Acrylonitrile, reaction solvent effects

Remarkable kinetic solvent effects reportedly occur in the reaction between 138 and acrylonitrile 2 the observed large differences in the activation parameters between chloroform (A// = 5.4 kcal moP AS = — 50.3 eu) and carbon tetrachloride (A// = 22.4 kcal mol AS = + 10.3 eu) have been criticized. ... 

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). 

Similarly small rate factors were obtained for 1,3-dipolar cycloadditions between diphenyl diazomethane and dimethyl fumarate [131], 2,4,6-trimethylbenzenecarbonitrile oxide and tetracyanoethene or acrylonitrile [811], phenyl azide and enamines [133], diazomethane and aromatic anils [134], azomethine imines and dimethyl acetylenedi-carboxylate [134a], diazo dimethyl malonate and diethylaminopropyne [544] or N-(l-cyclohexenyl)pyrrolidine [545], and A-methyl-C-phenylnitrone and thioketones [812]. Huisgen has written comprehensive reviews on solvent polarity and rates of 1,3-dipolar cycloaddition reactions [541, 542]. The observed small solvent effects can be easily explained by the fact that the concerted, but non-synchronous, bond formation in the activated complex may lead to the destruction or creation of partial charges, connected... 

Triethylamine is an effective catalyst for the cyanoethylation reaction." Thus when a solution of acetylacetone, acrylonitrile, and triethylamine in a mixture of t-butanol (45 ml.) and water (15 ml.) was allowed to stand at 25 for 2 days, y,y-diacetylpimelonitrile separated in high yield and purity. A striking solvent effect is... 

The rate of loss of epoxides increases with the percent acrylonitrile in the CTBN elastomer. Figure 9 plots the rate of loss of epoxides versus percent acrylonitrile. These data, however, do not discriminate the two possible mechanisms for the loss of epoxides 1. Enhancement of the rate of loss of epoxides via a "solvent" effect, and 2. A second side reaction involving reaction of epoxides and the rubber itself. 

Methanol addition results on irradiation of 2,3-dimethylbut-2-ene in a mixture of 1,4-dicyanobenzene and phenanthrene in the presence of acrylonitrile or methyl acrylate. Inoue and co-workers have studied the enantio-differentiating addition of alcohols to the 1,1-diphenylethene derivatives (52). The reactions are sensitized by the naphthalenecarboxylates (53) and (54), where the R groups are saccharide moieties. The ee of the products (55) is influenced by steric, electronic and solvent effects. Efficient addition of water to 3-hydroxystilbene can be brought about on irradiation in acetonitrile-water mixtures.Pincock has highlighted the importance of the discovery in 1973 of the formation of the radical cation of 1,1-diphenylethene. Grainger and Patel have described a new photochemical approach to cuparene (56). The reaction involves the electron-transfer induced cyclization of the styrene... 

In fact, recent theoreticaP and experimental studies of small radical addition reactions indicate that charge separation does occur in the transition state when highly electrophilic and nucleophilic species are involved. It is also known that copolymerization of electron donor-acceptor monomer pairs are solvent sensitive, although this solvent effect has in the past been attributed to other causes, such as a Bootstrap effect (see Section 13.2.3.4). Examples of this type include the copolymerization of styrene with maleic anhydride and with acrylonitrile. Hence, in these systems, the variation in reactivity ratios with the solvent may (at least in part) be caused by the variation of the polarity of the solvent. In any case, this type of solvent effect cannot be discounted, and should thus be considered when analyzing the copolymerization data of systems involving strongly electrophilic and nucleophilic monomer pairs. 

Solvents affect free-radical polymerization reactions in a number of different ways. Solvent can influence any of the elementary steps in the chain reaction process either chemically or physically. Some of these solvent effects are substantial, for instance, the influence of solvents on the gel effect and on the polymerization of acidic or basic monomers. In the specific case of copolymerization then solvents can influence transfer and propagation reactions via a number of different mechanisms. For some systems, such as styrene-acrylonitrile or styrene-maleic anhydride, the selection of an appropriate copolymerization model is still a matter of contention and it is likely that complicated copolymerization models, incorporating a number of different phenomena, are required to explain all experimental data. In any case, it does not appear that a single solvent effects model is capable of explaining the effect of solvents in all copolymerization systems, and model discrimination should thus be performed on a case-by-case basis. 

Similarly, with the acrylonitrile reaction the 10 mM -cyclodextrin increased the water rate by a factor of 9, while 5 mM a -cyclodextrin slowed it by a factor of 1.2. With the larger anthracene case, even /3-cyclodextrin slowed the water reaction, by a factor of 1.6, since the anthracene filled the cavity and did not permit simultaneous binding of the dienophile. However, the more striking rate effects were seen with the water solvent alone. 

A similtu dependence has been observed by Ruiz-Lopez et al. The introduction of solvent effects in the theoretical calculations shows that polar solvents stabilize with preference the endo transition states, leading to an increase in the endolexo selectivity. DFT calculations on the reactions of cyclopentadiene with acrolein (1) and acrylonitrile (5) predict an endolexo selectivity that is in good agreement with the experimental observations. ... 

Evidence for radical formation was given by acrylonitrile polymerization, and hydrogen-bonding and solvent effects are considered important in the formulation of the transition-state complexes. In the reaction of olefins with aliphatic ketones in the presence of oxidizing agents e.g. Ce, Cu )... 

Polymerizations conducted in nonaqueous media in which the polymer is insoluble also display the characteristics of emulsion polymerization. When either vinyl acetate or methyl methacrylate is polymerized in a poor solvent for the polymer, for example, the rate accelerates as the polymerization progresses. This acceleration, which has been called the gel effect,probably is associated with the precipitation of minute droplets of polymer highly swollen with monomer. These droplets may provide polymerization loci in which a single chain radical may be isolated from all others. A similar heterophase polymerization is observed even in the polymerization of the pure monomer in those cases in which the polymer is insoluble in its own monomer. Vinyl chloride, vinylidene chloride, acrylonitrile, and methacryloni-trile polymerize with precipitation of the polymer in a finely divided dispersion as rapidly as it is formed. The reaction rate increases as these polymer particles are generated. In the case of vinyl chloride ... 

A heavy-atom effect on the photocycloaddition of acenaphthylene to acrylonitrile has also been observed.<68) The effect of heavy atoms in this case is seen as an apparent increase in the quantum yield of product formation in heavy-atom solvents as opposed to cyclohexane (the time to achieve about 42% reaction in cyclohexane is greater than that required to produce the same conversion in dibromoethane by a factor of ten). An increase in the rate of acenaphthylene intersystem crossing due to heavy-atom perturbation was proposed to explain this increase in reaction rate. 

Copolymerizations of nonpolar monomers with polar monomers such as methyl methacrylate and acrylonitrile are especially comphcated. The effects of solvent and counterion may be unimportant compared to the side reactions characteristic of anionic polymerization of polar monomers (Sec. 5-3b-4). In addition, copolymerization is often hindered by the very low tendency of one of the cross-propagation reactions. For example, polystyryl anions easily add methyl methacrylate but there is little tendency for poly(methyl methacrylate) anions to add styrene. Many reports of styrene-methyl methacrylate (and similar comonomer pairs) copolymerizations are not copolymerizations in the sense discussed in this chapter. 

The potential activation of different Lewis acid catalysts and their load effect when used in combination with this solvent were explored, in order to determine the improvement of rates and selectivity to the endo and exo isomers. The list of Lewis acid catalysts included Li(OTf), Li(NTf2), Znl2, AICI3, BF3, HOTf, HNTf2, Ce(0Tf)4 5H20, Y(OTf)3, Sc(OTf)3, Sc(NTf2) and a blank without any Lewis acid. The reaction conditions were as follows 2.2 mmol of cyclopentadiene + 2.0 mmol of dienophile + 0.2 mol% of catalyst in 2 mL [hmim][BF4]. When no catalyst was added, the two ketones (R =Me-C=0 R2 = R3 = H and Ri=Et-C=0 R2 = R3 = H) showed modest activity ( 50% in 1 h) with endojexo selectivity = 85/15. Whereas acrolein showed modest activity (59% conversion in 2 h), methacrolein and crotonaldehyde were inert without a Lewis acid catalyst. Acrylonitrile and methyl acrylate underwent low conversions in 1 h (16-17%) whereas, N-phenylmaleimide, maleic anhydride and 2-methyl-1,4-benzoquinone showed complete reaction in 5 min with high endo isomer yields. 

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