Dibenzoyl peroxide as initiator

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. 

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]. 

N,2,4,6-Tetracbloroacetanilide, Cl3CeH2NClCOCH3. Mol. wt. 272.96, m.p. 75°. Preparation from 2,4,6-trichloroacetanilide and sodium hypochlorite. Chlorination. In the presence of dibenzoyl peroxide as initiator, the reagent chlorinates alkanes, cycloalkanes, and alkylbenzenes (side chain). ... 

These "polymer-polyols" are made by the in situ polymerization of vinyl monomers such as acrylonitrile (although grafting with other monomers has also been reported in a liquid polyol solution, e.g., polyether triol of molecular weight 3000) to give stable dispersions of the polymeric portion in the liquid polyol. Grafting is carried out with azobis(isobutyronitrile) or dibenzoyl peroxide as initiators at 80-90 °C. A polymer-polyol containing about 20% acrylonitrile appeared to be the best compromise between polyol viscosity and urethane foam properties (108). 

Polymerization conditions bulk polymerization using dibenzoyl peroxide as initiator. The polymerization was conducted under reduced pressure in sealed ampoules. 

Polymerization conditions Polymerization using dibenzoyl peroxide as initiator (1.12% of the monomer system) was conducted at 80.0° 0.2°C in sealed ampoules for 12 hr with degassing procedure as indicated. 

Radical cyclization with iodine atom transfer of a highly functionalized propiolic ester 103 using dibenzoyl peroxide as an initiator gave the a-methylene-y-butyrolactone 104 in good yield [95T11257]. The relative stereochemistry at carbon atoms 4 and 5 are established during the reaction. The intermediate 104 has been converted to the anti-tumor agent (-)-methylenolactocin 105. 

The most important autoxidation used industrially is the synthesis of cumene hydroperoxide from cumene and air (i.e., diluted oxygen) (Figure 1.37). It is initiated by catalytic amounts of dibenzoyl peroxide as the radical initiator (cf. Figure 1.11). The cumyl radical is produced... 

A number of radical reactions involving substitution at an allyUc position, for example with TV-bromosucdnimide (NBS), are useful synthetic methods. NBS, in the presence of dibenzoyl peroxide as an initiator, reacts more rapidly at a secondary rather than a primary allylic position. 

Polymerization conditions The water to monomer ratio was 2 to 1 by volume. Polymerization was conducted at 65°C using 1 gm poly(vinyl alcohol) per 100 ml water with dibenzoyl peroxide as the initiator. Considering the high conversion within relatively short reaction times, we suspect that the data refers to the use of 2,2 -azobisisobutyronitrile at 65 C, rather than dibenzoyl peroxide. 

Radical addition of tosyl chloride to norbornene and aldrin without skeletal rearrangement can be achieved using Dibenzoyl Peroxide as an initiator (eq 37). Reaction with 1,4-norborna-diene gives rise to a rearranged addition product. 

Aromatic diacyl peroxides such as dibenzoyl peroxide (BPO) [94-36-0] may be used with promoters to lower the usehil decomposition temperatures of the peroxides, although usually with some sacrifice to radical generation efficiency. The most widely used promoter is dimethylaniline (DMA). The BPO—DMA combination is used for hardening (curing) of unsaturated polyester resin compositions, eg, body putty in auto repair kits. Here, the aromatic amine promoter attacks the BPO to initially form W-benzoyloxydimethylanilinium benzoate (ion pair) which subsequentiy decomposes at room temperature to form a benzoate ion, a dimethylaniline radical cation, and a benzoyloxy radical that, in turn, initiates the curing reaction (33) ... 

According to this scheme, the intensity of CL is proportional to the rate of initiation (j/j) and depends on the concentrations of quenchers and activators. Some initiators, for example AIBN and dibenzoyl peroxide, act as strong quenchers [221] ... 

The initiators which are commonly used in these reactions range from azo-bis-isobutyronitrile (AIBN) to organic peroxides such as dibenzoyl peroxide, to ultra-violet light. In some cases, the reaction has been done with two different initiators42. A few illustrative examples of this reaction are presented in equations 57-59. 

The kinetic relationship, according to which the rate of polymerization increases and the average degree of polymerization decreases with increasing initiator concentration, is satisfied by most monomers when either unsubstituted or substituted dibenzoyl peroxides are used as initiators. 

In the polymerization of acrylic monomers by bulk, suspension, or in organic solution, the most common initiators are diacyl peroxide (e.g., dibenzoyl peroxide supplied as a paste in water) or azo compounds (e.g., 2,2 -azobisisobutyronitrile). For emulsion or aqueous solution polymerizations, sodium persulfate by itself or in combination with bisulfites or a host of other reducing agents may be used. 

With sensitizers, initiation stops when the source of radiation is turned off, which is followed by a rapid decay of the polymerization process. When a conventional initiator, such as dibenzoyl peroxide, is also present, the process is more rapid than when the sensitizer is used by itself. It also seems to continue after the radiation source has been discontinued. It is presumed that ultraviolet (UV)-induced decomposition of the peroxide becomes involved in the process. By this method, polymerizations may be carried out at temperatures well below those normally used with thermal initiators such as organic peroxides. 

Reported are extremely violent to expl reactions when vinyl cyanide is in contact with acids, bases, bromine, polymerization initiators (such as azoisobutyronitrile, dibenzoyl peroxide or di-tert-butyl peroxide),... 

Photoinitiation of free-radical reactions.2 Use of thermal initiators for radical sources, such as AIBN or dibenzoyl peroxide, requires temperatures >50°. This perester, in contrast, decomposes at room temperature or below on irradiation at 360 nm. This mode of initiation can be useful when stereoselectivity is enhanced at lower temperatures. 

The use of labelled initiators to obtain accurate information concerning the relative reactivities of radical scavengers towards reference radicals, has been reviewed (4). Product analysis, by isotope dilution analysis, has been used in the examinations of the decompositions of certain initiators in the absence of monomers. It is possible to work with very dilute solutions and small extents of decomposition so that the conditions are similar to those prevailing when the substances are used as initiators of polymerizations. The decompositions of dibenzoyl (12) and di-anisoyl peroxides (13), for example, have been followed by determinations of the carbon dioxide evolved. 

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