Anionic catalysis

Experience in PTC with cationic catalysts showed that, in general, the most suitable compounds have symmetrical structures, are lipophilic, and have the active cationic charge centrally located or sterically shielded by substituents. For anionic catalysis sodium tetraphenylborate fulfills these conditions, but it is not stable under acidic conditions. However, certain derivatives of this compound, namely sodium tetra-kis[3,5-bis(trifluoromethyl)phenyl]borate (TFPB, 12.162) and sodium tetrakis[3,5-bis-(l,l,l,3,3,3-hexafluoro-2-methoxy-2-propyl)phenyl]borate (HFPB) are sufficiently stable to be used as PTC catalysts for azo coupling reactions (Iwamoto et al., 1983b 1984 Nishida et al., 1984). These fluorinated tetraphenylborates were found to catalyze strongly azo coupling reactions, some of which were carried out with the corresponding diazotization in situ. 

The data can be explained, however, by a general anionic catalysis in which the anions encourage the removal of the water molecule from the primary coordination sphere, presumably by hydrogen bonding. The anion does not have to be the one which will eventually enter the complex, and the results suggest that CIO4- is better than N03- at abstracting the water molecule, with Cl probably even less effective. 

J. Remarks on the Catalytic Nature of the Coordinated Anionic Catalysis. 46... 

The coordinated anionic catalysis is one of the few examples of heterogeneous catalysis in which it is possible to estimate the actual number of active centers, present on the catalyst surface, which directly take part in the chemical catalytic process. 

This asymmetric end has the alkoxy group of alkyl vinylethers by cationic polymerization, phenyl group of styrene when either anionically or cationicaiiy polymerized, the vinyl group of butadiene under anionic catalysts to poly-1,2-butadiene, the ester and methyl of methylmethacrylate under anionic catalysis and the methyl of propylene by cationic catalysis. 

Anionic Catalysis Several bulky methacrylates afford highly isotactic, optically active polymers having a single-handed helical structure by asymmetric polymerization. The effective polymerization mechanism is mainly anionic but free-radical catalysis can also lead to helix-sense-selective polymerization. The anionic initiator systems can also be applied for the polymerization of bulky acrylates and acrylamides. The one-handed helical polymethacrylates show an excellent chiral recognition ability when used as a chiral stationary phase for high-performance liquid chromatography (HPLC) [97,98]. 

In this Chapter are described the possible mechanisms of electrophilic substitution at saturated carbon, as a preliminary to the discussion of the kinetics of substitution. Additionally, there is a description of the nomenclature that has been used to date. There has been no general agreement on the nomenclature of the mechanisms of electrophilic substitution at saturated carbon, and the notation used in subsequent chapters in the present work can thus usefully be enumerated here. We deal first of all with the fundamental mechanisms, that is with mechanisms that do not involve rearrangement or nucleophilic (anionic) catalysis. 

Two possible mechanisms of decomposition may be written, as shown for the one-anion catalysis, viz. 

Under GTP conditions conjugated dienoates as well as trienoates polymerize faster than methacrylates with anionic catalysis. The dienesilyl acetal 6a is a better initiator than MTS [16] (Scheme 6). 

Base hydrolysis of an ester in presence of metal ions, metal ion catalysis - analysis in terms of kinetically equivalent mechanisms, 330-331 Acid hydrolysis of a charged ester in the presence of SC>4 (aq) anion catalysis - analysis in terms of kinetically equivalent mechanisms, 332-336 Decarboxylation of /3-ketomonocarboxylic acids - formulation of the rate expression from the mechanism, 339-341... 

C 26 Cowie, J. M. G., D. J. Worsfeld and S. Bywater Light-scattering and osmotic pressure study on solutions of polystyrene of narrow molecular-weight distribution produced by anionic catalysis. Trans. Faraday Soc. 57,705 (1961). 

Figure 2. Copolymerization of styrene and methyl methacrylate A Anionic catalysis B Radical catalysis C Cationic catalysis 0 Radical catalyst, this work O AlEti.sCh.s, this work Radical catalyst plus AlEti.sCh.s...

It is important to note that even certain phase-transfer catalysts can be carbonylated to carboxylic acids, not by cobalt tetracarbonyl anion catalysis, but by acetylcobalt tetracarbonyl. This is a slow but high-yield reaction that occurs for quaternary ammonium salts that are capable of forming reasonably stable free radicals. For example, phenylacetic acid is formed in 95% yield from benzyltriethylammonium chloride (benzyl radi-... 

Polyacetals form a different subclass of compounds with oxygen in the backbone chain. In this group are included polymers that contain the group -0-C(R2)-0- and can be formed from the polymerization of aldehydes or ketones. A typical example of a polymer from this class is paraformaldehyde or polyformaldehyde or polyoxymethylene (CH20)n. Polyoxymethylene can be prepared by anionic catalysis from formaldehyde in an inert solvent. Acetylation of the -OH end groups of the polymeric chain is common since it improves the thermal stability of the polymer. Some results reported in literature regarding thermal decomposition of these polymers are indicated in Table 9.2.1 [1]. 

The successful utilization of Reaction Injection Molding (RIM) to fabricate complex polyurethane shapes In a single step from relatively low viscosity streams has led to a search for other chemical systems which can be fabricated by the RIM process. The rapid polymerization of molten caprolactam by anionic catalysis has been utilized to develop attractive nylon RIM systems. The incorporation of a rubber segment In the polymer chain allows the fabrication of high Impact or even elastomeric nylon parts. The combination of a rubber phase with the high melting (215°C) crystalline nylon phase provides useful properties at low temperatures as well as at elevated temperatures. 

Caprolactam is commercially-available at a reasonable price. Molten caprolactam can be polymerized by anionic catalysis in one to five minutes with low exotherm to produce a solid part. The polymerization is essentially complete in that time, although an equilibrium amount of monomer remains dependent upon the temperature (approximately two percent monomer at 160°C). No postcure is necessary. 

Phenyl-2-pyridyl-otolylmethyl methacrylate (PPyo-TMA, 27) having a chiral ester group is known to lead to highly enantiomer-selective and helix-sense-selec-tive polymerization by anionic catalysis.84-86 The selection was also found in the radical polymerization of optically active PPyoTMA having various ee s,... 

Nonactivated olefins fail to react even under strenuous conditions with cyanide anion catalysis. Due to this lack of reactivity coupled with the inherent desirability of the products, much research has focused on developing catalysts for the hydrocyanation of these nonactivated olefins. This has led to nickel, palladium, copper, and cobalt-based catalysts effective at 25-125°C with or without a solvent. Most were developed for the hydrocyanation of unactivated olefins, but many are equally applicable for oAer olefins. For example, much work has been reported on butadiene hydrocyanation employing all of the catalysts mentioned above except palladium. 

In the synthesis of nonionic surfactants (ethoxylated fatty alcohols), it was observed that in acidic catalysis (HBF4, BF3 etherate, SbF5, HSbF6, HPF6, HC104) a more uniform distribution of EO sequences per hydroxyl groups takes places, compared to the ethoxylation in anionic catalysis. 

Figure 4.27 shows that by the ethoxylation of an intermediary propoxylated triol (MW of 4500 daltons) in the presence of a Lewis acid (BF3) or a Bronstedt acid (HBF4), a primary hydroxyl of around 10-15% higher than in anionic catalysis is obtained, at the same EO content. 

The PU elastomers obtained from polyether diols with DMC catalysts (Acclaim Polyols of Bayer) have a spectacular improvement in the majority of physico-mechanical properties when compared with PU elastomers made from the polyether diols, obtained by anionic catalysis. 

Thus, PO is approximately 7500-8000 times more reactive in cationic catalysis than in anionic catalysis, at 30 °C and around 20-25 times more reactive in cationic catalysis, at 30 °C, than PO anionic polymerisation at 120 °C. It was observed that in cationic polymerisation, EO is around 50 times less reactive than PO, at 30 °C. However, in anionic catalysis there is a reversed order EO is around 2-3 times more reactive than PO. 

By propoxylation of this mixture of sucrose - water, in anionic catalysis (KOH or NaOFI), propylene oxide (or EO) react not only with the hydroxyl groups of sucrose but react with water too, which is not an inert compound in this reaction (see Chapter 4). The reaction of PO with water causes diols (propyleglycol, dipropyleneglycol, etc.) to be formed, which decrease markedly the functionality of the resulting sucrose polyol. In order to minimise as much as possible, the diol formation, the propoxylation reaction of the sucrose - water mixture is divided into two steps ... 

Highly hyperbranched polyolic structures are obtained by the polyaddition of an hydroxy epoxidic compound, such as glycidol, to a polyol in cationic [1] or anionic catalysis [11-... 

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