The chemiluminescence arising from the reaction between bis(pentachloropheny1)oxalate (PCPO) and hydrogen peroxide in the presence of the fluor 9,lO-diphenylanthracene (DPA) has been examined in detail. The effects of varying reactant, base catalyst and fluor concentrations on chemiluminescence decay rates and quantum yields have been investigated and a mechanism which accounts for the kinetics of the reaction has been proposed. The ratedetermining step is a reaction between PCPO and the hydroperoxide anion (OOH-) and does not involve the fluorescent activator. The lifetime of the reactive intermediate formed in the rate-determining step is short (5 x lop's) and consistent with the proposed mechanism.The investigation of chemiluminescence from organic compounds has received considerable attention14 and compounds involving the 1,2-dioxetane ring system provide some of the most thoroughly investigated examples. ls7 The bright chemiluminescence observed in the reaction between aryl oxalate esters and hydrogen peroxide in the presence of a base catalyst and fluorescence addend has been attributed to the presence of dioxatanedione as an intermediate.8'9 The overall reaction may be represented by 0 0
II I1ArO-C-C-OAr +H,O, +fluor -2ArOH +2CO, +fluor +light where Ar is an electronegative aryl group such as 2,4-dinitrophenyl trichlorophenyl. Efficient chemiluminescence occurs in several organic including chlorinated hydrocarbons and the viscous phthalate esters, and of fluors may be used to produce a range of colours.The volatile nature of the intermediate, reported in early work, has confirmed," and the existence of dioxetanedione is debatable.' '-13 The relative chemiluminescence efficiency of the peroxylate system for a variety of fluorescent acceptors has been examined, and it has been shown that it is possible to generate electronically excited singlet states whose energies are as high as 439 kJ m01-l.l~The nature of the chemielectronic step is not understood and there is little information on the rate-determining process(es). For this reason a detailed kinetic examination of the aryl oxalate ester +hydrogen peroxide system in the presence of a fluorescent addend has been attempted. 823 or 2,4,6-solvents, a variety not been
Absolute chemiluminescence quantum yields (phi CL) for reactions of bis-(pentachlorophenyl) oxalate (PCPO), hydrogen peroxide (H2O2) and 9:10 diphenyl anthracene (DPA) have been determined. A fully corrected chemiluminescence monitoring spectrometer was calibrated for spectral sensitivity using the chemiluminescence of the bis-(pentachlorophenyl) oxalate system as a liquid light source, the total photon output of which had previously been determined by chemical actinometry. At high (PCPO)/(H2O2) ratios phi CL was found to be independent of PCPO and H2O2 concentrations.
The effect of fluorescence activators on the quantum yields and emission decay rates of the chemiluminescence arising from the reaction between bis(pentachloropheny1)oxalate and hydrogen peroxide has been examined in detail. Chemiluminescence was detected for a range of fluors with excited-singlet-state energies <400 kJ mol-'. The chemiluminescence quantum yields were strongly dependent upon the nature and concentrations of the fluorescent activators, but the chemiluminescence decay rates were independent of the properties of the fluor. Delayed addition of the fluor had no effect upon both chemiluminescence quantum yields and decays.A quantitative relationship has been shown to exist between the normalised chemiluminescence quantum yields ( &L/ c $ ~) and the half-wave oxidation potential of the fluorescence activators. The results are discussed in terms of chemically initiated electron transfer between a reactive intermediate and the fluorescence activators. A mechanism involving 3-pentachlorophenoxy-3-hydroxy-1,2-dioxetanone as an intermediate is proposed.
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