Diacetyl peroxide, decomposition

The extent of decarboxylation primarily depends on temperature, pressure, and the stabihty of the incipient R- radical. The more stable the R- radical, the faster and more extensive the decarboxylation. With many diacyl peroxides, decarboxylation and oxygen—oxygen bond scission occur simultaneously in the transition state. Acyloxy radicals are known to form initially only from diacetyl peroxide and from dibenzoyl peroxides (because of the relative instabihties of the corresponding methyl and phenyl radicals formed upon decarboxylation). Diacyl peroxides derived from non-a-branched carboxyhc acids, eg, dilauroyl peroxide, may also initially form acyloxy radical pairs however, these acyloxy radicals decarboxylate very rapidly and the initiating radicals are expected to be alkyl radicals. Diacyl peroxides are also susceptible to induced decompositions ... 

B. M. Tolbert and M. Calvin Decomposition of Diacetyl Peroxide in Acetic Acid. (UCRL) 573 (1949). 

The back recombination of the pair of acetoxyl radicals with the formation of parent diacetyl peroxide was observed in special experiments on the decomposition of acetyl peroxide labelled by the lsO isotope on the carbonyl group [78,79]. The reaction of acetyl peroxide with NaOCH3 produces methyl acetate and all lsO isotopes are contained in the carbonyl... 

The higher the viscosity of the solvent, the higher the amount of the parent molecules formed due to the geminate recombination of radicals. The observed rate constant of decomposition of the initiator decreases with an increase in viscosity [3,90], This was observed in the decomposition of peresters and diacetyl peroxide in various solutions. Subsequently, the fraction fT of the radical pairs recombining to the parent molecule increases with an increase in the viscosity ... 

Diacetoxyscirpenol (DAS) immunoassay, 14 144-147 Diacetyl, 23 483 Diacetyl control, 10 293 Diacetyl peroxide, 1 148 Diacetyl rest, in beer making, 3 584 Diacrylamide, 1 293 Diacylglycerols, 10 802 Diacyl hydrazines, 13 599 Diacyl peroxides, 14 281 18 467 decomposition of, 18 473 as free-radical initiators, 14 282-284 hydrolysis and perhydrolysis of, 18 466, 473 preparation of, 18 476 properties of, 18 468-469t reaction with amines, 18 474 reduction of, 18 474 symmetrical or unsymmetrical, 18 477... 

The reaction of methyl radicals with substituted thiophenes has been studied (Scheme 60) (71ACS2183). The radicals were generated by the Fe2+ catalyzed action of H202 on DMSO. The decomposition of diacetyl peroxide in thiophenes gives low yields of a-methylated products (73TL637). 

This scheme explaining the copolymerization observed has not yet been explained in kinetic aspects. Indeed, if decomposition rate of diacetyl peroxide equals 10-5 s-1 at 60 °C [120], this value does not follow the classic evolution of rate vs temperature (according to Arrhenius law). The authors suggest induced decompositions of these peroxides by CH3 radicals existing in the medium, and also by macroradicals coming from growing chains during... 

Calvert and Hanst88 using infrared analysis, have also re-investigated the photooxidation of acetaldehyde at 20°C. using 3130 A. radiation. Acetaldehyde pressures were chiefly about 42.5 nun., but the oxygen pressure was varied from 0 to 745 mm. Analyses were made for carbon monoxide, carbon dioxide, formic acid, methanol, acetic acid, peracetic acid, acetyl peroxide, methyl hydroperoxide, and unreacted acetaldehyde (Table X). Chains were short. Although they do not detect methyl hydroperoxide or diacetyl peroxide, the non-observance of a peroxide does not necessarily mean it is not formed. The decomposition of hydroperoxides on the smallest particle of catalyst is remarkably fast. 

SAFETY PROFILE Poison by inhalation. Moderately toxic by ingestion. Can cause pulmonary edema. Reacts with hydrogen peroxide to form the explosive diacetyl peroxide. When heated to decomposition it emits acrid smoke and fumes. 

The effect of solvent on the rate of decomposition of diacyl peroxides has been studied extensively. Data for the decomposition of acetyl peroxide in various solvents at two different temperatures are given in Tables 84 and 85. It is apparent that the rates differ little with solvent variation. The decomposition of diacetyl peroxide in /-butyl alcohol and in ethyl alcohol do show appreciable rate differences, the rate coefficients are 0.31 x 10 and 10.1 x 10 secat 60 °C, respectively . This difference in rate is most likely associated with induced decomposition. Again only a small variation in rate is observed in the decomposition of pro-pionyl and butyryl peroxide with solvent change as seen in Table 86. 

EFFECT OF SOLVENT ON THE RATE AND ACTIVATION ENERGY FOR THE THERMAL DECOMPOSITION OF DIACETYL PEROXIDE AT 80 °C... 

Elastomers must be crosslinked to hold their final form. The crosslinking reaction takes place through generation of free radicals that promote bonding at sites of unsaturation. The most common crosslinking agents for this include reactive peroxides, such as dicumyl peroxide, diacetyl peroxide, di-tert butyl peroxide, and others. Since each has a different temperature at which thermal decomposition initiates, curing conditions vary with the peroxide type. 

The temperature of an initiator depends on the rate of decomposition as reflected in its half-life. A good rule-of-thumb in this regard is a ti/2 of about 10 h at the particular reaction temperature (Table 6.2). The practical use temperature ranges of some common initiators are diacetyl peroxide 70-90°C, dibenzoyl peroxide 75-95°C, dicumyl peroxide 120-140°C, and AIBN 50-70°C (Odian, 1991). 

Contact with readily oxidizable substances may produce spontaneous combustion. Concentrated solutions can detonate on heating. The rate of decomposition increases by 1.5 times for every — 12°C (10°F) increase in temperature (NFPA 1997). Mixing with organic compounds may cause violent explosions. This includes alcohols, acetone and other ketones, aldehydes, carboxylic acids, and their anhydrides. With acetic acid and acetic anhydride, peroxyacetic acid is formed. In the presence of excessive anhydride, diacetyl peroxide is formed. Both the peroxy acids and the organic peroxides are shock-sensitive explosive compounds. Spontaneous ignition occurs when added to cotton (cellulose). 

Study of the effect of viscosity on the geminate diffusive recombination of radicals produced in the decomposition of diacetyl peroxide. 

A signi cant proportion of primary radicals that are produced by the initiator decomposition in a reaction system do not aetually react with the monomer to form chain radicals, and the initiator ef ciency / in Eq. (6.11) usually hes in the range 0.3-0.8. A major cause of this low / is the wastage of primary radieals by the so-called cage reactions. To illustrate, the decomposition of diacetyl peroxide could lead to the following reactions (Rudin, 1982 Odian, 1991) ... 

The yield of cage reaction products increases with increasing viscosity of the solvent. The decomposition of diacyl peroxides was the object of intensive study. The values of rate constants of diacyl peroxides (diacetyl and dibenzoyl) decomposition (kf and initiation (ki = 2ekd) are collected in Tables 3.4 and Table 3.5. The values of e are collected in the Handbook of Radical Initiators [4]. 

Most of the isolated diacyl (including sulfonyl) peroxides are solids with relatively low decomposition temperatures, and are explosive, sensitive to shock, heat or friction. Several, particularly the lower members, will detonate on the slightest disturbance. Autocatalytic (self-accelerating) decomposition, which is promoted by tertiary amines, is involved [1]. Solvents suitable for preparation of safe solutions of diacetyl, dipropionyl, diisobutyryl and di-2-phenylpropionyl peroxides are disclosed [2], The class is reviewed, including hazards and safety measures [3], Cyclic diacyl peroxides are more stable, but scarcely to be trusted. Individually indexed compounds are ... 

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