Catalyst neutral

Active Raney nickel induces desulfurization of many sulfur-containing heterocycles thiazoles are fairly labile toward this ring cleavage agent. The reaction occurs apparently by two competing mechanisms (481) in the first, favored by alkaline conditions, ring fission occurs before desul-, furization, whereas in the second, favored by the use of neutral catalyst, the initial desulfurization is followed by fission of a C-N bond and formation of carbonyl derivatives by hydrolysis (Scheme 95). 

The process consists of pre-etching, etching, etch neutralization, catalyst appHcation, catalyst activation, and plating. Most commercial appHcations, except REl/EMl shielding, use the initial copper or nickel deposit as a base for subsequent electrolytic plating of electrolytic copper, nickel, or chromium. The exact types and thicknesses of metal used are determined by part usage, eg, automotive exterior, decorative, plumbing, and others (24). 

Ionic liquids formed by treatment of a halide salt with a Lewis acid (such as chloro-aluminate or chlorostannate melts) generally act both as solvent and as co-catalyst in transition metal catalysis. The reason for this is that the Lewis acidity or basicity, which is always present (at least latently), results in strong interactions with the catalyst complex. In many cases, the Lewis acidity of an ionic liquid is used to convert the neutral catalyst precursor into the corresponding cationic active form. The activation of Cp2TiCl2 [26] and (ligand)2NiCl2 [27] in acidic chloroaluminate melts and the activation of (PR3)2PtCl2 in chlorostannate melts [28] are examples of this land of activation (Eqs. 5.2-1, 5.2-2, and 5.2-3). 

Vanadium and sodium neutralize catalyst acid sites and can cause collapse of the zeolite structure. Figure 10-5 shows the deactivation of the catalyst activity as a function of vanadium concentration. Destruction of the zeolite by vanadium takes place in the regenerator where the combination of oxygen, steam, and high temperature forms vanadic acid according to the following equations ... 

Rapid distillation from the neutralized catalyst results in much smaller loss of ester than is encountered in the more usual procedure that includes washing with water and drying. 

A chiral diphosphine ligand was bound to silica via carbamate links and was used for enantioselective hydrogenation.178 The activity of the neutral catalyst decreased when the loading was increased. It clearly indicates the formation of catalytically inactive chlorine-bridged dimers. At the same time, the cationic diphosphine-Rh catalysts had no tendency to interact with each other (site isolation).179 New cross-linked chiral transition-metal-complexing polymers were used for the chemo- and enantioselective epoxidation of olefins.180... 

Scheme 7.1. Activation of a neutral catalyst precursor by chloroaluminate ionic liquids...

The first investigations of the rhodium-catalysed hydroformylation in room temperature ionic liquids were published by Chauvin et al. in 1995 [44], The hydroformylation of 1-pentene with the neutral catalysts [Rh(CO)2(acac)]/triarylphosphine was carried out in a biphasic reaction using [BMIM][PF6] as the ionic liquid (see Scheme 7.2). 

Acylation catalyst. CoCl2 in CH3CN is recommended as a neutral catalyst for acetylation of (3-hydroxy ketones, which can undergo elimination in the presence of DMAP-N(C2H5)v It is also effective for selective acylation of a primary or secondary hydroxyl group in the presence of a tertiary one. 

This intramolecular hydrosilylation can be extended to a-hydroxy enol ethers (2-alkoxy-l-alkene-2-ols) to provide access to 2,3-sy -l,2,3-triols.2 In this case a neutral catalyst, Pt(0)-vinylsiloxane,3 is preferred over H2PtCl6. 

Neutral catalysts, in phenolic resin polymerization, 18 761—762 Neutral extractants, of rare-earth elements, 14 642... 

Phenolic novolacs, 18 760-761 Phenolic resin adhesives, 18 783-784 Phenolic resin can coatings, 18 38 Phenolic resin composites, 18 792-794 Phenolic resin drying-oil varnishes, 18 783 Phenolic resin fibers, 18 797-798 mechanical properties of, 18 798 Phenolic resin foam, 18 795-796 Phenolic resin manufacturers, U.S., 18 774 Phenolic resin polymerization, 18 760-765 alkaline catalysts in, 18 762-765 neutral catalysts in, 18 761-762 strong-acid catalysts in, 18 760-761 Phenolic resin prepregs, 18 793 Phenolic resin production unit, 18 766 Phenolic resins, 10 409 18 754-755, 756-802 22 10 26 763 in abrasive materials, 18 786-787 in air and oil filters, 18 790 additional reactants in, 18 759 analytical methods for, 18 774-779 applications of, 18 781-798 batch processes for, 18 766 from biomass and biochemical processes, 18 769-770... 

In the third transition state (TS3), the neutral catalyst is recovered by transferring the proton back from the catalyst to the substrate. In other words, the (former) azlactone ether oxygen atom deprotonates the tertiary ammonium ion. For proton transfer, again an LBHB is formed (N-0 distance 2.479 A, <(0,H,N)=166.2°). In the product complex, the catayst is neutral and the A-acylamino acid ester is bound in its iminol form to the catalyst (Product(iininol)). Finally, an additional 66.6 kJ moF are gained by the subsequent iminol-amide tautomerization (Product(ainide)) (Fig. 1). 

Reactions performed at 50 bar with neutral catalysts prepared in situ from ]Rh(p C I)(cod) - and the DIOP or... 

Reactions performed in toluene at 25 °Cwith 1.1 equiv. of Ph2SiH2 using neutral catalysts prepared in situ from ]l hi i C I i cod)] 2 and the DIOP or boraDlOP ligand. aSubstrate Rh = 500. bSubstrate Rh = 300. 

The activation energies for the remaining acidic and neutral catalysts show a continuous decline for the apparent activation energies in the order Pt/LTL [0.47, small] > Pt/LTL [0.47, big] > Pt/LTL [0.82] > Pt/ASA Pt/Si02 [small] Pt/Si02 [big]. The pre-exponential factor increases in the opposite direction. These observations indicate an apparent compensation effect, as will be discussed later. 

The Pt/HT [ ] catalysts show a decrease in the Pt-Pt coordination number after evacuation. This indicates a change in morphology of the Pt particles after desorption of hydrogen. The decrease of Npt.pt can be explained by a flattening of the Pt particles. In contrast, the neutral catalyst, Pt/LTL [1.04] shows only minor changes in the morphology after evacuation and the catalysts Pt/LTL [0.82] and [1.53] show an increase in the Pt-Pt coordination number. 

Contamination of the product by trace amounts of (neutralized) catalyst is generally avoided when the latter is a solid. 

Ramesh C, Mahender G, Ravindranath N, Das B (2003) A Mild, Highly Selective and Remarkably Easy Procedure for Deprotection of Aromatic Acetates Using Ammonium Acetate as a Neutral Catalyst in Aqueous Medium. Tetrahedron 59 1049... 

Attachment of the catalyst to a polymeric support can also be facilitated using a bis-carbene as the ligand [253]. The bisimidazoUum salt featuring a hydroxyalkyl sidechain on each of the two imidazolium units was reacted with palladium (II) acetate to form the neutral catalyst complex (see Figure 4.82). Immobilisation was then achieved by reacting the functionalised catalyst with 4-(bromomethyl)phenoxy-methyl polystyrene, known as Wang resin, as the polymeric support. 

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