Aldehydes catalysts

The geometry of the aldol transition state was interpreted in terms of the variation in mode of the aldehyde/catalyst complexation [Felkin-Ahn (nonchelating) model versus chelating model] and size of KSA. The same complex efficiently catalyzes the Michael reaction of a,/9-unsaturated ketones with KSA [124],... 

Entry Aldehyde Catalyst X Yield syn/anti % ee syn anti ... 

Diene Aldehyde Catalyst Temperature (C) Yields syn anti ee(%)... 

The influence of a catalyst on the rate of oxidation may occur in two ways, either by direct interaction with aldehyde or by the catalytic decomposition of peracid or X peroxide. Initiation by aldehyde—catalyst... 

In order to get an insight on the plausible mechanism for the reaction and learn about the influence of aldehyde, catalyst, and temperature on the reaction rate, kinetic and thermodynamic measurements were performed. Kinetic studies of the Cp2 ThMe2-catalyzed Tishchenko reaction of benzaldehyde indicates that the reaction follows a first order dependence on both catalyst and aldehyde (23) [115]. 

From a meticulous analysis, Roush and VanNieuwenhze developed novel sugar-based chiral reagent 10 for the asymmetric alkylation of aldehydes. Catalyst 10 was designed in the expectation that significant diaster-eofacial bias would be exerted as a consequence of the conformational... 

The intramolecular hydroacylation of aldehydic olefins is catalyzed by cationic Rh complexes of chelating phosphines in polar nonprotic solvents. The rate decreases with increasing substrate Rh ratio since the substrate complex with the catalyst inhibits the reaction. However, since this complexation also prevents the decarbonylation of the aldehyde, catalyst deactivation decreases, leading to a higher turnover. The only effective catalytic C—H activations are carried out with [RhCl(CO)(PMe3)2] under photolysis which removes CO. Alkanes are converted to alkenes in the order cyclooctane > cyclohexane > n-decane n-hexane. Up to 200 turnovers cyclooctane per hour are observed. In order to generate terminal... 

Ketone aldehyde llgand benzoic acid 2 1 0.05 0.1 mol, 25°C. Method A conventional magnetic stirring. Method B aldehyde, catalyst, and benzoic acid were dissolved In THF and the solvent was evaporated prior to the addition of ketone. Method C ball milling, AOOrpm. 

Digital Mixer/Amalgamaton Nylamid cylinder (25xl0mm), one 5mm stainless steel ball, -20°C, 4h, 2760rpm, ketone aldehyde catalyst 1.1 1 0.07mol. isolated products. 

Fritsch planetary micro mill Pulverlsette 7, eoorpm, 30min, tungsten carbide vial (80mL) and 20x5mm balls, substrate aldehyde catalyst 1 1 0.05mol. 

Enders also developed, a so-called branehed domino reaetion. In this case a nitroalkene was combined with two equivalents of an aldehyde, catalyst and an oxidant. The most effective oxidation agent IBX oxidised enamine to iminium ion, which served as an acceptor in the last part of the cascade. In this way, cyclohexene derivatives were assembled in good yield and with high diastereomeric and enantiomeric purities (Scheme 8.19). 

Melchiorre and coworkers disclosed a primary amine-thiourea-mediated iminium ion activation of ot,p-unsaturated aldehydes. Catalyst 45 was applied successfully leading to high efficiency and stereocontrol in the challenging synthesis of compounds containing contiguous quaternary and... 

Entry Aldehyde Catalyst Base Additive Solvent Temp.(°C) Product Yield (%) ee (%)... 

The catalysts required by plastics may be classified as (1) strong add catalysts (e.g., sulfuric acid, hydrochloric acid, and phosphoric acid alone or in combination with modifiers), (2) latent acid catalysts (e.g., ammonium salts of strong acids such as ammonium chloride generally useful in accelerating the setting of urea or melamine resins), (3) aldehydic catalysts (e.g., catalysts peculiar to phenol-formaldehyde and urea-formaldehyde resins such as paraformaldehyde and hexamethylenetetramine often used in urea and resorcinol adhesives), and (4) peroxide catalysts (e.g., benzoyl peroxide and dicumyl peroxide promote polymerization of polyesters through a free radical mechanism). 

Phenolic resins are highly versatile, which has led to a broad range of applications in the aircraft, aerospace, automotive, electrical and electronic industries (Pilato et ah, 2008) as well as in the interiors of mass-transit cars and architectural and marine components (Lewark, 2007). Phenolic resins with diverse structures and properties can be obtained from different phenols, aldehydes and catalysts. In addition, resins with different properties can be prepared from a given set of parental or substituted phenol/aldehyde/catalysts by diversifying parameters sueh as the phenol/formaldehyde ratio and the reaction temperature and duration. 

Since no reaction occurred at all in the absence of either the aldehyde catalyst or the base or both of them, as well as other proofs such as control reactions using high purity bases (>99.99 % purity), the authors concluded that the reaction is a true TM-free transformation. In addition to the aldehydes catalytic effect, the authors proved that imine intermediates and other TM-free oxidants could also be employed to initiate the reaction, which is consistent with, and further supports, the TM-free N-aUcylation mechanism (Scheme 39). Along with other results of mechanistic studies, the authors proposed a mechanism for the aldehyde-catalyzed A -alkylation reaction (Scheme 41). Firstly, the external aldehydes condense with amines/amides to give imine intermediates, which were then reduced by alcohols via a TM-free MPV-0 transfer hydrogenation process to give product amines and regenerate byproduct aldehydes as the new alkyl source in next reaction cycle. In the key TM-ffee transfer... 

Crosslinkers and Accelerators. Besides the polymers themselves, changes and improvements are taking place in curing agents, hardeners, catalysts, and polymer modifiers. For example, if epoxy adhesives with improved heat resistance are needed, the hardeners can be aromatic anhydrides and amines such as benzophenone tetracarboxylic dianhydride, py-romellitic dianhydride, diaminodiphenyl sul-fone. To enhance curing speed, epoxy systems utilize mercaptan hardeners, while acrylic monomer/polymer blends avail themselves of amine/aldehyde catalysts with benzosulfimide (saccharin) accelerators. Radiation-curing systems for today and tomorrow utilize both visible light and laser beams. 

A kinetic study of intermolecular hydroamination of allylic amines by N-alkylhydroxylamines has revealed a first-order dependence on aldehyde catalyst. 

As further evidence, they isolated and characterized dioxolanone 48. In addition, they tested further pyridine-derived acyl-transfer catalysts 46 (Fig. 7.4) and detected that the ketone-derived catalysts are far more selective than the aldehyde-derived ones [55]. This was explained by an undirected background reaction from a nucleophilic attack of MeOH to the aldehyde catalyst. 

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