Catalysis cationic reactions

This does not occur in the case of catalyst and reactants here described. With Bronsted-type catalysis, the reaction between the benzoyl cation, Ph-C" =0, and the hydroxy group in phenol is quicker than the electrophilic substitution in the ring. This hypothesis has been also confirmed by running the reaction between anisole and benzoic acid in this case the prevailing products were (4-methoxy)phenylmethanone (the product of para-C-benzoylation) and methylbenzoate (obtained by esterification between anisole and benzoic acid, with the co-production of phenol), with minor amounts of phenylbenzoate, phenol, 2-methylphenol and 4-methylphenol. Therefore, when the 0 atom is not available for the esterification due to the presence of the substituent, the direct C-acylation becomes the more favored reaction. 

The active site in chain-growth polymerizations can be an ion instead of a free-radical. Ionic reactions are much more sensitive than free-radical processes to the effects of solvent, temperature, and adventitious impurities. Successful ionic polymerizations must be carried out much more carefully than normal free-radical syntheses. Consequently, a given polymeric structure will ordinarily not be produced by ionic initiation if a satisfactory product can be made by less expensive free-radical processes. Styrene polymerization can be initiated with free radicals or appropriate anions or cations. Commercial atactic styrene polymers are, however, all almost free-radical products. Particular anionic processes are used to make research-grade polystyrenes with exceptionally narrow molecular weight distributions and the syndiotactic polymer is produced by metallocene catalysis. Cationic polymerization of styrene is not a commercial process. 

Li T, Lemer RA, Janda KD. Antibody-catalyzed cationic reactions rerouting of chemical reactions via antibody catalysis. Acc. Chem. Res. 1997 30(3) 115-121. 

How is it possible to distinguish radical cation reactions from genuine transformations catalyzed by the zeolite, and what types of processes tend to intrade on the identification of products of catalysis To answer the first question, we rely on the ion-exchangeability of zeolites. Zeolites are crystalline aluminosilicates, natural or man-made, that can adopt a remarkable range of channel-type and cage-type lattice architectures, depending on the... 

Cationic reactions under phase transfer catalysis... 

SOMO Activation Within the field of aminocatalysis, asymmetric organo-SOMO (singly occupied molecular orbital) catalysis has recently emerged as a powerful technique for the preparation of optically active compounds. In this context, MacMillan and coworkers described in 2008 the formation of y-oxyaldehydes from aldehydes and styrenes by organo-SOMO catalysis [25]. The condensation between the amine catalyst 46 and an aldehyde gave rise to an enamine intermediate, which was then oxidized by ceric ammonium nitrate (CAN) to give a radical cation. Reaction of this radical cation with a nonactivated olefin, namely styrene, led to the... 

C-H Bond Functionalization Direct C2 Arylation. A room temperature and phosphine-free arylation of (V-methylindole has been developed involving a Pd ( catalysis. The reaction is realized in the presence of a silver salt to generate a highly electrophilic cationic palladium species that allows the palladation of the V-methylindole. The reaction occurs in very mild conditions to provide the 1-methyl-2-phenylindole in 92% yield (eq 16). ... 

In such catalysis, the reaction or the catalytic site in a catalyst is always electron-deficient and, consequently, it accepts a pair of electrons from an electron donor. In the catalytic reduction of overall free energy of activation for positive catalysis, the predominant destabilization of GS or predominant stabilization of TS must involve the pair of electron transfers (partially or fully) from the reaction site in the reactant (substrate) to the reaction site in the catalyst (neutral/cationic atom/molecule). The interaction between catalyst and reactant should involve... 

In this section the influence of micelles of cetyltrimethylammonium bromide (CTAB), sodium dodecylsulfate (SDS) and dodecyl heptaoxyethylene ether (C12E7) on the Diels-Alder reaction of 5.1a-g with 5.2 in the absence of Lewis-add catalysts is described (see Scheme 5.1). Note that the dienophiles can be divided into nonionic (5.1a-e), anionic (5.If) and cationic (5.1g) species. A comparison of the effect of nonionic (C12E7), anionic (SDS) and cationic (CTAB) micelles on the rates of their reaction with 5.2 will assess of the importance of electrostatic interactions in micellar catalysis or inhibition. 

---