Catalysis without

Hie process was S 2 -selective in the presence of catalytic amounts of ligands fS)-32 or Is, R, Rj-43 and CufOTf )2- Hiis is another example of ligand-accelerated catalysis without the ligand tlie reaction was much slower and proceeded witli low regioselectivity. 

For this specific task, ionic liquids containing allcylaluminiums proved unsuitable, due to their strong isomerization activity [102]. Since, mechanistically, only the linkage of two 1-butene molecules can give rise to the formation of linear octenes, isomerization activity in the solvent inhibits the formation of the desired product. Therefore, slightly acidic chloroaluminate melts that would enable selective nickel catalysis without the addition of alkylaluminiums were developed [104]. It was found that an acidic chloroaluminate ionic liquid buffered with small amounts of weak organic bases provided a solvent that allowed a selective, biphasic reaction with [(H-COD)Ni(hfacac)]. 

Transesterification has been carried out with phase-transfer catalysis, without an added solvent. In another procedure, RCOOR are converted to RCOOR" by treatment of the ester and an alcohol R OH with n-BuLi, which converts the R"OH to R"OLi. ... 

Cascade catalysis without Intermediate products recovery... 

The most important clue to explain the essence of chemical reaction has probably been the discovery of catalysis, without which a chemical industry would not exist. Catalysis is not understood in detail but it clearly dictates the course of a reaction by re-inforcing the spontaneous fluctuations that occur in a reaction medium. The most dramatic effects are produced in autocatalysis where a reaction product acts as a catalyst. Such feedback... 

Since better selectivity was obtained when the ligands were removed from the dihydropyran-derivatized polymer support, after synthesis they were cleaved from the polymer and used in catalysis without purification. Comparable selectivities were obtained with ligands that were used directly without purification and selected examples where the ligands were purified prior to use. For such an approach to be useful in catalyst development, it is critical that the material from the synthesis be of sufficient purity to be used without purification. 

Decreasing the number of reaction steps via a one-pot reaction associating two or more catalytic steps. This can be achieved by multistep reactions carried out by cascade catalysis without intermediate product recovery, thus decreasing the operating time and reducing considerably the amount of waste produced. 

Cascade catalysis without recovery of intermediate products may require more than two steps, involving enzymatic, homogeneous, and heterogeneous catalysis. Several examples of this approach have been given [72, 73] one of the most representative consists of a four-step conversion of glucoside into aminodeoxysugar without intermediate product recovery. 

The regiochemistry observed in the EGA-catalyzed displacement of methoxyl group with nucleophiles is promising For example, the carbenium ion formed from compound 29 in methanolic solution is trapped to produce the thermodynamically stable compound 30. However, in CHjClj, a concerted push-pull mechanism ( push by nucleophile and pull by EGA) is operative leading to the exclusive formation of 31. 1-Menthone 32 can be acetalized by EGA catalysis without epimerization at C-2... 

The various mechanisms outlined in Section 2 (p. 16) can, in principle, all be subject to nucleophilic catalysis. Without enumerating them again, the arguments and discussions of Section 3 can readily be applied to these substitutions with rearrangement. 

Loupy, A. Sansoulet, J. Diez-Barra, E. Carrillo, J. R. Phase transfer catalysis without solvent. Alkylation of phenol and derivatives. Synth. Commun. 1991, 21, 1465—1471. 

One process that may offer benefits of acid catalysis without the drawbacks of H2S04 is the use of carbonic acid. The pH of carbonic acid is determined by the partial pressure of C02 in contact with water, and thus it can be neutralized by releasing the reactor pressure. Carbonic acid is relatively mild and hence does not offer the same hydrolytic capability of H2S04. However, van Walsum (25) has demonstrated that at temperatures on the order of 200°C, carbonic acid does exhibit a catalytic effect on the hydrolysis of xylan. Van Walsum (25) observed an enhanced release of xylose and low-degree-of-polymerization xylan oligomers compared to pretreatment... 

It was generally believed that the characteristic non-linear dependence of the rate constant on n was associated with the existence of the preequilibrium (Bell, 1941). For the mutarotation of glucose a linear variation of rate constant with n had been reported (Hamill and La Mer, 1936c) and cited as an example of a mechanism of acid catalysis without pre-equilibrium. 

The last chapters might have led to the conclusion that transition metals will always react with allenes bearing functional groups in the direct neighborhood. But this is not automatically the case, such substrates can often be prepared by transition metal catalysis without reacting to another product in situ. 

Ribonuclease A is a member of a group of enzymes that cleave RNA using general acid-base catalysis without a metal ion in the enzyme. In ribonuclease A, such catalysis is performed by two imidazoles of histidine units, one as the free base (Im) and the other, protonated, as the acid (ImH+). To mimic this in an artificial enzyme, we prepared (3-cyclodextrin bis-imidazoles 41 [124]. The first one was a mixture of the... 

The newly formed C = C bonds have almost exclusively frans-configur-ation (> 98/2), and the excellent enantioselectivity, with which the reaction product is obtained (ee up to 98%), illustrates the considerable potential of complex 34 in asymmetric catalysis. Furthermore, this compound is air stable, may be purified by chromatography on silica, does not require dried solvents and may be reused after catalysis without significant loss in enantioselectivity. Since 34 was found to be slightly less active in olefin metathesis... 

A fundamental advance in the theory of adsorption phenomena was made in 1916 when Langmuir suggested that adsorption was to be regarded as a chemical process occurring on an energetically uniform surface and that the adsorbed phase was a unimolecular layer of non-interactive molecules. However, it soon became impossible to describe some important phenomena of catalysis without denying the concept of a uniform surface. 

In this context it is interesting to note the recent reports of fluorous catalysis without fluorous solvents [68]. The thermomorphic fluorous phosphines, P[(CH2)m(CF2)7CF3]3 (m=2 or 3) exhibit ca. 600-fold increase in n-octane solubility between -20 and 80 °C. They catalyze the addition of alcohols to methyl propiolate in a monophasic system at 65 °C and can be recovered by precipitation on cooling (Fig. 7.20) [68]. Similarly, perfluoroheptadecan-9-one catalyzed the epoxidation of olefins with hydrogen peroxide in e.g. ethyl acetate as solvent [69]. The catalyst could be recovered by cooling the reaction mixture, which resulted in its precipitation. 

Tzschucke, C.C., Marker , C., Glatz, H., and Bannwarth, W. 2002. Fluorous biphasic catalysis without perfluorinated solvents Application to Pd-mediated Suzuki and Sonogashira couplings. Angewandte Chemie International Edition, 41 4500-03. 

Under microwave irradiation, carbazole reacted remarkably fast with a number of alkyl halides to give Af-alkyl derivatives of carbazole (82) (Bogdal et al., 1997). The reaction was carried out with high yields by simply mixing carbazole with an alkyl halide, which was adsorbed on potassium carbonate. A facile synthesis of a series of A-alkylpyrrolidino fullerenes (83) by phase transfer catalysis without solvent under microwave irradiation has been described by De la Cruz et al. (1998), while Adamczyk and Rege (1998) have illustrated the dramatic rate acceleration for A-sulfopropylation of heterocyclic compounds using 1,3-propane sultone under microwave irradiation affording the A-sulfopropylated compounds in 68-95% yield. 

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