Oxidation of ethers with dimethyldioxirane

Abstract

Oxidation of a series of tert butyl ethers Bu t OR (R = Me, Et, CH 2 CH 2 Cl, Pr i , Bu i ), diethyl ether, diisopropyl ether, 1,2 dimethoxyethane, diisobutoxymethane, 1,4 dioxane, and tetra hydrofuran with dimethyldioxirane (DMDO) was studied. The reaction kinetics obeys the second order equation w = k[DMDO] [ether]. The rate constants in a range of 5-50 °C and the activation parameters of the reaction were determined. The solvent effect on the oxidation rate was studied. The oxidation products are the corresponding alcohols and carbonyl com pounds. The competition between the nonradical (oxygen insertion) and radical mechanisms of the reaction is discussed. The reactions of the parent dioxirane and DMDO with a series of methyl ethers MeOR´ (R´ = Me, Et, CH 2 CH 2 F, Pr i ) were studied by the density functional theory (DFT). The (U)B3LYP 6 311G(d,p) method was employed to calculate the geometry and energies of the reactants and transition states. The data obtained indicate a possible increase in the probability of oxidation via the radical route and an increase in the activation barrier for the substrates containing electron withdrawing substituents.The chemistry of dioxiranes was under intense devel opment for the last two decades. 1,2 A distinctive feature of these cyclic peroxides is a combination of high reactivity and selectivity of oxidation reactions. 3 The works con cerning the oxidation of ethers with dioxiranes are few and, as rule, synthetic. For instance, the transformation of steroid ethers to the corresponding ketones was stud ied. 4 The oxidation of O isopropylidene diol derivatives to 2 hydroxyketones and the oxidation of benzyl ethers were studied, 5,6 and a nonradical nature was postulated for these reactions. The oxidation of 1,3 dihydroiso benzofuran with dimethyldioxirane (DMDO) to 2 hydr oxymethylbenzaldehyde was assumed 7 to involve radi cals; however, the total composition of the products was not reported. The study 8 of the reaction products of dialkyl ethers with dioxiranes suggested the radical nature of this reaction, which has been developed further. 9,10 The study 10 of the products and kinetics of oxidation of ethers with DMDO concluded the competition of two processes: insertion of the oxygen atom at the C-H bond of the substrate and hydrogen atom abstraction followed by fast recombination of the radical pair that formed. The effect of oxygen on the yield of the products and conversion of the substrate were demonstrated for para substituted ana logs of 1 methoxy 1 phenylethane. Analysis of the ki netic data in the framework of the Hammett equation gives ρ = -0.74±0.03 (25 °C). 10 However, the mecha nism of oxidation of different ethers was not studied sys tematically. We have previously 11,12 shown that C-H bonds of alkanes and alcohols are oxidized with DMDO via two parallel channels, nonradical and homolytic. The ratio of these processes was determined. In the present work, we studied the products and kinetics of the reac tions of DMDO with aliphatic ethers 1-12 and the influ e...

Glymes as versatile solvents for chemical reactions and processes: from the laboratory to industry

“…Grabovskiy et al 320 studied the oxidation of a series of ethers including monoglyme by dimethyldioxirane (DMDO), and suggested a second-order reaction kinetics r = k [DMDO][ether]. They also determined the rate constants between 5 and 50 °C as well as the activation parameters of the reaction.…”

Three‐Membered Heterocycles. Structure and Reactivity

“…In any event, lability towards oxidation is enhanced by adjacent heteroatoms. For example, ethyl t-butyl ether (848) suffers practically quantitative oxidative degradation to t-butanol (850) and acetaldehyde (851) via an initially formed hemiacetal intermediate (849) [820], which explains the previously reported observation that DMD solutions lose titer in the presence of adventitious ether contaminants [821]. Through a similar mechanism, dioxiranes convert alcohols into ketones, as illustrated by the oxidation of epoxyal-cohol 852 to the corresponding ketone (853) in excellent yield upon treatment with TFD in methylene chloride and trifluoropropanone (TFP) [120].…”

An Expeditious Method for the Preparation of 2-Hydroxy-1,4-dioxane and Its Use in Reductive Alkylation of Amines

“…Previously reported preparations of 2-hydroxy-1,4-dioxane (2¢) are based on catalytic oxygenation of 1,4dioxane 3,4 and oxidative decomposition of N-nitrosomorpholine-3-carboxylic acid and some other N-nitrosomorpholine derivatives. 5 Both methods, however, require complex catalytic systems and proceed with low selectivity and yields.…”