Kinetics autoxidation

The photobleaching of P-carotene by fluorescent light in fatty acid ester solutions showed an autoxidation kinetic profile with the rate of degradation of P-carotene in the order laurate > oleate > linoleate (Carnevale et al. 1979). The presence of a radical scavenger retarded the autoxidation, thus leading to the view that protection against autoxidation is built into the system by the unsaturation in the fatty acid. 

This may indicate that factors other than the availability of empty coordination sites may also have important mechanistic implications. In the autoxidation kinetics of a series of Fe(II)-aminopolycarboxylato complexes the significance of steric effects was unequivocally confirmed (26). These results may also bear some relevance with respect to the Ru(III)-catalyzed reactions. 

The enhanced chemiluminescence associated with the autoxidation of luminol (5-amino-2,3-dihydro-1,4-phthalazinedione) in the presence of trace amounts of iron(II) is being used extensively for selective determination of Fe(II) under natural conditions (149-152). The specificity of the reaction is that iron(II) induces chemiluminescence with 02, but not with H202, which was utilized as an oxidizing agent in the determination of other trace metals. The oxidation of luminol by 02 is often referred to as an iron(II)-catalyzed process but it is not a catalytic reaction in reality because iron(II) is not involved in a redox cycle, rather it is oxidized to iron(III). In other words, the lower oxidation state metal ion should be regarded as a co-substrate in this system. Nevertheless, the reaction deserves attention because it is one of the few cases where a metal ion significantly affects the autoxidation kinetics of a substrate without actually forming a complex with it. 

Although these reports demonstrate the contribution that can be made by use of variant forms of Mb in the study of long-recognized but incompletely understood behavior of the protein, they represent only part of the extensive literature concerning the pH dependence, dioxygen dependence, and species dependence of autoxidation kinetics. A detailed discussion of all the relevant mechanistic issues related to autoxidation of oxyMb is beyond the scope of the current chapter, but a thorough survey of this subject has been provided by Shikama (162). 

Litwinienko, G, Daniluk, A., and Kasprzyska-Guttman, T. 2000. Study on Autoxidation Kinetics of Fats by Differential Scanning Calorimetry. 1 Saturated C12-C18 Fatty Acids and Their Esters. Ind. Eng. Chem. Res., 39,7-12. 

SA Wallick, KV Sarkanen. Effect of pH on the autoxidation kinetics of vanillin. Wood Sci Technol 17 107-116, 1983. 

In order to elucidate the contribution of the main phenolic components [esculin (1), esculetin (2), fraxin (3) and fraxetin (4)] in the extract to its stabilizing action, we studied the autoxidation kinetics of the two natural lipid systems (TGL and TGSO) in the presence of different concentrations of 1-4. 

Ford, P. C., Wink, D. A., and Stanbury, D. M, (1993). Autoxidation kinetics of aqueous nitric oxide. FEES Lett. 326, 1-3. 

Spectroscopy in the ultraviolet and visible range has been used to follow the evolution of NO2 in order to study the autoxidation kinetics (29), and symmetric NO3 has been characterized by the method already in the early twentieth century (5,48) it can be prepared in easily detectable quantities by the reaction of N2O5 or NO2 with ozone. It is, however, not very fikely an intermediate of NO autoxidation, because its formation would require the splitting of02, and because the electrode potential ofits reduction to NOs" has been estimated to be higher than 2 V, which would lead to side reactions that would have been hardly overlooked. In contrast, the electronic spectrum of ONOO is not known, and it would most likely not be helpfijl in detecting it at steady-state concentrations, since known extinction coefficients of N-O compounds in the visible and near ultraviolet spectrum are all below 1000 cm Thus, the absorption of ONOO during autoxidation would vanish under the contribution of the product, NO2. ... 

A review of autoxidation and autoxidation kinetics has been published. A DFT study of autoxidation of diethyl ether (DEE) supported the basic mechanism involving steps such as chain initiation, propagation, and termination reactions as in alkane oxidations but inferred that the reaction could be different in the presence or absence of... 

Adachi, S., Ishiguro, T. and Matsuno, R. 1995. Autoxidation kinetics for fatty acids and their esters. J. Amer. Oil Chem. Soc. 72(5) 547-551. 

Further quantitative investigations on autoxidation kinetics have led to a more detailed picture of the initiation and of chain termination steps [6, 7]. Details of the steps leading to chemiluminescence are as follows. 

Thermal Oxidative Stability. ABS undergoes autoxidation and the kinetic features of the oxygen consumption reaction are consistent with an autocatalytic free-radical chain mechanism. Comparisons of the rate of oxidation of ABS with that of polybutadiene and styrene—acrylonitrile copolymer indicate that the polybutadiene component is significantly more sensitive to oxidation than the thermoplastic component (31—33). Oxidation of polybutadiene under these conditions results in embrittlement of the mbber because of cross-linking such embrittlement of the elastomer in ABS results in the loss of impact resistance. Studies have also indicated that oxidation causes detachment of the grafted styrene—acrylonitrile copolymer from the elastomer which contributes to impact deterioration (34). 

Kinetic data exist for all these oxidants and some are given in Table 12. The important features are (i) Ce(IV) perchlorate forms 1 1 complexes with ketones with spectroscopically determined formation constants in good agreement with kinetic values (ii) only Co(III) fails to give an appreciable primary kinetic isotope effect (Ir(IV) has yet to be examined in this respect) (/ ) the acidity dependence for Co(III) oxidation is characteristic of the oxidant and iv) in some cases [Co(III) Ce(IV) perchlorate , Mn(III) sulphate ] the rate of disappearance of ketone considerably exceeds the corresponding rate of enolisation however, with Mn(ril) pyrophosphate and Ir(IV) the rates of the two processes are identical and with Ce(IV) sulphate and V(V) the rate of enolisation of ketone exceeds its rate of oxidation. (The opposite has been stated for Ce(IV) sulphate , but this was based on an erroneous value for k(enolisation) for cyclohexanone The oxidation of acetophenone by Mn(III) acetate in acetic acid is a crucial step in the Mn(II)-catalysed autoxidation of this substrate. The rate of autoxidation equals that of enolisation, determined by isotopic exchange , under these conditions, and evidently Mn(III) attacks the enolic form. 

The autoxidation of V(ni) to V(IV) in aqueous HCIO4 also displays the kinetics ... 

This slow process generates Cu(I) which rapidly reduces O2 to HOj vide infra). The kinetics of autoxidation of ferrous ion depend on the acidity of the medium... 

The kinetics of the autoxidation of Pu(ni) in aqueous sulphuric acid resemble those of Fe(II), viz. 

Although the kinetic studies summarised here are useful guides to the gross features of mechanism it is evident from apparently closely related autoxidations, e.g. those of V(III) and U(IV), that subtle factors operate. Fallab has pointed out that these reductants give similar kinetics and possess similar reduction potentials, yet differ in autoxidation rate by a factor of 3 x 10 , and has discussed differences of this type in terms of the stereochemistry of the electron-transfer process in the coordination sphere. 

The reaction is strongly acid-inverse below pH 4 but becomes acid-independent above pH 5.5. The rate and kinetics are identical with those of the autoxidation of Mo( V)2 and it seemd probable that dissociation of the dimer is rate-determining, viz. 

The speed of autoxidation was compared for different carotenoids in an aqueous model system in which the carotenoids were adsorbed onto a C-18 solid phase and exposed to a continnons flow of water saturated with oxygen at 30°C. Major products of P-carotene were identified as (Z)-isomers, 13-(Z), 9-(Z), and a di-(Z) isomer cleavage prodncts were P-apo-13-carotenone and p-apo-14 -carotenal, and also P-carotene 5,8-epoxide and P-carotene 5,8-endoperoxide. The degradation of all the carotenoids followed zero-order reaction kinetics with the following relative rates lycopene > P-cryptoxanthin > (E)-P-carotene > 9-(Z)-p-carotene. 

Takahashi, A., Shibasaki-Kitakawa, N., and Yonemoto, T., Kinetic model for autoxidation of beta-carotene in organic solutions, J. Am. Oil Chem. ScL, 76, 897, 1999. 

Chloroprene monomer will autoxidise very rapidly with air, and even at 0°C it produces an unstable peroxide (a mixed 1,2- and 1,4-addition copolymer with oxygen), which effectively will catalyse exothermic polymerisation of the monomer. The kinetics of autoxidation have been studied [1], It forms popcorn polymer at a greater rate than does butadiene [2],... 

Recently, we have demonstrated another sort of homogeneous sonocatalysis in the sonochemical oxidation of alkenes by O2. Upon sonication of alkenes under O2 in the presence of Mo(C0) , 1-enols and epoxides are formed in one to one ratios. Radical trapping and kinetic studies suggest a mechanism involving initial allylic C-H bond cleavage (caused by the cavitational collapse), and subsequent well-known autoxidation and epoxidation steps. The following scheme is consistent with our observations. In the case of alkene isomerization, it is the catalyst which is being sonochemical activated. In the case of alkene oxidation, however, it is the substrate which is activated. 

The fact that the kinetic chain length of dimedone autoxidation is very low appears to indicate structural effects in autoxidation reactions. These may account for some of the discrepancies found in autoxidation chemiluminescence studies of different types of compounds. 

Kinetics of Autoxidation of Organic Compounds Inhibited by Acceptors of Peroxyl Radicals... 

KINETICS OF AUTOINITIATED HYDROCARBON OXIDATION 4.7.1 Initial Stage of Autoxidation... 

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