Diphenoyl peroxide

The decomposition of this peroxide is reasonably chemiluminescent in the presence of typical fluorescent acceptors. Although the first mechanisms advanced by its discoverer [4] invoked a ground state forbidden cycloreversion, analogous to that of the dioxetans, this compound now stands as a good example of the CIEEL mechanism. It was the first in which the requirements were explicitly stated. 

Thermolysis of diphenoyl peroxide in solution yields benzocoumarin and CO2 as the main products. In the absence of easily oxidized acceptors, light yields are very low, with little evidence for the formation of triplet or singlet excited states of benzocoumarin. 

Catalysis of the decomposition is observed with the rate law now characteristic of CIEEL, where D is the donor or activator  

Chemiluminescence intensity is proportional to [D], and the activation energy for light emission is derived solely from k2. This suggests that the principal light reaction has been properly identified as the bimolecular reaction. The catalysis of the reaction can be correlated with the ionisation potential of the activator. 

The reaction mechanism proposed by Koo and Schuster [4], is that of a cage charge annihilation  

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Figure 13 Chemiluminescent reaction of diphenoyl peroxide based on CIEEL mechanism.

In 1977, Koo and Schuster studied the CL emission produced when diphe-noyl peroxide was decomposed at 24°C in dichloromethane in the dark producing benzocoumarin and polymeric peroxide [111, 112]. No CL emission was observed directly as benzocoumarin is nonfluorescent however, in the presence of aromatic hydrocarbons light was produced because of the fluorescence of these hydrocarbons. The explanation of this phenomenon was based on the above-mentioned CIEEL the aromatic hydrocarbons, which have a low oxidation potential, transfer one electron to diphenoyl peroxide to form a charge-transfer complex, from which benzocoumarin and the corresponding hydrocarbon in the excited state are produced (Fig. 13). 

Diphenoyl peroxide is the cyclic peroxide of diphenic acid (2,2 -biphenyldicar-boxylic acid) (Fig. 7). It undergoes thermal decomposition to form 3,4-benzocou-... 

The CIEEL mechanism has been utilized to explain the catalyzed decomposition of several cyclic and linear peroxides, including diphenoyl peroxide (4), peroxyesters and 1,2-dioxetanones. Special interest has focused on this mechanism when it was utilized to explain the efficient excited state formation in the chemiexcitation step of the firefly s luciferin/luciferase bio luminescence. However, doubts have been voiced more recently about the validity of this mechanistic scheme, due to divergences about the... 

However, the most severe criticism of the CIEEL hypothesis relates to the chemiexcita-tion efficiency experimentally obtained for the standard CIEEL systems, diphenoyl peroxide (4) and 1,2-dioxetanone (2) . In a study on the electron transfer catalyzed decomposition of l,4-dimethoxy-9,10-diphenylanthracence peroxide (21), Catalan and Wilson obtained very low chemiexcitation quantum yields with various commonly utilized activators (4>s =2 10 EmoH ) and reinvestigated the CL of diphenoyl peroxide (4), determining quantum yields in the same order of magnitude (4>s = (2 1)10 Emol ) as those obtained by 21 (Table 1). We have more recently determined the quantum yields in the rubrene-catalyzed decomposition of dimethyl-1,2-dioxetanone (9) and also found a much lower value than the one initially reported (Table 1) °. Since the diphenoyl peroxide and the 1,2-dioxetanone systems are the two prototype CIEEL systems, the validity of this hypothesis itself might be questioned due to its low efficiency in excited-state formation. ... 

Chemiluminescence. The mechanisms behind this phenomenon, as induced by the reaction of, e.g. diphenoyl peroxide and an easily oxidized fluorescent molecule has been brilliantly illuminated by Schuster and co-workers (Schuster, 1979b Koo and Schuster, 1978) who proposed the CIEEL pathway (Chemically Initiated Electron Exchange Luminescence) according to (12). Note that two electron-transfer steps are postulated, the... 

The chemiluminescent reaction of diphenoyl peroxide [26] with easily oxidized, aromatic hydrocarbons, reported by Koo and Schuster (1977b, 1978), was the first well-defined example of an electron-exchange chemiluminescent reaction of an organic peroxide. Its study led to the postulation of chemically initiated electron-exchange luminescence as a generalized mechanism for efficient chemical light formation (Schuster, 1979 Schuster et al., 1979). 

Fig. 10 The CIEEL mechanism for the thermal reaction of diphenoyl peroxide 1261 with aromatic hydrocarbons (act)...

More recently, direct experimental verification of the existence of radical ions in the reaction of [261 with activators and of their intermediacy in the chemiluminescence process was obtained by applying nanosecond laser spectrophotometric techniques to the study of this reaction (Horn and Schuster, 1979). Excited singlet pyrene was generated by irradiation with a nitrogen laser. The fluorescence of pyrene was quenched by diphenoyl peroxide... 

Another route to cyclic diacyl peroxides was discovered by Ramirez et al.73 A mixture of phenanthraquinone and trimethyl phosphite in methylene chloride gives an adduct (85) at room temperature, and this adduct is ozonized at —70°. Diphenoyl peroxide (86) is formed in 50% yield. 

Iodine is liberated quantitatively from acidic iodide solution by 84 and 86.71-72 Reduction of the cyclic diphenoyl peroxide (86) with triphenylphosphine or trimethyl phosphite leads to an 80% yield of... 

Ozonolysis of the adduct affords diphenoyl peroxide (6). Benzil and diacetyl give adducts melting at 50 and at 46° respectively. 

The 1,2-dioxocin ring system has received a rather surprising amount of attention, at least in relation to the other compounds discussed in this chapter (with the exception of the 1,2-diazocines). The vast majority of these reports deal with essentially two compounds, namely the 5,8-dialkoxy-5,8-dihydro-dibenzo[fi /][l,2]dioxocins (50) obtained from the ozonolysis of phenanthrene, and the corresponding 5,8-dione (51) ( diphenoyl peroxide ), but a substantial number of other derivatives have also appeared since the publication of CHEC-I in which only a single derivative was reported. 

The chemistry of the peroxide bond has featured prominently in the reported reaction chemistry of 1,2-dioxocin derivatives. Diphenoyl peroxide (51) readily oxidizes triphenylphosphine and trimethylphosphite to the corresponding P-oxides, in the process being reduced to diphenic anhydride (Equation (20)) <61JA492,64JA4394,64MI921-01 >. Compound (56 R = H) also oxidizes triphenylphosphine the fate of the dioxocin in this case has not been determined, but alcohol and/or epoxide derivatives appear to be formed <82CL38i>. 

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