Catalysis results

Fluorochloro, fluorobromo, and fluoroiodoalkanes react selectively with aromatics under boron trifluoride catalysis to provide chloro-, bromo- and iodoalkylated products (48). The higher reactivity of the C—F bond over C—Cl, C—Br, and C—I bonds under Lewis acid catalysis results in the observed products. 

Alkaline Catalysts, Resoles. Resole-type phenoHc resins are produced with a molar ratio of formaldehyde to phenol of 1.2 1 to 3.0 1. For substituted phenols, the ratio is usually 1.2 1 to 1.8 1. Common alkaline catalysts are NaOH, Ca(OH)2, and Ba(OH)2. Whereas novolak resins and strong acid catalysis result in a limited number of stmctures and properties, resoles cover a much wider spectmm. Resoles may be soHds or Hquids, water-soluble or -insoluble, alkaline or neutral, slowly curing or highly reactive. In the first step, the phenolate anion is formed by delocali2ation of the negative charge to the ortho and para positions. 

The relative importance of the potential catalytic mechanisms depends on pH, which also determines the concentration of the other participating species such as water, hydronium ion, and hydroxide ion. At low pH, the general acid catalysis mechanism dominates, and comparison with analogous systems in which the intramolecular proton transfer is not available suggests that the intramolecular catalysis results in a 25- to 100-fold rate enhancement At neutral pH, the intramolecular general base catalysis mechanism begins to operate. It is estimated that the catalytic effect for this mechanism is a factor of about 10. Although the nucleophilic catalysis mechanism was not observed in the parent compound, it occurred in certain substituted derivatives. 

C15-0130. If chlorofluorocarbons catalyze O3 decomposition, which is exothermic by 392 kJ/mol, they must also catalyze O3 production from O2. Using the energies shown in Figure 15-20. explain why catalysis results in net O3 destruction even though reactions in both directions are accelerated. 

Both reaction paths are acid-catalysed and are subject to retardation by specific ions probably by removal of free Br . The second-order dependence with respect to reductant has several precedents, e.g. Fe(iri) oxidation of 1 and Mn(III) oxidation of HN3. The acid catalysis results from suppression of the hydrolysis to MnOH which is ineffective in this oxidation. 

The traditional catalyst used for esterification of acids to methyl esters is sulfuric acid. Homogeneous sulfuric acid catalysis has many downsides. When using sulfuric acid, much capital expense is required for Hastalloy and/or other specialty metals of construction. Homogeneous catalysis results in the contamination of the product by sulfur containing species. Therefore, neutralization and removal of acid is required to meet biodiesel specifications and to protect the downstream transesterification reactor. Inevitably, when using sulfuric acid, organic sulfur compounds will be produced. These products will cause the resultant biodiesel to fail specification tests. 

Ring B of pyrimido[l,6-tf]pyrimidines has been most frequently synthesized from [3+3] atom fragments. The 6-aminopyrimidin-2-one derivative, cytidine 211, on reaction with acrylic acid under thermal conditions gave the pyrimido[l,6- ]pyrimidin-4,6-dione 212 <1996MI301> while reaction with 3-chloropropionaldehyde under base catalysis resulted in the pyrimido[l,6- ]pyrimidine-6-one 213 (Scheme 33) <1996MI501, 1996BAP209>. 

The systematic work carried out by Fetzner group with enzymatic catalysis resulted in the identification of four pathways of aerobic degradation of quinoline (and its derivatives) [326], shown in Fig. 23. The four pathways are named on the basis of the metabolic intermediates identified in the respective pathways, some steps and reactions have been considered in previously described pathways, but are included here to show the comprehensive nature of this work. 

Gauging catalysis by reference to an electrode where electrons are delivered (or eaten up) in an outer-sphere manner, redox catalysis is not expected to operate at a monolayer coated electrode (Figure 4.10), since, as discussed in Section 4.2.1, redox catalysis results from the three-dimensional dispersion of the catalyst. In contrast, there is no reason that chemical catalysis could not be operative at a monolayer coated electrode. For the same reasons, both redox catalysis and chemical catalysis are expected to function at multilayer electrode coatings (Figure 4.10). 

Standard methods of preparing samples for metallurgical examination sometimes involve extremely hazardous combinations of oxidants, such as nitric or perchloric acid, and organic solvents. These are frequently destabilised by metal catalysis. Resultant incidents will be recorded under the entry for the oxidant in question. 

The action of the valine derivatives 87 on the diene 86 under EtAlCU catalysis resulted in a mixture of cycloadducts 88, which on hydrolysis with aqueous methanolic sodium carbonate furnished a mixture of the dihydro-2-pyridones 89 and 90 and the esters 91 and 92. In the case of imines derived from aliphatic aldehydes, e.g. 87 (R = Pr), all four types of product were isolated, whereas imines from aromatic aldehydes, 87 (R = Ph, 3-CIC6H4 etc.), gave only the esters 91 and 92 (equation 55). All products were formed in yields of 64-84% and in high de49. 

The conventional synthesis of aliphatic polyesters based on adipic acid and a range of diols, such as 1,4-butanediol or 1,6-hexanediol, involves a high-temperature esterification reaction typically at 240-260 °C and an organometallic catalyst such as stannous octano-ate. The use of enzyme catalysis results in a much lower reaction temperature, but also the possibility of removing the esterification catalyst, giving the polyester significantly improved hydrolysis resistance. 

Table 3. Catalysis results for the Barbier reaction of benzaldehyde and allyl bromide in presence of homogeneous palladium catalyst (entry 1) and those prepared by complexing palladium to amine functionalized mesoporous silica (entry 2-4) [74]...

We first studied group 4 metals (titanium, zirconium and hafnium) supported on a silica dehydroxylated especially at 700 °C (Table 3.8). Following the laboratory-developed strategy, surface-species have been well-characterized by classical techniques (IR, solid-state NMR gas evolvement, reactivity, etc.). Catalysis results show that titanium is the most active even if its activity is far less than that of homogeneous catalysts. In addition, an important amount of metal was lost by lixiviation even if this phenomenon seemed to stop after a certain time. 

Y = OMe, Ph, OPh), acid catalysis resulted in a concerted El decomposition of the protonated intermediate (117) and release of benzyl cation in the rate-determining step according to Scheme 21. 

A comparable mechanism was also proposed by Keim ( ) from homogeneous catalysis results. 

Reaction of thiophenes and benzo[6]thiophenes with 2,4-dinitrobenzenesulfenyI chloride, trifluoromethanesulfenyl chloride or chloroformylsulfenyl chloride, under SnCl4 catalysis, results in efficient sulfenylation (Scheme 22) (62JOC1301, 76CB2475). The reaction with CF3SCI has also been carried out in the presence of pyridine (75JHC845). 

Slow couplings (48 h) to the aromatic amino group of Abz-peptides are reported and the use of DMAP catalysis results in racemizationJ111 Fmoc amino acid chlorides can be coupled in good yield without any racemizationJ11 Similarly, Fmoc-Gly-Cl can be coupled to o-, m-,... 

Intramolecular cyclization. Knoevenagel condensation of diphenylacetaldehyde with diethyl malonate (piperidinium acetate catalysis) results in only a trace of the expected product when molecular sieves are present, the a-naphthol 1 is formed in 52% yield.2 A similar reaction is observed with ethyl acetoacetate and ethyl benzoylacetate. 

The formation of the complex creates a very strong electron-withdrawing group which helps the withdrawal of the electrons from the carbon-carbon bond which is breaking. Catalysis results because this electron-withdrawing effect is much stronger than the effect of the anion in the uncatalysed decarboxylations. 

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