Peroxides as initiators

In studies of the polymerization kinetics of triaUyl citrate [6299-73-6] the cyclization constant was found to be intermediate between that of diaUyl succinate and DAP (86). Copolymerization reactivity ratios with vinyl monomers have been reported (87). At 60°C with benzoyl peroxide as initiator, triaUyl citrate retards polymerization of styrene, acrylonitrile, vinyl choloride, and vinyl acetate. Properties of polyfunctional aUyl esters are given in Table 7 some of these esters have sharp odors and cause skin irritation. 

Fig. 1. Bulk polymerization of vinyHdene chloride at 45°C, with 0.5 wt % benzoyl peroxide as initiator (29).

Eor bulk copolymerization of methyl, octyl, dodecyl, and octadecyl vinyl ethers using benzoyl peroxide as initiators at 40—100°C with the following comonomers (M, ), where is 0 in all cases (6), the values of are... 

Aliphatic acyloxy radicals undergo facile fragmentation with loss of carbon dioxide (Scheme 3,69) and, with few exceptions,428 do not have sufficient lifetime to enable direct reaction with monomers or other substrates. The rate constants for decarboxylation of aliphatic acyloxy radicals are in the range l 10xl09 M 1 s at 20 °C.429 lister end groups in polymers produced with aliphatic diacyl peroxides as initiators most likely arise by transfer to initiator (see 3.3.2.1,4). The chemistry of the carbon-centered radicals formed by (3-scission of acyloxy radicals is discussed above (see 3.4.1). 

The chlorination of methyl chloroformate in sunlight was first reported by Hentschel, but without a detailed description of either the procedure or the results. The first step of the present procedure for the preparation of trichloromethyl chloroformate utilizes an ultraviolet light source and affords a simple and reproducible way to obtain this reagent. Although trichloromethyl chloroformate may also be synthesized by photochemical chlorination of methyl formate,the volatility of methyl formate causes losses during the reaction and increases the hazard of forming an explosive mixture of its vapor and chlorine gas. The preparation of trichloromethyl chloroformate by chlorination of methyl chloroformate in the dark with diacetyl peroxide as initiator has been reported. However, the procedure consists of several steps, and the overall yield is rather low. 

In chemically-cured materials, one example of an initiator/activator system is hydrogen peroxide as initiator, ascorbic acid as activator and cupric sulphate as co-activator. In light-cured materials, camphorquinone is used as a visible-light photochemical initiator, sodium p-toluene-sulphinate as activator and ethyl 4-dimethylaminobenzoate as photoaccelerator. 

There is a discussion of some of the sources of radicals for mechanistic studies in Section 11.1.4 of Part A. Some of the reactions discussed there, particularly the use of azo compounds and peroxides as initiators, are also important in synthetic chemistry. One of the most useful sources of free radicals in preparative chemistry is the reaction of halides with stannyl radicals. Stannanes undergo hydrogen abstraction reactions and the stannyl radical can then abstract halogen from the alkyl group. For example, net addition of an alkyl group to a reactive double bond can follow halogen abstraction by a stannyl radical. 

Sebastian, D. H. et al., Polym. Eng. Sci., 1976, 16, 117-123 The conditions were determined for runaway/non-runaway polymerisation of styrene in an oil-heated batch reactor at 3 bar, using dibenzoyl peroxide as initiator at 3 concentrations. Results are presented diagrammatically. 

Xanthates serve as a reliable source of electrophilic radicals, and this was exploited by Zard and coworkers for a short synthesis of ( )-matrine (3-304), a naturally occurring alkaloid which has been claimed to have anti-ulcerogenic and anticancer properties [116]. Heating a mixture of xanthate 3-299 and the radical acceptor 3-300 (3 equiv.) in benzene in the presence of lauroyl peroxide as initiator, gave 3-301 in 30% yield and a 3 1 mixture of the tetracylic products 3-302 and 3-303 in 18% yield (Scheme 3.76) [117]. The three compounds could be converted into the... 

VL Antonovskii. Organic Peroxides as Initiators. Moscow Khimiya, 1972 [in Russian],... 

VI Galibey. Study of Acyl Peroxides as Initiators of Radical Polymerisation. Ph.D. thesis Dissertation, OGU, Odessa, 1965 [in Russian]. 

The oxidation of primary and secondary alcohols in the presence of 1-naphthylamine, 2-naphthylamine, or phenyl-1-naphthylamine is characterized by the high values of the inhibition coefficient / > 10 [1-7], Alkylperoxyl, a-ketoperoxyl radicals, and (3-hydroxyperoxyl radicals, like the peroxyl radicals derived from tertiary alcohols, appeared to be incapable of reducing the aminyl radicals formed from aromatic amines. For example, when the oxidation of tert-butanol is inhibited by 1-naphthylamine, the coefficient /is equal to 2, which coincides with the value found in the inhibited oxidation of alkanes [3], However, the addition of hydrogen peroxide to the tert-butanol getting oxidized helps to perform the cyclic chain termination mechanism (1-naphthylamine as the inhibitor, T = 393 K, cumyl peroxide as initiator, p02 = 98 kPa [8]). This is due to the participation of the formed hydroperoxyl radical in the chain termination ... 

The kinetic resolution of racemic trans ester 76a using catalytic amounts of chiral amine-borane 78 and di-f-butyl peroxide as initiator under pho-tolytic conditions at - 74 °C provided the enantioenriched (R,R) product in 74% ee after 52% consumption of the racemate [64-67]. For the ester 76b, (R,R) product in 97% ee was isolated after 75% consumption at -90°C (Scheme 20). 

The reduction of thiocarbonyl derivatives by EtsSiH can be described as a chain process under forced conditions (Reaction 4.50) [89,90]. Indeed, in Reaction (4.51) for example, the reduction of phenyl thiocarbonate in EtsSiD as the solvent needed 1 equiv of dibenzoyl peroxide as initiator at 110 °C, and afforded the desired product in 91 % yield, where the deuterium incorporation was only 48% [90]. Nevertheless, there are some interesting applications for these less reactive silanes in radical chain reactions. For example, this method was used as an efficient deoxygenation step (Reaction 4.52) in the synthesis of 4,4-difluoroglutamine [91]. 1,2-Diols can also be transformed into olefins using the Barton-McCombie methodology. Reaction (4.53) shows the olefination procedure of a bis-xanthate using EtsSiH [89]. 

In the synthesis of peroxides as initiators why is added care wise ... 

Polymer Preparation. Polymers were typically prepared in ethyl acetate solution at reflux temperature using benzoyl peroxide as initiator. They were isolated by two precipitations from ethyl acetate solution into methanol and were dried under vacuum. Molecular parameters of the polymers prepared are listed in Table II. Materials ... 

Gas-phase oxidations of isobutane at 100°C. were carried out with di-ferf-butyl peroxide as initiator as described above. These are summarized in Figure 2, and most are detailed in Table II. Even though conversions were held below 1%, long reaction times (up to 100 hours) were required because of the slow decomposition of the initiator. 

Copolymers of TFE and 2,2-bis(trifluoromethyl)-4,5-difluoro-l,3-dioxole (PDD) were synthesized in C02 at low temperatures using bis(perfluoro-2-N-propoxypro-pionyl) peroxide as initiator [102, 103]. In this case, the copolymers were prepared with different compositions and having a broad range of Tg-values, from 340 to 607 K. No difference could be found between a fluorinated commercial sample (Teflon AF 1601) and a copolymer synthesized in C02 having a similar composition, by using 19F NMR spectroscopy, IR spectroscopy, and differential scanning calorimetry (DSC). 

Tatemoto et al. used peroxides as initiators of polymerisation. Improvement is also possible by using diiodide and polyiodide compounds [316,382],... 

The efficient reductions observed for various organic halides when treated with Et3SiHin two-fold excess in the presence of catalytic amounts of a thiol and di-tert-butyl hyponitrite as initiator confirmed the validity of this approach. Silane-thiol couples were also used, in boiling octane with di-terf-butyl peroxide as initiator, for the reduction of the methylxanthate of 1,2 5,6-di- O -isopropylidene-a-D-glucofuranose, to yield the corresponding deoxy sugar in 60%173 and 70%174... 

A study of the photoaddition of formamide to olefins was undertaken with the aim of finding a new process for converting olefins to higher amides and possibly further to amines by reduction or by the use of the Hofmann rearrangement. Since hydrolysis of the amides to the corresponding carboxylic acids can be effected by standard procedures, this reaction provides a new process for carboxylation of olefins under mild conditions at room temperature. A similar reaction has been shown to take place in a thermal process, using peroxides as initiators (60). 

We conceived that, if the alcohol was to be deoxygenated to a radical, an olefinic linkage would be formed by -elimination of a phenylsulfonyl radical. The xanthate function is a convenient radical source and gave the olefin in about 80% yield in toluene under reflux using AIBN or benzoyl peroxide as initiators and Ph2SiH2.22... 

We have prepared polymethacrylic anhydride by polymerization at 100° in toluene solution with benzoyl peroxide as initiator and at... 

The styrene copolymers were prepared by bulk polymerization at 100°, using benzoyl peroxide as initiator. Methyl methacrylate styrene mole ratios in the feed were 10 90, 25 75, 50 50, 75 25, and 90 10. Conversions varied from 4.5 to 8.1%. Methyl methacrylate a-methyl-styrene copolymers were prepared using benzoyl peroxide at lower a-methylstyrene ratios and U.V. or Co60 gamma radiation to initiate copolymerization at the highest a-methylstyrene ratios, in which reaction is very slow. The mole ratios in the monomer feed were 12 88, 28 72, 54 46, 78 22, and 91.5 8.5. 

Table II shows molecular weight distributions of products from monomer mixtures A and B using 3% dicumyl peroxide as initiator. The molecular weight distributions of the products from the six polymerizations are 3 or less. When, however, the percent of dicumyl peroxide was decreased in the reaction mixture, considerably wider molecular weight distributions resulted (Table III). With less initiator, the chains grow longer and terminate more often by chain transfer.

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