Rhodium(I) catalyzed E/Z isomerization of dimethyl butenedioate

1985 ◽  
Vol 50 (6) ◽  
pp. 1274-1282 ◽  
Author(s):  
Jaroslav Podlaha ◽  
Miloš Procházka
Keyword(s):  
Experimental Evidence ◽  
Triphenylphosphine Oxide ◽  
Active Species ◽  
Equimolar Mixture ◽  
Rhodium Complexes ◽  
Hydride Complexes ◽  
High Substrate ◽  
First Order ◽  
Highly Effective ◽  
Catalytically Active

Hydride complexes of Rh(I) represent highly effective homogeneous catalysts of the isomerization of (Z)-dimethyl butenedioate (I) yielding (E)-dimethyl butenedioate (II) in benzene at 25 °C. The reaction catalyzed by RhH(P(C6H5)3)4 is first order both in I and in the catalyst, k = 0.51 l mol-1 s-1, Ea = 48 kJ mol-1, ΔS≠ = -46 J mol-1 K-1. At high substrate-to-catalyst ratios the catalyst is inactivated, which consists mainly in deoxygenation and decarbonylation of the E- and Z-esters with formation of methyl 2-butenoate, triphenylphosphine oxide, and carbonylocomplexes of Rh(I). Statistical redistribution of deuterium during the isomerization of equimolar mixture of I and [2,3-2H2]-I and other experimental evidence are consistent with the addition-elimination hydride mechanism of the isomerization involving σ-alkyl rhodium complexes as the intermediates and RhH(P(C6H5)3)2 as the catalytically active species.

The uncatalysed, and the imidazole and o-mercaptobenzoic acid catalysed, hydrolysis of p-nitrophenyl N-benzyloxycarbonylglycinate

1969 ◽  
Vol 22 (1) ◽  
pp. 109 ◽  
Author(s):  
RW Hay ◽  
RJ Trethewey
Keyword(s):  
Active Species ◽  
Ion Concentration ◽  
Nucleophilic Catalysis ◽  
First Order ◽  
Catalysed Reaction ◽  
Catalytically Active ◽  
Ph Range ◽  
Rapid Hydrolysis ◽  
Rate Profile ◽  
Hydrolysis Of

The uncatalysed hydrolysis of p-nitrophenyl N- benzyloxycarbonylglycinate has been studied in 40% (v/v) ethanol-water over the pH range 7.6-8.5. The reaction shows a first-order dependence on the hydroxide ion concentration. The quite rapid hydrolysis (k = (4.4�0.4) x 104 1. mole-1 min-1 at 20�) may possibly indicate the formation of a 2-benzyloxyoxazoline-5-one intermediate. ��� Unlike the hydrolysis of the p-nitrophenyl esters of α-amino acids, the hydrolysis of the N-protected derivatives is not catalysed by carbon dioxide. The hydrolysis of p-nitrophenyl N- benzyloxycarbonylglycinate is, however, catalysed by imidazole in 40% v/v ethanol-water. Unprotonated imidazole (Im) is the catalytically active species. N-Benzyloxycarbonylaminoacetylimidazole has been detected spectrophotometrically as an intermediate in the reaction, indicating nucleophilic catalysis by the base. o-Mercaptobenzoic acid was also found to catalyse the hydrolysis of p-nitrophenyl N- benzyloxycarbonylglycinate. pH-rate profile studies indicate that the dianion of o-mercaptobenzoic acid is the catalytically active species, the substrate presumably hydrolysing via the thioester intermediate Z- NHCH2COSC6H4COO-, although efforts to detect such an intermediate have been unsuccessful. Some evidence for a thioester intermediate in the L- cysteine-catalysed reaction has been obtained.

Kinetics and Mechanism of the Copper-Catalyzed Etching of Silicon by F2

1987 ◽  
Vol 111 ◽  
Author(s):  
N. Selamoglu ◽  
J. A. Mucha ◽  
D. L. Flamm ◽  
D. E. Ibbotson
Keyword(s):  
Etch Rate ◽  
Reaction Rate ◽  
Active Species ◽  
Zero Order ◽  
Feature Size ◽  
First Order ◽  
Size Dependent ◽  
Copper Compounds ◽  
Catalytically Active ◽  
Active Intermediates

AbstractThe copper catalyzed fluorination of silicon is first-order in [F2] and in [Cu]s until the coverage reaches ∼4 monolayers. Above ∼4 monolayers the reaction rate is zero order in copper, suggesting a limited number of catalytically active Cu/Si sites. Surface diffusion of copper leads to decrease in the etch rate as a function of time as well as feature size-dependent etch depths. The copper compounds CuF2, CuO, and copper silicides, Cu5 Si and Cu3 Si all catalyzed the F2-Si reaction which suggests that they are all converted to the same active species. The results can be explained by mechanisms involving copper fluorides or copper silicides as active intermediates.

scholarly journals Direct speciation methods to quantify catalytically active species of AlCl3in glucose isomerization

RSC Advances ◽  
2018 ◽  
Vol 8 (31) ◽  
pp. 17101-17109 ◽  
Author(s):  
Angela M. Norton ◽  
Hannah Nguyen ◽  
Nicholas L. Xiao ◽  
Dionisios G. Vlachos
Keyword(s):  
Experimental Evidence ◽  
Active Species ◽  
Metal Halides ◽  
Direct Experimental Evidence ◽  
Catalytically Active ◽  
Glucose Isomerization

While homogeneous metal halides have been shown to catalyze glucose to fructose isomerization, direct experimental evidence in support of the catalytically active species remains elusive.

Sewage sludge as a precursor of adsorbents/catalysts for environmental applications

2007 ◽  
Vol 2 (1) ◽  
Author(s):  
A. Ros ◽  
C. Canals-Batlle ◽  
M.A. Lillo-Ródenas ◽  
E. Fuente ◽  
M. A. Montes-Morán ◽  
...  
Keyword(s):  
Sewage Sludge ◽  
Room Temperature ◽  
Waste Water Treatment ◽  
Textural Properties ◽  
Active Species ◽  
Elemental Sulphur ◽  
Gaseous Emissions ◽  
Removal Experiments ◽  
Catalytically Active

This paper focuses on the valorisation of solid residues obtained from the thermal treatment of sewage sludge. In particular, sewage sludge samples were collected from two waste water treatment plants (WWTPs) with different sludge line basic operations. After drying, sludges were heated up to 700 °C in appropriate ovens under diluted air (gasification) and inert (pyrolysis) atmospheres. The solids obtained, as well as the dried (raw) sludges, were characterised to determine their textural properties and chemical composition, including the speciation of their inorganic fraction. All the materials under study were employed as adsorbents/catalysts in H2S removal experiments at room temperature. It was found that, depending on the particular sludge characteristics, outstanding results can be achieved both in terms of retention capacities and selectivity. Some of the solids outperform commercially available sorbents specially designed for gaseous emissions control. In these adsorbents/catalysts, H2S is selectively oxidised to elemental sulphur most likely due to the presence of inorganic, catalytically active species. The role of the carbon-enriched part on these solids is also remarked.

Probing the Catalytically Active Species in POM‐catalysed DNA‐model Hydrolysis

2021 ◽  
Author(s):  
Frederico F Martins ◽  
Ángel Sánchez-González ◽  
Jose Lanuza ◽  
Haralampos N. Miras ◽  
Xabier Lopez ◽  
...  
Keyword(s):  
Active Species ◽  
Catalytically Active

scholarly journals Shedding light on the nature of the catalytically active species in photocatalytic reactions using Bi2O3 semiconductor

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Paola Riente ◽  
Mauro Fianchini ◽  
Patricia Llanes ◽  
Miquel A. Pericàs ◽  
Timothy Noël
Keyword(s):  
Experimental Studies ◽  
Heterogeneous Photocatalysis ◽  
Active Species ◽  
Organic Transformations ◽  
Alkyl Bromides ◽  
Catalytically Active ◽  
Visible Light Driven ◽  
Photocatalytic Reactions ◽  
Insight Into ◽  
Photocatalytic Processes

AbstractThe importance of discovering the true catalytically active species involved in photocatalytic systems allows for a better and more general understanding of photocatalytic processes, which eventually may help to improve their efficiency. Bi2O3 has been used as a heterogeneous photocatalyst and is able to catalyze several synthetically important visible-light-driven organic transformations. However, insight into the operative catalyst involved in the photocatalytic process is hitherto missing. Herein, we show through a combination of theoretical and experimental studies that the perceived heterogeneous photocatalysis with Bi2O3 in the presence of alkyl bromides involves a homogeneous BinBrm species, which is the true photocatalyst operative in the reaction. Hence, Bi2O3 can be regarded as a precatalyst which is slowly converted in an active homogeneous photocatalyst. This work can also be of importance to mechanistic studies involving other semiconductor-based photocatalytic processes.

In Search of Catalytically Active Species in the Surfactant-Mediated Biphasic Alkene Epoxidation with Mimoun-Type Complexes

2001 ◽  
Vol 3 (3) ◽  
pp. 329-332 ◽  
Author(s):  
Dirk V. Deubel ◽  
Jörg Sundermeyer ◽  
Gernot Frenking
Keyword(s):  
Active Species ◽  
Catalytically Active

scholarly journals Surprisingly high sensitivity of copper nanoparticles toward coordinating ligands: consequences for the hydride reduction of benzaldehyde

2018 ◽  
Vol 8 (19) ◽  
pp. 5073-5080 ◽  
Author(s):  
Xavier Frogneux ◽  
Ferenc Borondics ◽  
Stéphane Lefrançois ◽  
Florian D'Accriscio ◽  
Clément Sanchez ◽  
...  
Keyword(s):  
Copper Nanoparticles ◽  
High Sensitivity ◽  
Active Species ◽  
Hydride Reduction ◽  
Catalytically Active

Depending on the ligand, ligand-induced leaching of copper nanoparticles may produce catalytically active species for the reduction of benzaldehyde.

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