Dibenzoyl peroxide thermal

Fig. 12.3. NMR spectra recorded during thermal decomposition of dibenzoyl peroxide. Singlet at high field is due to benzene other signals are due to dibenzoyl peroxide. [From H. Fischer and J. Bargon, Acc. Chem. Res. 2 110 (1969). Reproduced by permission of the American Chemical Society.]...

The free-radical reaction may be equally initiated by photoactivated sulfur dioxide (3S02)442 (equation 79). On the other hand, polysulfones are obtained by radical copolymerization of appropriate olefins with sulfur dioxide443-449, and similarly, uptake of sulfur dioxide by a radical-pair formed by nitrogen extrusion from an azo compound yields the corresponding sulfone450 (equation 80). Correspondingly, alkylbenzenes, dibenzoyl peroxide, and sulfur dioxide yield sulfones under thermal conditions451... 

At pressures above 6000 bar, free radical polymerisation sometimes proceeded explosively [ 1 ]. The parameters were determined in a batch reactor for thermal runaway polymerisation of acrylonitrile initiated by azoisobutyronitrile, dibenzoyl peroxide or di-/er/-butyl peroxide [2],... 

Biesenberg, J. S. etal., J. Polym. Eng. Sci., 1976,16, 101-116 Polymerisation of methyl methacrylate initiated by oxygen or peroxides proceeds with a steady increase in velocity during a variable induction period, at the end of which a violent 90°C exotherm occurs. This was attributed to an increase in chain branching, and not to a decrease in heat transfer arising from the increasing viscosity [ 1 ]. The parameters were determined in a batch reactor for thermal runaway polymerisation of methyl methacrylate, initiated by azoisobutyronitrile, dibenzoyl peroxide or di-ferf-butyl peroxide [2],... 

The explosive decomposition of the solid has been studied in detail [6], The effect of moisture upon ignitibility and explosive behaviour under confinement was studied. A moisture content of 3% allowed slow burning only, and at 5% ignition did not occur [7], Thermal instability was studied using a pressure vessel test, ignition delay time, TGA and DSC, and decomposition products were identified [8], The presence of acyl chlorides renders dibenzoyl peroxide impact-sensitive [9], There is a further report of a violent explosion during purification of the peroxide by Soxhlet extraction with hot chloroform [10], Residual traces of the peroxide in a polythene feed pipe exploded when it was cut with a handsaw [11]. The heat of decomposition has been determined as 1.39 kJ/g. The recently calculated value of 69° C for critical ignition temperature coincides with that previously recorded. 

The Rate Constants of the Thermal Decay of Dibenzoyl Peroxide in Different Solvents ... 

The generation of the benzoyloxyl radical relies on the thermal or photoinitiated decomposition [reaction (49)] of dibenzoyl peroxide (DBPO). An early study (Janzen et al., 1972) showed that the kinetics of the thermal reaction between DBPO and PBN in benzene to give PhCOO-PBN" could be followed by monitoring [PhCOO-PBN ] from 38°C and upwards. The reaction was first order in [DBPO] and zero order in [PBN], and the rate constants evaluated for the homolysis of the 0—0 bond in DBPO (k = 3.7 x 10-8 s-1 at 38°C) agreed well with those of other studies at higher temperatures. Thus in benzene the homolytic decomposition mechanism of DBPO seems to prevail. 

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. 

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 parameters were determined in a batch reactor for thermal runaway polymerisation of styrene, initiated by azoisibutyronitrile, dibenzoyl peroxide or di-ferf-butyl peroxide. 

Table 3. Thermal and radical telomerisations of vinylidene fluoride (DTBP, DBP and sc-mean-ditertiarybutyl peroxide, dibenzoyl peroxide and supercritical, respectively) ...

Radical initiators are thermally labile compounds, which decompose into radicals upon moderate heating or photolysis. These radicals initiate the actual radical chain through the formation of the initiating radical. The most frequently used radical initiators are azobis-isobu-tyronitrile (AIBN) and dibenzoyl peroxide (Figure 1.11). AIBN has has a half-life of 1 h at 80 °C, and dibenzoyl peroxide a half-life of 1 h at 95 °C. 

Other compounds prepared by halolactamization of alkenes (and preceding the above woik ) include (64),(65), (66),2 (67), (bS), (69) and (70). Note that related sulfeno-, seleno- and tellu-ro-cyclizations have been discussed earlier (Section 3.5.5). Finally, related products may be obtained by radical reactions of N-haloamides, giving the following (71-73) representative products in reactions promoted thermally (71),photochemically (72 and 73),279.2so dibenzoyl peroxide (73) ° or chro-mous chloride (73). ... 

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