Rate-determining step chlorination

In hydroxyUc solvents, the reaction with aniline follows a bi-molecular course but is complicated by competing solvolysis. This is a striking result when compared with the behavior of picryl chloride, which is much more selective with regard to the same reagents (aniline and alcohol), and has been interpreted to mean that bond-breaking has made appreciable progress in the rate-determining step of the reaction of phosphonitrilic chloride. Furthermore, the same indication is obtained from the fact that in the reactions of the halides, the fluorine chlorine ratios are less than one. ... 

The evolution of methylchlorosilanes between 450 and 600 K is consistent with the 550 - 600 K typical for the catalytic Rochow Process [3]. It is also reasonably consistent with the evolution of methylchlorosilanes at 500 - 750 K reported by Frank and Falconer for a temperature programmed reaction study of the monolayer remaining on a CuaSi surface after catalytic formation of methylchlorosilanes from CHaCl at higher pressures [5]. Both of these observations suggest that the monolayer formed by methyl and chlorine adsorption on pure CuaSi is similar to that present on active catalysts. For reference, methylchlorosilanes bond quite weakly to tiie surface and desorb at 180 - 220 K. It can thus be concluded that the rate-determining step in the evolution of methylchlorosilanes at 450 - 600 K is a surface reaction rather an product desorption. 

PCMT produces very small, and approximately equal, increases in rate. Alternative reaction mechanisms that invoke as rate-determining steps either i). attack by chloride ion, or ii). unassisted SnI dissociation of the carbon-chlorine bond are inconsistent with this result. 

The apparent lack of dependence of the propagation reaction on the surface area of the sodium suggests that the reaction of a chlorine ended chain with sodium is probably fast and not the rate determining step. The rate determining process is probably the reaction of the sodium ended chain with the dichloride. This latter reaction is presumably not on the sodium surface because of the lack of dependence on the surface area. This is supported by the observation that if the sodium is allowed to settle part way through the reaction most of the polymer appears to be in the solution and not absorbed on the sodium surface via the longlived active chain ends. 

Kinetic studies of the stoichiometric carbonylation of [Ir(CO)2l3Me] were conducted to model the rate-determining step of the catalytic cycle [73,85]. The reaction can form both fac,cis and mer,trans isomers of [Ir(CO)2l3 (COMe)] (Scheme 13), the product ratio varying with the solvent and temperature used. An X-ray crystal structure was obtained for the fac,cis isomer. Carbonylation of [Ir(CO)2l3Me] is rather slow and requires temperatures > 80 °C in chlorinated solvents (e.g. PhCl). However, the presence of protic solvents (e.g. methanol) has a dramatic accelerating effect. This is interpreted in terms of the protic solvent aiding iodide dissociation by solvation. 

The electrochemical reaction occurs at the surface of graphite anode [37 39]. At potentials lower than 1.25 V, chlorine is formed by a Volmer/Heyrovsky mechanism with the latter being the rate determining step. Chloride ions are initially discharged on surface sites that are not covered by chlorine atoms (Volmer reaction (14.4a)), followed by the discharge of chloride ions on adsorbed chlorine ions (Heyrovsky reaction (14.4b)) [39] ... 

Several trends emerge in these data (1) The reductive elimination of bromine is 6-13kJmol more facile than reductive elimination of chlorine in similar structures, which is consistent with weaker chalcogen-bromine bonds relative to chalcogen-chlorine bonds.(2) The reductive elimination of chlorine is accelerated by the presence of a chloride counterion as opposed to a less nucleophilic counterion such as hexafluorophosphate. (3) The rate of reductive elimination is accelerated by the presence of a more polar solvent (acetonitrile) relative to tetrachloroethane, which is consistent with development of charge in the rate-determining step. These observations suggest mechanisms for oxidative... 

How does the rate-determining step relate to the rate law for the overall equation Consider the reaction of nitrogen dioxide with chlorine. 

The key to figuring out such a mechanism is to recognize from the half power in the rate expression that a Cl atom is involved in the rate determining step and that there must be an equilibrium between the chlorine atoms and mo.lecules. The overall stoichiometry is governed by the chain steps which occur many times more often than the other steps. 

The results demonstrate that the rate of the chlorine abstraction reaction (Eq. (47)), which is usually the rate determining step in this process, is affected by (a) the redox potential of the Cun/IL couple (solvents such as acetonitrile, that form complexes with Cu1 and anodically shift its redox potential, decrease the reactivity),... 

If the concerted four-center mechanism for formation of chloromethane and hydrogen chloride from chlorine and methane is discarded, all the remaining possibilities are stepwise reaction mechanisms. A slow stepwise reaction is dynamically analogous to the flow of sand through a succession of funnels with different stem diameters. The funnel with the smallest stem will be the most important bottleneck and, if its stem diameter is much smaller than the others, it alone will determine the flow rate. Generally, a multistep chemical reaction will have a slow rate-determining step (analogous to the funnel with the small stem) and other relatively fast steps, which may occur either before or after the slow step. 

Kinetic studies of the reactivity of allyltrialkylsilanes towards the p-methoxy substituted diphenylcarbenium ion revealed an increase of the reaction rate by several orders of magnitude compared to olefins lacking the silyl group383. These studies also indicated that the /i-silylcarbenium ion is generated in the rate-determining step. The reaction rate, however, is dramatically decreased when one or more alkyl groups on silicon are replaced by chlorine atoms383. 

For chlorination, the formation of the (7-complex would be expected to be the rate-determining step since the aromatic chlorination of other substrates does not appear to give rise to deuterium isotope effects (Baciocchi et al., 1960 de la Mare and Lomas, 1967). The effect of the experimental conditions on the rate-determining step in the aqueous bromination of aromatic amines has been investigated in detail by Dubois and his co-workers (Dubois et al., 1968a, b, c Dubois and Uzan, 1968). This work suggests that, for tertiary aromatic amines, the proton loss is fast for para-bromination but partly or wholly rate-determining for ortho-bromination. There is however some... 

The 5-position in 1,2,4-thiadiazoles is most reactive in nucleophilic substitution reactions. Chlorine, for example, may be displaced by nucleophiles (Nu) such as fluoride, hydroxide, thiol, amino, hydrazino, sulfite and azido groups (Scheme 11). Active methylene compounds such as malonic, acetoacetic and cyanoactic esters as their sodio derivatives also displace the 5-halo substituent (65AHC(5)ll9). The reaction follows second-order kinetics, the rate determining step being addition of the nucleophile at C-5 followed by rapid elimination of X. 

This reaction mechanism su ests that the removal of the first chlorine atom is the rate determining step. 

When Aroclor 1268 (a commercial PCB fraction that contains a mixture of CI7, Clg, CI9, and Clio polychloro-biphenyls) is combined with excess O2 , the entire mixture is degraded. Samples taken during the course of the reaction confirm that (a) the most heavily chlorinated members react first (the initial nucleophihc addition is the rate-determining step) and (b) all components are completely dehalogenated. Tests with other PCB mixtures establish that those components with three or more chlorine atoms per phenyl ring are completely degraded by 02--, within several hours. 

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