Free radicals cumyl

Cumyl aUyl peroxide, determination, 708 Cumyl free radical, 697 Cumyl hydroperoxide (CHP) hydrogen bonding, 103-4 hydrogen peroxide determination, 629, 637, 643, 680, 682-3... 

DIITIATORS - FREE-RADICAL INITIATORS] (Vol 14) tert-Cumyl peroxyneoheptanoate [104852-44-0]... 

Polymers, Resins, and Coatings. Peroxyesters of neodecanoic acid, such as / i -butylperoxyneodecanoate [26748-41-4] and a-cumyl peroxyneodecanoate [26748-47-0], constitute one of the most important uses for neodecanoic acid. These materials are used as free-radical initiators in the polymeri2ation of vinyl chloride (85), acrylates (86), ethylene (87), styrene [100-42-5] (87), and in the copolymeri2ation of vinyl chloride with other monomers, such as propylene [115-07-1] (88), or acrylates (89). The peroxyesters are also used as curing agents for resins (90). 

Hock and Kropf [253] studied cumene oxidation catalyzed by Pb02. They proposed that Pb02 decomposed cumyl hydroperoxide (ROOH) into free radicals (R0 , R02 ). The free radicals started the chain oxidation of cumene in the liquid phase. Lead dioxide introduced into cumene was found to be reduced to lead oxide. The reduction product lead oxide was found to possess catalytic activity. The following tentative mechanism was proposed. 

By the free radical acceptor method in the decomposition of cumyl hydroperoxide catalyzed by Fe203 (343 K, 0.25 g cm-3 Fe203, ionol as acceptor of free radicals [257])... 

Hydroperoxides oxidize aromatic amines more readily than analogous phenols. Thus, at 368 K cumyl hydroperoxide oxidizes a-naphthylamine and a-naphthol with ku = 1.4 x 10 4 and 1.7 x 10 5L mol-1 s 1, respectively [115,118], The oxidation of amines with hydroperoxides occurs apparently by chain mechanism, since the step of free radical generation proceeds much more slowly. This was proved in experiments on amines oxidation by cumyl hydroperoxide in the presence of /V,/V -diphcnyl-l, 4-phcnylcnediamine (QH2) as a radical acceptor [125]. The following reactions were supposed to occur in solution (80% decane and 20% chlorobenzene) ... 

These reactions produce free radicals, as follows from the fact of consumption of free radical acceptor [42]. The oxidation of ethylbenzene in the presence of thiophenol is accompanied by CL induced by peroxyl radicals of ethylbenzene [43]. Dilauryl dithiopropionate induces the pro-oxidative effect in the oxidation of cumene in the presence of cumyl hydroperoxide [44] provided that the latter is added at a sufficiently high proportion ([sulfide]/[ROOH] > 2). By analogy with similar systems, it can be suggested that sulfide should react with ROOH both heterolytically (the major reaction) and homolytically producing free radicals. When dilauryl dithiopropionate reacts with cumyl hydroperoxide in chlorobenzene, the rate constants of these reactions (molecular m and homolytic i) in chlorobenzene are [42]... 

Many organic peroxides and hydroperoxides are known.30 Peroxo carboxylic acids (e.g., peroxoacetic acid, CH3CO OOH) can be obtained by the action of H202 on acid anhydrides. Peroxoacetic acid is made as 10 to 55% aqueous solutions containing some acetic acid by interaction of 50% H202 and acetic acid, with H2S04 as catalyst at 45 to 60°C the dilute acid is distilled under reduced pressure. It is also made by air oxidation of acetaldehyde. The peroxo acids are useful oxidants and sources of free radicals [e.g., by treatment with Fe2+(aq)]. Dibenzoyl peroxide, di-r-butyl peroxide, and cumyl hydroperoxide are moderately stable and widely used as polymerization initiators and for other purposes where free-radical initiation is required. 

Most phenol nowadays is obtained from isopropylbenzene (cumene), which is oxidized by air in the cumene proces.s (Scheme 4.1). Acetone (propanone) is a valuable by-product of the process and this route is a major source of this important solvent. The formation of cumene hydroperoxide proceeds by a free radical chain reaction initiated by the ready generation of the tertiary benzylic cumyl radical, which is a further illustration of the ease of attack at the benzylic position, especially by radicals (see Chapter 3). 

Such reactions take place with p-xylene [28], ethylbenzene [28], and especially readily with isopropylbenzene (cumene) [29], where the intermediate free radical is stabilized not only by the aromatic ring but also by the two adjacent methyl groups. The oxidation of cumene to cumyl hydroperoxide (equation 162) followed by acid treatment is a basis for the large-scale production of phenol. 

Post-heating of a shaped polyethylene which induces its crosslinking may sometimes lead to an undesired deformation of the product. To overcome this difficulty, two-component redox-initiating systems producing free radicals at lower temperatures have been designed [108]. The reaction system involved cumyl hydroperoxide and a transition metal ion, whose higher and lower oxidation states differ by one electron. The decomposition of hydroperoxide proceeds by an electron transfer mechanism an electron is transferred from the metallic ion (e.g. Co ) to the peroxidic bond which splits into two fragments. 

When the ferrocenium salts are applied in conjunction with alkyl hydroperoxides such as cumyl hydroperoxide, they yield, on exposure to light, reactive free radicals, as shown in Scheme 10.5. 

Table 20-1. Half-Lives and Activation Energies of Decomposition of Some Free Radical Initiators AI BN, Azobisisobutyronitrile BPO, Dibenzoyl Peroxide MEKP, Methyl Ethyl Ketone Peroxide IPP, Diisopropyl Peroxide Dicarbonate Dicup, Dicumyl Peroxide CuHP, Cumyl Hydroperoxide...

Several amino-styrenic monomers are known for example see 19C—23C in Figure 38. The simplest of these, the primary amine species 4-vinylaniline (or 4-aminostyrene), 23C, is susceptible to polymerization imder conventional free radical conditions, as are 19C-22C. For example, the UV-induced graft polymerization of 23C from a Si surface was recently disclosed (218). These monomers tend to polymerize most effectively in aqueous media in their hydrochloride salt form. Given the reactive nature of the amine functionality in 23C it is also a suitable precursor for the synthesis of novel amide-based styrenics (219). The controlled polymerization of 19C, 20C, and 22C, under classical anionic conditions is also possible (220,221). For example, AB diblock copol5uners of22C with styrene can be prepared at -78°C, in THF using cumyl potassium as the initiator with 22C being polymerized first. Near-monodisperse w-butyl quats of 19C, 20C, and 22C have also been reported. These were prepared by the post-polymerization modification of polymers from 19C, 20C, and 22C with R-butyl bromide (220). 

The reaction of cumyl radical with oxygen is a propagation step in the free-radical chain reaction that converts cumene to cumene hydroperoxide. Write an equation for the next step in the chain. Hint What is the hydrogen atom donor )... 

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