Cyclic peroxides, formation from

Depending on the reaction conditions— primarily pH, concentration of reagents— the cyclic dimer, trimer form from their linear analogs. Cyclic dimer and trimer crystallize from the reaction mixture when catalyzed by an acid. The reaction mechanisms of cyclic peroxide formation have been investigated by several authors and are schematically summarized below [1-7]. 

The oxidation of naphthalic acid (1,8-naphthalenedicarboxylic acid) by peroxide, rather surprisingly, does not proceed by formation of a cyclic peroxide but rather via a dioxirane [53] (a three-membered ring containing a carbon atom and a peroxide group). CL is observed from this reaction. 

A CIEEL approach can also be used to explain chemiexcitation in luminol chemilumi-nescence . Two possibilities arise (i) an electron transfer from the amino group to the peroxidic moiety in the antiaromatic peroxide 33, resulting in bond cleavage followed by intramolecular back-electron transfer and formation of excited 3-aminophthalate (Scheme 24) (ii) the equilibrium between the peroxycarboxylic aldehyde 34, formed after elimination of nitrogen, and the cyclic peroxy semiacetal 35 is shifted in the direction of 35, as the result of an electron transfer from the amino group to the cyclic peroxide moiety, followed by 0—0 bond cleavage . Back-electron transfer would result in chemiexcitation (Scheme 25). 

The photochemical oxidation reactions of unsaturated organic molecules lead to the formation of peroxides which are characterized by the weak bond O-O. In terms of bond energies this is one of the weakest covalent bonds weak enough to be split in thermal processes. When a cyclic peroxide dissociates into carbonyl compounds, one of these may be formed in an electronically excited state (Figure 4.83). The energy difference results from the loss of the weak 0-0 bond and the formation of two C=0 tt bonds over 60kcalmol-1 is then available as free energy. There are also reasons of... 

There are many different light-emitting dyes used for bioluminescence, usually called luciferins . The overall chemical reaction is rather complex and involves at least one enzyme-catalysed step in the formation of the excited dye molecule, but the energy is always derived from the decomposition of a cyclic peroxide. In this respect it is quite similar to the process of chemiluminescence (Figure 5.26). 

Furans also form cyclic peroxides on reaction with singlet oxygen these undergo some interesting rearrangements as shown by the formation of the 2-aroyl enol esters 226 from the peroxides derived from 2-arylfurans. 

Cyclic peroxides are obtained from diketones when a five- or six-membered peroxide ring can be formed, as is the case with acetyl-acetone, acetonylacetone, triacetylmethane, and benzalacetylace-tone. In the reaction of 1,2-diketones with hydrogen peroxide, the C—C bond is broken to give carboxylic acids, without intermediate formation of a four-membered peroxide ring.37... 

A mechanism has been devised to explain the formation of 27 and 33 from 30 it suggests a step in which a cyclic peroxide is formed from the hydroperoxide (30) (Scheme III). Under basic conditions, and in the... 

Figure 3. The formation of hydroperoxy cyclic peroxides and prostaglandin-like endoperoxides from the 13S-hydroperoxide of linolenic acid by peroxy radical rearrangement. Structures are...

Cyclic peroxiiles. The complete paper on the formation of cyclic peroxides from unsaturated hydroperoxides using this radical source has been published. 

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