Homogenous catalytic

Homogeneous catalysts. With a homogeneous catalyst, the reaction proceeds entirely in the vapor or liquid phase. The catalyst may modify the reaction mechanism by participation in the reaction but is regenerated in a subsequent step. The catalyst is then free to promote further reaction. An example of such a homogeneous catalytic reaction is the production of acetic anhydride. In the first stage of the process, acetic acid is pyrolyzed to ketene in the gas phase at TOO C ... 

The selective addition of the second HCN to provide ADN requires the concurrent isomerisation of 3PN to 4-pentenenitrile [592-51 -8] 4PN (eq. 5), and HCN addition to 4PN (eq. 6). A Lewis acid promoter is added to control selectivity and increase rate in these latter steps. Temperatures in the second addition are significandy lower and practical rates may be achieved above 20°C at atmospheric pressure. A key to the success of this homogeneous catalytic process is the abiUty to recover the nickel catalyst from product mixture by extraction with a hydrocarbon solvent. 2-Methylglutaronitrile [4553-62-2] MGN, ethylsuccinonitfile [17611-82-4] ESN, and 2-pentenenitrile [25899-50-7] 2PN, are by-products of this process and are separated from adiponitrile by distillation. 

Acetic Acid and Anhydride. Synthesis of acetic acid by carbonylation of methanol is another important homogeneous catalytic reaction. The Monsanto acetic acid process developed in the late 1960s is the best known variant of the process. 

Direct Chlorination of Ethylene. Direct chlorination of ethylene is generally conducted in Hquid EDC in a bubble column reactor. Ethylene and chlorine dissolve in the Hquid phase and combine in a homogeneous catalytic reaction to form EDC. Under typical process conditions, the reaction rate is controlled by mass transfer, with absorption of ethylene as the limiting factor (77). Ferric chloride is a highly selective and efficient catalyst for this reaction, and is widely used commercially (78). Ferric chloride and sodium chloride [7647-14-5] mixtures have also been utilized for the catalyst (79), as have tetrachloroferrate compounds, eg, ammonium tetrachloroferrate [24411-12-9] NH FeCl (80). The reaction most likely proceeds through an electrophilic addition mechanism, in which the catalyst first polarizes chlorine, as shown in equation 5. The polarized chlorine molecule then acts as an electrophilic reagent to attack the double bond of ethylene, thereby faciHtating chlorine addition (eq. 6) ... 

Acetic Acid. Manufacture of acetic acid [64-19-7] by homogeneous catalytic methanol carbonylation has become the leading commercial route to acetic acid (eq. 8) (34,35). 

Volume 66 Dioxygen Activation and Homogeneous Catalytic Oxidation. Proceedings of the Fourth International Symposium on Dioxygen Activation and Homogeneous Catalytic Oxidation, Balatonfiired, September 10-14,1990 edited by L.l. Simandi... 

A catalyst is defined as a substance that influences the rate or the direction of a chemical reaction without being consumed. Homogeneous catalytic processes are where the catalyst is dissolved in a liquid reaction medium. The varieties of chemical species that may act as homogeneous catalysts include anions, cations, neutral species, enzymes, and association complexes. In acid-base catalysis, one step in the reaction mechanism consists of a proton transfer between the catalyst and the substrate. The protonated reactant species or intermediate further reacts with either another species in the solution or by a decomposition process. Table 1-1 shows typical reactions of an acid-base catalysis. An example of an acid-base catalysis in solution is hydrolysis of esters by acids. 

Homogeneous catalytic deuteration of various unsaturated 5a-spirostane derivatives is an excellent method for the preparation of side chain labeled analogs. Thus, saturation of the double bonds at positions 20(21), 23 and 24 provided the corresponding deuterated compounds (144), (145) and (146) in high isotopic purity. The preparation of (146) is a rare example of the saturation of an isolated trisubstituted double bond in the steroid field. 

PaRshall, Homogeneous catalytic activation of C-H bonds, Acc. Chem. Res. 8, 113-7 (1975). 

The only weakness of the homogeneous catalytic hydrogenation of elastomer is the removal of the catalyst from... 

The situation has now changed and currently an area of considerable research interest is in heterogenizing homogeneous catalysts. One such instance is to be found in the ethylene based manufacture of vinyl acetate (11). A homogeneous catalytic process based on palladium and copper salts was first devised, but corrosion problems were made much less serious in a heterogeneous system based on the same chemical principles. 

The Homogeneous Catalytic Isomerization of Olefins by Transition Metal Complexes... 

Sulfided bimetallic clusters which mimic the metal composition of commercial hydrodesulfurization (HDS) catalysts have been prepared and their homogeneous catalytic behavior studied. Reaction of thiophenol with [Mo2Co2(/z4-S)... 

Generally, the above transesterification reactions are catalyzed by strong acids or alkalis [1, 2]. In the homogeneous catalytic process by acids or alkalis, neutralization is required of the product. This post-treatment produces waste water, and increases equipment investment and production cost. Recently, more attention has been paid to the heterogeneous catalysis process [3] for an easier production process and to reduce pollution of the environment. 

Volume 66 Dioxygen Activation and Homogeneous Catalytic Oxidation. Proceedings of the... 

As depicted above, there is a large variety of NHCs, and their access is relatively easy. This is a veritable advantage in the use of NHCs for homogeneous catalytic systems. However, it is probably their unique electronic and steric properties that make NHCs an exceptional class of molecules. These unique features are described in the following sections. 

HCR Homogeneous catalytic reaction including hydrogenation, Heck coupling, and Suzuki reaction. 

Solvated Metal Atoms as Homogeneous Catalytic Precursors... 

In this chapter the potential of nanostructured metal systems in catalysis and the production of fine chemicals has been underlined. The crucial role of particle size in determining the activity and selectivity of the catalytic systems has been pointed out several examples of important reactions have been presented and the reaction conditions also described. Metal Vapor Synthesis has proved to be a powerful tool for the generation of catalytically active microclusters SMA and nanoparticles. SMA are unique homogeneous catalytic precursors and they can be very convenient starting materials for the gentle deposition of catalytically active metal nanoparticles of controlled size. 

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