Complexes acrylonitrile-zinc chloride

Hirooka et al. (27, 29) recently reported that an equimolar mixture of acrylonitrile and ethylaluminum dichloride form a complex whose infrared spectrum is similar to that of the acrylonitrile-zinc chloride complex of Imoto et al. (33). The complex is a liquid above 0°C. and... 

The increased reactivity of propagating radicals complexed with the metal salt towards uncomplexed monomer has been postulated (87) to account for the increased susceptibility of methyl methacrylate to ultraviolet light or free radicals in the presence of aluminum chloride or aluminum bromide. A similar explanation has been considered to account for the enhanced reactivity in the methyl methacrylate-zinc chloride and acrylonitrile-zinc chloride polymerization systems. However, the complex shown in Reaction 20 must equally be considered. 

As previously discussed, the copolymers produced in the zinc chloride-free radical system are not necessarily random copolymers but are probably the result of the copolymerization of the acrylonitrile-complexed acrylonitrile complex with the olefin-complexed acrylonitrile complex. Further, the olefin-alkylaluminum halide complexed acrylonitrile complex only differs from the olefin—zinc chloride complexed acrylonitrile complex in degree rather than in kind—i.e., the former is an unstable charge transfer complex capable of spontaneous uncoupling of the diradical system followed by intermolecular diradical coupling, while the latter is a stable charge transfer complex requiring radical attack to uncouple the diradical system. 

F. W. Billmeyer. The free-radical polymerization of methyl methacrylate, acrylonitrile, and other polymer monomers can be accelerated by adding Lewis acids, like zinc chloride or alkylaluminum chloride. The polar monomer forms a complex with the Lewis acid and becomes more electron accepting. In the presence of a nonpolar olefin or conjugated diene, the complexed polar monomer transfers its charge and copolymerizes readily, as described by N. G. Gaylord and A. Takahashi. 

T he free radical initiated polymerization of polar monomers containing pendant nitrile and carbonyl groups—e.g., acrylonitrile and methyl methacrylate—in the presence of metal halides such as zinc chloride and aluminum chloride, is characterized by increased rates of polymerization (2, 3, 4, 5,10, 30, 31, 32, 33, 34, 53, 55, 65, 66, 75, 76, 77, 87). Imoto and Otsu (30, 33, 34) have attributed this effect to the formation of a complex between the polar group and the metal halide. The enhanced reactivity of the complexed monomer extends to copolymerization with uncomplexed monomers, such as vinylidene chloride, which are readily responsive to... 

The free radical copolymerization of methyl methacrylate or acrylonitrile in the presence of zinc chloride with allylic compounds such as allyl alcohol, allyl acetate, and allyl chloride or butene isomers such as isobutylene, 1-butene, and 2-butene is characterized by the incorporation of greater amounts of comonomer than is noted in the absence of zinc chloride (35). Analogous to the radical homopolymerization of allylic monomers in the presence of zince chloride, the increase in the electron-accepting capability of the methyl methacrylate or acrylonitrile as a result of complexation results in the formation of a charge transfer complex which undergoes homopolymerization and/or copolymerization with a polar monomer-complexed polar monomer complex. 

The process improvement patent (73) also describes the preparation of an acrylonitrile-isoprene copolymer using azobisisobutyronitrile as free radical initiator and zinc chloride as complexing agent. The reaction is carried out using 1-50 moles of acrylonitrile per mole of isoprene and a 10 1 molar ratio of acrylonitrile to zinc chloride. The copolymer, obtained in 16.8% yield (calculated as a 1 1 copolymer), contains 48.2 weight % of acrylonitrile, corresponding to a 1.2 1 acrylonitrile-isoprene molar ratio, and is soluble in acetone and chloroform, in marked contrast to the solubility of the corresponding copolymer prepared with free radical initiators. 

Hirooka has proposed that the products are alternating copolymers produced through complex copolymerization and that the latter process differs from that of Imoto and Otsu (30, 33, 34) in which a free radical initiator is necessary for the random copolymerization of olefins with acrylonitrile or methyl methacrylate in the presence of zinc chloride. 

Charge transfer complexes of styrene and acrylonitrile have been shown to exist when in the presence of zinc chloride. Proton nuclear magnetic resonance spectroscopy has been used to establish this effect. In the proper solvents styrene and acrylonitrile will form occluded macroradicals which may then be used to form block copolymers. These block copolymers occur both in the presence and absence of zinc chloride. Pyrolysis gas chromatography, differential scanning calorimetry, and solubility studies show the properties of the two copolymers and their various block copolymers to be quite similar. Differences in the copolymers may be seen from carbon-13 nuclear magnetic resonance spectroscopy. Yield data for the block copolymers is reported. 

Statistical copolymers of 1,3-butadiene and ethene are obtained with bis(cyclopen-tadienyl)zirconium dichloride and aluminoxane. The copolymers contain up to 13% trans-1,4 bonded butadiene [515]. 1,3-Butadiene forms alternating copolymers with acrylonitrile and esters of acrylic acid when the latter is complexed by strong Lewis acids (e.g., alkylaluminum halogenides and zinc chloride) [516,517]. Selective hydrogenation of the double bond yields nitrile rubbers with a low swelling capacity. 

Lewis acid complex with styrene faults in the formation of styrene-alt-acrylo-nitrile having far superior color stability to styrene-stat-acrylonitril Cmnpari-son of the SAN copolymer curves obtained at three levels of zinc chloride is shown in Fig. 12 [6]. 

Ohashi et al. [128] found that the yields of ortho photoaddition of acrylonitrile and methacrylonitrile to benzene and that of acrylonitrile to toluene are considerable increased when zinc(II) chloride is present in the solution. This was ascribed to increased electron affinity of (meth)acrylonitrile by complex formation with ZnCl2 and it confirmed the occurrence of charge transfer during ortho photocycloaddition. This was further explored by investigating solvent effects on ortho additions of acceptor olefins and donor arenes [136,139], Irradiation of anisole and acrylonitrile in acetonitrile at 254 nm yielded a mixture of stereoisomers of l-methoxy-8-cyanobicyclo[4.2.0]octa-2,4-diene as a major product. A similar reaction occurred in ethyl acetate. However, irradiation of a mixture of anisole and acrylonitrile in methanol under similar conditions gave the substitution products 4-methoxy-a-methylbenzeneacetonitrile (49%) and 2-methoxy-a-methylbenzeneacetonitrile (10%) solely (Scheme 43). 

The rate of polymerization of polar monomers, for example, maleic anhydride, acrylonitrile, or methyl methacrylate, can be enhanced by coraplexing them with a metal halide (zinc or vanadium chloride) or an organoaluminum halide (ethyl aluminum sesqui-chloride). These complexed monomers participate in a one-electron transfer reaction with either an uncomplexed monomer or another electron-donor monomer, for example, olefin, diene, or styrene, and thus form alternating copolymers (11) with free-radical initiators. An alternating styrene/acrylonitrile copolymer (12) has been prepared by free-radical initiation of equimolar mixtures of the monomers in the presence of nitrile-coraplexing agents such as aluminum alkyls. 

The solution to this synthesis problem goes back to the work of Reiner Sust-mann, who successfully carried out the formal, nickel(0)-mediated addition of alkyl or aryd halides to electron-deficient alkenes, like acrylate esters or acrylonitrile. [101] Sub-stoichiometric amounts of nickel(ll) chloride hexahydrate (15-20 mole %) are reduced with zinc in presence of pyridine to nickel(O), which forms together with pyridine a complex with the alkene. Oxidative addition of the alkyl halide leads to an alkyl-nickel species, the carbon-metal bond of which undergoes an alkene insertion. Hydrolysis gives ultimately the product. Heck reaction products are not observed. 

The catalyst is similar for all three steps, and consists of a zero valent nickel phosphite complex, promoted with zinc or aluminium chlorides. The direct addition of hydrogen eyanide to butadiene is particularly attractive with the availability of by-product hydrogen cyanide form the manufactnie of acrylonitrile by the ammoxidation of propylene. 

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