AIBN-analogy initiators

A similar experiment is reported in (60) in-situ polymerization of PMMA in presence of MWCNT at analogous experimental conditions (in methanol, using PVP as stabilizer and AIBN as initiator) produced monodisperse PMMA/MWCNT microspheres only with the help of mechanical stirring. The spheres diameters decreased from about 11.6 pm to 6.0 pm as the content of MWCNT increased from 0 to 0.03 wt%. Additional analyses identified carbon nanotubes to be present both in the interior and on the surface of the particles. 

Alternatively, l,3-dithiol-2-ones have been obtained by reacting di-isopropylxanthogen disulfide with unsaturated substrates, such as disubstituted alkynes R2C2, in the presence of AIBN (azoisobutyrylnitrile), a radical initiator.78 Finally, vinylene dithiocarbonates can be obtained by reacting mer-cury(II) acetate with the corresponding trithiocarbonates, generated by reaction of electrophilic alkynes with ethylene trithiocarbonate.79 Analogously,... 

Initiator decomposition studies of AIBN in supercritical C02 carried out by DeSimone et al. showed that there is kinetic deviation from the traditionally studied solvent systems.16 These studies indicated a measurable decrease in the thermal decomposition of AIBN in supercritical C02 over decomposition rates measured in benzene. Kirkwood correlation plots indicate that the slower rates in supercritical C02 emanate from the overall lower dielectric constant (e) of C02 relative to that ofbenzene. Similar studies have shown an analogous trend in the decomposition kinetics ofperfluoroalkyl acyl peroxides in liquid and supercritical C02.17 Rate decreases of as much as 30% have been seen compared to decomposition measured in 1,1,2-trichlorotrifluoroethane. These studies also served to show that while initiator decomposition is in general slower in supercritical C02, overall initiation is more efficient. Uv-visual studies incorporating radical scavengers concluded that primary geminate radicals formed during thermal decomposition in supercritical C02 are not hindered to the same extent by cage effects as are those in traditional solvents such as benzene. This effect noted in AIBN decomposition in C02 is ascribed to the substantially lower viscosity of supercritical C02 compared to that ofbenzene.18... 

Cyclization of either of the thiols (24) with acid provided the saturated thia-PGIi analogs (26) as a 2.7 1 mixture of the exo and endo isomers.271 Although many addition reactions of thiols to alkenes are radical reactions catalyzed by light, oxygen, or other radical initiators, conversion to (26) was not effected under photolytic conditions or with AIBN. A radical chain mechanism for selenothiolactonization has also been reported recently.275... 

In contrast to HBr, the acids HC1 and HI do not undergo free-radical addition to alkenes, even in the presence of peroxides or O2. Abstraction of H- from HC1 is too endothermic, and addition of I- to an alkene is too endothermic. However, thiols (RSH) add to alkenes by a free-radical mechanism exactly analogous to the addition of HBr. The initiator is usually AIBN or (BzO)2- The alkene may be electron-rich or electron-poor. Note that the conjugate addition of thiols to electron-poor alkenes can occur either by a free-radical mechanism or by a polar, nucleophilic mechanism. 

Ester hydrolysis is most conveniently used because (1) its reaction mechanism is well established, and (2) both substrate and transition state analogs are easy to obtain. In Fig. 8.8b, phosphonic acid (2) is used as a transition state analog of the hydrolysis of substrate 3 [26]. A vinyl monomer of amidine 1 is chosen as a functional monomer because it readily forms stable complexes with the carboxylic acid ester and the phosphonic acid monoester. The imprinted polymers are synthesized in THF from 1 (the monomer), 2 (the template), and ethylene glycol dimethacrylate (the cross-linker) by using AIBN as the radical initiator. 

Unlike deazatation (denitrogenation) of azoalkanes, loss of N2O from aliphatic azoxy compounds is rarely observed. Thus they are neither free radical initiators nor thermally labile, contrary to published comments. For example, the common free radical initiator azoisobutyronitrile (AIBN) decomposes readily at 80 C but the azoxy analog 1 is stable up to 180 Thermolysis of azoxycumene 2 is very slow and does not yield N2O, leading instead... 

The reactions are performed by slow addition (10-15 h) of benzene solution of tri-K-butyltin hydride (1.3 eq.) and AIBN (0.7 eq.) to the boiling benzene solution of the corresponding Motherwell s precursor. Tri- -butyltin hydride in the presence of radical initiator such as AIBN is well known reagent for the generation of aryl radicals from aryl iodides and bromides [5]. Side-reactions in this approach are the formation of direct free-radical addition and dehalogenation products. The formation of the latter side-product is minimized by slow addition of tin hydride. However, the formation of direct free-radical addition, the Pschorr-type product is a serious side-reaction. For example, compound 423 at 75% conversion gives 34% of biaryl 424 as zp o-product (Motherwell reaction pathway), and 39% of biaryl 425, as the product of direct free-radical arylation, analogously to the Pschorr reaction pathway [1], Scheme 2. 

Several copolymers were synthesized in an organic solvent in order to analyze the final product in the absence of any additive required for a water dispersion. AIBN was used as the radical initiator and the reactions were performed in nitrogen atmosphere. The spectroscopic characteristics of the copolymers were compared with those of an analogous PVAc homopolymer obtained with the same procedure. 

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. 

Levesque " has observed that dithioacids (221) add to alkenes under AIBN initiation to give 1,3-dithiolanes (223) in high yield when the alkene is of the styrene type. This must involve intrlamolecular addition of the radical 222 to the sulfur atom (Scheme 94). Analogous results are obtained in the free radical addition of thiols to compounds 224 [X = Ikyl, OMe, NMc2, or SMe Z = CHj, (CH2)2, O, or S] where the radical 225 adds intramolecularly to the sulfur atom to give 226. 

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