Cyanopropyl radical

C, decomposes slowly into cyanopropyl radicals and is useful for initiation of radical reactions. 

In discussing mechanism (5.F) in the last chapter we noted that the entrapment of two reactive species in the same solvent cage may be considered a transition state in the reaction of these species. Reactions such as the thermal homolysis of peroxides and azo compounds result in the formation of two radicals already trapped together in a cage that promotes direct recombination, as with the 2-cyanopropyl radicals from 2,2 -azobisisobutyronitrile (AIBN),... 

The use of nitrone scavengers was precedented by the work of Iwamura and Inamoto (1967), who had used esr spectroscopy to detect the nitroxide formed by addition of cyanopropyl radicals to the cyclic nitrone, 5,5-dimethyl-pyrroline-N-oxide (DMPO) [2], and had actually isolated the cyanopropyl radical adduct of the nitrone [3]. 

Although the yield and product selectivity require further improvement, the three-component coupling reaction of azo-bis-isobutyronitrile (AIBN), phenylacetylene, and p-methoxyphenyl isonitrile proceeds to give a quinoxaline derivative (Scheme 6.9) [16]. Decomposition of AIBN gives a cyanopropyl radical, which adds to phenylacetylene to form a vinyl radical. Addition of the vinyl radical to the isoni-... 

Becerra, M. R. Fernandez-Sanchez, E. Fernandez-Torres, A. Garcia-Dominguez, J. A. Santiuste, J. M., "Evaluation of the Effect of the Cyanopropyl Radical on the Interaction of the Methylene Group with Silicon Stationary Phases," J. Chromatogr., 547, 269 (1991). 

Cage effects also account for the fact that not all the radicals produced from the decomposition of initiators such as azobisisobutyronitrile (AIBN) are effective in initiating radical polymerizations. In the somewhat simplified reaction Scheme (5-168) depicting the thermolysis of AIBN, two types of cyanopropyl radicals are shown, one still within the solvent cage, whereas the others have reached their statistical separation... 

The activation energy, 30.8 kcal.mole of the decomposition of this molecule IS much lower than that with unsubstituted azoalkanes, and some 12 kcal.mole lower than with 2,2 -azoisobutane. This drop in activation energy caused by the introduction of the cyano groups into the molecule is interpreted by the resonance stabilization of the 2-cyanopropyl radical... 

Puriflcation is effected by recrystallization from methanol and drying in vacuum over phosphorus pentoxide. Under mild conditions (4(F) the reagent decomposes into cyanopropyl radicals and hence is useful for initiation of radical reactions. ... 

The final products of its decomposition are two cyanopropyl radicals and a molecule of nitrogen ... 

A bimolecular initiating system, based in 2,2 -azobisisobutyronitrile was reported by Michl and co workers [26]. It consists of weakly solvated lithium in combination with the cyanopropyl radical (from AIBN). The combination can initiate polymerizations of olefins. The reaction was illustrated as follows ... 

When AIBN is used as the initiator for radical polymerization of vinyl compounds, the cyanopropyl radical either reacts with BNO or adds to the monomer to form a propagating radical. Therefore, assuming that all the propagating radicals are eventually trapped by BNO, we may estimate approximately the relative ease of formation of trapped propagating radicals from ESR measurements in which the trapped cyanopropyl radical is used as an internal reference. This idea was used by Kunitake et al. who found the relative reactivity of vinyl monomers with an initiating radical to vary as follows AN > MA > VAc > styrene > divinyl ether. 

BEC Becerra, M.R., Femandez-Sanchez, E., Femandez-Torres, A., Garcia-Dominguze, J.A., and Santiuste, J.M., Evaluation of the effect of the cyanopropyl radical on the interaction of the methylene group with silicone stationary phases, J. Chromatogr., 547, 269, 1991. 

The emerging cyanopropyl radicals not only can initiate the polymerization reactions but may also recombine with the formation of dinitril tetra-methyl succinate or a corresponding ketenimine. 

Azo compounds will decompose both with the application of heat and by photolysis. Azobisisobutyronitrile breaks down into cyanopropyl radicals and nitrogen at ambient temperature under the action of ultra-violet radiation. 

Stationary phases in capillary SFC [30] are usually based on a polysiloxane backbone, cross-linked by means of a free-radical initiator, and methyl, phenyl, octyl, biphenyl, and cyanopropyl substituents are incorporated into them. These polysiloxane phases exhibit wide ranges between their glass transition and decomposition temperatures, and this feature sets them apart from most high molecular-mass polymers, as they allow useful operating conditions for chromatography. Polysiloxanes can be tailor-made for specific... 

Chemically bonded silicas include eilkyl-bonded (C4-C.18), perfluoropropyl-, cyanopropyl-, aminopropyl-, diolphenyl- and other radicals [4,... 

Polymerization of the multimonomer obtained was carried out in a very diluted benzene solution with a high concentration of AIBN used as an initiator. Such a procedure was used to minimize intermolecular readion. The high concentration of the initiator leads to a preferential reaction between primary radicals with growing chains. It was proved that every oligomeric molecule was terminated from both sides by cyanopropyl groups. The stmdure predided by the authors was as follows ... 

Goto and coworkers attached a surface-immobilizing initiator IHE onto a siliccm wafer (Scheme 5) and prepared polymer brushes by RTCP [66]. The IHE-immobUized silicon wafer was inunersed in a mixture of MMA, 2-cyanopropyl iodide (a free iodide initiator), azobis(isobutyronitrile) (a radical source), and NIS (a catalyst). The system was purged with an inert gas and heated at 70°C for 4 h to induce polymerization. The and M IM values of the free polymer were 15,000 and 1.31, respectively. From the thickness of the graft polymer and the M of the free polymer, the a value was calculated to be 0.28. This result indicates the successful controlled synthesis of a concentrated polymer brush by RTCP. Another example of the graft polymerization is depicted in Fig. 6,... 

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