AIBN-initiated oxidation

Table I. AIBN-Initiated Oxidation of Organic Phosphorus Compounds in ferf-Butylbenzene at 70°C.

Small but significant effects of solvent polarity were found in the autoxidation of a variety of alkenes and aralkyl hydrocarbons [216-220] (styrene [216, 218, 219], ethyl methyl ketone [217], cyclohexene [218], cumene [218, 219], tetralin [219], etc.). An extensive study on solvent effects in the azobisisobutyronitrile (AIBN)-initiated oxidation of tetralin in a great variety of solvents and binary solvent mixtures was made by Kamiya et al. [220],... 

AIBN-initiated oxidation of cumene and Tetralin in the presence of deuterated amines were unsuccessful. They proposed an alternative mechanism involving reversible formation of a complex of antioxidant with peroxy radical as the kinetically controlling process. We observed an isotope effect, dAh = 1.8, consistent with the hydrogen-donation mechanism in the retarded oxidation of SBR polymer with deuterated amines (7,8). Our results were confirmed by observation of significant isotope effects in the initial stage of oxidation of purified cfc-l,4-polyiso-prene with both hindered phenols and amines (9). Table I shows the effect of temperature and antioxidant concentration on the rates of oxidation and the observed deuterium isotope effects. 

Thus, it has been proposed that the homolytic decomposition of hydroperoxides can be induced by sulfenic acid (12,13). There is evidence that various carboxylic acids can promote radical formation from hydroperoxides at elevated temperatures (II, 14). The intermediate thiosul-furous acid (Reaction 7) itself may function as the source of radicals, since sulfinic acid is known to initiate the radical polymerization of vinyl monomers at 20°C (15). Based on the AIBN-initiated oxidation of cumene, Koelewijn and Berger (16) proposed that pro-oxidant effects arise from catalysis of the radical decomposition of hydroperoxides by intermediate compound formation between the hydroperoxide and sulfoxide. However, under our conditions hydroperoxide was stable in the presence of sulfoxide alone. 

The rare example of synergistic action of a binary mixture of 1-naphthyl-A-phcnylaminc and phenol (1-naphthol, 2-(l,l-dimethylethyl)hydroquinone) on the initiated oxidation of cholesterol esters was evidenced by Vardanyan [34]. The mixture of two antioxidants was proved to terminate more chains than both inhibitors can do separately ( > /[xj). For example, 1-naphtol in a concentration of 5 x 10 5 mol L-1 creates the induction period t=170s, 1 -naphthyl-A-phenylamine in a concentration of 1.0 x 10-4 mol L 1 creates the induction period t = 400s, and together both antioxidants create the induction period r = 770 s (oxidation of ester of pelargonic acid cholesterol at 7= 348 K with AIBN as initiator). Hence, the ratio fs/ZfjXi was found equal to 2.78. The formation of an efficient intermediate inhibitor as a result of interaction of intermediate free radicals formed from phenol and amine was postulated. This inhibitor was proved to be produced by the interaction of oxidation products of phenol and amine. 

Homolytic hydrostannation can also be initiated at room temperature by thiophenols, when a trace of oxygen may oxidize the thiol to the ArS radical, which abstracts hydrogen from the stannane to give the stannyl radical (Equation (15)).93 With azoisobutyronitrile (AIBN) initiation, alkynes undergo only monohydrostannation, but with the thiol, simple alkynes show bis(hydrostannation) or bis(stannation). 

The data given in Tables IV and V have been plotted in Figures 1 and 2 together with the theoretical curves for the best values of fctra °H and fctransH derived from Equations 21 and 22. The rate constants at 30° and 56°C., respectively, are fctra °H = 600 and 1100 Mole"1 sec."1, ktra°°H = 2500 and 2800 Mole"1 sec."1 (At 56°C. rate constants were obtained from both photoinitiated and AIBN thermally initiated oxidations.) and... 

AIBN represents azobisisobutyronitrile, the initiator used in work, and e is the efficiency with which it initiates oxidation chains. this The... 

The results of a study of the zinc diisopropyl dithiophosphate-inhib-ited oxidation of cumene at 60°C. are shown in Figures 1 to 3. The initial oxidation rate is directly proportional to the AIBN concentration, but the dependence of initial rate on the cumene concentration or the reciprocal of the zinc salt concentration, although reasonably linear, is not in direct proportion. 

Figure 1. Initial oxidation rate of 7.2M eumene at 60°C. containing 0.02M ZnP as a function of AIBN concentration...

Figure 3. Initial oxidation rate as a function of concentration of cumene in tert-butylbenzene at 60°G. containing 0.06M AIBN and 0.02M ZnP...

AIBN is, however, virtually unaffected by the presence of dithio-phosphates (Table II). Further, with specific reference to the oxidation of the disulfide in Table I, which has no effect on the rate of AIBN-initi-ated autoxidation of cumene (6), it is unlikely that the efficiency of radical production from AIBN increases since this would produce a prooxidant effect in cumene. Thus, the zinc salt inhibitor is being oxidized in competition with the main chain reaction. 

For oxidation, different stressing schemes can be used, and this depends generally on the structure of the drug substance (active component) autooxidation, metals, peroxide-mediated, peroxy-mediated, bubbled oxygen, and pressurized oxygen. Auto-oxidation involves a free radical initiator such as AIBN (2,2 -azobisisobutyronitrile) or AMVN (2,2 -azobis(2,4-dimethylvaleronitrile) to initiate oxidation [37] and has been used to mimic long-term room temperature degradation related to oxidation. The concentration... 

The effectiveness of dibenzylhydroxylamine as a inhibitor of AIBN-initiated tetralin oxidation can be seen from the data in Figure 6. A comparison between dibenzylhydroxylamine and butylated hydroxytoluene (BHT) can be made from those data. The lower rate of oxygen consumption in the solution containing dibenzylhydroxyl-... 

The radical homo- and copolymerization of the ferrocene-containing monomer 154 allowed for the isolation of polymers containing pendent ferrocene moieties (Scheme 2.41).228 High molecular-weight polymers were obtained from AIBN-initiated reactions, whereas other cationic initiators gave only low molecular-weight materials. Electrochemical studies showed that homopolymer 155 underwent two oxidations at Ey2 = —0.13 V and Ey2 = +0.05V in... 

Oxidation may be initiated by an agent that is able to decompose and produce free radicals. This is so with benzoyl peroxide (Bz202) and azo-bisisobutyronitrile (AIBN). Initiation by benzoyl peroxide produces initial rates which fit, in the experimental range defined by the boundary conditions 0.0446 < [RCHO]0 < 0.224 mole l-1 105 < PQl < 580 torr 20 < T< 35° C solvent, benzene. [Bz2O2]0 = 2.95 X 10-3 mole per mole of solution, the equation... 

Under these circumstances, a plot of r/[AIBN]1/2 versus 1/[AH]1/2 should be linear for initial oxidation rates, as has been observed experimentally [8-10]. 

Figure 12. Inhibitory Activity of Curcuminolds (24 and 32 against AIBN initiated Linoleic Acid Oxidation (Linolcic Acid 54 mM, AIBN 81 mM, ( urcuminoid 170 tiM).

RgurelQ. tnhibitnry Activity of Curcuminoids (25-29) against AIBN-initiated Unoleic Acid Oxidation (Linoletc Acid 54 mM, AIBN 81 mM, Curcuminoid 170 mM). 

Polymers with metals in the side groups can be produced by polymerization of the corresponding monomers or by polymer analog conversion. For example, vinyl ferrocene copolymerizes to high-molar-mass products with, for example, styrene under the influence of nonoxidizing free radical initiators such as AIBN. BPO oxidizes the iron. 

In case the degradation process takes place via reaction (7), then W -Wqj. In order to elaborate the mechanism of degradation process we have carried out an initiated oxidation of PS [AIBN]=2%, 60 C, W=lxl0 5 mol/(kg.s), where AIBN - azoisobutyronitrile. For the inhibited oxidation W has been found as 9x10 breaks/(kg.s) and upon ozonation a similar value for has been obtained at Wq3=1.5x10 moI/(kg.s) (Fig. 38,3). 

Fig. 3 1. Number of chain scissions as a function of time of photo-oxidation of different hydroperoxidized polystyrenes (a) redox hydroperoxide (b) redox polystyrene (c) AIBN (azo-bis-isobutyro nitrile) initiated hydroperoxide (d) AIBN initiated polystyrene and (e) anionic hydroperoxide [2242]. (Reproduced with permission from [2242] published by Elsevier Science Publishers Ltd, 1989.)...

The synthesis of polyferrocenophanes has been achieved by the radical homo- and co-cyclopolymerization of monomer 48 as shown in Scheme 10." The homopolymerization reaction was also investigated in the presence of cationic initiators only AIBN-initiated reactions yielded high molecular weight polymers. Cyclic voltammetry of the homopolymer 49 showed two oxidation waves at —0.13 and +0.05 V in dichloromethane, while copolymer 50 showed only one oxidation wave at -0.03 V The conductivity of these polymers was also examined. Doping of 49 and 50 with iodine under an argon atmosphere resulted in conductivities of 5.3 X 10 and 1.6 X 10 S/cm, respectively. However, rmder ambient condi-... 

Kondo maintained his interest in this area, and with his collaborators [62] he recently made detailed investigations on the polymerization and preparation of methyl-4-vinylphenyl-sulfonium bis-(methoxycarbonyl) meth-ylide (Scheme 27) as a new kind of stable vinyl monomer containing the sulfonium ylide structure. It was prepared by heating a solution of 4-methylthiostyrene, dimethyl-diazomalonate, and /-butyl catechol in chlorobenzene at 90°C for 10 h in the presence of anhydride cupric sulfate, and Scheme 27 was polymerized by using a, a -azobisi-sobutyronitrile (AIBN) as the initiator and dimethylsulf-oxide as the solvent at 60°C. The structure of the polymer was confirmed by IR and NMR spectra and elemental analysis. In addition, this monomeric ylide was copolymerized with vinyl monomers such as methyl methacrylate (MMA) and styrene. 

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