Alkyl peroxyesters

Organic peroxides can be classified according to peroxide stmcture. There are seven principal classes hydroperoxides dialkyl peroxides a-oxygen substitued alkyl hydroperoxides and dialkyl peroxides primary and secondary ozonides peroxyacids diacyl peroxides (acyl and organosulfonyl peroxides) and alkyl peroxyesters (peroxycarboxylates, peroxysulfonates, and peroxyphosphates). 

Saponification of alkyl peroxyesters yields alkyl hydroperoxides and carboxylic acids or their alkali metal salts. a-Ether-substituted peroxides can be hydrolyzed to the unsubstituted alkyl hydroperoxides, eg, tert-huty hydroperoxide from tert-huty 2-oxacyclohexyl peroxide [28627-46-5] (62) ... 

Alkyl peroxyesters are commonly named like their nonperoxidic counterparts, except for incorporation of the peroxy- prefix. Trivial names are also commonly used, eg, tert-huty peracetate. Alkyl peroxyesters derived from di- and polybasic peroxyacids use 00- or O- when required to locate groups, eg, 00-tert-huty 0-isopropyl monoperoxycarbonate and 00-tert-huty 0-hydrogen monoperoxymaleate. Descriptions of alkyl peroxyesters have been given in the chemical hterature (1,4—6,19,20,44,168,213). 

Fig. 2. Synthetic routes to alkyl peroxyesters. The acylating agent reacts with R OOH in each case.

Physical Properties. Properties of some alkyl peroxyesters are Hsted in Table 13 and the properties of some alkyl areneperoxysulfonates are given in Table 14. Mass spectra (226), total energies, and dipole moments (227) oxygen—oxygen bond-dissociation energies (44,228) and boiling points, melting points, densities, and refractive indexes (44,168,213) have been reported for a variety of tert-huty peroxycarboxylates. 

Chemical Properties. Alkyl peroxyesters are hydroly2ed more readily than the analogous nonperoxidic esters and yield the original acids and hydroperoxides from which they were prepared rather than alcohols and peroxyacids ... 

The alkyl peroxyesters undergo homolysis, thermally and photochemically, to generate free radicals (168,213,229—232) ... 

Table 15. Effect of ferf-Alkyl Peroxyester Structure on 10-h HLT, R-C(0)-00-R ...

Piimaiy and secondary alkyl peroxyesters thermally decompose by a nonradical process, giving almost quantitative yields of carboxylic acids and carbonyl compounds (213,241) ... 

Alkyl peroxyesters are much less sensitive to radical-induced decompositions than diacyl peroxides. Induced decomposition is only significant in peroxyesters containingnonhindered a-hydrogens or a, P-unsaturation (213,242). 

The main industrial use of alkyl peroxyesters is in the initiation of free-radical chain reactions, primarily for vinyl monomer polymerizations. Decomposition of unsymmetrical diperoxyesters, in which the two peroxyester functions decompose at different rates, results in the formation of polymers of enhanced molecular weights, presumably due to chain extension by sequential initiation (204). 

Alkyl orthophosphate triesters, 79 41 terteAlkyl peroxycarbamates, decomposition of, 78 486 Alkyl peroxyesters, 78 478-487 chemical properties of, 78 480 487 physical properties of, 78 480 primary and secondary, 78 485 synthesis of, 78 478-480 synthetic routes to, 78 479 tert-Alkyl peroxyesters, 78 480 84, 485 as free-radical initiators, 74 284-286 properties of, 78 481-483t uses of, 78 487 Alkylperoxy radical, 74 291 Alkyl phenol ethoxylates, 8 678, 693 ... 

Free-radical initiators, 74 274-311 tert-alkyl hydroperoxides, 74 290-291 tert-alkyl peroxyesters, 74 284-286 azo compounds, 74 293-296 carbon-carbon initiators, 74 296-297 chemical methods for radical generation, 74 299... 

Cnegee rearrangement -m tert-alkyl peroxyesters [PEROXIDES AND PEROXIDE COMPOUNDS - ORGANIC PEROXIDES] (Vol 18)... 

Physical Properties. Properties of some ten-alkyl peroxyesters are listed in Table 13 and the properties of some rerr-alkyl areneperoxysul-fonates are given in Table 14. 

The main industrial use of rert-alkyl peroxyesters is in the initiation of free-radical chain reactions, primarily for vinyl monomer polymerizations. 

TABLE 13 PROPERTIES OF SOME TERT-ALKYL PEROXYESTERS... 

For S- and M-PVC manufacturing a range of initiators has been used, but currently relatively few are widely employed. At one time benzoyl peroxide and azo initiators (AIBN) were typically used, but diacetyl peroxides, peroxydicarbonates (PDC) and alkyl peroxyesters are now preferred. AIBN is also employed as a blowing agent for PVC foam. Typical organosoluble initiators are Diacyl peroxides... 

Diacetyl peroxide, peroxydicarbonates, alkyl peroxyesters and AIBN used as initiator... 

The results of the experimental kj studies into alkyl peroxyester decomposition in CO2 [17] may be summarized as follows at least at pressures up to 100 MPa, which range encompasses the entire area of technical relevance, kj values for peroxyester decomposition in SCCO2 differ by less than 20%, and mostly by less than 10%, from the associated values measured in n-heptane solution. A more detailed inspection of the data reveals that peroxyesters which undergo single-bond scission decompose faster in CO2, whereas, in the case of close-to-concerted two-bond scission, decomposition of the peroxyester seems to occur at a slightly slower rate in CO2 than in solution in n-heptane. 

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