Peroxide initiators alkyl

In general, aliphatic diacyl peroxide initiators should be considered as sources of alkyl, rather than of aeyloxy radicals. With few exceptions, aliphatic acyloxy radicals have a transient existence at best. For certain diacyl peroxides (36) where R is a secondary or tertiary alkyl group there is controversy as to whether loss of carbon dioxide occurs in concert with 0-0 bond cleavage. Thus, ester end groups observed in polymers prepared with aliphatic diaeyl peroxides are unlikely to arise directly from initiation, but rather from transfer to initiator (see 3.3,2.1.4),... 

Solvent dependence of k, for di-r-alkyl peroxides is small when compared to most other peroxide initiators.128 212 For di-/-butyl peroxide,128 d is slightly greater (up to two-fold at 125 °C) in protic (/-butanol, acetic acid) or dipolar aprotic solvents than in other media (cyclohexane, triethylamine, tetrahydrofuran). 

In 1993, Linford firstly reported a quite useful method to prepare monolayers of alkyl chains by thermal hydros-ilylation of hydrogen-terminated silicon surfaces [25]. Alkyl chains are covalently bound to Si surface by Si-C bonds. This thermal hydrosilylation could be attributed to a free-radical process with 1-alkene. First, a diacyl peroxide initiator was used to produce free radicals. However, at higher temperature, only hydrogen-terminated silicon and a neat solution of 1-alkene or 1-alkyne can form Si-C linkages [26]. Furthermore, lately it is found that such Si-C covalent links can be observed even in dilute solutions of 1-alkenes [27]. In that case, the density of monolayer packing strongly depends on the reaction temperature. 

Robert and Meunier also observed that the most promising leads for antimalarial drug development are all lipophilic (allowing rapid diffusion through ceU membranes) and all adopt a boat conformation of the peroxide ring, allowing the peroxide bond to dock closely with heme and initiate alkylation. 

Organic peroxides acyl peroxides (benzoyl, acetyl, lauryl peroxides, etc), alkyl peroxides, hydroperoxides, etc. are used as polymerization initiators. Azocompounds (for example, redox systems, etc. are also widely used as initiators. In... 

Attachment of substituents incompatible to ozone required a different general synthetic route. For example, allyl acid 59 displayed poor chemoselectivity on exposure to ozone. Contrary to reports of alkaline decomposition of the lactone-acetal-peroxide functionality,16 the enolate of the prefabricated tetracycle 42 could be generated at low temperature and alkylated. As a notable example, this methodology produced a single allylated tetracycle, the a-epimer 59. This initial alkylation product was unchanged after prolonged acid treatment, and structure 57 was... 

Chapter 1 is used to review the history of polyethylene, to survey quintessential features and nomenclatures for this versatile polymer and to introduce transition metal catalysts (the most important catalysts for industrial polyethylene). Free radical polymerization of ethylene and organic peroxide initiators are discussed in Chapter 2. Also in Chapter 2, hazards of organic peroxides and high pressure processes are briefly addressed. Transition metal catalysts are essential to production of nearly three quarters of all polyethylene manufactured and are described in Chapters 3, 5 and 6. Metal alkyl cocatalysts used with transition metal catalysts and their potentially hazardous reactivity with air and water are reviewed in Chapter 4. Chapter 7 gives an overview of processes used in manufacture of polyethylene and contrasts the wide range of operating conditions characteristic of each process. Chapter 8 surveys downstream aspects of polyethylene (additives, rheology, environmental issues, etc.). However, topics in Chapter 8 are complex and extensive subjects unto themselves and detailed discussions are beyond the scope of an introductory text. 

An autoxidative procedure has been described by the initial alkylation of phenol with cyclopentadiene in the presence of phosphoric add at ambient temperature giving 4-(cyclopenten-2-yl)phenol, in more than 80% yield followed by isomerisation in 91% yield to the 1-isomer during 2 hours in refluxing benzene solution with a catalytic quantity of dichlorobis(benzonitrile)palladium(ll). The conjugated product with 30% hydrogen peroxide and hydrochloric add upon stirring at 50°C for 3 hours afforded 1,4-dihydroxybenzene in 92% yield accompanied by cyclopentanone (ref.46). 

The reaction between dialkyl hydrogen phosphonates and monocarbonyl compounds to give dialkyl (l-hydroxyalkyl)phosphdnates is catalysed by alumina such esters have been condensed with phthalimide to give the phosphonates (38). The peroxide-initiated addition of aliphatic aldehydes R CHO to the appropriate dialkyl (alkenyl)phosphonate yields the 3- or 5-oxoalkyl-phosphonates (39 = 0 or 1 R = H or Ci—Cy alkyl). ... 

Diacetyl peroxide, peroxydicarbonates, alkyl peroxyesters and AIBN used as initiator... 

Low-density polyethylene (LDPE) is industrially synthesized by a free-radical process using peroxide initiators at high temperatures and pressures. LDPE has a highly branched structure due to hydrogen atom shifts that convert a primary alkyl radical to a secondary alkyl radical. Plants that can accomodate this high-pressure process are expensive to build and operate. Therefore, LDPE formed by radical reactions is slowly being replaced by LLDPE prepared by reactions catalyzed by transition metal complexes. 

The characteristic feature of a chain-initiation step is the formation of radicals from a molecule with only paired electrons. In the case of peroxide-initiated polymerizations of alkenes, chain initiation is by (1) heat cleavage of the O—O bond of a peroxide to give two alkoxy radicals and (2) reaction of an alkoxy radical with a molecule of alkene to give an alkyl radical. In the general mechanism shown, the initiating catalyst is given the symbol In-In and its radical is given the symbol In. ... 

Di(fert-alkyl) Peroxides. Some commercially available dialkyl peroxides and their corresponding 10-h half-life temperatures in dodecane are hsted in Table 6 (111). Dialkyl peroxides initially cleave at the oxygen-oxygen bond to generate alkoxy radical pairs ... 

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