Rate constants for the addition of the enolate ion of acetone to quinolinium and acridinium cations

1990 ◽  
Vol 68 (10) ◽  
pp. 1762-1768 ◽  
Author(s):  
John W. Bunting ◽  
Cynthia Fu ◽  
James W. Tam
Keyword(s):  
Ionic Strength ◽  
Aqueous Solutions ◽  
Rate Constants ◽  
Nucleophilic Addition ◽  
Ph Dependence ◽  
Adduct Formation ◽  
Kinetic Control ◽  
Thermodynamic Control ◽  
Hydroxide Ion ◽  
Kinetically Controlled

The reaction of acetone with four heteroaromatic cations (10-methylacridinium (1), 3-aminocarbonyl-1-methylquinolinium (2a), 3-cyano-1-methylquinolinium (2b), and 3-bromo-1-methylquinolinium (2c)) has been investigated in basic aqueous solutions (pH 9–12, ionic strength 0.1, 25 °C). For each of 2a and 2b, the kinetically controlled product is a 35:65 mixture of the C-2 and C-4 enolate ion adducts; the C-2 adduct subsequently isomerizes to give the C-4 adduct as the only observable species under thermodynamic control. For 2c, the C-2 enolate adduct appears to be favoured both kinetically and thermodynamically. Under kinetic control, the pH-dependence of adduct formation from each cation is consistent with rate-determining attack of the enolate ion upon the heterocyclic cation. Comparisons of regiochemical control of acetone enolate ion attack with hydroxide ion attack upon these same cations indicate that acetone enolate ion shows a more pronounced preference for C-4 attack over C-2 attack than does hydroxide ion. The thermodynamically controlled regiochemistry is similar for each of these two nucleophiles. Keywords: nucleophilic addition, regioselectivity, kinetic control, thermodynamic control, quinolinium cations.

KINETICS OF THE OXIDATION OF URANIUM (IV) BY IRON (III) IN AQUEOUS SOLUTIONS OF PERCHLORIC ACID

1955 ◽  
Vol 33 (12) ◽  
pp. 1780-1791 ◽  
Author(s):  
R. H. Betts
Keyword(s):  
Electron Transfer ◽  
Ionic Strength ◽  
Aqueous Solutions ◽  
Perchloric Acid ◽  
Rate Constants ◽  
Kcal Mole ◽  
Kinetics Of Oxidation ◽  
Temperature Coefficients ◽  
Kinetics Of ◽  
Rate Controlling Step

The kinetics of oxidation of uranium (IV) by iron (III) in aqueous solutions of perchloric acid have been investigated at four temperatures between 3.1 °C. and 24.8 °C. The reaction was followed by measurement of the amount of ferrous ion formed. For the conditions (H+) = 0.1–1.0 M, ionic strength = 1.02, (FeIII) = 10−4–10−5 M, and (UIV) = 10−4–10−5 M, the observed rate law is d(Fe2+)/dt = −2d(UIV)/dt[Formula: see text]K1 and K2 are the first hydrolysis constants for Fe3+ and U4+, respectively, and K′ and K″ are pseudo rate constants. At 24.8 °C., K′ = 2.98 sec.−1, and K″ = 10.6 mole liter−1 sec−1. The corresponding temperature coefficients are ΔH′ = 22.5 kcal./mole and ΔH″ = 24.2 kcal./mole. The kinetics of the process are consistent with a mechanism which involves, as a rate-controlling step, electron transfer between hydrolyzed ions.

Kinetic and thermodynamic control of pseudobase formation from C-3 substituted 1-methylquinolinium cations

1984 ◽  
Vol 62 (7) ◽  
pp. 1301-1307 ◽  
Author(s):  
John W. Bunting ◽  
Norman P. Fitzgerald
Keyword(s):  
Aqueous Solutions ◽  
Rate Constants ◽  
Kinetic Data ◽  
Mixing Time ◽  
Equilibrium Constants ◽  
Substituent Effects ◽  
Stopped Flow ◽  
Thermodynamic Control ◽  
Preferred Species ◽  
Substituted 1

The kinetic and thermodynamic control of pseudobase formation from 3-W-1-methylquinolinium cations has been studied for a variety of substituents (W). Spectral data indicate that, in both aqueous and methanolic solution, the C-2 pseudobases predominate at equilibrium for W = H and Br, while the C-4 pseudobases are the thermodynamically preferred species for W = CONH2, CO2CH3, CN, and NO2. Stopped-flow studies indicate that in all cases the C-2 pseudobases are the kineticallycontrolled products upon basification of the aqueous solutions of these cations. Equilibrium constants (pKR+) have been measured for pseudobase formation at both C-2 and C-4 for each W in all cases where they are experimentally accessible. Substituent effects upon [Formula: see text] correlate with σm for W, while [Formula: see text] depends upon σp−. These substituent effects allow the prediction of [Formula: see text] and [Formula: see text] for the 1-methylquinolinium cation. Rates of C-2 to C-4 pseudobase equilibration have been measured in all cases where the latter species is thermodynamically more stable. These kinetic data allow the evaluation of rate constants for C-4 pseudobase equilibration with each cation. In all cases except W = CN, C-2 pseudobase formation is complete within the mixing time of the stopped-flow instrument.

Substituent effects upon cation–pseudobase equilibration for isoquinolinium and phthalazinium cations

1981 ◽  
Vol 59 (22) ◽  
pp. 3195-3199 ◽  
Author(s):  
John W. Bunting ◽  
Vivian S.-F. Chew ◽  
Shinta Sindhuatmadja
Keyword(s):  
Ionic Strength ◽  
Rate Constants ◽  
Reasonable Agreement ◽  
Ph Dependence ◽  
Substituent Effects ◽  
Correlation Equation ◽  
First Order ◽  
Substituent Constants ◽  
Pseudo First Order ◽  
Correlation Line

pKR+ values have been measured for cation–pseudobase equilibration by 4-X-2-methylisoquinolinium cations (1) (X = Br, CONH2, COC6H5, CN, NO2) at 25 °C, ionic strength 0.1. These pKR+ values are well correlated by Hammett equations using either σ or σ−para substituent constants. The best correlation gives: pKR+ = −8.8 (± 0.3) σp− + 16.5 (± 0.2) (r = 0.998). The value pKR+ = 16.29 measured by Cook et al. (Tetrahedron, 32, 1773 (1976)) for the 2-methylisoquinolinium cation in dimethyl sulfoxide – water solutions is in reasonable agreement with this correlation equation. For the 2-methyl-5-nitrophthalazinium cation, pKR+ = 7.87, and pKRO− = 12.10 for alkoxide ion formation by the pseudobase of this cation.The pH dependence of the pseudo first-order rate constants (kobs) for cation–pseudobase equilibration has been measured for 1:X = CONH2, COC6H5, CN and for the 2-methylphthalazinium cation (3) and its 5-NO2 derivative (4). For each of these cations, [Formula: see text] and kd = k1[H+] + k2 and the parameters [Formula: see text] have been evaluated. For 1:X = CONH2 and CN and 3, kOH is consistent with a correlation line between log kOH and pKR+ established for other isoquinolinium cations (J. Am. Chem. Soc. 99, 1189 (1977)). For 1:X = COC6H5, kOH is seven-fold smaller, and for 4, kOH is five-fold greater than predicted by this correlation line.

The retroaldol reaction of chalcone

1983 ◽  
Vol 61 (11) ◽  
pp. 2621-2626 ◽  
Author(s):  
J. Peter Guthrie ◽  
John Cossar ◽  
Patricia A. Cullimore ◽  
Nayyer Monshizadeh Kamkar ◽  
Kathleen F. Taylor
Keyword(s):  
Ionic Strength ◽  
Sodium Hydroxide ◽  
Rate Constants ◽  
Equilibrium Constants ◽  
Aqueous Sodium Hydroxide ◽  
Adduct Formation ◽  
Aqueous Sodium ◽  
Catalyzed Reactions

All four rate constants required to describe the hydration and aldolization/dealdolization reactions of chalcone (1,3-diphenyl-2-propen-1-one) have been determined in aqueous sodium hydroxide solutions. Kinetics were studied starting with chalcone, with its hydrate, 1,3-diphenyl-3-hydroxy-1-propanone, and with benzaldehyde in the presence of excess acetophenone. The rate constants for hydroxide catalyzed reactions, defined in terms of eq. [1] are: k12 = 10.5 ± 0.5 × 10−4 M−1 s−1; k21 = 0.026 ± 0.002 M−1 s−1; k23 = 0.194 ± 0.017 M−1 s−1; and k32 = 0.84 ± 0.12 M−2 s−1 (all at ionic strength 0.1). The corresponding equilibrium constants for aldol adduct formation and dehydration are 4.3 M−1 and 25.

Kinetics of the reduction of the tropylium and xanthylium cations by 1,4-dihydropyridine derivatives

1990 ◽  
Vol 68 (4) ◽  
pp. 537-542 ◽  
Author(s):  
John W. Bunting ◽  
M. Morgan Conn
Keyword(s):  
Ionic Strength ◽  
Rate Constants ◽  
Ph Dependence ◽  
Second Order ◽  
Order Rate ◽  
Heteroaromatic Cation ◽  
Absolute Magnitudes ◽  
Kinetics Of ◽  
Kinetics Of Reduction ◽  
Dihydropyridine Derivatives

The pH-dependences of the apparent second-order rate constants [Formula: see text] for the reduction of 2,4,6-cycloheptatrien-1-ol and 9-xanthydrol by each of 1-benzyl-1,4-dihydronicotinamide (BNH) and 10-methyl-9,10-dihydroacridine (MAH) have been measured in 20% acetonitrile – 80% water, at 25 °C and ionic strength 1.0. For each of these reactions, the pH-dependence of [Formula: see text] is only consistent with reduction occurring via the aromatic cation (either tropylium or xanthylium) that is present in equilibrium with these alcoholic species. The relative second-order rate constants [Formula: see text] for reductions by these two reducing agents (1700 for tropylium and 770 for xanthylium) are similar for these two cations. These ratios are also similar to those observed for a variety of nitrogen heteroaromatic hydride acceptors, even though the absolute magnitudes of these rate constants vary by 1010-fold. The second-order rate constants for the reductions of the tropylium and xanthylium cations are predicted reasonably well by their [Formula: see text] values, with the latter cation being (7 × 105)-fold more reactive than its π-isoelectronic N-methyl acridinium cation. The xanthylium cation has the greatest [Formula: see text] ratio yet observed for any heteroaromatic cation, and this value further extends the known range of this ratio as a function of reactivity. Keywords: hydride transfer, kinetics of reduction, 1,4-dihydropyridine derivatives, tropylium cation, xanthylium cation.

scholarly journals Disproportionation and Polymerization of Plutonium(IV) in Dilute Aqueous Solutions

1983 ◽  
Vol 26 ◽  
Author(s):  
T. W. Newton ◽  
V. L. Rundberg
Keyword(s):  
Ionic Strength ◽  
Aqueous Solutions ◽  
Rate Constants ◽  
Second Order ◽  
Disproportionation Reaction ◽  
Reaction Products ◽  
Constant Ph ◽  
Low Concentrations ◽  
Dilute Aqueous Solutions ◽  
Ph Range

ABSTRACTThe rates of polymerization and disproportionation of Pu(IV) have been studied using low concentrations: (1.7 − 10) × 10−6M Pu, (0.8 − 12) × 10−4M HCI and 0.01M ionic strength. Osmium(II) complexes such as the tris−4,41−2,21−bipyridine complex were found to react rapidly with Pu(IV) but very slowly, if at all, with Pu(IV) polymer, Pu(lll), or Pu(V). Thus, it is possible to determine unreacted Pu(IV) in the presence of reaction products by using Os(II) complexes. Disproportionation reaction products, Pu(IlI) and Pu(V), were determined using their reactions with Ce(IV) sulfate. We find −d[Pu(IV)]/dt = k'[Pu(IV)]2 at constant pH. Log k1 varies from about 4.25 at pH 3 to about 7.0 at pH 4.1 (units for k1 are M−1min−1). The [H+] dependence varies from about −2 to −3 over the pH range studied. The measured rate is the sum of those for polymerization and disproportionation; the latter reaction amounts to about 75% of the total at pH 3 and 20% at pH 4. The second-order rate constants for disproportionation are very much larger than expected on the basis of extrapolation from 0.2 to 1.OM HClO, solutions. The products of the reaction do not affect the rate, but U(VI), aged Pu(IV) polymer, and CO2 increase the rate.

Kinetic study of the reaction between cystine and sulfide in alkaline solutions

1987 ◽  
Vol 65 (4) ◽  
pp. 770-774 ◽  
Author(s):  
David K. Liu ◽  
S. G. Chang
Keyword(s):  
Hydrogen Sulfide ◽  
Amino Acid ◽  
Ionic Strength ◽  
Rate Constants ◽  
Amino Acid Analysis ◽  
Ph Dependence ◽  
Alkaline Solutions ◽  
Visible Spectroscopy ◽  
Uv Visible ◽  
Ph Dependent

The reaction between cystine (CySSCy) and hydrogen sulfide ion (HS−) in alkaline solutions has been studied by amino acid analysis and uv–visible spectroscopy. The reaction occurs in two reversible steps to form cysteine (CySH), S-thiocysteine (CySS−), and disulfide (S22−), as represented by the reactions [Formula: see text] and [Formula: see text]. The equilibrium and rate constants were pH dependent due to the presence of various charge types of reactants and products. The rate constants at 25 °C, pH 10.0, and μ = 0.17 M were determined to be: k1 = 3.7 ± 0.4 M−1 min−1, k−1 = 5.5 ± 0.6 M−1 min−1, k2 = 6.1 ± 0.5 M−1 min−1, and k−2 = 122 ± 20 M−1 min−1. When the rate constant k1 is expressed as k1 = A exp (−Ea/RT), values of A = (4.7 ± 0.3) × 1011 M−1 min−1 and Ea = 15.8 ± 0.9 kcal mol−1 were obtained. The ionic strength and pH dependence of k1 were also studied.

Residual phase lignin in haft cooking related to the conditions in the cook

1997 ◽  
Vol 12 (4) ◽  
pp. 225-229
Author(s):  
Cart-in A-S. Gustavsson ◽  
Chritofer T. Lindgren ◽  
Mikael E. Lindström
Keyword(s):  
Hydrogen Sulfide ◽  
Ionic Strength ◽  
Sodium Ion ◽  
Ion Concentration ◽  
Constant Composition ◽  
Hydroxide Ion ◽  
Sulfide Ion ◽  
Residual Phase ◽  
Kraft Cooking ◽  
Very High

Abstract The amount of lignin reacting according to the slow residual phase, i.e. the residual phase lignin, is in many perspectives an interesting issue. The purpose of the present investigation was to develop a mathematical model to show how the amount of residual phase lignin in the kraft cooking of spruce chips (Picm ahies) depends on the conditions in the earlier phases of the cook. The variables studied were hydroxide ion concentration, hydrogen sulfide ion concentration and ionic strength. The liquor-to-wood ratio during pulping was very high to maintain approximately constant chemical concentrations throughout each experiment (so called "constant composition" cooks). An increase in hydroxide ion concentration andtor hydrogen sulfide ion concentration leads to a decrease in the amount of residual phase lignin, while an increase in ionic strength, i.e. sodium ion concentration, leads to an increase. A signiticant result is that the hydrogen sulfide ion concentration has a pronounced influence on the amount of residual phase lignin during a cook at a low hydroxide ion concentration. The amount of residual phase lignin expressed as % lignin on wood, L,, can be described by the following equation developed for "constant composition" cooks (when cooking with a constant sodium ion concentration of 2 mol/L): LT=0,55-0.32*[HO-](-1,3)*ln[HS-] This equation is valid for a concentration of HO- in the range from 0.17 to 1.4, and a hydrogen sulfide ion concentration from 0.07 to 0.6 mol/L.

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.

Sorption of Cadmium and Lead by Chelating Ion Exchangers Ostsorb OXIN, Ostsorb DETA, and Ostsorb DTTA

1994 ◽  
Vol 59 (6) ◽  
pp. 1311-1318 ◽  
Author(s):  
Ladislav Svoboda ◽  
Petr Vořechovský
Keyword(s):  
Ionic Strength ◽  
Aqueous Solutions ◽  
Sodium Perchlorate ◽  
Exchange Capacity ◽  
Chloride Ions ◽  
Point Of View ◽  
Alkaline Media ◽  
Ion Exchangers ◽  
Acidic Media ◽  
Cadmium And Lead

The properties of cellulose chelating ion exchangers Ostsorb have been studied in the sorption of cadmium and lead from aqueous solutions. The Cd(II) and Pb(II) ions are trapped by the Ostsorb OXIN and Ostsorb DETA ion exchangers most effectively in neutral and alkaline media but at these conditions formation of stable hydrolytic products of both metals competes with the exchange equilibria. From this point of view, Ostsorb DTTA appears to be a more suitable sorbent since it traps the Pb(II) and Cd(II) ions in acidic media already. Chloride ions interfere with the sorption of the two metals by Ostsorb DTTA whereas the ionic strength adjusted by the addition of sodium perchlorate does not affect the exchange capacity of this ion exchanger.

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