Reusable catalysts

Scandium trifluoromethansulfonate (Sc(OTf)3). A novel reusable catalyst in the Diels-Alder reaction [108]... 

Rossi, L.M., Silva, F.P., Vono, L.L.R., Kiyohara, P.K., Duarte, E.L., Itri, R., Landers, R. and Machado, G. (2007) Superparamagnetic nanopartide-supported palladium a highly stable magnetically recoverable and reusable catalyst for hydrogenation reactions. Green Chemistry, 9 (4), 379-385. 

Corma, A. and Garcia, H. (2006) Silica-bound homogenous catalysts as recoverable and reusable catalysts in organic synthesis. Advanced Synthesis and Catalysis, 348 (12-13), 1391-1412. 

Mevellec, V., Roucoux, A., Ramirez, E., Philippot, K. and Chaudret, B. (2004) Surfactant-stabilized aqueous iridium(O) colloidal suspension an effident reusable catalyst for hydrogenation of arenes in biphasic media. Advanced Synthesis and Catalysis, 346 (1), 72-76. 

Bigi F, Chesini L, Maggi R, Sartori G (1999) Montmorillonite KSF as an inorganic, water stable, and reusable catalyst for the knoevenagel synthesis of coumarin-3-carboxylic acids. J Org Chem 64 1033-1035... 

V. K. Rajput and B. Mukhopadhyay, Sulfuric acid immobilized on silica An effcient reusable catalyst for the synthesis of O-isopropylidene sugar derivatives, Tetrahedron Lett., 47 (2006) 5939-5941. 

J. S. Yadav, S. Raghavendra, M. Satyanarayana, and E. Balanarsaiah, Phospho-molybdic acid supported on silica gel An efficient, mild and reusable catalyst for the chemoselective hydrolysis of acetonides, Synlett, 16 (2005) 2461-2464. 

The group of Ley has reported on the use of palladium-doped perovskites as recyclable and reusable catalysts for Suzuki couplings [151]. Microwave-mediated cross-couplings of phenylboronic acid with aryl halides were achieved within 1 h by utilizing the supported catalyst (0.25 mol% palladium) in aqueous 2-propanol (Scheme 7.127). The addition of water was crucial as attempted transformations in non-aqueous mixtures did not proceed. 

Roucoux A, Schultz J, Patin H (2002) Reduced transition metal colloids a novel family of reusable catalysts. Chem Rev 102 3757-3778 Toyooka K, Kanamitsu N, Yoshimra M (2004) PCT international application W02004/048332... 

A Soluble Polymer-Bound Ruthenium Carbene Complex A Robust and Reusable Catalyst for Ring-Qosing Olefin Metathesis, Q. Yao, Angew. Chem. 2000,... 

The standard Hantzsch procedure does not involve the use of additive or reagent, but to improve reaction time and yield, the use of a large variety of catalysts has been developed, which makes possible to operate at room temperature in some cases. In the last few years, particular efforts have been devoted to the utilization of low cost, nontoxic, environmentally benign and reusable catalysts [22, 29 0]. 

Biemeyer N, Ley SV, Ramarao C, Shirley IM, Smith SC. Palladium acetate in pol3mrea microcapsules a recoverable and reusable catalyst for hydrogenations. Synlett 2002 1843-1844. 

Several new effective Friedel-Crafts catalysts have been developed. These include triflate93 (trifluoromethanesulfonate) derivatives of boron, aluminum, and gallium [M(0S02CF3)3]. Trichlorolanthanides have also been proved to be active reusable catalysts in benzylation.94 Superacids as catalysts are also very efficient in many Friedel-Crafts alkylations.95... 

The zeolite can easily be regenerated by heating. Similar high para selectivity can be achieved in the case of toluene by use of tert-butyl hypobromite as reagent with zeolite HX in a solvent mixture (CCI4 and ether). ZnBr2 supported on mesoporous silica or acid-activated montmorillonite is a fast, effective, reusable catalyst for the para-bromination of alkylbenzenes.257... 

Yet, research in this area is far from being concluded. Notably, the use of scC02 will undoubtedly open interesting future perspectives, including the quest for more eco-friendly reusable catalysts capable of promoting the fixation of the heterocumu-lene with high yield and selectivity, under as much as possible mild conditions. 

Scheme 6.10 Montmoril Ionite I<10—Fe (111) as reusable catalyst for the quantitative acylation of anisole by p-nitrobenzoyl chloride.

Fe(III)-exchanged fluorotetrasilicic mica acts as a highly effective and reusable catalyst for solvent-free Michael reactions of P-oxo esters with MVK (41a). The immobilized catalyst shows higher activity than homogenous Fe(III) catalysts. Product 42a (cf. Scheme 8.27), for example, is formed in 99% yield even if the catalyst is reused four times [92]. 

Supported versions of such silver-catalyzed, three-component couplings have been recently reported. Silver oxide on multiwall carbon nanotubes or on alumina,102 as well as silver-doped zeolites,103 proved to be efficient and reusable catalysts for such coupling reactions. In the former, water was used as solvent, while in the latter, no solvent was required, making it a truly green process. 

Naves AF, Carmona-Ribeiro AM, Petri DFS (2007) Immobilized horseradish peroxidase as a reusable catalyst for emulsion polymerization. Langmuir 23 1981-1987... 

Roucoux, A., J. Schulz and H. Patin (2002). Reduced transition metal colloids A novel family of reusable catalysts Chemical Reviews, 102(10), 3757-3778. 

Synthesis of the anti-inflammatory drug flurbiprofen by an environmentally efficient Suzuki coupling that uses water as the solvent and palladium on carbon as a reusable catalyst. 

Several non-carbonyl cobalt sources used recently show high efficiency in the catalysis of the PKR. Chung has reported different reusable catalysts like cobalt supported on mesoporous silica or on charcoal that work under high CO pressures [ 127]. Most recently they have described milder conditions with the use of colloidal cobalt nanoparticles, which react at lower CO pressures and can be used in aqueous media [128]. 

LDG, which stands for LENGTH AND DENSITY GRADING, is a new development in the management of spent catalysts. The objective of this new technology developed by Catalyst Recovery, Inc. is to pick out reusable catalyst particles from undesirable catalyst particles. The ability to efficiently segregate individual catalyst particles... 

---