Homogeneous Hydrogenation of Unsaturated Carboxylic Acids Using Chlororhodate(I) Complexes and Rhodium(I) Diethylsulfide Complexes

1975 ◽  
Vol 53 (6) ◽  
pp. 797-804 ◽  
Author(s):  
Brian R. James ◽  
Flora T. T. Ng
Keyword(s):  
Carboxylic Acids ◽  
Rate Constants ◽  
Maleic Acid ◽  
Activation Parameters ◽  
Kinetic Studies ◽  
Homogeneous Hydrogenation ◽  
Chloride Solutions ◽  
Rate Determining Step ◽  
Square Planar ◽  
Unsaturated Carboxylic Acids

N,N-Dimethylacetamide solutions of the cyclooctene complex [Rh(C8H14)2Cl]2, in the presence of excess chloride or diethylsulfide, are effective for the homogeneous hydrogénation of unsaturated carboxylic acids at ca. 80 °C and 1 atm H2. Kinetic studies on the hydrogenation of maleic acid are consistent with a rate determining step involving oxidative addition of H2 to square planar rhodium(I) olefin species. Rate constants and activation parameters agree with those determined previously from similar studies using corresponding rhodium(III) complexes and give confirmation that rhodium(I) catalysts are involved in the rhodium(III) systems. Discussion of the systems is limited by the somewhat uncertain nature of the catalysts; however, chlororhodate(I) species are involved in the chloride solutions, and bis(diethylsulfide) complexes appear likely in the sulfide systems.

scholarly journals Understanding the reaction mechanism of the regioselective piperidinolysis of aryl 1-(2,4-dinitronaphthyl) ethers in DMSO: Kinetic and DFT studies

2021 ◽  
Vol 46 ◽  
pp. 146867832110274
Author(s):  
Yasmen M Moghazy ◽  
Nagwa MM Hamada ◽  
Magda F Fathalla ◽  
Yasser R Elmarassi ◽  
Ezzat A Hamed ◽  
...  
Keyword(s):  
Carbon Atom ◽  
Density Functional ◽  
Function Analysis ◽  
Density Functional Theory Method ◽  
Activation Parameters ◽  
Kinetic Studies ◽  
Nucleophilic Attack ◽  
Common Mechanism ◽  
Slow Step ◽  
Rate Determining Step

Reactions of aryl 1-(2,4-dinitronaphthyl) ethers with piperidine in dimethyl sulfoxide at 25oC resulted in substitution of the aryloxy group at the ipso carbon atom. The reaction was measured spectrophotochemically and the kinetic studies suggested that the titled reaction is accurately third order. The mechanism is began by fast nucleophilic attack of piperidine on C1 to form zwitterion intermediate (I) followed by deprotonation of zwitterion intermediate (I) to the Meisenheimer ion (II) in a slow step, that is, SB catalysis. The regular variation of activation parameters suggested that the reaction proceeded through a common mechanism. The Hammett equation using reaction constant σo values and Brønsted coefficient value showed that the reaction is poorly dependent on aryloxy substituent and the reaction was significantly associative and Meisenheimer intermediate-like. The mechanism of piperidinolysis has been theoretically investigated using density functional theory method using B3LYP/6-311G(d,p) computational level. The combination between experimental and computational studies predicts what mechanism is followed either through uncatalyzed or catalyzed reaction pathways, that is, SB and SB-GA. The global parameters of the reactants, the proposed activated complexes, and the local Fukui function analysis explained that C1 carbon atom is the most electrophilic center of ether. Also, kinetics and theoretical calculation of activation energies indicated that the mechanism of the piperidinolysis passed through a two-step mechanism and the proton transfer process was the rate determining step.

KINETIC STUDIES OF CHLORO COMPLEXES OF RHODIUM AS HYDROGENATION CATALYSTS

1966 ◽  
Vol 44 (2) ◽  
pp. 233-242 ◽  
Author(s):  
B. R. James ◽  
G. L. Rempel
Keyword(s):  
Maleic Acid ◽  
Kinetic Studies ◽  
Homogeneous Catalyst ◽  
Ferric Ion ◽  
Homogeneous Hydrogenation ◽  
Acid Complex ◽  
Olefinic Bond ◽  
Hydrogenation Catalysts ◽  
Chloro Complexes ◽  
Anionic Complexes

The anionic complexes [RhCl6]3−, [Rh(H2O)Cl5]2−, and [Rh(H2O)2Cl4]− activate molecular hydrogen for the reduction of ferric ion in aqueous acid solution; the catalytic activity increased with increasing number of chloride ligands present. Cationic and neutral chloroaquorhodium(III) complexes did not homogeneously catalyze the reduction of ferric ion, the complexes themselves being reduced to metallic rhodium, a powerful heterogeneous catalyst.Chloro complexes of rhodium(III) and rhodium(I) were not effective catalysts in aqueous solution for the homogeneous hydrogenation of the olefinic bond in maleic acid. Anionic chlororhodate(III) complexes were reduced by hydrogen to the univalent state, this state being stabilized against further reduction to the metal by complexing with the maleic acid present. Preliminary studies indicate that in dimethylacetamide solution rhodium (III) trichloride is an effective homogeneous catalyst for the reduction of maleic acid to succinic acid by hydrogen, the reaction proceeding through a rhodium (I) – maleic acid complex.

KINETIC STUDIES OF PROTON TRANSFER FROM PHENOLS TO TRINITROBENZYL ANION

1966 ◽  
Vol 44 (2) ◽  
pp. 119-124 ◽  
Author(s):  
J. A. Blake ◽  
M. J. B. Evans ◽  
K. E. Russell
Keyword(s):  
Proton Transfer ◽  
Rate Constants ◽  
Dissociation Constants ◽  
Kinetic Studies ◽  
Sodium Cation ◽  
Rate Determining Step ◽  
Rate Of Reaction ◽  
Hammett Relationship ◽  
Measurable Concentration ◽  
Acetic Acids

The rates of reaction of various phenols with the 2,4,6-trinitrobenzyl anion in the solvent ethanol have been determined by a spectrophotometric method. The rate constants at −40 °C are related to the dissociation constants of the phenols in water at 25 °C and the value of α in the Brönsted relation is 0.84 ± 0.07; α drops to 0.44 ± 0.05 if the results for the substituted acetic acids (1) are included. The rate constants for the phenols are also correlated by the Hammett relationship, the ρ value at −40 °C being 1.82 ± 0.2. The activation energies range from 9.4 to 10.9 kcal/mole.The rate of reaction of trinitrobenzyl anion with 3-methylphenol at −30 °C is reduced by a factor of 12 if the phenol is deuterated at the OH group and the solvent is deuteroethanol. The large isotope effect confirms that the rate-determining step involves proton transfer from the OH group of the phenol. Substitution of lithium or potassium cations for the sodium cation does not affect the rate constant at −10 °C.In the reaction with 3-methylphenol, a measurable concentration of trinitrobenzyl anion remains at equilibrium and the equilibrium constant for the reaction is 1.3 ± 0.2 at 25 °C. The heat and entropy changes are approximately −6.5 kcal/mole and −21 e.u./mole respectively.

Kinetic studies of the reactions of 4-nitrobenzofuroxan with cyanide ion and isopropoxide ion in isopropanol

1980 ◽  
Vol 58 (16) ◽  
pp. 1691-1696 ◽  
Author(s):  
Michael E. Moir ◽  
Albert R. Norris
Keyword(s):  
Rate Constants ◽  
Activation Parameters ◽  
Kinetic Studies ◽  
Specific Rate ◽  
Stopped Flow ◽  
Cyanide Ion ◽  
Temperature Range ◽  
Flow Reaction

Kinetic studies of the reactions in isopropanol of 4-nitrobenzofuroxan with cyanide ion and isopropoxide ion have been carried out over the temperature range 15.0 to 35.0 °C. For both bases, the first species identifiable using stopped-flow reaction techniques is postulated to be a C-7 σ-complex of 4-nitrobenzofuroxan and base. Specific rate constants and activation parameters for the formation of these σ-complexes are compared to corresponding data relating to the formation of cyanide ion and isopropoxide ion—σ-complexes of 1,3,5-trinitrobenzene in isopropanol.

Kinetic studies of ring closures in platinum(II) chelates. Rate constants and activation parameters for chelation of platinum(II) by bis(2-aminoethyl) sulfide in aqueous solution

1979 ◽  
Vol 18 (6) ◽  
pp. 1451-1454 ◽  
Author(s):  
G. Albertin ◽  
E. Bordignon ◽  
A. A. Orio ◽  
B. Pavoni ◽  
Harry B. Gray
Keyword(s):  
Aqueous Solution ◽  
Rate Constants ◽  
Activation Parameters ◽  
Kinetic Studies

Free radical mechanisms for the oxidation of 2,3-dihydroxy-2-propenal (triose reductone) by hexacyanoferrate(III)

1985 ◽  
Vol 63 (5) ◽  
pp. 1005-1008 ◽  
Author(s):  
Yasuo Abe ◽  
Takaaki Dohmaru ◽  
Hideo Horii ◽  
Setsuo Taniguchi
Keyword(s):  
Free Radical ◽  
Ionic Strength ◽  
Rate Constants ◽  
Sodium Perchlorate ◽  
Activation Parameters ◽  
Kinetic Studies ◽  
Second Order ◽  
Probable Mechanism ◽  
Acidic Media ◽  
The Media

Kinetic studies of the oxidation of 2,3-dihydroxy-2-propenal (triose reductone, RH2) by hexacyanoferrate(III), [Fe(CN)6]3−, were carried out in acidic media ([H+] = 0.02–0.1 M (1 M = 1 mol dm−3)) at various temperatures (10–30° C). The ionic strength of the media (I = 0.04–0.4 M) was adjusted using sodium perchlorate. The second-order rate constants in M−1 s−1 are (0.86 ± 0.06) – (2.83 ± 0.14) for the reactions of hexacyanoferrate(III) with RH2, and [(4.16 ± 0.03) − (12.4 ± 0.2)] × 103 for those with RH− ion. Activation parameters for the oxidation have been reported and compared with those of the oxidation of triose reductone with peroxodisulfate ion. A probable mechanism is proposed for the reaction.

The Lewis-acidity of square-planar nickel(II) complexes. III. A kinetic study of the effects of substituents on the addition of 1,10-Phenanthroline to Bis(monothioacetylacetonato)nickel(II) and Bis(dithiophosphato)nickel(II) complexes in toluene

1978 ◽  
Vol 31 (7) ◽  
pp. 1439 ◽  
Author(s):  
MU Fayyaz ◽  
MW Grant
Keyword(s):  
Kinetic Study ◽  
Rate Constants ◽  
Activation Parameters ◽  
Adduct Formation ◽  
Second Order ◽  
Lewis Acidity ◽  
Order Rate ◽  
Measured Rate ◽  
Square Planar ◽  
Inductive Effects

The second-order rate constants and activation parameters for the addition of 1,10-phenanthroline to bis(dialkyldithiophosphato)nickel(II) complexes and substituted bis(monothioacetylacetonato)-nickel(II) complexes in toluene have been measured. Rate constants are in the range 102-108 1. mol-1 s-1 at 25°C, while ΔH‡ is in the range 10-50 kJ mol-1 and ΔS‡ is in the range from -30 to -110 J mol-1 K-1. The higher rate constants, smaller ΔH‡ and more negative ΔS‡ values are associated with complexes with electron- withdrawing substituents. The results are related to the thermo- dynamics of adduct formation, the inductive effects of the substituents and the pKa of the ligands.

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