Oxidative coupling, rate

This first step would involve the displacement of a pyridine ligand by the aromatic amine. Some evidence points to this being the rate-determining step. A strict positive correlation between the basicity of the diamine relative to pyridine and the oxidative coupling rate (as measured by the oxygen absorption) was established (3). 

The extent of coupling is also influenced by the solvent. In the hydrogenation of aniline over ruthenium oxide, coupling decreased with solvent in the order methanol > ethanol > isopropanol > t-butanol. The rate was also lower in the lower alcohols, probably owing to the inhibiting effect of greater concentrations of ammonia (44). Carboxylic acid solvents increase the amount of coupling (42). 

So, both effects maintain an enlarged local concentration of active catalytic centers and cause the rate of oxidative coupling with polymeric catalysts to be higher than with equivalent amounts of low molecular weight analogs, especially for low 1igand/copper ratios. This rate enhancement is clearly demonstrated in Figure 5 for polydentates (I) vs. DMBA (J 7), and was also found for polydentate (II) vs. pyridine (18). 

In Fig.5 we also saw that the initial rates,R0,of oxidative coupling showed a limiting value with increasing substrate concentration, which resembles the... 

The rate of oxidative coupling is said to decrease with decreasing acidity of the ethynyl hydrogen. Thus oct-l-yne underwent only limited reaction after being heated with the reagent under reflux for 24 hours. 

There are no reports of chiral complex catalysts that could catalyze the aerobic oxidative coupling of 2-naphthol at a reasonable reaction rate with high enantioselectivity. The reactions mentioned above are accomplished in 24 h or in 7-10 days. These drawbacks should be overcome in the near future. 

The oxidative coupling of 2-halo-4,6-di-t-butylphenols with potassium hexacyanofer-rate(III) in benzene was investigated the 2-bromophenol (227) yielded l,4-dihydro-4-bromo-2,4,6,8-tetra-t-butyl-l-oxodibenzofuran (228 81%) and 2,4,6,8-tetra-t-butyldiben-zofuran (229) (81JOC3784). 

The anomeric specificities of a number of glycolytic enzymes have been determined by using the reduced triphosphopyridine nucleotide (TPN)-coupled rate of oxidation with glucose-6- phosphate dehydrogenase, or by the enzyme glucose oxidase, which is also specific for the /3-anomer (106). 

The structure of copolymers produced by oxidative coupling is determined largely by the rate and other characteristics of the redistribution reaction, as is true of polyesters and other types of polymers which are... 

Kinetically slow steps in the formation of melanin from DOPA are the formation of dopaquinone from DOPA (step 1, kD), the reaction of dopachrome to dihydroxyindole (step 2), and the polymerization to form melanin (step 3, kM). Step 1 and step 2 proceed with about the same rate in the oxidative coupling polymerization catalyzed by tyrosinase. However, step 1 becomes remarkably slow when a macromolecule-metal complex is used as a catalyst. The copper complex in poly(l-vinylimidazole-co-vinylpyrrolidone) has been found [38] to act as an excellent catalyst and to exhibit the highest activity for melanin formation. The ratio of the rate constants ( m/ d) is approximately 3 (tyrosinase... 

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