Dimerization reactions kinetic study

Conjugate additions lo a,/ -unsalutaled kelones and eslets ate die most Impotlanl ctiptale reactions. Kinetic studies by Ktauss and Sniidi on MezCuIi and a variety of ketones teveaied die following kinetic cliatacterislics lEq. 10.5), fitsl otdet bodi in cuprate dimer and in die etione [60]. 

Conjugate additions to a, j5-unsaturated ketones and esters are the most important cuprate reactions. Kinetic studies by Krauss and Smith on Me2CuLi and a variety of ketones revealed the following kinetic characteristics (Eq. 10.5), first order both in cuprate dimer and in the enone [60]. 

Aluminium.—A. review on the organometallic chemistry of aluminium contains some mechanistic work, particularly n.m.r. studies of exchange reactions. Kinetic studies of the exchange between bridging and terminal sites for alkyl aluminium dimers indicate that, for the methyl compound, reaction proceeds by a dissociative mechanism but that for meta- and para-to y alkyls the mechanism involves only partial dissociation of the brid. For the addition of (Bu 2AlH)3 to oct-4-yne, the kinetic order of i for the aluminium compound indicates that the monomer, Bu AlH, is the active species. Further studies on the Lewis acid behaviour of a range of species, including aluminium compounds, have been published. ... 

A. Maltz, E. V. Albano. Kinetic phase transitions in dimer-dimer surface reaction models studied by means of mean-field and Monte Carlo methods. Surf Sci 277-A A-42S, 1992. 

The HKR of epichlorohydrin (ECH) was studied as a representative reaction for kinetic studies. For dimer catalyst lb and lb and corresponding monomers la and la, show the two-term rate equation involving both infra and intermolecular components[10]. 

Kinetic studies by Butts and Richmond indicate that both the monomer and dimer of dichloroacetic acid promote the reaction in an aromatic solvent, equations 12a and 12b, (20). 

Although the above model was developed under non-catalytic conditions, some of the results may bear significance under natural conditions or in the presence of excess sulfite ions. Thus, the decomposition of the mono-sulfito complex was considered to be the rate-determining step in the catalytic cycle, but only estimates could be given for the rate constant in earlier studies. The comprehensive data treatment used by Lente and Fabian yielded a well established value for this parameter (106), which can then be used to improve previous kinetic models. Furthermore, the participation of reactions of the [Fe2(0H)(S03)]3+ complex was never considered in kinetic studies where excess sulfite ion was used over low iron(III) concentration in mildly acidic solution (pH 2.5-3.0). The above model predicts that in some cases the formation of the dimeric sulfito complex could make a substantial contribution to the spectral changes and omission of this species could lead to biased conclusions. Reevaluation of data sets reported earlier by including the reactions of [Fe2(0H)(S03)]3+ may resolve some of the controversies found in literature results. 

A kinetic study of nitrous acid-catalyzed nitration of naphthalene with an excess of nitric acid in aqueous mixture of sulfuric and acetic acids (Leis et al. 1988) shows a transition from first-order to second-order kinetics with respect to naphthalene. (At this acidity, the rate of reaction through the nitronium ion is too slow to be significant the amount of nitrous acid is sufficient to make one-electron oxidation of naphthalene as the main reaction path.) The reaction that initially had the first-order in respect to naphthalene becomes the second-order reaction. The electron transfer from naphthalene to NO+ has an equilibrium (reversible) character. In excess of the substrate, the equilibrium shifts to the right. A cause of the shift is the stabilization of cation-radical by uncharged naphthalene. The stabilized cation-radical dimer (NaphH)2 is just involved in nitration ... 

A kinetic study has been carried out in order to elucidate the mechanism by which the cr-complex becomes dehydrogenated to the alkyl heteroaromatic derivative for the alkylation of quinoline by decanoyl peroxide in acetic acid. The decomposition rates in the presence of increasing amounts of quinoline were determined. At low quinoline concentrations the kinetic course is shown in Fig. 1. The first-order rate constants were calculated from the initial slopes of the graphs and refer to reaction with a quinoline molecule still possessing free 2- and 4-positions. At high quinoline concentration a great increase of reaction rate occurs and both the kinetic course and the composition of the products are simplified. The decomposition rate is first order in peroxide and the nonyl radicals are almost completely trapped by quinoline. The proportion of the nonyl radicals which dimerize to octadecane falls rapidly with increase in quinoline concentration. The decomposition rate in nonprotonated quinoline is much lower than that observed in quinoline in acetic acid. 

The first kinetic study of the aquation of [MoCl ] to [MoClgfHjO)] = 87 min at 0 °C) has been reported. No conclusive proof that the final product is [Mo(H20)g] could be obtained, and the spectral profile reported earlier for [Mo(H20)e] is not considered to preclude the existence of dimeric molybdenum(iii) species. The reaction of [WCl (MeCN)2] with... 

The alkylation of quinoline by decanoyl peroxide in acetic acid has been studied kineti-cally, and a radical chain mechanism has been proposed (Scheme 207) (72T2415). Decomposition of decanoyl peroxide yields a nonyl radical (and carbon dioxide) that attacks the quinolinium ion. Quinolinium is activated (compared with quinoline) towards attack by the nonyl radical, which has nucleophilic character. Conversely, the protonated centre has an unfavorable effect upon the propagation step, but this might be reduced by the equilibrium shown in equation (167). A kinetic study revealed that the reaction is subject to crosstermination (equation 168). The increase in the rate of decomposition of benzoyl peroxide in the phenylation of the quinolinium ion compared with quinoline is much less than for alkylation. This observation is consistent with the phenyl having less nucleophilic character than the nonyl radical, and so it is less selective. Rearomatization of the cr-complex formed by radicals generated from sources other than peroxides may take place by oxidation by metals, disproportionation, induced decomposition or hydrogen abstraction by radical intermediates. When oxidation is difficult, dimerization can take place (equation 169). 

A more recent kinetic study has indicated that under acidic conditions a-ketonitrosoalkanes may rearrange rapidly to the oxime [33]. Amines also bring about the isomerization of nitrosocyclohexane [34], These observations along with the older observations mentioned in Touster s review [2] imply that the whole question of the nitrosation of aliphatic carbon atoms should be reexamined with modern techniques to establish the reaction conditions under which the true aliphatic nitroso compounds (or their dimers) can be isolated. 

The influence of diphenyl ether and anisole on the association of the polystyryllithium and 1,1-di-phenylmethyllithium active centers has been measured. Severe disaggregation of the polystyryllithium dimers, present in pure benzene, was found to occur at levels of ether addition at which several reliable kinetic studies reported in the literature unequivocally demonstrate a 1/2 order dependence upon polystyryllithium. These results indicate that a necessary connection between the degree of aggregation of organo1ithium polymers and the observed kinetic order of the propagation reaction need not exist. 

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