General acid catalyst

All lation of Phenols. The approach used to synthesize commercially available alkylphenols is Friedel-Crafts alkylation. The specific procedure typically uses an alkene as the alkylating agent and an acid catalyst, generally a sulfonic acid. Alkene and catalyst interact to form a carbocation and counter ion (5) which interacts with phenol to form a 7T complex (6). This complex is held together by the overlap of the filled TT-orbital of the aromatic... 

Abstract The term Lewis acid catalysts generally refers to metal salts like aluminium chloride, titanium chloride and zinc chloride. Their application in asymmetric catalysis can be achieved by the addition of enantiopure ligands to these salts. However, not only metal centers can function as Lewis acids. Compounds containing carbenium, silyl or phosphonium cations display Lewis acid catalytic activity. In addition, hypervalent compounds based on phosphorus and silicon, inherit Lewis acidity. Furthermore, ionic liquids, organic salts with a melting point below 100 °C, have revealed the ability to catalyze a range of reactions either in substoichiometric amount or, if used as the reaction medium, in stoichiometric or even larger quantities. The ionic liquids can often be efficiently recovered. The catalytic activity of the ionic liquid is explained by the Lewis acidic nature of then-cations. This review covers the survey of known classes of metal-free Lewis acids and their application in catalysis. 

A combined theoretical and experimental study of the Baeyer-Villiger reaction of acetone and pentan-3-one, including their fluorinated and chlorinated derivatives, with performic acid revealed that the first step is rate determining for all substrates examined, even in the presence of acid. Acid catalysts generally decrease the A of the first transition state (TS1), but increase the Aof the second (TS2). The optimal... 

Catalytic enantioselective allylations of aldehydes already published can be classified into two methods carried out under the influence of chiral Lewis acid catalysts and chiral Lewis base catalysts. The process by chiral Lewis acid catalysts generally uses allyltrimethylsilane or allyltrialkylstannane as an allylating agent, both of which show low reactivity toward aldehydes without these catalysts. The process by chiral Lewis base catalysts employs allyltrichlorosilane or allylmetals possessing relatively higher reactivity. Both processes can be successfully applied to various substituted allylmetal compounds or allenylmetal compounds. 

Many researchers have conducted a number of experiments to study the mechanism and kinetics of esterifications promoted by mineral acids (Cardoso et al., 2008). Summarizing recent research and development, esterification is an additive-eliminate course in the presence of mineral acid catalyst, generally complying with the following four typical and mature mechanisms. 

Except in the presence of strongly acidic catalysts, general acid catalysed breakdown of the tetrahedral intermediate to products by proton transfer to the P-lactam nitrogen is a relatively unimportant pathway in aminolysis. This is expected because of the weakly basic P-lactam nitrogen in the tetrahedral intermediate (Morris and Page, 1980a). 

Sodium enolates of ketones and disodium enediolates of substituted phenylacetic acids reacted with activated aziridines to afford 7-amido ketones and -y-amidobutyric acids, respectively (Scheme 72). Aziridine-2-carboxylic acid esters can be utilized as versatile precursors for amino acid derivatives. Although the product distribution resulting from the reaction of activated aziridine-2-carboxylates with amines depends on the structure of the reactants, the reactions with alcohols or thiols in the presence of acidic catalysts generally gave the a-amino acid derivatives (Scheme 73). >49, iso Qn the other hand, free 3-methyl-2-aziridinecarboxylic acids (168) reacted with thiophenol, cysteine and glutathione to afford 3-amino acid derivatives with sulfur substituents at the a-position as the main product (Scheme 73). ... 

As described below, dehydration over acidic catalysts generally yields Saytzeff products, while dehydration over basic oxides such as Th02 and Z1O2 yields Hofmann elimination products. Dehydration over strongly basic catalysts such as MgO and CaO is always accompanied by appreciable dehydrogenation. 

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