Disproportionation base catalysis

Reactions were studied under the pseudo first-order condition of [substrate] much greater than [initial dihydroflavin]. Under these conditions, the reactions are characterized by a burst in the production of Flox followed by a much slower rate of Flox formation until completion of reaction. The initial burst is provided by the competition between parallel pseudo first-order Reactions a and b of Scheme 3. These convert dihydroflavin and carbonyl compound to an equilibrium mixture of carbinolamine and imine (Reaction a), and to Flox and alcohol (Reaction b), respectively. The slower production of Flox, following the initial burst, occurs by the conversion of carbinolamine back to reduced flavin and substrate and, more importantly, by the disproportionation of product Flox with carbinolamine (Reaction c followed by d). Reactions c and d constitute an autocatalysis by oxidized flavin of the conversion of carbinolamine back to starting dihydroflavin and substrate. In the course of these studies, the contribution of acid-base catalysis to the reactions of Scheme 3 were determined. The significant feature to be pointed out here is that carbinolamine does not undergo an elimination reaction to yield Flox and lactic acid (Equation 25). The carbinolamine (N(5)-covalent adduct) is formed in a... 

Many industrial processes are based on acid/base catalysis (over 130). Examples include alkylation, etherification, cracking, dehydration, condensation, hydration, oligomerizations, esterification, isomerization and disproportionation. The dimensions of the processes range from very large scale in the field of refinery (thousand tons per day) to very small productions in fine and specialty chemical industries. In the latter case, adds and bases are often used in stoichiometric quantities, leading thus to large amounts of waste. 

Antelo, J.M., Arce, F., Calvo, R, Crugeiras, J., Rios, A. General acid-base catalysis in the reversible disproportionation reaction of N-chlorotaurine. J. Chem. Soc. Perkin Trans. 2. 2000, 2109-2114. 

Catalysis. As of mid-1995, zeoHte-based catalysts are employed in catalytic cracking, hydrocracking, isomerization of paraffins and substituted aromatics, disproportionation and alkylation of aromatics, dewaxing of distillate fuels and lube basestocks, and in a process for converting methanol to hydrocarbons (54). 

The redox reactivity of divanadium salen615 and other complexes555 have been investigated. Disproportionation of [ V(salen) 2(//-0)] was observed under electrochemical conditions.6 The reduced, [Vin(salen)]+ complex was found to be the essential species in the catalysis of the electroreduction of 02 by four electrons in CH2C12.616 While [ V(salcn) 2(/x-0)] was proposed to be the active species in the redox reaction, more recently [Vin(salen)]+ was identified as a reservoir from which the active species forms.616 Schiff base complexes encapsulated in zeolite Y are catalytically active in the oxidation of thioanisole with H202.14 Acid-promoted disproportionation of a Vlv phenolate under anaerobic conditions was proposed as a model reaction for the vanadium uptake in tunicates.139... 

Medium pore aluminophosphate based molecular sieves with the -11, -31 and -41 crystal structures are active and selective catalysts for 1-hexene isomerization, hexane dehydrocyclization and Cg aromatic reactions. With olefin feeds, they promote isomerization with little loss to competing hydride transfer and cracking reactions. With Cg aromatics, they effectively catalyze xylene isomerization and ethylbenzene disproportionation at very low xylene loss. As acid components in bifunctional catalysts, they are selective for paraffin and cycloparaffin isomerization with low cracking activity. In these reactions the medium pore aluminophosphate based sieves are generally less active but significantly more selective than the medium pore zeolites. Similarity with medium pore zeolites is displayed by an outstanding resistance to coke induced deactivation and by a variety of shape selective actions in catalysis. The excellent selectivities observed with medium pore aluminophosphate based sieves is attributed to a unique combination of mild acidity and shape selectivity. Selectivity is also enhanced by the presence of transition metal framework constituents such as cobalt and manganese which may exert a chemical influence on reaction intermediates. 

The reaction of alkylntagnesium reagents with di-r-bulyl peroxide leads to alkyl /-butyl ether, /-buiyl alcohol, and disproportionation products of the alkyl [96). Mechanistic studies showed that the initial step is ET. This conclusion was i.a. based on a linear correlation of log rale with the oxidation potentials of the Grignard reagents. Reactions of peroxides are extremely sensitive to metal catalysis, but take place even when high-purity magnesium is used. 

The electrogenerated chemiluminescence (eel) is therefore specific of the triplet-triplet annihilation for A-type compounds. In such processes, the triplet formation, on which the eel phenomenon is based is in competition with the expected reactions already established for redox catalysis, namely homogeneous electron exchange reactions (SET and then disproportionation reactions) ... 

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