Activation parameters acetal oxidation

Ru(edta)(H20)] reacts very rapidly with nitric oxide (171). Reaction is much more rapid at pH 5 than at low and high pHs. The pH/rate profile for this reaction is very similar to those established earlier for reaction of this ruthenium(III) complex with azide and with dimethylthiourea. Such behavior may be interpreted in terms of the protonation equilibria between [Ru(edtaH)(H20)], [Ru(edta)(H20)], and [Ru(edta)(OH)]2- the [Ru(edta)(H20)] species is always the most reactive. The apparent relative slowness of the reaction of [Ru(edta)(H20)] with nitric oxide in acetate buffer is attributable to rapid formation of less reactive [Ru(edta)(OAc)] [Ru(edta)(H20)] also reacts relatively slowly with nitrite. Laser flash photolysis studies of [Ru(edta)(NO)]-show a complicated kinetic pattern, from which it is possible to extract activation parameters both for dissociation of this complex and for its formation from [Ru(edta)(H20)] . Values of AS = —76 J K-1 mol-1 and A V = —12.8 cm3 mol-1 for the latter are compatible with AS values between —76 and —107 J K-1mol-1 and AV values between —7 and —12 cm3 mol-1 for other complex-formation reactions of [Ru(edta) (H20)]- (168) and with an associative mechanism. In contrast, activation parameters for dissociation of [Ru(edta)(NO)] (AS = —4JK-1mol-1 A V = +10 cm3 mol-1) suggest a dissociative interchange mechanism (172). 

The kinetics of the oxidation of aromatic aldehydes by A-chloronicotinamide in aqueous acetic acid are first order in both reactants and in proton.339 The effect of substituents has been studied, and data at different temperatures yield activation parameters. 

The activation parameters (Table 3) are characterized by positive values of H koA negative values of and indicate that bond-formation plays an important role in forming the transition state. This is in agreement with previous work which showed that oxidative addition proceeds via an associative mechanism." For 2 in ethyl acetate, the oxidative addition rate constants could not be determined accurately, but /cr could be used for the calculation of the activation parameters. The values suggest less ordered transition states in which significant solvent interaction may occur, but it is clear that additional research is still required. 

Likewise, Kishan and Sundaram (1985, 1980) report that substituted phenacyl bromides (CgHjCOBr) are oxidized (in 40-70% acetic acid/H2S04) without complex formation. The reaction is catalyzed by acid, but the pseudo-first-order fits depend on the initial [Ce(lV)]. This observation is attributed to the presence of an unreactive Ce(IV) trimer, which has been reported to be present in acetic acid solutions. The rate of reaction of phenacyl bromides substituted with either electron-withdrawing or electron-donating substituents is faster than that of unsubstituted phenacyl bromide. The activation parameters for the p-methyl and p-methoxyl substituents suggest that a different mechanism operates for these systems. Where comparable substituents exist, the rates for oxidation of phenacyl bromides compare favorably with those for benzaldehyde dted above. 

Kinetics of the oxidation of crotonaldehyde by tetraethylammonium chlorochromate have been measured in 50/50 aqueous acetic acid, including derivation of activation parameters. ... 

Propionic and butyric acids have structures similar to acetic acid and are expected to display much the same chemical and kinetic behavior. Virtually no experimental studies of their decarboxylation kinetics in aqueous solutions have been reported, although it is expected that these reactions are also catalyzed heterogeneously. The rate constant for decarboxylation of a 1.1 mol kg solution of n-butyric acid is 4.20 x 10 s (titanium oxide surface at 359 °C), whereas the comparable value for acetic acid is 3.89 x 10 s (Palmer and Drummond 1986). However, there are no corresponding data on the activation parameters for these acids so that the expected similarity of the linear isokinetic plots for these and acetic acid has not yet been tested. 

As a result of the Rowing interest in the GC route to obtain information on polymer-solute systems, a large body of data, activity coefficients and/or interaction parameters, has been reported. Polystyrene 51,59), poly(vinyl chloride) (60), polyethylene (60-62), poly(ethylene oxide) (65) and copolymers of ethylene with propylene and vinyl acetate (62) have been studied with a variety of probes. 

Thus, several mechanistic pathways based on polarization effects have been proposed to explain the catalysis of the alcohol-isocyanate reaction. These propositions appear to be often unsatisfactory and cannot explain even the majority of the experimental results reported in the literature. For an example, why is the polyurethane formation catalyzed by potassium acetate (JJ and not at all by MgC03 nor CsCl (14) The role played by the nature of the metal remains also unexplained. Robins reports the incremental temperature rise noted 1 minute after the mixing of reagents and catalyst (7, 16). This parameter is related to the catalytic activity and is an effective way to show the role played by the organometallic compound in its interaction with the alcohol. A similar conclusion can be drawn from Table I (15) where the Sn+ derivative is much more active than the Sn+2 oxidation state or Pb+. ... 

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