Self-catalyzed effect

Further information about the position of attack and the nature of the rate-determining step was obtained by Grimson and Ridd98 who studied the kinetics of iodination of some deuterio derivatives of imidazole. The kinetic data on the iodination of 2,4,5-trideuterio-imidazole enabled them to calculate the isotope effects for both the uncatalyzed (fcH/fcD = 4.36) and the self-catalyzed (fcH/fcD = 4.47) reactions. A comparison of the istope effects observed in the iodination... 

Shrinkage control and fabric smoothness with little, if any, effect on shade are very desirable properties for textile uses where very sensitive dyestuffs are needed to produce the desired shade. PERMAFRESH 125 can provide this with many direct and reactive dyestuffs. PERMAFRESH 125 is self-catalyzed with a specially selected system. Although designed primarily for knit fabrics it can be used on cellulose containing woven fabrics. 

Minimum effect on shade of reactive and direct dyestuff Self-catalyzed for ease of formulation Good strength retention properties... 

Self-catalyzed transesterification with 2-dimethylaminoethanol in DMF has been found effective in cleaving protected peptides from the Mer-rifield resin, in the absence of side-chain benzyl ester protecting groups (Barton et al., 1973). This mild, virtually racemization-free procedure may prove extremely useful for fragment condensation because it yields N-Z-and iV-Boc-protected peptides. Since the reagent, 2-dimethyl-amino-ethanol, specifically cleaves of the benzylic ester group, the benzyl esters of glutamic acid and aspartic acid, if present, will also be hydrolyzed (Barton et al., 1973 Savoie and Barton, 1974). 

Fig. 63. - Ideal and the actual course of a potential solid-state reaction [3] where two leaclams. A and B, undergo synthesis to product, AB, via transient products, AiB and A3B. The formation of the intermediates depends, besides the standard thennodynamic and kinetic factors, on the local concentration (particle closeness) dependent to the degree of reactant segregation. If mixed ideally the models discussed previously Chapter 8 and 9) are applicable. If the agglomeration is effective the synthesis becomes favorable to produce intermediates and the entire course of reaction becomes self-catalyzed and may even exhibit oscillatory character. ...

Neutral Fat Saponification. In the saponification of triglycerides with an alkali, the two reactants are rather immiscible. Because saponification is a bimolecular nucleophilic substitution (Sn ), the kinetic rate enhancement of this reaction is achievable by both a high-shear mixing and an increase in the reaction temperature during the processing. The saponifiction reaction is self-catalyzed to some extent the formation of soap product effects the emulsification of the two immiscible reactants, causing an acceleration of the reaction rate. 

These oscillatory changes were observed not only for the optically pure enantiomers but also with the racemic 2-phenyl propionic acid sample. The molecular mechanism was attributed to keto-enol tautomerism that is acid catalyzed as well. All the profens are carboxylic acids with relatively well-pronounced electrolytic dissociation. Thus, the keto-enol transenantiomerization of profens in aqueous media was considered justified because of the self-catalytic effect of the protons originating from the dissociated carboxyl groups. Since reducing the temperature stabilizes the short-lived tautomers there was greater amplitude of oscillation at 6°C than at 22- C. 

In low density reactant compacts, the reaction is believed to involve gas phase oxygen diffusion whereas under conditions of improved contact, in high-density material, the mobile species is identified as Fe2+. The metal catalyzes decomposition of the oxidant (KMn04), an effect that is inhibited by small quantities of certain additives (e.g. NaF). There is a large and specialist literature devoted to self-heating reactions. 

Multiparticle collision dynamics provides an ideal way to simulate the motion of small self-propelled objects since the interaction between the solvent and the motor can be specified and hydrodynamic effects are taken into account automatically. It has been used to investigate the self-propelled motion of swimmers composed of linked beads that undergo non-time-reversible cyclic motion [116] and chemically powered nanodimers [117]. The chemically powered nanodimers can serve as models for the motions of the bimetallic nanodimers discussed earlier. The nanodimers are made from two spheres separated by a fixed distance R dissolved in a solvent of A and B molecules. One dimer sphere (C) catalyzes the irreversible reaction A + C B I C, while nonreactive interactions occur with the noncatalytic sphere (N). The nanodimer and reactive events are shown in Fig. 22. The A and B species interact with the nanodimer spheres through repulsive Lennard-Jones (LJ) potentials in Eq. (76). The MPC simulations assume that the potentials satisfy Vca = Vcb = Vna, with c.,t and Vnb with 3- The A molecules react to form B molecules when they approach the catalytic sphere within the interaction distance r < rc. The B molecules produced in the reaction interact differently with the catalytic and noncatalytic spheres. 

Self-assembly processes in nature are sometimes catalyzed by enzymes. Zeolites are, in many ways, the inorganic counterparts of enzymes, with their ability to selectively bind other substances and perform catalysis. Can templates or catalysts be effective in increasing rates and reducing defects in a wide range of nanostructured materials ... 

In contrast to that of solvents, the effect of the electrolyte solute, LiPFe, on the thermal decomposition of the cathode, LiCo02, was found to be suppression instead of catalyzation. The SHR of a partially delithiated cathode was measured in a series of electrolytes with various salt concentrations, and a strong suppression of the self-heating behavior was found as the concentration of LiPEe increased above 0.50 M. The mechanistic rationale behind this salt effect is still not well understood, but the authors speculated that the salt decomposition coated the cathode with a protective layer that acted as a combustion retardant. On the basis of these results, the authors recommended a higher salt concentration (>1.50 M) for LiCo02-based lithium ion cells is preferred in terms of thermal safety. 

The RNA world hypothesis requires a nucleotide polymer to reproduce itself. Can a ribozyme bring about its own synthesis in a template-directed manner The self-splicing rRNA intron of Tetrahymena (Fig. 26-26) catalyzes the reversible attack of a guanosine residue on the 5 splice junction (Fig. 26-37). If the 5 splice site and the internal guide sequence are removed from the intron, the rest of the intron can bind RNA strands paired with short oligonucleotides. Part of the remaining intact intron effectively acts as a template for the... 

Important extensions of proline catalysis in direct aldol reactions were also reported. Pioneering work by List and co-workers demonstrated that hydroxy-acetone (24) effectively serves as a donor substrate to afford anfi-l,2-diol 25 with excellent enantioselectivity (Scheme 11) [24]. The method represents the first catalytic asymmetric synthesis of anf/-l,2-diols and complements the asymmetric dihydroxylation developed by Sharpless and other researchers (described in Chap. 20). Barbas utilized proline to catalyze asymmetric self-aldoli-zation of acetaldehyde [25]. Jorgensen reported the cross aldol reaction of aldehydes and activated ketones like diethyl ketomalonate, in which the aldehyde... 

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