Nonionic catalytic activity

The rate constants for the catalysed Diels-Alder reaction of 2.4g with 2.5 (Table 2.3) demonstrate that the presence of the ionic group in the dienophile does not diminish the accelerating effect of water on the catalysed reaction. Comparison of these rate constants with those for the nonionic dienophiles even seems to indicate a modest extra aqueous rate enhancement of the reaction of 2.4g. It is important to note here that no detailed information has been obtained about the exact structure of the catalytically active species in the oiganic solvents. For example, ion pairing is likely to occur in the organic solvents. 

In this area, recent unrelated efforts of the groups of Bhattacharya and Fife toward the development of new aggregate and polymer-based DAAP catalysts deserve mention. Bhattacharya and Snehalatha [22] report the micellar catalysis in mixtures of cetyl trimethyl ammonium bromide (CTAB) with synthetic anionic, cationic, nonionic, and zwitterionic 4,4 -(dialkylamino)pyridine functional surfactant systems, lb-c and 2a-b. Mixed micelles of these functional surfactants in CTAB effectively catalyze cleavage of various alkanoate and phosphotriester substrates. Interestingly these catalysts also conform to the Michaelis-Menten model often used to characterize the efficiency of natural enzymes. These systems also demonstrate superior catalytic activity as compared to the ones previously developed by Katritzky and co-workers (3 and 4). 

The thermoregulated phase-transfer function of nonionic phosphines has been proved by means of the aqueous-phase hydrogenation of sodium cinnamate in the presence of Rh/6 (N =32, R = n-CsHu) complex as the catalyst [16]. As outlined in Figure 2, an unusual inversely temperature-dependent catalytic behavior has been observed. Such an anti-Arrhenius kinetic behavior could only be attributed to the loss of catalytic activity of the rhodium complex when it precipitates from the aqueous phase on heating to its cloud point. Moreover, the reactivity of the catalyst could be restored since the phase separation process is reversible on cooling to a temperature lower than the cloud point. 

More recently, the application scope of thermoregulated phase-separable transition metal complex with nonionic phosphine ligand has been expanded from hy-droformylation to hydrogenation, and the central metal varied from Rh to Ru. The first experimental study is the hydrogenation of styrene catalyzed by thermoregulated phase-separable Ru3(CO)12/PETPP complex catalyst. Under the conditions of Ph2 = 2.0 MPa, T=90°C, catalyst/substrate (mol/mol) = 1/1000, 3 hours, the Ru3(CO)12/PETPP complex catalyst exhibited good activity (Table 5). Compared with other catalysts, Ru3(CO)12/PETPP complex showed the same catalytic activity compared to the lipophilic Ru3(CO)9(TPP)3, while the hydrophilic Ru3(CO)9-(TPPTS)3 and Ru3(CO)9(TPPMS)3 are less active (Table 6). 

A sample of montmorillonite was pillared with aluminium polyoxycations in presence of different amounts of tween-80, a nonionic surfactant, ranging from 0.01 to 0.20 mmol/meq of clay. The amount of aluminium sorbed was found to vary with the amount of surfactant added during pillaring. Vapour phase catalytic activity of the samples for alkylation of toluene with methanol in a fixed bed down flow reactor showed that the rate of deactivation, in general, increased with decrease in the pillar density. The samples treated with 0.06 to 0.08 mmol/meq of surfactant showed the lowest deactivation and also an enhancement in the mesopores which did not change on calcining to 540 C. Suppression of deactivation is attributed to the distribution of pillars by the surfactant in such a way as to decrease the coke formation. 

Palladium on charcoal, as the most simple Pd(0)-species, is capable of catalysing the coupling of aryl halides to produce biaiyls. The molecular hydrogen is also a suitable stoichiometric reductant, compatible with Pd-C, which converts the Pd(Il) back to the catalytically active Pd(0)-species as illustrated in the method J. The reactions have been conducted in water in the presence of nonionic surfactant, PEG-400, to provide the water soluble forms, e.g. micelles, of hydrophobic substrates such as chlorobenzene. Due to the nature of reductant, molecular hydrogen, the reactions were performed in an autoclave under pressure of hydrogen (4 atm.). This reaction is apparently an important basis for environmental friendly, inexpensive and economic process for scale-up production of symmetrical biaryls, however, the formation of dehalogenated products (up to 45%) is still an unsolved side-reaction. 

Sun, C. Bao, H. Determination of trace iron (111) by catalytic photometry in the presence of nonionic surface active agent. Fushun Shiyou Xueyuan Xuebao 2000, 20,16-18 Chem. Abstr. 2001,134, 125262. 

It is not necessarily true that formation of nonionized complexes will reduce the catalytic activity of metals on fat oxidation. The great increase in fat oxidase activity of iron porphyrins over inorganic iron has already been discussed. Still more active catalysts are formed by complexing iron with phenanthroline (Simon et al., 1944). 

Stable platinum colloids were prepared by reducing dihydrogen hexachloroplatinate H2PtCl in the presence of protective polymers. In this chapter, we report the results for several nonionic polymers and cationic polyelectrolytes and their ability to stabilize such platinum colloids. The sizes of the platinum particles were investigated by transmission electron microscopy (TEM) and found to be in the nanometer size range. The catalytic activity of these systems was tested by the hydrogenation of cyclohexene, dsp-cyclooctene, and 1-hexene. A variety of polymer-protected platinum nanoparticles showed catalytic activity, and conversions of 100 % were obtained in most cases. 

Remarkably nonionic complexes of nickel containing chelating ligands of the acetylacetonate type are able to convert olefins such as butene, hexene, or octene into predominantly linear structures. The acidity of the ligand is essential for a catalytic activity and best results are obtained with hexafluoro (or trifluoro) acetylacetone (Table V). The oligomers contain all... 

In addition to AOT-based microemulsions, a nonionic reverse micelle (GGDE/TX-100), containing a functional nonionic surfactant N-gluconyl glutamic acid didecyl ester (GGDE) and Triton X-100 (TX-lOO), was evaluated as a good alternative in which YADH exhibits higher catalytic activity and stability [89]. 

Phosphatidylcholine was demonstrated to play an essential role in the biological activity of the microsomal hydroxylation system (Lu et al., 1969), functioning in some poorly understood manner in electron transfer from NADPH to cytochrome P-450. Reconstitution studies of the microsomal hydroxylation system from its isolated components have demonstrated the ability of a number of nonionic detergents in low concentration to substitute for phospholipid in the process of benzphetamine N-demethylation (Lu et al., 1974). While restoration of catalytic activity was not complete, it is likely that the natural lipid and the detergents act in a similar manner, perhaps enhancing the interaction of the two proteins of this system. 

For UP, adding nonionic surfactants into AOT reverse micelles could reduce but not eliminate the electrostatic interaction between UP and the inner surface of the AOT reverse micelles [13-16]. So a reverse micelle composed of nonionic surfactants may be a good choice. However, most of the commerdaUy available nonionic surfactants need cosurfactants such as straight-chain alcohols to form a W/O microemulsion, and the size of the reverse micelles can be tuned only in a narrow range [17-19]. The use of commercially available nonionic surfactant to enhance the catalytic activity of an enzyme is limited by the size mismatch between... 

Figure 15.4 Mechanism of the effect of a nonionic surfactant on the catalytic activity of enzyme in cationic reverse micelles.

A catalytic cycle is composed of a series of elementary processes involving either ionic or nonionic intermediates. Formation of covalently bound species in the reaction with surface atoms may be a demanding process. In contrast to this, the formation of ionic species on the surface is a facile process. In fact, the isomerization reaction, the hydrogenation reaction, and the H2-D2 equilibration reaction via ionic intermediates such as alkyl cation, alkylallyl anion, and (H2D)+ or (HD2)+ are structure-nonrequirement type reactions, while these reactions via covalently bound intermediates are catalyzed by specific sites that fulfill the prerequisites for the formation of covalently bound species. Accordingly, the reactions via ionic intermediates are controlled by the thermodynamic activity of the protons on the surface and the proton affinity of the reactant molecules. On the other hand, the reactions via covalently bound intermediates are regulated by the structures of active sites. 

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