Diacyl peroxides structure

Chemical Properties. Diacyl peroxides (16) decompose when heated or photolyzed (<300 mm). Although photolytic decompositions generally produce free radicals, thermal decompositions can produce nonradical and radical intermediates, depending on diacyl peroxide structure. Symmetrical aliphatic diacyl peroxides of certain structures, i.e, diacyl peroxides (16, R1 = R2 = alkyl) without a-branches or with a mono-ce-methyl substituent,... 

Acyl peroxides of structure (20) are known as diacyl peroxides. In this structure and are the same or different and can be alkyl, aryl, heterocychc, imino, amino, or fiuoro. Acyl peroxides of stmctures (21), (22), (23), and (24) are known as dialkyl peroxydicarbonates, 00-acyl O-alkyl monoperoxycarbonates, acyl organosulfonyl peroxides, and di(organosulfonyl) peroxides, respectively. and R2 ia these stmctures are the same or different and generally are alkyl and aryl (4—6,44,166,187,188). Many diacyl peroxides (20) and dialkyl peroxydicarbonates (21) ate produced commercially and used ia large volumes. 

Thermal decomposition of dialkyl peroxides, diacyl peroxides, hydroperoxides and peracids depending on the structure of the peroxidic compound occurs in a measurable rate usually above 60°C. Diacyl peroxides and peracids are considerably less stable than dialkyl peroxides and hydroperoxides. 

McBride and co-workers have studied extensively the reactions of such free-radical precursors as azoalkanes and diacyl peroxides (246). By employing a variety of techniques, including X-ray structure analysis, electron paramagnetic resonance (EPR), and product studies, and comparing reactions in the crystal and in fluid and rigid solvents, they have been able to obtain extremely detailed pictures of the solid-state processes. We will describe here some of the types of lattice control they have elucidated, and the mechanisms that they suggest limit the efficacy of topochemical control. 

Work on the deflagration hazards of organic peroxides has been done using a revised Time-Pressure test, to determine the characteristics of ignition sensitivity and violence of deflagration. Some correlation is evident between these characteristics and the AO content within each structurally based peroxide type. Also, for the same AO content, the nature of the characteristics appears to decrease hi the order diacyl peroxides, peroxyesters, dialkyl peroxides, alkylhydroperoxides [18],... 

The NOBS system undergoes an additional reaction that forms a diacyl peroxide as a result of the nucleophilic attack of the peracid anion on the NOBS precursor as shown in equation 21. This undesirable side reaction can be minimized by the use of an excess molar quantity of hydrogen peroxide (91,96) o by the use of shorter dialkyl chain acid derivatives. However, the use of these acid derivatives also appears to result in less efficient bleaching. The dependence of the acid group on the side product formation is apparendy the result of the proximity of the newly formed peracid to unreacted NOBS in the micellar environment (91). A variety of other peracid precursor structures can be found (97—118). 

Organic peroxides can be classified according to peroxide structure. There are seven principal classes hydroperoxides dialkyl peroxides a-oxygen substituted alkyl hydroperoxides and dialkyl peroxides primary and secondary ozonides peroxyacids diacyl peroxides (acyl and organosul-fonyl peroxides) and alkyl peroxyesters (peroxyearboxylales. peroxysul-fonates, and peroxyphosphates). 

Cooper, W. The effect of structure of diacyl peroxides on their radical induced decomposition in vinyl monomers. J. Chem. Soc. 1952, 2408. 

EFFECT OF STRUCTURE ON THE THERMAL DECOMPOSITION OF ALKYL AND ARYL ALKYL DIACYL PEROXIDES (RCOjIj... 

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. 

In an infrared spectrophotometric investigation, Vasilyev and Emanuel [13] attribute the 847 cm 1 band to the O—O bond of a hydroperoxidic structure and favor structure II for the X peroxide. The authors base their argument on the fact that, in peracetic acid, this band is 856 cm 1 and, generally speaking, it is 835—855 cm"1 in hydroperoxides, Nevertheless, the band corresponding to the 0—0 bond is 840—842 cm"1 in acyl peroxides [14], whereas, in diacyl peroxides [15], it is 890—904 cm 1 and hence the argument put forward is not decisive. 

Some characteristics of initiators used for thermal initiation arc summarized in Table 3.1. These provide some general guidelines for initiator selection. In general, initiators which afford carbon-ccntcrcd radicals e.g. dialkyldiazcncs, aliphatic diacyl peroxides) have lower efficiencies for initiation of polymerization than those that produce oxygen-centered radicals. Exact values of efficiency depend on the particular initiators, monomers, and reaction conditions. Further details of initiator chemistry are summarized in Sections 3.3.1 (azo-compounds) and 3.3.2 (peroxides) as indicated in Table 3,1. In these sections, we detail the factors which influence the rate of decomposition i.e. initiator structure, solvent, complexing agents), the nature of the radicals formed, the susceptibility of the initiator to induced decomposition, and the importance of transfer to initiator and other side reactions of the initiator or initiation system. The reactions of radicals produced from the initiator arc given detailed treatment in Section 3.4. 

Peroxides that are reduced irreversibly at the mercury electrode can be analyzed by polarography. IR, UV, NMR, and GC/MS are useful in structure characterization. IR absorption bands at 800-900 cm and in the region of carbonyl group are characteristics of diacyl peroxides, peroxydicarbonates, and peroxyesters. 

Detailed studies of the photodecomposition of diacyl peroxide guest molecules within the urea tunnel structure have been carried out. and have provided interesting contrasts to the photodecomposition behavior of the same molecules in their pure. crystalline phases, which have been investigated in considerable depth by McBride, Hollingsworth, and coworkers. 

Harris, K.D.M. Hollingsworth, M.D. Structural properties of the guest species in diacyl peroxide/urea inclusion compounds An x-ray diffraction investigation. Proc. R. Soc., A 1990, 431, 245. 

Table 2 shows that commercial organic peroxides are available with 10-h half-life temperature activity varying from about room temperature to about 130°C. Organic peroxide classes such as diacyl peroxides and peroxyesters show a strong correlation between structural variation and 10-h half-life temperature activity. Other organic peroxide classes, eg, peroxydicarbonates and monoperox-ycarbonates, show very little change in activity with structural variation. The... 

The rate of peroxide decomposition is strongly dependent on the structure of the molecule in question. The rate of decomposition for diacyl peroxides and peresters increases when going from aryl to primary alkyl to secondary alkyl to tertiary alkyl substituents (39). In the case of peresters, the structure of the molecule governs both the rate of fragmentation and the above mentioned mode... 

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