Endoperoxides luminol chemiluminescence

The attempt to prepare a compound analogous to endoperoxide 30 from the reaction of 1,4-dimethoxyphthalazines with singlet oxygen resulted in the formation of the corresponding phthalate by elimination of N2, albeit no chemiluminescence was observed . Even though no experimental evidence indicates its existence, the endoperoxide intermediate 30 is one of the most well-accepted HEI postulated for the chemiexcitation step in luminol chemiluminescence. 

Semiempirical calculations indicate that there is a local energy minimum for the endoperoxide 37 with a barrier height of 6 kcalmoE corresponding to a lifetime of ca 10 s, in agreement with experimental results However, the most important result, which corroborates the hypothesis of 37 as the HEI in luminol chemiluminescence, is the state correlation between the ground state of 37 and the excited state of 3-AP. ... 

In the first proposal of a mechanism for chemiluminescent luminol oxidation, Albrecht postulates a bicyclic endoperoxide as the high-energy intermediate. The endoperoxide is presumably formed by nucleophilic attack of hydrogen peroxide monoanion on one of the diazaquinone 27 carbonylic groups to form 28, followed, after deprotonation to 29, by ring closure to 30 (Scheme 21) . 

Smith and Schuster (1978) have reported the observation of chemiluminescence from endoperoxide [36] which is structurally related to [35], the proposed luminol intermediate (44). This observation suggests yet another possibility for the structure of the key chemiluminescent intermediate from luminol, the o-xylylene peroxide analogous to [37]. 

The chemiluminescence of Luminol proceeds through the decomposition of the 1,4-endoperoxide. The reaction intermediate leading to the excited state may be represented by Eq. (47) and (48). Roswell and White (1978) report that the position of the amino group and the substitution for the amino group of a variety of adducts can significantly affect the value of (p. ... 

This chemiluminescent reaction of (52) can serve as model for the chemiluminescent decomposition of the luminol endoperoxide [67] the only problem being at present that evidence for the luminol endoperoxide is so hard to obtain. 

The decomposition of the endoperoxide via the o-xylene derivative (48) in an intramolecular electron transfer mechanism would also give the substituents a decisive role in the excitation step itself - not only affecting the fluorescence efficiency of the phthalate dianion. A high fluorescence efficiency is of course a necessary, but not sufficient, requirement in luminol type chemiluminescence [9, 16],... 

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