High pressure–temperature aqueous oxidations. III. A kinetic study of the enolization and oxidation of cyclohexanone

1988 ◽  
Vol 66 (2) ◽  
pp. 294-299 ◽  
Author(s):  
John W. Thomas ◽  
Jay E. Taylor
Keyword(s):  
High Pressure ◽  
Kinetic Study ◽  
Aqueous Media ◽  
Activation Parameters ◽  
Oxygen Molecule ◽  
First Order ◽  
Partial Pressures ◽  
Butanedioic Acid ◽  
Pentanedioic Acid ◽  
Hexanedioic Acid

The rates of enolization of cyclohexanone have been determined at 145 and 172 °C in D2O and with buffers. The rates of oxidation were evaluated at temperatures of 145, 172, and 193.5 °C with oxygen partial pressures of 20.4 to 131 atm. The rate of enolization was 10–160 times faster than the rate of oxidation thereby supporting the previously proposed concept of enol intermediacy for the oxidation of ketones. The oxidation was first order in cyclohexanone and 1/2 order in oxygen. The rate of oxidation was increased by the addition of traditional phenolic inhibitors. The products isolated were formic, acetic, butanedioic, pentanedioic, hexanedioic, and 5-oxohexanoic acids. The activation parameters were calculated to be ΔH≠, 22 kcal/mol; ΔS≠, −27 eu, log A, 7.6 for the oxidation and ΔH≠, 12 kcal/mol; ΔS≠, −42.3 eu, log A, 4.13 for the enolization. Based on these observations a mechanism has been postulated whereby an oxygen molecule forms a transitory adduct with two enolates of cyclohexanone. The latter may then split by a reversible reaction to form an intermediate which may then isomerize or oxidize to either 2-hydroxycyclohexanone or 1,3-cyclohexanedione. Upon further oxidation the former yields hexanedioic acid. The latter then undergoes a reverse condensation in the aqueous media to 5-oxohexanoic acid which upon further oxidation yields formic plus pentanedioic acid and acetic plus butanedioic acid.

Kinetics and Activation Parameters for the Alkaline Aqueous Rearrangement of Trichorfon [O,O-Dimethyl-(2,2,2-Trichloro-1-Hydroxyethyl) Phosphonate] to Dichlorvos [O,O-Dimethyl-O-(2,2-Dichloroethenyl)Phosphate]

2001 ◽  
Vol 36 (3) ◽  
pp. 589-604 ◽  
Author(s):  
Julian M. Dust ◽  
Christopher S. Warren
Keyword(s):  
Activation Energy ◽  
High Pressure ◽  
Activation Parameters ◽  
Base Catalysis ◽  
Rearrangement Product ◽  
Exponential Factor ◽  
First Order ◽  
Pseudo First Order ◽  
Order Plot ◽  
Kinetics Of

Abstract The kinetics of the alkaline rearrangement of O,O-dimethyl-(2,2,2-trichloro-1- hydroxyethyl)phosphonate, (trichlorfon, 1), the active insecticidal component in such formulations as Dylox, was followed at 25±0.5°C by high pressure liquid chromatography (UV-vis detector, 210 nm). The rearrangement product, O,Odimethyl- O-(2,2-dichloroethenyl)phosphate (dichlorovos, 2), which is a more potent biocide than trichlorfon, undergoes further reaction, and the kinetics, consequently, cannot be treated by a standard pseudo-first-order plot. A two-point van't Hoff (initial rates) method was used to obtain pseudo-first-order rate constants (kѱ) at 25, 35 and 45°C: 2.6 × 10-6, 7.4 × 10-6 and 2.5 × 10-5 s-1, respectively. Arrhenius treatment of this data gave an activation energy (Ea) of 88 kJ·mol-1 with a pre-exponential factor (A) of 5.5 × 109 s-1. Kinetic trials at pH 8.0 using phosphate and tris buffer systems show no buffer catalysis in this reaction and indicate that the rearrangement is subject to specific base catalysis. Estimates are reported for pseudo-first-order half-lives for trichlorfon at pH 8.0 for environmental conditions in aqueous systems in the Corner Brook region of western Newfoundland, part of the site of a recent trichlorfon aerial spray program.

Electron-Transfer Reactions in Non-Aqueous Media. V. Solvent Effects in the Reduction of CoN3(NH3)52+ by Iron(II)

1979 ◽  
Vol 32 (10) ◽  
pp. 2139 ◽  
Author(s):  
TJ Westcott ◽  
DW Watts
Keyword(s):  
Electron Transfer ◽  
Aqueous Media ◽  
Activation Parameters ◽  
Transfer Reactions ◽  
Tetrahedral Coordination ◽  
First Order ◽  
Precursor Complex ◽  
Stage Process ◽  
Pseudo First Order ◽  
Reversible Formation

The reduction of CoN3(NH3)52+ by iron(II) is rate-determined by a two-stage process involving the reversible formation of an azide-bridged precursor complex prior to electron transfer in each of the solvents water, Me2SO, aqueous Me2SO and HCONMe2. The activation parameters in H2O and Me2SO, and the trends shown with increasing Me2SO concentrations in aqueous Me2SO, are similar to the properties of the previously studied CoCl(NH3)52+ and CoBr(NH3)52+ systems and contrast with the reduction of COF(NH3)52+. The results are consistent with a bridged precursor complex octahedral at both the iron and cobalt atoms in water but with tetrahedral coordination about the iron in Me2SO. In HCONMe2, as in the reduction of COF(NH3)52+, COCl(NH3)52+ and COBr(NH3)52+, the precursor complex is a significant part of the reacting solutions, and as a result the experimental pseudo-first-order rate constants for the loss of CoIII are not linearly dependent on the concentration of FeII. The initial spectra of the reacting solutions in this system also indicate significant concentrations of the precursor complex.

scholarly journals Kinetic Study of Photocatalytic Degradation of Tolonium Chloride Under High Pressure Irradiation in Aquatic Buffer Systems

2011 ◽  
Vol 8 (s1) ◽  
pp. S19-S26 ◽  
Author(s):  
M. Montazerozohori ◽  
S. Nezami ◽  
S. Mojahedi
Keyword(s):  
High Pressure ◽  
Photocatalytic Degradation ◽  
Kinetic Study ◽  
Rate Constants ◽  
Order Kinetic ◽  
Optimum Conditions ◽  
First Order ◽  
Reactor Cell ◽  
Order Kinetic Model ◽  
Tolonium Chloride

Anatase titanium dioxide catalyzed photodegradation of tolonium chloride at various bufferic pH of 2, 7, 9 and 12 in aqueous solution is presented. The effect of some physicochemical parameters such as initial concentration of dye, catalyst amount and reaction time on photocatalytic degradation has been investigated in a photo-reactor cell containing high pressure mercury lamp to obtain the optimum conditions in each bufferic pH at constant temperature. A complete spectrophotometric kinetic study of tolonium chloride under high pressure irradiation at buffer media was performed. The photocatalytic degradation observed rate constants (kobs) were found to be 2.90×10-3, 3.30×10-3, 3.20×10-3and 5.20×10-3min-1for buffer pH of 2-12 respectively. It was found that a pseudo-first-order kinetic model based on Langmuir-Hinshelwood one is usable to photodegradation of this compound at all considered buffer pH. In addition to these, the Langmuir-Hinshelwood rate constants, krfor the titled compound at various pH are reported.

scholarly journals Kinetic and High-Pressure Mechanistic Investigation of the Aqua Substitution in the Trans-Aquaoxotetracyano Complexes of Re(V) and Tc(V): Some Implications for Nuclear Medicine

2008 ◽  
Vol 2008 ◽  
pp. 1-9 ◽  
Author(s):  
J. Mattheus Botha ◽  
Andreas Roodt
Keyword(s):  
High Pressure ◽  
Nuclear Medicine ◽  
Kinetic Study ◽  
Rate Constants ◽  
Formation Rate ◽  
Activation Parameters ◽  
Second Order ◽  
Associative Mechanism ◽  
Mechanistic Investigation

A kinetic study of the aqua substitution in the [TcO(OH2)(CN)4]− complex by different thiourea ligands (TU = thiourea, NMTU = N-methyl thiourea, NNDMTU = N, N′-dimethylthiourea) yielded second-order formation rate constants (25∘C) as follows [NNDMTU, NMTU, TU, respectively]: kf = 11.5 ± 0.1, 11.38 ± 0.04, and 7.4 ± 0.1 M−1s−1, with activation parameters: ΔHkf#:55±2, 42±3, 35±5 kJ mol−1; ΔSkf#:−40±8, −84±11, −110±17 J K−1mol−1. A subsequent high-pressure investigation of the aqua substitution in the [ReO(OH2)(CN)4]− and [TcO(OH2)(CN4)]− complexes by selected entering ligands yielded ΔVkf# values as follows: Re(V): −1.7±0.3(NCS−), −22.1±0.9 (TU) and for Tc(V): −3.5±0.3(NCS−), −14±1 (NNDMTU), and−6.0±0.5 (TU) cm3mol−1, respectively. These results point to an interchange associative mechanism for the negative NCS− as entering group but even a pure associative mechanism for the neutral thiourea ligands.

High temperature–pressure aqueous oxidations. IV. A kinetic study of the oxidation and enolization of cyclohexanone in the presence of catalytic metal ions

1989 ◽  
Vol 67 (1) ◽  
pp. 165-170 ◽  
Author(s):  
John W. Thomas ◽  
Jay E. Taylor
Keyword(s):  
High Pressure ◽  
High Temperature ◽  
Kinetic Study ◽  
Metal Ion ◽  
Copper Ions ◽  
Copper Ion ◽  
Oxidation Products ◽  
Initial Reaction ◽  
Temperature Oxidation ◽  
First Order

The aqueous high pressure–temperature oxidation of cyclohexanone was found to be strongly catalyzed by silver, iron(III), and copper ions but not by aluminum, cobalt, manganese(II), or nickel ions. The reactivities of the catalytic ions were inhibited by the acidic oxidation products. Accordingly, initial reaction velocities were determined and used to correlate the kinetic data. A detailed kinetic study of copper ion catalysis has shown that in the presence of that ion the reaction was first order in cyclohexanone, one-half order in copper ion, and zero order in oxygen. The rate of enolization of cyclohexanone appeared to be unaffected by the presence of copper ion under conditions of constant acidity but was strongly catalyzed by both deuterium ion and acetate ion. Further, the rate of oxidation exceeded the rate of enolization at higher copper ion concentrations. These data contrast with the uncatalyzed oxidation, for which the kinetic reaction was first order in cyclohexanone, one-half order in oxygen, and the rate of oxidation was much less than the rate of enolization. The activation energies for the catalyzed and uncatalyzed oxidations were about the same, but the entropies of activation were quite different. From these data it is concluded that the enol is not a major intermediate for the catalyzed reaction. It is suggested that the copper ion may form an active peroxy complex with the oxygen molecule to serve as the reactive oxidant. Keywords: metal ion catalysis, kinetics, cyclohexanone, high temperature oxidation, high pressure oxidation.

Kinetics and Mechanism of Hexachloroiridate(IV) Oxidation of Arsenic(III) in Acidic Perchlorate Solutions

1992 ◽  
Vol 57 (7) ◽  
pp. 1451-1458 ◽  
Author(s):  
Refat M. Hassan
Keyword(s):  
Ionic Strength ◽  
Fractional Order ◽  
Activation Parameters ◽  
Order Reaction ◽  
First Order Reaction ◽  
Intermediate Complex ◽  
Constant Ionic Strength ◽  
Kinetics Of Oxidation ◽  
First Order ◽  
Kinetics Of

The kinetics of oxidation of arsenic(III) by hexachloroiridate(IV) at lower acid concentrations and at constant ionic strength of 1.0 mol dm-3 have been investigated spectrophotometrically. A first-order reaction in [IrCl62-] and fractional order with respect to arsenic(III) have been observed. A kinetic evidence for the formation of an intermediate complex between the hydrolyzed arsenic(III) species and the oxidant was presented. The results showed that decreasing the [H+] is accompanied by an appreciable acceleration of the rate of oxidation. The activation parameters have been evaluated and a mechanism consistent with the kinetic results was suggested.

Kinetic Studies of [4n+2]π-Thermal Cyclodimerization of 1-(3-Pyridazinyl)-3-oxidopyridinium Betaines

1992 ◽  
Vol 57 (9) ◽  
pp. 1951-1959 ◽  
Author(s):  
Madlene L. Iskander ◽  
Samia A. El-Abbady ◽  
Alyaa A. Shalaby ◽  
Ahmed H. Moustafa
Keyword(s):  
Energy Gap ◽  
Activation Parameters ◽  
Kinetic Studies ◽  
Cyclic Transition ◽  
Concerted Mechanism ◽  
First Order ◽  
Thermodynamic Activation Parameters ◽  
Cyclic Transition State ◽  
Complete Dissociation ◽  
Homo Lumo

The reactivity of the base induced cyclodimerization of 1-(6-arylpyridazin-3-yl)-3-oxidopyridinium chlorides in a pericyclic process have been investigated kinetically at λ 380 nm. The reaction was found to be second order with respect to the liberated betaine and zero order with respect to the base. On the other hand dedimerization (monomer formation) was found to be first order. It was shown that dimerization is favoured at low temperature, whereas dedimerization process is favoured at relatively high temperature (ca 70 °C). Solvent effects on the reaction rate have been found to follow the order ethanol > chloroform ≈ 1,2-dichloroethane. Complete dissociation was accomplished only in 1,2-dichloroethane at ca 70 °C. The thermodynamic activation parameters have been calculated by a standard method. Thus, ∆G# has been found to be independent on substituents and solvents. The high negative values of ∆S# supports the cyclic transition state which is in favour with the concerted mechanism. MO calculations using SCF-PPP approximation method indicated low HOMO-LUMO energy gap of the investigated betaines.

Thermal and High-Pressure Inactivation of Tomato Polygalacturonase: A Kinetic Study

2002 ◽  
Vol 67 (5) ◽  
pp. 1610-1615 ◽  
Author(s):  
D. Fachin ◽  
A. Van Loey ◽  
A. VanLoeyIndrawati ◽  
L. Ludikhuyze ◽  
M. Hendrickx
Keyword(s):  
High Pressure ◽  
Kinetic Study
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