Catalysts comparative studies

The conclusion may be drawn that the data obtained of comparative studies of olefin polymerization by the one-component catalyst (TiCl2) and two-component systems (TiCl2 + AlEtxCl ) confirm the concept of monometallic active centers on the surface of titanium chlorides developed by Cossee and Arlman (170-173). 

Cationic bis(oxazoline) and pyridil-bis(oxazoline) Cu(ll) and Zn(ll) Lewis-acid catalysts. A comparative study in catalysis of Diels-Alder and aldol reactions [101]... 

The catalytic pyrolysis of R22 over metal fluoride catalysts was studied at 923K. The catalytic activities over the prepared catalysts were compared with those of a non-catalytic reaction and the changes of product distribution with time-on-stream (TOS) were investigated. The physical mixture catalysts showed the highest selectivity and yield for TFE. It was found that the specific patterns of selectivity with TOS are probably due to the modification of catalyst surface. Product profiles suggest that the secondary reaction of intermediate CF2 with HF leads to the formation of R23. 

A comparative study ethylene/l-hexene copolymerization with [t-BuNSiMe2Flu]TiMe2 catalyst via various activators... 

GP 2] [R 2] A comparative study with laser-LIGA OAOR silver, etched OAOR silver and sawn Aluchrom catalyst was reported (Table 3.2) [4]. The selectivity was 44-69% (laser-LIGA OAOR silver), 38-69% (etched OAOR silver) and 42-58% (sawn Aluchrom catalyst) for details of the experimental protocols, see [4]. The conversions were 2-15% (laser-LIGA OAOR silver) 5-20% (etched OAOR silver), and 2-6% (sawn Aluchrom catalyst). The space-hme yields were 0.01-0.07 t h m (laser-LIGA OAOR silver), 0.03-0.13 t h m (etched OAOR silver), and 0.01-0.061 h m (sawn Aluchrom catalyst). 

Allylic substitutions catalysed by palladium NHC complexes have been studied and the activity and selectivity of the catalysts compared to analogous Pd phosphine complexes. A simple catalytic system involves the generation of a Pd(NHC) catalyst in situ in THF, from Pdj(dba)j, imidazolium salt and Cs COj. This system showed very good activities for the substitution of the allylic acetates by the soft nucleophilic sodium dimethyl malonate (2.5 mol% Pdj(dba)3, 5 mol% IPr HCl, 0.1 equiv. C (CO ), THF, 50°C) (Scheme 2.22). Generation of the malonate nncleophile can also be carried out in situ from the dimethyhnalonate pro-nucleo-phile, in which case excess (2.1 equivalents) of Cs COj was used. The nature of the catalytic species, especially the number of IPr ligands on the metal is not clear. 

In 2001, Furstner reported the preparation and characterisation of the NHC-Ru complex 22 containing iV,iV -bis[2,6-(diisopropyl)phenyl]imidazolidin-2-ylidene (SIPr) [29] (Fig. 3.6), which is the congener of complex 20. Subsequently, Mol and co-workers revealed that complex 22 was a highly active metathesis initiator [30]. More recent comparative studies showed that catalyst 22 could catalyse the RCM of 1 faster than any other NHC-Ru catalyst, while it was not stable enough to obtain complete conversion in the RCM of 3 and was inefficient for the construction of the tetrasubstituted double bond of cyclic olefin 6 [31]. 

Grunwaldt J-D, Maciejewski M, Becker OS, et al. 1999. Comparative Study of Au/Ti02 and AU/Z1O2 catalysts for low-temperature CO oxidation. J Catal 186 458-469. 

The oxidation of alcohols is an important reaction in organic chemistry. While this transformation is traditionally performed in organic solvents, the use of aqueous orgarric solutions has just recently become a field of intense study (1-6). The effect of water on transition metal-catalyzed reactions, however, remains widely unexplored as most of these reactions require dry organic solvents to avoid decomposition of the transition metal catalyst, of water sensitive reagents, and/or intermediates by a nucleophilic attack of water (1). Comparative studies focusing on the effect of water as a co-solvent on the catalyst and the proceedings of a reaction are therefore rare (7). 

The relative reactivity of Friedel-Crafts catalysts has not been described in a quantitative way, but comparative studies using a series of benzyl halides has resulted in the qualitative groupings shown in Table 11.1. Proper choice of catalyst can minimize subsequent product equilibrations. 

Joubert, E., Courtois, X., Marecot, P. et al. (2006) NO reduction by hydrocarbons and oxygenated compounds in 02 excess over Pt/Al203 catalyst. A comparative study of the efficiency of different reducers (hydrocarbons and oxygenated compounds), Appl. Catal. B 64, 103. 

Demidouk, V., Ravi, V., Chae, J.-O. et al. (2005) Pt-Al203 catalyst and discharge plasma pre-treatment techniques for enhancing selective catalytic reduction of nitrogen oxides A comparative study, React. Kinet. Catal. Lett. 85, 239-44. 

Prochiral aryl and dialkyl ketones are enantioselectively reduced to the corresponding alcohols using whole-cell bioconversions, or an Ir1 amino sulfide catalyst prepared in situ.695 Comparative studies show that the biocatalytic approach is the more suitable for enantioselective reduction of chloro-substituted ketones, whereas reduction of a,/ -unsaturated compounds is better achieved using the Ir1 catalyst. An important step in the total synthesis of brevetoxin B involves hydrogenation of an ester using [Ir(cod)(py) P(cy)3 ]PF6.696... 

These results prompted us to ask how do these catalysts compare with enzymes What is the rate of uncatalyzed alkyne hydration Our search of the literature thus far has not revealed a study of the uncatalyzed reaction. 

Freeder, B. G. et al., J. Loss Prev. Process Ind., 1988, 1, 164-168 Accidental contamination of a 90 kg cylinder of ethylene oxide with a little sodium hydroxide solution led to explosive failure of the cylinder over 8 hours later [1], Based on later studies of the kinetics and heat release of the poly condensation reaction, it was estimated that after 8 hours and 1 min, some 12.7% of the oxide had condensed with an increase in temperature from 20 to 100°C. At this point the heat release rate was calculated to be 2.1 MJ/min, and 100 s later the temperature and heat release rate would be 160° and 1.67 MJ/s respectively, with 28% condensation. Complete reaction would have been attained some 16 s later at a temperature of 700°C [2], Precautions designed to prevent explosive polymerisation of ethylene oxide are discussed, including rigid exclusion of acids covalent halides, such as aluminium chloride, iron(III) chloride, tin(IV) chloride basic materials like alkali hydroxides, ammonia, amines, metallic potassium and catalytically active solids such as aluminium oxide, iron oxide, or rust [1] A comparative study of the runaway exothermic polymerisation of ethylene oxide and of propylene oxide by 10 wt% of solutions of sodium hydroxide of various concentrations has been done using ARC. Results below show onset temperatures/corrected adiabatic exotherm/maximum pressure attained and heat of polymerisation for the least (0.125 M) and most (1 M) concentrated alkali solutions used as catalysts. 

Marchal, N. Kasztelan, S., and Mignard, S., A comparative study of catalysts for the deep aromatic reduction in hydrotreated gas oil. In Catalytic Hydroprocessing of Petroleum and Distillates, M.C. oballa, S.S.S. editor. 1994, Marcel Dekker New York. pp. 315-327. 

Palladium catalyzed reaction of aryl halides and olefins provide a useful synthetic method for C-C bond formation reaction [171, 172], The commonly used catalyst is palladium acetate, although other palladium complexes have also been used. A sol-vent-free Heck reaction has been conducted in excellent yields using a household MW oven and palladium acetate as catalyst and triethylamine as base (Scheme 6.51) [173], A comparative study revealed that the longer reaction times and deployment of high pressures, typical of classical heating method, are avoided using this MW procedure. 

Hilaire, S., Wang, X., Luo, T., Gorte, R.J., and Wagner, J. 2001. A comparative study of water-gas-shift reaction over ceria supported metallic catalysts. Appl. Catal. A Gen 215 271-78. 

Table 41.7 Comparative studies of the biphasic hydrogenation reactions of arenes in [BMIM][BF4] and water with [H4Ru4( 76-C6H6)4][BF4]2 as the catalyst precursor [88].

Another substituted derivative of BINAP was used by Lemaire et al. [109]. The ammonium salt catalysts (7 and 8, Fig. 41.10) were prepared in situ from the bro-mohydrates and [Ru( /3-2-methylallyl)2(/72-COD)], and immobilized in several ionic liquids. By comparative studies of the hydrogenation of ethyl acetoacetate, the best results were obtained with imidazolium- and pyridinium-containing ionic liquids. No significant ee was observed with the phosphonium salt. This observation was attributed to problems of solubility and to the ability of complexation for the phosphonium ion. From the anionic side, use of the [BF4] anion appeared superior compared to [PF6] and [(CF3S02)2N]A... 

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