Structure dialkyl peroxides

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. 

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],... 

Three peroxides with aromatic substituents have reported enthalpy of vaporization data, all from the same source". The enthalpies of vaporization of cumyl hydroperoxide and ferf-butyl cumyl peroxide are the same, which makes us skeptical of at least one of these values. The calculated b value for cumyl hydroperoxide is 31.5, consistent with the alkyl hydroperoxides. The calculated b value for tert-butyl cumyl peroxide is 15.4 and more than twice that for the mean of the dialkyl peroxides. The structurally related tert-butyl p-isopropylcumyl peroxide has a b value of 8.8 and so is consistent with the other disubstituted peroxides. 

An important paper by Salomon, Clennan and coworkers on dialkyl peroxides , where also one ozonide was reported, appeared in 1985. In this paper, a correlation among and 0 chemical shifts was established, and the influence of several factors like concentration, temperature, solvent and, naturally, chemical structure was thoroughly studied but confined to dialkyl peroxides. There was a gap of several years before the appearance of a further note reporting data of seven 1,2,4-trioxolanes (ozonides), 1-4, and of the 1,2,4,5-tetroxane 5. Their 0 NMR data are given in Table 2. Spectra were obtained at natural isotopic abundance, in toluene at 27 °C. 

Teeth whiteners, percarbamide, 623 Temperature, reaction rates, 903-12 Terminal olefins, selenide-catalyzed epoxidation, 384-5 a-Terpinene, peroxide synthesis, 706 a-Terpineol, preparation, 790 Terrorists, dialkyl peroxide explosives, 708 Tertiary amines, dioxirane oxidation, 1152 Tertiary hydroperoxides, structural characterization, 690-1... 

I. 463 A) is close to the value for tert-butyl hydroperoxide (1) (95° and 104°, two crystallo-graphically independent molecules), which points to a comparatively small steric demand of the acyl group in peresters. Due to its structural similarity to dialkyl peroxides, it is reasonable that the ortho ester 56 (P2, 0—0 = 1.481 A, C—O—O—C = 145.1°) exhibits a significantly larger peroxide dihedral angle than 54170. 

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). 

Physical Properties. The structures and the boiling and melting points of several dialkyl peroxides are listed in Table 2 a comprehensive list is given in the literature. 

The susceptibility of dialkyl peroxides to acids and bases depends on peroxide structure and the type and strength of the acid or base. In acidic environments, unsyinmetrical acyclic alkyl aralkyl peroxides undergo carbon-oxygen fission, forming acyclic alkyl hydroperoxides and aralkyl carbonium ions. The latter react with nucleophiles, X. ... 

Thus, reactions of carbonyl compounds with hydrogen peroxide and acids lead to products similar to those obtained by the ozonization of olefins (Section III), which also yields 1,2,4-trioxolans and 1,2,4,5-tetroxans. The similarity of the two reactions is understandable, since the intermediates )C+—OO- in the ozonization27a and )C+—OOH in the hydrogen peroxide reactions are related as a conjugate base-acid pair. A number of cyclic peroxides of structure 7 are prepared from bis(hydroperoxy)dialkyl peroxides (5) by reaction with lead(IV) acetate, as described by Criegee et al.la This reaction is also thought to involve a carbonium ion intermediate,31 which reacts with the second OOH group. 

Applications The Karl Fischer reagent can be applied directly to the determination of water in a variety of organic compoimds, including saturated or unsaturated hydrocarbons, alcohols, halides, acids, acid anhydrides, esters, ethers, amines, amides, nitroso and nitro compounds, sulfides, hydroperoxides, and dialkyl peroxides. The use of sodium tartrate dihydrate for standardization of the response of the Karl Fischer reagent has been shown to lead to a small error because of occlusion of about 2% (relative) water in the crystal structure. 

Many types of peroxides (R-O-O-R ) are also utilized, including diacyl peroxides, peroxydicarbonates, peroxyesters, dialkyl peroxides, and inorganic peroxides such as persulfate, the latter being used mainly in water-based systems. The rate of peroxide decomposition as well as the subsequent reaction pathway is greatly affected by the nature of the peroxide chemical structure, as illustrated for fert-butyl peroxyesters in Scheme 4.2. Pathway (a), the formation of an acyloxy and an alkoxy radical via single bond scission, is favored for structures in which the carbon atom in the a-position to the carbonyl group is primary (for example, terf-butyl peroxyace-tate, R = CHg). Pathway (b), concerted two-bond scission, occurs for secondary and tertiary peroxyesters (for example, terf-butyl peroxypivalate, R = C(CH3)3) [1, 2]. The tert-butoxy radical formed in both pathways may decompose to acetone and a methyl radical, or abstract a hydrogen atom to form tert-butanol. 

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. 

The mechanisms of inhibition by peroxide decomposers, metal deactivators, and ultraviolet absorbers are fairly well understood in general terms, although many details of the individual reactions remain to be elucidated. Classifying a preventive antioxidant into one of the three categories above will only rarely describe its entire function. The dual behavior of dialkyl dithiophosphates in the liquid phase has been mentioned. Many other phosphorus- and sulfur-containing antioxidants commonly classified as peroxide decomposers can also act as chain breakers. Similarly, the structure of many metal deactivators and ultraviolet absorbers indicates that they must also have some chain-breaking activity. 

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). 

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