Vinyl compounds, peroxide-forming

List B contains all compounds that form peroxides which become dangerous when they reach a critical concentration. The danger will often become apparent during distillation operations. For hydrocarbons, this is the case for deca- and tetrahydronaphthalene, cyclohexene, dicyclopentadiene, propyne and butadiene. S ondary alcohols such as 2-butanol also form part of this list. Finally, for ethers there are diethyl ethers, ethyl and vinyl ethers, tetrahydrofuran, 1,4-dioxan, ethylene glycol diethers and monoethers. 

Thus, a large number of substances with the structural features shown above may form peroxides. However, these substances do not present a peroxide hazard to the same extent. The tendency of organic compounds to form peroxides decreases according to their structures as follows ethers and acetals > olefins > halogenated olefins > vinyl compounds > dienes > aUcynes > alkylbenzenes > isoparaffins > alkenyl esters > secondary alcohols > ketones > aldehydes > ureas and amides. 

A molar equivalent of hydrogen peroxide to monomer and horseradish peroxidase is a well-known redox system that catalyzes the free radical polymerization of phenol, anilines, and their derivatives [6-14]. Horseradish peroxidase-mediated polymerization of styrene and methyl methacrylate, with a monomer (styrene or methyl methacrylate) to hydrogen peroxide ratio of 40 1, did not occur in the absence of 2,4-pentanedione. Therefore, it is likely that this compound is involved in the initiation of free radical formation. A reasonable hypothesis for the horseradish peroxidase-catalyzed polymerization of vinyl monomers is that the enzyme is oxidized by hydrogen peroxide and passes from its native state through two catalytically active forms (Ez and Ezz). Each of these active forms oxidizes the initiator (b-diketone, 2,4-pentanedione) while the enzyme returns to the native form. The Ezz state of enzyme is oxidized by hydrogen peroxide to produce inactive enzyme, Ezzz, which spontaneously reverts to the native form of enzyme. The free radicals produced from the initiator generate radicals in the vinyl monomer to form polymer (Fig. 2). 

Polymerization reactions. There are two broad types of polymerization reactions, those which involve a termination step and those which do not. An example that involves a termination step is free-radical polymerization of an alkene molecule. The polymerization requires a free radical from an initiator compound such as a peroxide. The initiator breaks down to form a free radical (e.g., CH3 or OH), which attaches to a molecule of alkene and in so doing generates another free radical. Consider the polymerization of vinyl chloride from a free-radical initiator R. An initiation step first occurs ... 

Such copolymers of oxygen have been prepared from styrene, a-methylstyrene, indene, ketenes, butadiene, isoprene, l,l-diphen5iethylene, methyl methacrjiate, methyl acrylate, acrylonitrile, and vinyl chloride (44,66,109). 1,3-Dienes, such as butadiene, yield randomly distributed 1,2- and 1,4-copolymers. Oxygen pressure and olefin stmcture are important factors in these reactions for example, other products, eg, carbonyl compounds, epoxides, etc, can form at low oxygen pressures. Polymers possessing dialkyl peroxide moieties in the polymer backbone have also been prepared by base-catalyzed condensations of di(hydroxy-/ f2 -alkyl) peroxides with dibasic acid chlorides or bis(chloroformates) (110). 

Methyl ethyl ketone may also he produced hy the catalyzed dehydrogenation of sec-hutanol over zinc oxide or brass at about 500°C. The yield from this process is approximately 95%. MEK is used mainly as a solvent in vinyl and acrylic coatings, in nitrocellulose lacquers, and in adhesives. It is a selective solvent in dewaxing lubricating oils where it dissolves the oil and leaves out the wax. MEK is also used to synthesize various compounds such as methyl ethyl ketone peroxide, a polymerization catalyst used to form acrylic and polyester polymers and methyl pentynol by reacting with acetylene ... 

Inhibitors can be injected into the system in order to kill active species present, for example, by neutralizing the catalyst or by capturing free radicals in a polymerization. For example, the Lewis acid, BF3-complex can be killed using gaseous NH3 since the inactive compound BF3 NH3 is formed, and the reaction stops for lack of active centers. An antioxidant such as hydroquinone can be used to capture peroxide radicals to control reactions involving vinyl-type monomeric substances. 

Solid styrene was exposed at — 196°C to ozone, in an attempt to discern whether the behavior of the system is similar to that of olefinic compounds, yielding an ozonide, or to that of aromatic compounds, yielding a 7r-complex. On heating to about — 100°C, an adduct is formed that is stable until about —55 °C, when benzaldehyde and a peroxidic polymer are slowly obtained. The structure of the adduct is probably that of a POZ, based on the similarity of the IR spectrum with the ozone adduct of vinyl chloride described in the preceding paragraph . 

The title compound, 1,3-dideuteriated malondialdehyde, MDA-46, formed in a lipid peroxidation process involved in the pathogenesis of many human diseases45,46, has been needed for quantitative determination of MDA in human blood or urine by isotope dilution mass spectrometry. It has been synthesized47 by condensation of deuteriated butyl vinyl ether with deuteriated triethyl orthoformate in the presence of montmorillonite clay K-10 (equation 18). 

In addition (chain) polymerization, monomers containing an unsaturated (vinyl) bond polymerize in the presence of an initiator, which generates an active site at the end of the chain. Several chemical reactions take place simultaneously in the course of the polymerization. First, an initiation reaction via photo- or heat-decomposition of the initiator occurs to form the active species, which are either peroxides or azo compounds. The active species react with a monomer to generate the active site (i.e., initiation). 

The color change and the sensitivity of conversion to order of addition of monomers and peroxide indicate that in order to obtain an AFR polymer the polar monomers must first be complexed or allowed to react with the active or living end of the anionic polymer chain, or otherwise solvate it before the polymer chain is attacked by the peroxide. Success or failure of the subsequent free radical block polymerization depends on the nature of the complex or reaction product formed. The resultant species are no longer active for propylene polymerization. The necessity of complex formation has also been observed by Milovskaya and coworkers (4). They have shown that vinyl chloride, a weak complexing agent, can be polymerized effectively with triethylaluminum peroxide only when it is present with a more active complexing compound such as an ester or an ether. 

Vinyl-substituted aromatic compounds such as a-methylstyrene,148 /S-isopropylstyrene,148 1-phenylcyclohexene,153 indene, 149 and 1,2-dihydronaphthalene151,152 give cyclic peroxides on autoxidation. For example, /3-isopropylstyrene gives the 1,2-dioxene derivative (149) together with polymeric peroxide. After the alkyl hydroperoxide formed by attack of oxygen on the isopropyl group had been reduced with sodium sulfite, 149 could be isolated in 26.4% yield by means of an alumina column. 

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