Benzoyl peroxide estimation

Cumene hydroperoxide [95], benzoyl peroxide, or tert-h iiy peroxide [96]. can be used as accelerators with alkylboron initiators. The chain transfer constant for MMA to tributylborane has been estimated to be 0.647, which is comparable to tripropylamine [97]. 

The accepted kinetic scheme for free radical polymerization reactions (equations 1-M1) has been used as basis for the development of the mathematical equations for the estimation of both, the efficiencies and the rate constants. Induced decomposition reactions (equations 3 and 10) have been Included to generalize the model for initiators such as Benzoyl Peroxide for... 

The free radical arylation of thiazole (391) has been performed either by the Gomberg-Bachmann (392) decomposition of aryldiazonium chlorides (119,393), by the thermal decomposition of benzoyl peroxide (394-397) or N-nitrosoacetanilide (398), or by the photolysis of benzoyl peroxide or iodobenzene (398). The three monophenylthiazoles are obtained in the practically constant proportions 2-phenyl, 60% 5-phenyl, 30% 4-phenyl, 10%, giving the order, 2>5>4, of decreasing reactivity of the three positions of thiazole toward phenyl radicals (398). Competition reactions with nitrobenzene (397) gave an estimation of the globed reactivity of thiazole relative to benzene of 0.75 with the partial rate factors f2 = 2.2, /s=1.9, /4 = 0.5. When the thermolysis of benzoyl peroxide is performed in acetic acid solution, the substrate in reaction is the conjugate acid of thiazole the global reactivity is enhanced to 1.25,... 

Subsequent loss of carbon dioxide from the alkyl acyl carbonate may occur. It was estimated, in the decomposition of Ira 5-4-I-butylcyclohexanecarbonyl peroxide in carbon tetrachloride, that two-thirds of the reaction occurs via the inversion process and one-third by the homolytic process It is suspected that inversion may be major decomposition route for other secondary aliphatic diacyl peroxides as well as for some bridgehead peroxides . Confirmation that the inversion process does contribute to the decomposition of i-butyryl peroxide is given . Further evidence for the inversion process is found in the volumes of activation for the decomposition of i-butyryl peroxide in isooctane at 50° and ram-4-r-butylcyclohexanecarbonyl peroxide in -butane at 40 °C. The AF values are —5.1 and —4.1 cm. mole , respectively. These values may be compared to the positive values of A F for benzoyl peroxide (Table 77) where there is no inversion. While the transition states for homolytic decomposition and inversion for secondary and tertiary diacyl peroxides are both polar, it is felt that the transition state for inversion is more polar . The extent of contribution of structure (V) to the transition state in the homolytic decomposition must be held with considerable reservation. In general much of the reported data for the decomposition of secondary and tertiary alkyl diacyl peroxides should be viewed with some scepticism unless efforts were made to assess the importance of the inversion process. One clue that may be used to evaluate the importance of this process is the yield of ester, which is a product of this reaction. 

Reagents. Hydroxyethyl methacrylate (HEMA) was extracted with hexane to remove bis-esters and distilled in vacuo, b.p. 69 / 0.1 mm Hg. p-Mltrobenzenesulfonyl isocyanate (b.p. 160 /A mm Hg) was synthesized in 63% yield by phosgenatlon of p-nltrobenzene-sulfonamlde in the presence of butyl isocyanate (9 ). Homo- and copolymers of HEMA were prepared by solution polymerization in DMF in the presence of benzoyl peroxide and the results are summarized in Table I. The hydrolytic stability of the hydrogels was estimated by slurrying 0.5-1.0 g of polymer in 5.0 mL 0.35 KOH in 10 mL culture tubes equipped with teflon lined screw caps. The samples were heated at 100 for up to 24 hr in an aluminum constant temperature block. Immediately upon removal from the heating block, the samples were cooled and acidified with 6N HCl. The precipitated gel was washed and soaked in distilled water for 30 min before the carboxylic acid content was estimated by titration with standard NaOH. 

The difficulty of removing acetaldehyde completely by distillation is indicated by the fact that a sample, presumably purified by Nozaki and Bartlett s [22] best techniques still contained about 3 X 10 A/acetaldehyde as estimated by UV spectroscopy at 290 nm (the absorption maximum for acetaldehyde) [13]. Using as a criterion the conversion after 4 hr when the purified monomer is warmed at 45°C with benzoyl peroxide (cone 8.27 X 10 moles/ liter), after two degassing cycles at oil pump pressure of 30 min each, in sealed ampoules, the most satisfactory procedure used by them consisted of fractional distillation through a distillation column of at least 50 theoretical plates (cf. Table III). 

Procedure 2-1 is an example of a bulk polymerization of vinyl fluoride. It should be noted that the conversion is quite low. At 62°C benzoyl peroxide has a half-life of approximately 35 hr. Consequently heating the reaction mixture for 112 hr represents only a little over 3 half-life periods. From the literature [37] no estimate of the pressure inside the reactor could be made. Table II does indicate that in the presence of acetone or of aqueous acetone the conversion increased substantially. In fact, the procedure of the sixth experiment was found to be highly reproducible. Acetone was thought to enhance the solubility of the initiator in the monomer [37]. 

Benzoyl peroxide is used mainly in acne treatment and is an irritant. Allergic contact dermatitis to this compound is not infrequent. Eaglstiein (1968) reported two cases. The sensitization rate has been estimated to be 1 %-2.5%. In a human maximization test, 76% became sensitized (Leyden and Kligman 1977). Crossreactions to benzoic acid and related compounds were not found. The drug has been advocated for treatment of chronic leg ulcers. Eight of 16 patients showed positive patch tests to 2% benzoyl peroxide after 6 weeks of leg ulcer treatment with 10% benzoyl peroxide (Jensen et al. 1980). Patients sensitized to benzoyl peroxide may be at risk in certain occupations (e.g., baking and the plastics industry). 

The half-life of the initial benzoyloxy radicals from decompositions of benzoyl peroxide is estimated to be 10 to 10 seconds. Past that time, they decompose into phenyl radicals and carbon dioxideThis is sufficient time for the benzoyloxy radicals to be trapped by reactive monomers. Unreactive monomers, however, are more likely to react with the phenyl radicals that form from the elimination reaction. In effect there are two competing reactions. ... 

Free-radical and Photolytic Reactions.—In the course of their systematic study of the free-radical phenylation in the heterocyclic series, Metzger et have examined the behaviour of isothiazole and its 3-, 4-, and 5-methyl homologues from this point of view. The reaction is induced by benzoyl peroxide in the presence of traces of copper at 110 C, and the proportion of the resulting phenylated isomers was estimated by gas chromatography. Analysis of the extensive numerical results shows that the radical activity of isothiazole and its homologues exceeds that of thiazole. The observed free-valency distribution and the radical localization energies are similar for the 3- and 5-positions in isothiazole the observations conflict with the theoretical calculations, and are rationalized by introducing suitable corrections. 

The infiaied spectra of the benzoyl peroxide symmetrical derivatives (4-R-PhCOO)2 withR NOCF3-, CF3O-, 1- Br- C1-, F- H- CH3- CH3O- were studied by the semiempirical methods. There is a linear relationship between the fiequencies of the normal vibrations of the experimental and calculated (PM6, PDDG and AM 1) spectra for this series of peroxides. The effect of the DFT level on the normal vibrations frequencies of C = O group of benzoyl peroxide was estimated. The best reproduction of these frequencies is observed in the case of BLYP calculation method with 6-31IG (d, p) basis set. 

The positions of the normal vibrations mode of carbonyl groups can be used as an analytical signal of qualitative and quantitative analysis of this class of peroxides by IR-spectroscopy. DFT methods are promising for computer stractural chemistry of peroxide compounds because they with sufficient accuracy reproduce parameters of the molecular geometry and electronic structiue of peroxides [5]. The opportunity of different DFT methods to reproduce the values of the normal vibrations frequencies of the benzoyl peroxide C = O group was estimated. The calculations were performed using the 6-3IIG (d, p) basis set in all cases. The results are hsted in Table 11.3. 

As previously mentioned, Bartlett and Nozaki " thoroughly studied the benzoyl peroxide (BPO) initiated copolymerization of allyl acetate with MA. They estimated that a 4.58-wt. % initiator concentration produced a copolymer of 36 600 kinetic chain length. Under comparable conditions, allyl acetate and MA gave very low-molecular-weight homopolymers. For the copolymerization, it was clearly established that the cross-propagation step is able to compete fairly effectively with allyl termination. 

For benzoyl and acetyl peroxides, loss of carbon dioxide occurs in a stepwise process. Estimates of the rate constants for step c in Scheme 1 are 7 x 10 sec (benzene, 60°). The corresponding process for acetyl peroxide has k = 2x 10 sec (n-hexane, 60°), so that the lifetime of radical pairs containing acetoxy radicals is comparable to the time necessary for nuclear polarization to take place (Kaptein, 1971b Kaptein and den Hollander, 1972 Kaptein et al., 1972). Propionoxy radicals are claimed to decarboxylate 15-20 times faster than acetoxy radicals (Dombchik, 1969). 

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