Grafting catalysts

Ti alkoxides are well-known transesterification catalysts. Grafting of these alkoxides on to a silica surface in a nitrogen atmosphere, followed by steam hydrolysis and calcination, gives stable catalysts for the transesterification of soybean oil at... 

Different approaches have been used in the preparation of heterogeneous Sharpless-type catalytic systems for the asymmetric epoxidation of allylic alcohols, although in most cases the chiral induction was modest (50-60%). Li and coworkers described the preparation of an organic-inorganic hybrid chiral catalyst grafted onto the surface of silica and in mesopores of MCM-41, and its successful application in asymmetric epoxidation . Enantiomeric excesses were higher than 80% with conversions in the range 22-76%. 

Whatever the nature of the template, among possible applications such as catalysts, grafting supports, or filtration medium, the use of MTS for chromatography applications has been claimed for years. However, this latter application requires the ability to synthesize homogeneous batches of spherical particles with a mean diameter at least equal to 5 pm. Such particles were observed only once, in a pH-dependent synthesis of MCM-41 particles, performed by Yang, Ozin and co-workers [1], Most of the time, the synthesis of submicrometer-size particles of MCM-41 or MCM-48 materials was only reported [2-4], We present the synthesis of MSU-X silica with perfectly controlled size and shape suitable for chromatography applications. 

Example 2 Sharpless catalysts grafted onto mesoporous MCM-41[71]... 

S. Xiang, Y. Zhang, Q. Xin, and C. Li, Asymmetric Epoxidation of Allyl Alcohol on Organic-inorganic Hybrid Chiral Catalysts Grafted onto the Surface of Silica and in the Mesopores of MCM-41. Angew. Chem., Int. Ed, 2002, 41, 821-824. 

Irradiation at 300 nm in CCl, CHCl, or CH2CI2 promotes am irreversible reaction and formation of what is probably [Os(IV)(TTP)Cl2l. Optimum conditions have been reported for determination of osmium by measurement of the luminescence of its 1 3-complex with 1,10-phenanthroline.A catalyst, prepared by reducing the product of grafting OsO on to the C-C bond of sepiolite, has been found to mediate the photooxidation of water but to do so less efficiently than RuOjj. This is the first exaunple of a dispersed water oxidation catalyst grafted on to a solid support. 

Figure 1. Synthesis route of the Rh catalyst grafted onfluoroacrylate...

Figure 9.8 (a) Schematic representation of oxidized to H. (b) Structure of the the structure and reactivity of the bio-inspired membrane-electrode assembly used for the H2-evolving nickel catalyst grafted on a carbon electrocatalytic characterization of the nanotube [51]. Electrons are exchanged Ni-functionalized CNTs under conditions... 

Figure 27 Hydrolysis of / ara-nitrophenyl choline carbonate by Mn(salen) catalyst grafted on a resorcinarene cavity that interacts with ammonium groups. (a) Resorcinarene ligand (b) host-guest adducts (c) reactivity.

An important direction in the development of heterogeneous catalysts grafted onto mesoporous silicas is exploiting the rich chemistry of metal cluster catalysts bearing carbonyl or alkylphosphine ligands or both is exploiting a broad library of trialkylsilyl precursors with cluster functions, developed in particular by Bronstein et al. [28]. 

Typical values for mf n are 0.5 to 2.5. Gommercially used bases include sodium hydroxide, potassium hydroxide, calcium hydroxide (lime), magnesium hydroxide, sodium carbonate, sodium alurninate, calcium carbonate, or various mixtures. For certain appHcations, PAG can be made from waste grades of aluminum chloride [7446-70-0] such as spent catalyst solutions from Friedel-Grafts synthesis (see Friedel-Grafts reaction). 

Friedel-Grafts Reactions. In the presence of Friedel-Crafts catalysts, succinic anhydride reacts with alkyl benzenes to form alkylben2oylpropionic acids (103), eg, the reaction with iadane gives a 97% yield of 4-oxo-(4,5-iQdanyl)butyric acid (eq. 6). 

Copolymers of VDC can also be prepared by methods other than conventional free-radical polymerization. Copolymers have been formed by irradiation and with various organometaHic and coordination complex catalysts (28,44,50—53). Graft copolymers have also been described (54—58). 

Another important use of BCl is as a Ftiedel-Crafts catalyst ia various polymerisation, alkylation, and acylation reactions, and ia other organic syntheses (see Friedel-Crafts reaction). Examples include conversion of cyclophosphasenes to polymers (81,82) polymerisation of olefins such as ethylene (75,83—88) graft polymerisation of vinyl chloride and isobutylene (89) stereospecific polymerisation of propylene (90) copolymerisation of isobutylene and styrene (91,92), and other unsaturated aromatics with maleic anhydride (93) polymerisation of norhornene (94), butadiene (95) preparation of electrically conducting epoxy resins (96), and polymers containing B and N (97) and selective demethylation of methoxy groups ortho to OH groups (98). 

Type AD-G is used in an entirely different sort of formulation. The polymer is designed for graft polymerisation with methyl methacrylate. Typically, equal amounts of AD-G and methyl methacrylate are dissolved together in toluene, and the reaction driven to completion with a free-radical catalyst, such as bensoyl peroxide. The graft polymer is usually mixed with an isocyanate just prior to use. It is not normally compounded with resin. The resulting adhesive has very good adhesion to plasticised vinyl, EVA sponge, thermoplastic mbber, and other difficult to bond substrates, and is of particular importance to the shoe industry (42,43). 

The cross-linking stage is facilitated by the use of a cross-linking catalyst, which is typically an organo-tin compound. A number of variations of this process exist and in one of these compounding, grafting and extmsion onto wire are carried out in the same extruder. 

T. C. Chung, New utilities of metallocene catalysts and borane reagents in the functionalization and block/graft reactions of polyolefins, MetCon 95 Proceedings, USA, May 1995. 

If a vinyl monomer is polymerized in the presence of cellulose by a free radical process, a hydrogen atom may be abstracted from the cellulose by a growing chain radical (chain transfer) or by a radical formed by the polymerization catalyst (initiator). This leaves an unshared electron on the cellulose chain that is capable of initiating grafting. As cellulose is a very poor transfer agent [10], very little copolymer results from the abstraction of hydrogen atoms by a growing chain radical. The... 

The grafting reaction requires primary or secondary aliphatic hydroxyl functions as initiation sites and uses Ce4+ ions as the catalyst. This type of grafting was first developed by Mino and Kaizerman and applied to preparation of the polyacrylamide-polyvinylalcohol copolymer [102],... 

Anionic polymerization of pivalolactone with the polystyrene anion produced only homopolymer mixtures, but the polystyrene carboxylate anion was able to give a block copolymer336. The block efficiency depends on catalyst ratio and conversion because the initiation step is slow compared with propagation337. Tough and elastic films were obtained by graft copolymerization or block copolymerization of pivalolactone onto elastomers containing tetrabutylammonium carboxylate groups338,339. ... 

Synthesis of comb (regular graft) copolymers having a PDMS backbone and polyethylene oxide) teeth was reported 344). These copolymers were obtained by the reaction of poly(hydrogen,methyl)siloxane and monohydroxy-terminated polyethylene oxide) in benzene or toluene solution using triethylamine as catalyst. All the polymers obtained were reported to be liquids at room temperature. The copolymers were then thermally crosslinked at 150 °C. Conductivities of the lithium salts of the copolymers and the networks were determined. 

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