Iodide reaction

The reaction involving chlorite and iodide ions in the presence of malonic acid, the CIMA reaction, is another that supports oscillatory behaviour in a batch system (the chlorite-iodide reaction being a classic clock system the CIMA system also shows reaction-diffusion wave behaviour similar to the BZ reaction, see section A3.14.4). The initial reactants, chlorite and iodide are rapidly consumed, producing CIO2 and I2 which subsequently play the role of reactants . If the system is assembled from these species initially, we have the CDIMA reaction. The chemistry of this oscillator is driven by the following overall processes, with the empirical rate laws as given ... 

A1 9 OCTALONE 2, 46, 80 A9(10,-Octdlone 2,45, 80 Octanal, 47, 96 Octanoyl fluoride, 46, 6 M-Octyl iodide, reaction with tnmethyl amine oxide to yield octanal, 47, 96... 

Melhylenecydobutane-l,2-dicar-boxylic anhydride, 43,27 Methylenecydobutanes by addition of allenes to alkenes, 43, 30 Methylenecyclohexane, 40, 66 Methylene iodide, reaction with zinc-copper couple and cyclohexene, 41, 73... 

It is important that in the two organic equilibria involving iodide reaction (Equation (2)) shows complete conversion of methanol to methyl iodide, whereas the reaction with acetyl iodide shows complete conversion to acetic acid and hydrogen iodide (Equation (3)) ... 

Fox, R. O., G. Erjaee, and Q. Zou (1994). Bifurcation and stability analysis of micromixing effects in the chlorite-iodide reaction. Chemical Engineering Science 49, 3465-3484. 

The KIE in the 2,6-dimethylpyridine-methyl iodide reaction is more than twice the KIE in the 2-methylpyridine-methyl iodide reaction. This is also consistent with a steric origin for the KIE because the 2,6-dimethylpyridine transition state must be much more sterically crowded than the 2-methyl-pyridine transition state. If the increase had been due to an inductive effect, the increase in the KIE in the 2,6-dimethylpyridine reaction should have been approximately twice the KIE for the 2-methylpyridine reaction, i.e. approximately 0.94 rather than the 0.91 that was observed. 

The steric rather than the inductive origin of the secondary deuterium KIE is also suggested because kH/kD = 0.994 per deuterium found in the per-deuteropyridine-methyl iodide reaction is smaller (less inverse) than the kH/kn = 0.988 per deuterium found for the 4-deuteropyridine reaction. A secondary inductive KIE should be more inverse when a deuterium is substituted for a hydrogen nearer the reaction centre, i.e. at the meta- or ortho-rather than at the para-position of the pyridine ring. Thus, if the KIE were inductive in origin, the KIE in the perdeuteropyridine reaction should be more inverse than that observed for the 4-deuteropyridine reaction. If the observed KIE were the result of a steric KIE, on the other hand, a less inverse KIE per deuterium could be found in the perdeuteropyridine reaction, i.e. a less inverse KIE per deuterium would be expected if there were little or no increase in steric hindrance around the C—H(D) bonds as the substrate was converted into the SN2 transition state. Since the KIE per D for the perdeuteropyridine reaction is less than 1%, the transition state must not be sterically crowded and the KIE must be steric in origin. Finally, the secondary deuterium KIEs observed in the reactions between 2-methyl-d3-pyridine and methyl-, ethyl- and isopropyl iodides (entries 3, 7 and 9, Table 17) are not consistent with an inductive KIE. If an inductive KIE were important in these reactions, one would expect the same KIE for all three reactions because the deuteriums would increase the nucleophilicity of the pyridine by the same amount in each reaction. The different KIEs for these three reactions are consistent with a steric KIE because the most inverse KIE is observed in the isopropyl iodide reaction, which would be expected to have the most crowded transition state, and the least inverse KIE is found in the methyl iodide reaction, where the transition state is the least crowded. 

Large (near the theoretical maximum) a-carbon KIEs for the Menshutkin reactions between 3,5-disubstituted pyridines and methyl iodide [reaction (22) Table 20] have also been reported by Yamataka and co-workers (Ando et al., 1987). Although the a-carbon KIEs increase slightly as more electron-withdrawing substituents are added to the nucleophile, they are all large and... 

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