Dialkyl ketone peroxides

The a-oxygen-substituted hydroperoxides and dialkyl peroxides comprise a great variety as shown in Figure 1. When discussing peroxides derived from ketones and hydrogen peroxide, (1) is often referred to as a ketone peroxide monomer and (2) as a ketone peroxide dimer. 

Other peroxides used to initiate polymerization are acyl atkylsulfonyl peroxides (Va), dialkyl peroxydicarbonates (Vb), diperoxyketals (Vc), and ketone peroxides (Vd). ... 

Starting with ketones and hydrogen peroxide in the presence of a catalytic amount of acid, mixtures of up to eight components have been identified, i.e.. (1, X = OH. R3 = H), (1, X = OOH, R3 = H), (2, X = Y = OH). (2, X = Y = OOH), (2, Y = OH, Y = OOH), (3). (4), and (5). The ketone structure and reaction conditions, i.e., acid strength, reactant molar ratios, temperature, and time, determine which compounds form and predominate. Mixtures of several peroxide structures usually are present. Individual peroxides have been isolated from several ketones under different conditions (Table 5). The pure peroxides should be handled with extreme caution since most, especially those derived from the low moleculai weight ketones, ate shock- and friction-sensitive and can explode violently. Methyl ethyl ketone peroxide (MEKP) mixtures are produced commercially only as solutions containing <40 wt% MEKPs in solvents, commonly dialkyl phthalates. 

Dialkyl ketones have been little studied as precursors in this reactioiL Selenium dioxide with hydrogen peroxide and r-butyl alcohol effects a similar reaction with these substrates to give 35-40% yield of the conesponding carboxylic acid. In methyl alkyl ketones, the regioselectivity is of the order of 5 1 in favor of meAyl migration. ... 

The family of dialkyl peroxides includes dicumyl peroxide, which accounts for one-third of the volume of dialkyls world-wide and is the workhorse of this family of peroxides. Dicumyl peroxide is commonly used as a catalyst in polyester resin systans and for cross-linking polyethylene. Benzoyl peroxide is the most common of the diacyl peroxides. It is also used as a catalyst for curing polyester resins. Hydroperoxides are generally used as a raw material to produce other organic peroxides. The most common peroxides in this family include cumene hydroperoxide and t-butyl hydroperoxide. Ketone peroxides are mixtures of peroxides and hydroperoxides that are commonly used for room-temperature curing of polyester resins. Methyl ethyl ketone peroxide (MEKP) is the major product in this family. Peroxydicarbonates are largely used to initiate polymerization of polyvinyl chloride (PVC). 

The cyclic trimer ketone peroxides (eg, methyl ethyl ketone peroxide cyclic trimer [24748-23-0]) have been selectively prepared in dilute solution (in a safety solvent due to the shock sensitivity of the pure peroxide) for use as impromoted, thermal initiators (124,125). They have been shown to effectively modify polyolefins under certain conditions in a manner similar to dialkyl peroxides. 

The world s most popular method of PVC polymerization is the suspension method. Around 80% of PVC is produced this way. The difference in this method is that it uses initiators soluble in the monomer. They are dialkyl and diacyl peroxides, ketone peroxides, peroxo-dicarbonates, peroxo-ketals, alkyl peresters or azo compoimds. Seldom is the role of emulsifiers played by alkalies or buffers in order to improve the plasticizer adsorption in PVC. In this process, in order to obtain proper porosity and particle granulation, so-called suspension stabilizers are used, which are derivatives of meth-ylhydroxypropyl cellulose, karboxymethyl cellulose and poly(vinyl alcohols). PVC obtained this way is of high purity. Its molecular mass depends on the temperature of polymerization. Other parameters depend on the interfacial tension at the water-monomer interface. 

Unsaturated polyester-vinyl monomer systems often require or utilize complicated initiator-accelerator-inhibitor combinations to provide optimum cure-stability profiles.The accelerator is a compound that reacts with the peroxide initiator to generate free radicals at a lower temperature than would be the case in the absence of the accelerator. A wide variety of activators or accelerators have been evaluated and are available for ambient curing of unsaturated polyesters.The combination of methyl ethyl ketone peroxide and cobalt octoate or benzoyl peroxide and N,A-dimethylaniline are particularly effective, commonly employed initiator-accelerator combinations. Of all the combinations studied, the benzoyl peroxide-dialkyl-aniline pair is probably best for obtaining the most complete cure at room temperature. 

Organic peroxides act through the splitting of the —0—0— bond into free radicals, thereby initiating the polymerization or crosslinking of monomers or polymers. Their exceptionally broad line includes diacyl peroxides, dialkyl peroxides, hydroperoxides, ketone peroxides, peroxyketals, peroxydicarbonates, and peroxyesters. The last two are particularly important in PVC resin manufacture as initiators in the polymerization of vinyl chloride monomer. 

Dialkyl peroxides, ozonides, and dimeric and trimeric ketone peroxides do not react. 

Decomposition products from primary and secondary dialkyl peroxides include aldehydes, ketones, alcohols, hydrogen, hydrocarbons, carbon monoxide, and carbon dioxide (44). 

Because di-/ fZ-alkyl peroxides are less susceptible to radical-induced decompositions, they are safer and more efficient radical generators than primary or secondary dialkyl peroxides. They are the preferred dialkyl peroxides for generating free radicals for commercial appHcations. Without reactive substrates present, di-/ fZ-alkyl peroxides decompose to generate alcohols, ketones, hydrocarbons, and minor amounts of ethers, epoxides, and carbon monoxide. Photolysis of di-/ fZ-butyl peroxide generates / fZ-butoxy radicals at low temperatures (75), whereas thermolysis at high temperatures generates methyl radicals by P-scission (44). 

In the presence of base, di-Z f/-alkyl peroxides are stable, however primary and secondary diaLkyl peroxides undergo oxygen—oxygen bond cleavage, forming alcohols, aldehydes, and ketones (44,66) ... 

Hydroxyalkyl hydroperoxides from cycHc ketones (1), where X = OH, R =, H and R, R = alkylene, apparentiy exist in solution as equihbrium mixtures of the cycHc ketone, hydrogen peroxide, and other peroxides, eg, the dihydroperoxide (1) in which X = OOH, and dialkyl peroxides (2) where X = OH and Y = OH or OOH. Due to the existence of this equihbrium, the latter two dialkyl peroxides react as mixtures of monomeric hydroperoxides in solution. 

Condensation with Aldehydes and Ketones. Succinic anhydride and succinic esters in the presence of different catalysts react in the gas phase with formaldehyde to give citraconic acid or anhydride and itaconic acid (94—96). Dialkyl acyl succinates are obtained by reaction of dialkyl succinates with C 4 aldehydes over peroxide catalysts (97). 

Dialkyl peroxides and hydroperoxides which have either a hydroxy, hydroperoxy, alkoxy, or alkylpcroxy group on the carbon adjacent to the parent peroxide group arc considered separately from the parent compounds due to their unique reactions and properties, hut mainly because of their unique syntheses. Their primary preparation from aldehydes and ketones via reaction with hydrogen peroxide, alkyl hydroperoxides and pcroxyacids is unique and makes it almost impossible to discuss diem without referring to the parent carbonyl compound(s). 

The photooxidation of mono-ketones appears to proceed at all wavelengths as if one were studying the oxidation of the radicals produced by photolysis. This appears to be true also for dialkyl peroxides, aldehydes, and azoalkanes. In the photooxidation of diacetyl there is evidence that at longer wavelengths reaction occurs between excited molecules and oxygen, whereas with ketene under similar conditions deactivation of the excited molecule appears to be the chief reaction. 

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