Dimethyl peroxide, decomposition

There is no evidence in any of the gas phase systems for initial multiple bond rupture (i.e., fragmentation reactions). Because of the low reaction temperatures, the alkoxy radical intermediates of the bond fission reactions (or radicals resulting from alkoxy radicals) are mainly involved in radical-radical termination processes ( 0) rather than participating in hydrogen abstraction from the parent peroxide E oi 6-8). Thus it has been commonly believed that the peroxide decompositions were classic examples of free radical non-chain processes. Identification of the rate coefficients and the overall decomposition Arrhenius parameters with the initial peroxide bond fission kinetics were therefore made. However, recent studies indicate that free radical sensitized decompositions of some peroxides do occur, and that the low Arrhenius parameters obtained in many of the early studies (rates measured by simple manometric techniques) were undoubtedly a result of competitive chain processes. The possible importance of free radical reactions in peroxide decompositions is illustrated below with specific regard to the dimethyl peroxide decomposition. 

A number of chemiluminescent reactions may proceed through unstable dioxetane intermediates (12,43). For example, the classical chemiluminescent reactions of lophine [484-47-9] (18), lucigenin [2315-97-7] (20), and transannular peroxide decomposition. Classical chemiluminescence from lophine (18), where R = CgH, is derived from its reaction with oxygen in aqueous alkaline dimethyl sulfoxide or by reaction with hydrogen peroxide and a cooxidant such as sodium hypochlorite or potassium ferricyanide (44). The hydroperoxide (19) has been isolated and independentiy emits light in basic ethanol (45). 

The kinetics of the oxidation of CO by methoxyl radicals (produced by the thermal decomposition of dimethyl peroxide), as shown in equation (41),... 

Dimethyl-I,l -biphenyl has been prepared by a wide variety of procedures, but few of these are of any practical synthetic utility Classical radical biarjl syntheses such as the Gomberg reaction or the thermal decomposition of diaroyl peroxides give complex mixtures of products m which 4,4 dimethyl-l.l -biphenyl is a minor constituent A radical process maj also be involved in the formation of 4,4 dimethyl-1, l -biphenyl (13%) by treatment of 4-bromotoluene with hydrazine hydrate 5 4,4 -Dimethyl-l,l -biphenyl has been obtained in moderate to good yield (68-89%) by treatment of either dichlorobis(4-methyl phenyl)tellurium or l,l -tellurobis(4-methylbenzene) with degassed Raney nickel in 2 methoxyethyl ether 6... 

The rapid decomposition of benzoyl peroxide by dimethyl sulfide is explosive in absence of solvent. 

Experimental evidence of the involvement of a biradical intermediate in the decomposition of 3,3-dimethyl-l,2-dioxetane (10) has been obtained by radical trapping with 1,4-cyclohexadiene (CHD). Decomposition of 10 in neat CHD was shown to result in the formation of the expected 1,4-dioxy biradical trapping product, 2-methyl-1,2-propanediol (11) ° . However, more recently, it has been shown that the previously observed trapping product 11 was formed by induced decomposition of the dioxetane, initiated by the attack of the C—C double bond of the diene on the strained 0—0 bond of the cyclic peroxide (Scheme 9)"°. 

Intensive studies in the field of mechanistic CL by several research groups have resulted in the description of a large variety of peroxides which, in the presence of appropriate activators, show decomposition in an activated CL process and might involve the CIEEL mechanism . Even before the formulation of the CIEEL mechanism, Rauhut s research group obtained evidence of the involvement of electron-transfer processes in the excitation step of the peroxyoxalate CL. Results obtained in the activated CL of diphe-noyl peroxide (4) led to the formulation of this chemiexcitation mechanism , and several 1,2-dioxetanones (a-peroxylactones), such as 3,3-dimethyl-l,2-dioxetanone (9) and the first a-peroxylactone synthesized, 3-ierr-butyl-l,2-dioxetanone (14), have been shown to possess similar CL properties, compatible with the CIEEL mechanism Furthermore, the CL properties of secondary peroxyesters, such as 1-phenethylperoxy acetate (15) , peroxylates (16) , o-xylylene peroxide (17) , malonyl peroxides... 

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. ... 

Lucigenin (10,10 -dimethyl-9,9 -biacridinium or bis-Af-methylacridinium (38)), in the presence of hydrogen peroxide in alkaline media, exhibits chemiluminescence with a maximum emission wavelength at 445 nm. Lucigenin chemiluminescence was first reported in 1935 by Glen and Petsch, and the 1,2-dioxetane 39 was postulated as a key intermediate. Nevertheless, the mechanism of lucigenin chemiluminescence was only elucidated by McCapra and Richardson, who also proposed the thermal decomposition... 

Acetyl peroxide (solid) explodes on shock. It should be prepared and used without interruption and should be handled by remote control (Refs 54 71). The commercially available 30% solution in dimethyl phthalate will not give crystalline acetyl peroxide under ordinary-circumstances. The solution has a flash point of 45°C. Heating it above 50°C causes orderly, but fairly rapid decomposition (Ref 62)... 

Thne-of-flight (TOF) mass spectrometric analysis of the pyrolysis fragments of di-t-butyl peroxide suggests t-BuCO as the primary product, followed by decomposition of this radical into CHj.253 Elsewhere, the kinetics of the pyrolysis of dimethyl, diethyl, and di-t-butyl peroxides in a modified adiabatic bomb calorimeter have been investigated.254 The lifetime of acyloxy radicals, generated by the photolysis or thermolysis of acetyl propionyl peroxide, have been studied. Chemical nuclear polarization has been used to determine the rate constant for the decarboxylation of these radical intermediates.255... 

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