Peroxycarboxylic esters

Radiation-induced decomposition, 5,6-dihydrothymine, 930 Radiation stress, polymers, 685 Radical polymerization dialkyl peroxides, 707 peroxycarboxylic esters, 697 Radicals... 

Free radicals may be generated by oxidation, reduction, or by homolytic cleavage of one or more covalent bonds, such as C—C bonds e.g. dimers of triarylmethyl radicals), N—N bonds e.g. tetrasubstituted hydrazines), O—O bonds e.g. hydroperoxides, dialkyl and diacyl peroxides, peroxycarboxylic esters), C—N bonds e.g. dialkyl azo compounds), and N—O bonds (as in the thermolysis of nitrogen pentoxide O2N— O—NO2). Two typical examples, which have been investigated in different solvents, are given in Eqs. (5-56) and (5-57) cf. also reaction (5-39a) in Section 5.3.2. 

The effect of the medium on the thermolysis of peroxycarboxylic esters deserves particular mention. Some examples are compiled in Table 5-9. An interesting aspect of this reaction is that the peresters, depending on structure, substituents, and medium, can decompose by two different mechanisms given in Eqs. (5-62a) and (5-62b) [195, 196]. 

Table 5-9. Solvent influence Eqs. (5-62a) and (5-62b). on rates of monomolecular decomposition of various peroxycarboxylic esters R—CO—O- 0—CR according to... 

Hydrolysis of Peroxycarboxylic Systems. Peroxyacetic acid [79-21-0] is produced commercially by the controlled autoxidation of acetaldehyde (qv). Under hydrolytic conditions, it forms an equiHbrium mixture with acetic acid and hydrogen peroxide. The hydrogen peroxide can be recovered from the mixture by extractive distillation (89) or by precipitating as the calcium salt followed by carbonating with carbon dioxide. These methods are not practiced on a commercial scale. Alternatively, the peroxycarboxyHc acid and alcohols can be treated with an estetifying catalyst to form H2O2 and the corresponding ester (90,91) (see Peroxides and peroxy compounds). 

Another consequence of application of organic solvents as a reaction medium is associated with the mechanism of enzyme-catalyzed transformations. According to the commonly accepted mechanism, the first product of the interaction of a hydrolytic (serine) enzyme with an ester is an O-acylenzyme (Scheme 5.4). When the reaction is performed in an aqueous solution, water acts as a nucleophile in the next step, to give acid B. If more nucleophilic hydrogen peroxide is present in the reaction mixture, peroxycarboxylic acids C are formed. However, in organic solvents the O-acylenzyme also reacts readily with other nucleophiles, such as... 

For the mechanism of azolide hydrolysis under specific conditions like, for example, in micelles,[24] in the presence of cycloamyloses,[25] or transition metals,[26] see the references noted and the literature cited therein. Thorough investigation of the hydrolysis of azolides is certainly important for studying the reactivity of those compounds in chemical and biochemical systems.[27] On the other hand, from the point of view of synthetic chemistry, interest is centred instead on die potential for chemical transformations e.g., alcoholysis to esters, aminolysis to amides or peptides, acylation of carboxylic acids to anhydrides and of peroxides to peroxycarboxylic acids, as well as certain C-acylations and a variety of other preparative applications. 

The RP-HPLC method based on the CL reaction of luminol (124) catalyzed by Co(II) (Section in.B.2.c) can be applied for determination of peroxycarboxylic acids, esters and diacyl peroxides (see examples of LOD in equation 67, Section V.B.2.c) . The biosensor prepared according to equation 70, that is effective in the determination of hydroperoxides (Section V.B.6.b), becomes deactivated after three days of operation when trying to determine t-butyl peracetate. ... 

The IR and Raman spectra of esters derived from peroxycarboxylic and peroxycarbonic esters show a band near 860 cm, assigned to a stretching mode of the OO gronp. The band of the carbonyl gronp in these componnds is shifted to higher frequencies by 30-40 cm , as compared to ordinary esters . ... 

In this section we discuss the thermochemistry of some species with the general formulas, RC(=0)00H, RC(=0)00R and RC(=0)00C(=0)R. These species have the generic names peracids (peroxycarboxylic acids), peresters (percarboxylate esters) and acyl peroxides. The enthalpy of formation values are in Table 3. Three formal reactions that are discussed here are conceptually the same as in the earlier sections. Because now there is a carbonyl group present, we rewrite equations 5, 6 and 9 as equations 14, 15 and 16. 

Peroxyeslerx include the alkyl esters of peroxycarboxylic acids tnonoper-oxydicarboxylic acids diperoxycarboxylic acids monoperoxy- (24) and diperoxycarhonic (25) acids monoperoxy- (26) and diperoxyoxalic (27) acids peroxycarbamic acids (28) peroxysulfonic acids (29) and perox-yphosphoric acids. 

Sulfoxides are readily available via oxidation of sulfides with peroxycarboxylic acids (e.g., mCPBA, 1.0 eq) or sodium or potassium periodate. The sulfides themselves can be prepared by nucleophilic displacement of tosylate or mesylate esters with sodium alkyl- or phenylsulfides. In the example shown below, the sulfoxide approach worked better than direct E2 elimination of the mesylate precursor. ... 

Sulfonyl carbanions of primary and secondary sulfones may also be converted to the ketones by reaction with either BTSP (185) (method 1) or chlorodimethoxyborane (186) (method 2). With the latter reagent, subsequent treatment of the intermediate boric ester with sodium perbenzoate affords the ketone (Scheme 74). The use of the sodium salt of the peroxycarboxylic acid avoids side reactions and hence increases the yield of the ketone. 

Another early discovery was that CALB accepts H202 as nucleophile to produce peroxycarboxylic acids from esters or carboxylic acids (perhydrolysis activity can also be found in other serine hydrolases) [46, 47]. The in situ formed peracid can subsequently be used to epoxidize an alkene by (non-enzymatic) Prileshajev epoxidation. Hence, oleic acid incubated with CALB and H202 will produce 9,10-epoxyoctadecanoic acid [48]. Other alkenes can be epoxidized by H202 and a catalytic amount of carboxylic acid (and CALB) (Scheme 13.2) [49],... 

Peroxycarboxylic acid esters are utilized as initiators for radical polymerization and are interesting intermediates for the decarboxylation of carboxylic acids. They are generally prepared by the acylation of hydro peroxides with acid chlorides, acid anhydrides, or imidazolides in the presence of a base. Condensation of carboxylic acids (20) with /-butyl-hydroperoxide (21) has been smoothly achieved by the use of diethyl phophorocyanidate and NEt3 under mild conditions giving f-butyl peroxycarboxylates (22) in good yield.9... 

Baeyer-Villiger oxidation Addition of peroxycarboxylic acid to a ketone followed by rearrangement to an ester. 

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