Oxidation of hydrocarbons. 11. Kinetics and mechanism of the reaction between methyl (E)-cinnamate and quaternary ammonium permanganates

Abstract

A study of the reaction of methyl (£)-cinnamate with quaternary ammonium permanganates in methylene chloride solutions has been completed. The rate of reaction is fastest for those ions which permit the interionic distance in the quaternary ammonium ion pair to be minimized. The Hammett p value for the reaction is 0.95 at 20 °C, and an inverse secondary deuterium isotope effect is observed at the ß-position but not at the «-position. The sign of the p value for this reaction is in direct contrast to the reported value (-0.6) for the oxidation of alkyl vinyl ethers in aqueous dioxane solutions. On the other hand, the fact that the activation parameters for the two reactions are almost identical suggests that the reaction mechanisms cannot be widely divergent. An attempt has been made to visualize a mechanism in which the reactions can proceed through similar intermediates but via either an electron-rich or an electron-deficient transition state depending on the demands of the substituents. The apparent change in mechanism is considered to be simply a reflection of nature's ability to find the lowest energy surface between two points.

Oxidation of hydrocarbons. 17. Solvent and substituent effects on the oxidation of styrene derivatives by quaternary ammonium permanganates

“…Plots of In (A -A 3 against time were linear (lo), thus indicating that the reaction is first order in pennanganate. The pseudo-first-order rate constants, obtained from the slopes of these plots, were found to be directly proportional to the concentration of the reductant, thereby confirming that the reaction is also first order in reductant concentration (10).…”

“…Since some substituted alkenes (such as methyl cinnamates) that are capable of delocalizing negative charges exhibit positive p values, while other alkenes (such as vinyl ethers) that are able to stabilize positive charges exhibit negative p values, it is not surprising that for certain reactions, the sign of p actually changes when different substituents are present. The oxidation of substituted stilbenes, which has been studied by Henbest et al (28), is one example of this phenomenon; the rate of reaction is accelerated by both electron-donating and electron-withdrawing substituents (10). The oxidation of substituted P-methoxy and P-bromostyrenes also gives Hammett plots with a distinctive Can.…”

“…For example, this reaction has been used for the oxidation of aliphatic hydrocarbons (2), arenes (2,3), alcohols (4,5), aldehydes (5,6), ethers (7), sulfides (8), amines (9), and alkenes (10).…”

Oxidation of hydrocarbons. 15. A study of the oxidation of alkenes by methyltributylammonium permanganate

“…Since there is an overwhelming abundance'bf evidence (3) that these reactions are initiated by the formation of a cyclic manganese(V) diester, 1, it has previously been suggested that the detected product of the reaction could actually be a dimer or a polymer of 1 (5). This possibility appears, however, to be inconsistent with an oxidation state of +4, and with the observation that products of similar properties are also obtained from the reduction of permanganate by alkynes, alcohols, and amines under these conditions (Table 2).…”

“…Equation [5] implies that a linear relationship should exist between A(526) and A(418). However, Fig.…”