Initiation Of Radical Processes Research Articles

ChemInform Abstract: Iron Catalyzed Oxidative Coupling, Addition, and Functionalization

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Iron Catalyzed Oxidative Coupling, Addition, and Functionalization

AbstractWe cover the achievements and thought process that have emerged as a result of the recent use of iron salts as catalysts for the oxidative coupling, addition, and functionalization on constructing C−C bonds, C−N bonds, C−O bonds, C−S bonds, and C−P bonds. These transformations concomitantly require a stoichiometric oxidant to activate the catalyst: The low‐cost and ubiquity of peroxides is often used as a result of their high oxidative reactivity, resulting in the widespread utilizations of iron catalysis through the initiation of radical processes. Here, we summarize the formation of diverse chemical bonds by using iron oxidative catalysis strategies, including 1) the oxidative coupling strategy and 2) the oxidative addition and functionalization strategy. The oxidative coupling strategy focuses on the formation of one chemical bond in a single reaction, whereas the oxidative addition and functionalization strategy includes the transformations that construct at least two chemical bonds.

Reactions of N-alkylhydrazones of aliphatic ketones

For the first time data concerning the reactions of N-alkylhydrazones of aliphatic ketones have been systematized. The possible reaction centres of hydrazones and the main lines of attack for electrophilic and nucleophilic reagents have been distinguished. Differences in the reactivity of N-alkyl and N-arylhydrazones have been studied. The types of tautomerism of hydrazones and their impact on the reactivity of these compounds have been considered. Most reactions occurring on the sp2-hybridized carbon atom lead to formation of azocompounds, which are generally aliphatic radical sources or initiators of radical processes. The interaction of hydrazones with oxidising reagents leading to the corresponding bisazocompounds has been studied. For a number of N-acylation hydrazones the ring-chain tautomerism has been described, as a result these compounds exist in cyclic and acyclic forms. The general methods for construction of heterocyclic compounds based on N-alkylhydrazones of aliphatic ketones due to cyclization of hydrazones with bis-functional reagents on both nitrogen atoms, as well as the nitrogen atom and the carbon atom have been considered. Hydrazone-enhyidrazine tautomerism is inherent to hydrazones of aliphatic ketones with the α-methylene group; it causes a simultaneous attack of dielectrophiles on the sp3-hybridized carbon atom and the nitrogen atom of hydrazone and can be used to construct derivatives of pyridazine and pyrazole, and the use of compounds of phosphorus and of silicon as dielectrophiles results in formation of phosphodiazoles and silapyrazolines, respectively. Reduction reactions for C=N bond of N-alkylhydrazones of aliphatic ketones have been studied.

Synthesis of α-hydroxyalkyl peroxide esters and ethers as initiators of radical processes

α-Hydroxyalkyl peroxide esters and ethers containing, along with the peroxy bond, also acyloxy and alkoxy groups, are effective initiators of radical processes. The initiation efficiency is due to the capability of these molecules to generate simultaneously oxygen- and carbon-centered radicals capable of hydrogen abstraction from the substrate and of addition to 〉C=C〈 bonds. The selectivity of the synthesis of α-hydroxyalkyl peroxide esters and ethers is mainly determined by the steps of the synthesis and isolation of the intermediate α-chloroalkyl peroxides, because of their high reactivity. Experimental conditions allowing control of the synthesis of α-hydroxyalkyl peroxide esters and ethers were found.

The Hydrophobisation of Activated Carbon Surfaces by Organic Functional Groups

A technique of hydrophobic surface design with a high degree of structural homogeneity has been developed for catalytic materials. Mesoporous activated carbons and silica gel were modified by (A) treatment with vinyltrimethoxysilane (vtms) or (B) chlorination with carbon tetrachloride followed by reaction with a Grignard reagent. Evidence for silica gel modification was obtained from FT-IR and 13C NMR spectroscopy and from elemental analysis. Carbons chemically modified with alkanes and olefins were studied using thermogravimetry (TG) and the results compared with those for the modified silica gel. TG and differential scanning calorimetry (DSC) revealed that the polymerisation of vinyl groups occurred on the carbon surface. The participation of the carrier surface in the initiation of radical processes has been discussed.

Rearrangement of aliphatic sulfoxides in the presence of dicyclohexyl peroxydicarbonate

1. Dialkyl sulfoxides undergo rearrangement in the presence of dicyclohexyl peroxydicarbonate at 55–60°, or using UV-illumination at 60°, to yield the corresponding carbonyl compounds. 2. It was postulated that the reaction has a homolytic character, since carbonyl compounds are not formed at this temperature in the absence of initiators of radical processes.

Redox Systems in the Initiation of Radical Processes. Mechanism of Action

Abstract The following redox systems capable of initiating radical polymerizations are discussed: (1) Systems of the first type, where the reaction leads to the formation of a single radical: (a) Mechanism of action of reversible systems involving dienols and salts of metals of variable valency. (b) Mechanism of the decomposition of hydroperoxides by the action of salts of metals of variable valency in their higher oxidation states. (2) Systems of the second type, where the reaction leads to the formation of two radicals. Mechanism of action and effectiveness of systems involving hydroperoxides, quinol, and sulfite. (3) Systems of the third type, in which the formation of free radicals is not directly linked to the redox process. Mechanism of action of systems involving diazoamino compounds and “polyamine” systems. (4) Crosslinking of unsaturated polymers at low temperatures by the action of redox systems. Transition from crosslinking to destructive processes in presence of oxygen.

Oxidation-Reduction Systems for Initiation of Radical Processes. VI. Systems Involving Oxygen for Initiation of Oxidative Degradation of Polymers

Abstract 1. The mechanism of action of various oxidation-reduction systems containing organic reducing agents, iron salts, and oxygen, is investigated, and it is shown that in hydrocarbon media these systems are an effective source of free radicals at low temperatures. 2. The possibility of utilization of these systems for initiation of a chain process of oxidative degradation of unsaturated and some saturated polymers, at low temperatures, is shown.

Redox systems in the initiation of radical processes and the mechanism of their action

AbstractThe following redox systems capable of initiating radical polymerizations will be discussed: (1) Systems of the first type, where the reaction leads to the formation of a single radical: (a) Mechanism of action of reversible systems involving dienols and salts of metals of variable valency. (b) Mechanism of the decomposition of hydroperoxides by the action of salts of metals of variable valency in their higher oxidation states. (2) Systems of the second type, where the reaction leads to the formation of two radicals. Mechanism of action and effectiveness of systems involving hydroperoxides, quinol, and sulfite. (3) Systems of the third type, in which the formation of free radicals is not directly linked to the redox process. Mechanism of action of systems involving diazoamino compounds and “polyamine” systems. (4) Crosslinking of unsaturated polymers at low temperatures by the action of redox systems. Transition from crosslinking to destructive processes in presence of oxygen.

Oxidation-reduction systems for initiation of radical processes 4. Oxidation-reduction systems for initiation of polymerizations in hydrocarbon media

1. A study was made of the mechanism of action of an oxidation-reduction system comprising isopropylbenzene hydroperoxide (benzoyl peroxide), diethyl dihydroxymaleate (benzoin) and iron naphthenate. 2. Initiation of polymerization in a homogeneous medium under the influence of these systems was demonstrated. 3. It was shown that naphthenates of salts of the -ic form of metals with varying valences in hydrocarbon media greatly speed up the breakdown of isopropylbenzene hydroperoxide, and the possibility of utilizing this reaction for initiation of polymerization was established.