk matrix after bulk autoradiography.

Kinetics of hydrolysis of peroxodisulphate ions in acidic medium to peroxomonosulphuric acid

1981 ◽  
Vol 46 (5) ◽  
pp. 1229-1236 ◽  
Author(s):  
Jan Balej ◽  
Milada Thumová
Keyword(s):  
Ionic Strength ◽  
Rate Constants ◽  
Acidic Medium ◽  
Measured Data ◽  
Molar Ratios ◽  
Starting Solution ◽  
Kinetics Of Hydrolysis ◽  
Rate Of Hydrolysis ◽  
Kinetics Of ◽  
Hydrolysis Of

The rate of hydrolysis of S2O82- ions in acidic medium to peroxomonosulphuric acid was measured at 20 and 30 °C. The composition of the starting solution corresponded to the anolyte flowing out from an electrolyser for production of this acid or its ammonium salt at various degrees of conversion and starting molar ratios of sulphuric acid to ammonium sulphate. The measured data served to calculate the rate constants at both temperatures on the basis of the earlier proposed mechanism of the hydrolysis, and their dependence on the ionic strength was studied.

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