Radicals fumarate

These materials are obtained through free-radical polymerization of acrylic or methacrylic monomers, or of fumarates. 

Free-radical reaction rates of maleic anhydride and its derivatives depend on polar and steric factors. Substituents added to maleic anhydride that decrease planarity of the transition state decrease the reaction rate. The reactivity decreases in the order maleic anhydride > fumarate ester > maleate ester. 

The reaction rate of fumarate polyester polymers with styrene is 20 times that of similar maleate polymers. Commercial phthaHc and isophthaHc resins usually have fumarate levels in excess of 95% and demonstrate full hardness and property development when catalyzed and cured. The addition polymerization reaction between the fumarate polyester polymer and styrene monomer is initiated by free-radical catalysts, commercially usually benzoyl peroxide (BPO) and methyl ethyl ketone peroxide (MEKP), which can be dissociated by heat or redox metal activators into peroxy and hydroperoxy free radicals. 

The free radicals initially formed are neutralized by the quinone stabilizers, temporarily delaying the cross-linking reaction between the styrene and the fumarate sites in the polyester polymer. This temporary induction period between catalysis and the change to a semisoHd gelatinous mass is referred to as gelation time and can be controUed precisely between 1—60 min by varying stabilizer and catalyst levels. 

As the quinone stabilizer is consumed, the peroxy radicals initiate the addition chain propagation reactions through the formation of styryl radicals. In dilute solutions, the reaction between styrene and fumarate ester foUows an alternating sequence. However, in concentrated resin solutions, the alternating addition reaction is impeded at the onset of the physical gel. The Hquid resin forms an intractable gel when only 2% of the fumarate unsaturation is cross-linked with styrene. The gel is initiated through small micelles (12) that form the nuclei for the expansion of the cross-linked network. 

Styryl free radicals simultaneously initiate micelle nuclei at points of high fumarate concentration. The micelles continue to expand, interacting with free... 

Vinyl ethers can also be formulated with acryHc and unsaturated polyesters containing maleate or fumarate functionaHty. Because of their abiHty to form alternating copolymers by a free-radical polymeri2ation mechanism, such formulations can be cured using free-radical photoinitiators. With acryHc monomers and oligomers, a hybrid approach has been taken using both simultaneous cationic and free-radical initiation. A summary of these approaches can be found in Table 9. 

Bamford and Mullik [23] have also investigated a new photoinitiating system composed of Mn2(CO)io or Re2(CO)io with acetylene, acetylene dicarboxylic acid, diethyl fumarate, diethyl maleate, or maleic anhydride. It was concluded that the primary radical responsible... 

The presence of a hot spot is known to generate free radicals. Thus, reactions that are initiated by the presence of free radicals can be carried out with less or no catalyst, as has been discovered in the case of isomerization of maleic acid to fumaric acid with an 3 to 16 fold increase in the isomerization rates at reduced catalyst (thiourea) concentrations (Muzumdar, 1988). 

Recently, Uneyama et al. have systematically investigated the anodic generation of CF3 radicals and their utilization (Scheme 7.3) [68-72], They have clarified that trifluoromethyl radicals can be generated almost quantitatively in the oxidation of TFA at 0 °C in an aq. MeOH/Pt system using an undivided cell [70]. They have also found that the trifluoromethylation of electron-deficient olefins can be controlled by the current density, reaction temperature, and the substituents of the olefins. Interestingly, anodic trifluoromethylation of fumar-... 

Radical cyclization to macrolides.111 Cyclization of iodoalkyl acrylates (1) by reaction with Bu3SnH (1 equiv.) in the presence of AIBN is useful for formation of macrolides (2) containing 11 or more members. Similar cyclization of iodoalkyl fumarates (3) results in two macrolides with the endo-product predominating except when n is 16 or higher. Tertiary iodides undergo this free radical cyclization more... 

Unsaturated polyesters are low-molecular-weight fumarate esters containing various chemical structures designed for their specific cost and performance purposes. The two most important features of unsaturated polyesters are the fumarates, which provide the active sites for radical cross-linking with the diluent monomer and the random, low molecular weight, irregular nature of the rest of the molecule, which provide the necessary solubility in the diluent monomer. The preparation of the polyester thus requires the following considerations ... 

Photolysis of peroxydisulphate anions in aqueous solution produces the S04 sulphate radical. This radical reacts with phosphoric acid and its anions to generate phosphorus-containing radicals which can be trapped by such compounds as fumaric acid.31... 

Further supporting evidence for the occurrence of diradicals was obtained by Reich and Cram when they heated [2.2]paracyclophane with either dimethyl maleate or fumarate esters at 200 °C for 40 h in the absence of air. The cis- and trans-2,3-dicarboxymethyl[4.2]paracyclophanes 162 and 163 were formed in about equal amounts, irrespective of the configuration of the olefin employed. Other similar reactions would also suggest a radical mechanism for this reaction furthermore, a concerted addition of the olefinic double bond to 2, or to the postulated intermediate diradical 157, can be ruled out because of lack of stereospecificity of insertion. 

Several products were obtained on heating 164 with dimethyl maleate or dimethyl fumarate in addition to 168, mixtures of the stereoisomers of l-vinyl-2,3-biscarbomethoxy[2.2]paracyclophan-l-ene (170) and of the cis-4,5-biscarbomethoxy[2.2]paracyclophan-l-ene (171) were isolated. A similar product pattern was obtained on reaction of 165 with dimethyl maleate. The non-stereospecificity of these reactions as well as the kinetic data are in complete agreement with the previously postulated multi-step radical mechanism. 

Type iii-b This reaction leads to products (67). The electrochemical oxidation of the sodium salts of acetic, propionic, and isovaleric acids in the presence of ethylenic compounds bearing electron-withdrawing substituents gives 1,2-dialkylated adducts as the main products. A methyl radical generated from an acetate ion reacts with diethyl fumarate to give diethyl 2,3-dimethylsuccinate in 80% yield [106]. 

The cathodic coupling of prenyl chloride with diethyl fumarate and methyl crotonate proceeds with different regios-electivities as shown in Fig. 17 [94]. Also in this case, the change in the regioselectivity appears to be due to the reduction of the diethyl fumarate to a radical anion that undergoes a nucleophilic substitution at the prenyl chloride, and in the other case there is a 2e reduction of the prenyl... 

The addition of (TMS)3SiH to prochiral diethyl methyl fumarate (5) gave both diastereoisomers with preferential formation of the threo isomer (Reaction 5.7) [25]. This suggests that the intermediate adduct 6 adopts a preferred conformation due to the allylic strain effect, in which the silyl moiety shields one face of the prochiral radical center, favouring hydrogen transfer to the opposite face, and therefore the threo product is predominantly formed. 

The carbon dioxide anion-radical was used for one-electron reductions of nitrobenzene diazo-nium cations, nitrobenzene itself, quinones, aliphatic nitro compounds, acetaldehyde, acetone and other carbonyl compounds, maleimide, riboflavin, and certain dyes (Morkovnik and Okhlobystin 1979). The double bonds in maleate and fumarate are reduced by CO2. The reduced products, on being protonated, give rise to succinate (Schutz and Meyerstein 2006). The carbon dioxide anion-radical reduces organic complexes of Co and Ru into appropriate complexes of the metals(II) (Morkovnik and Okhlobystin 1979). In particular, after the electron transfer from this anion radical to the pentammino-p-nitrobenzoato-cobalt(III) complex, the Co(III) complex with thep-nitrophenyl anion-radical fragment is initially formed. The intermediate complex transforms into the final Co(II) complex with the p-nitrobenzoate ligand. 

The reactions enumerated lead to the adducts that are observable by means of the ESR method. In the cases of maleic and fumaric acids, ESR spectra can be recorded at high enough pH values only Being a strong electrophile, radical SO4 is more active toward a carboxylate ion than to neutral molecules of unsaturated acids. 

The decay of a radical-anion can be followed directly by generating the intermediate within the cavity of an esr spectrometer through application of a controlled potential pulse to the cathode of a thin electrochemical cell [46]. Loss of the radical-anion is then followed by decay of the esr signal. Decay is second order in radical-ion concentration for dimethyl fumarate (k = 160 M s ) and for cin-namonitrile (k = 2.1 x 10 M s ) in dimethylformamide with tetrabutylammonium counter ion. Similar values for these rate constants have been obtained using purely electrochemical techniques [47]. 

A general type of chemical reaction between two compounds, A and B, such that there is a net reduction in bond multiplicity (e.g., addition of a compound across a carbon-carbon double bond such that the product has lost this 77-bond). An example is the hydration of a double bond, such as that observed in the conversion of fumarate to malate by fumarase. Addition reactions can also occur with strained ring structures that, in some respects, resemble double bonds (e.g., cyclopropyl derivatives or certain epoxides). A special case of a hydro-alkenyl addition is the conversion of 2,3-oxidosqualene to dammara-dienol or in the conversion of squalene to lanosterol. Reactions in which new moieties are linked to adjacent atoms (as is the case in the hydration of fumarate) are often referred to as 1,2-addition reactions. If the atoms that contain newly linked moieties are not adjacent (as is often the case with conjugated reactants), then the reaction is often referred to as a l,n-addition reaction in which n is the numbered atom distant from 1 (e.g., 1,4-addition reaction). In general, addition reactions can take place via electrophilic addition, nucleophilic addition, free-radical addition, or via simultaneous or pericycUc addition. 

Corresponding data for the alternating radical copolymerization of styrene (Mi)-diethyl fumarate (M2)(n = 0.30 and r2 = 0.07) are shown in Figs. 6-6 and 6-7. This system undergoes azeotropic copolymerization at 57 mol% styrene. Feed compositions near the azeotrope yield narrow distributions of copolymer composition except at high conversion where there is a drift to pure styrene or pure fumarate depending on whether the initial feed contains more or less than 57 mol% styrene. The distribution of copolymer compositions becomes progressively wider as the initial feed composition differs more from the azeotropic composition. 

Penultimate effects have been observed for many comonomer pairs. Among these are the radical copolymerizations of styrene-fumaronitrile, styrene-diethyl fumarate, ethyl methacrylate-styrene, methyl methacrylate l-vinylpyridine, methyl acrylate-1,3-butadiene, methyl methacrylate-methyl acrylate, styrene-dimethyl itaconate, hexafluoroisobutylene-vinyl acetate, 2,4-dicyano-l-butene-isoprene, and other comonomer pairs [Barb, 1953 Brown and Fujimori, 1987 Buback et al., 2001 Burke et al., 1994a,b, 1995 Cowie et al., 1990 Davis et al., 1990 Fordyce and Ham, 1951 Fukuda et al., 2002 Guyot and Guillot, 1967 Hecht and Ojha, 1969 Hill et al., 1982, 1985 Ma et al., 2001 Motoc et al., 1978 Natansohn et al., 1978 Prementine and Tirrell, 1987 Rounsefell and Pittman, 1979 Van Der Meer et al., 1979 Wu et al., 1990 Yee et al., 2001 Zetterlund et al., 2002]. Although ionic copolymerizations have not been as extensively studied, penultimate effects have been found in some cases. Thus in the anionic polymerization of styrene t-vinylpyri-dine, 4-vinylpyridine adds faster to chains ending in 4-vinylpyridine if the penultimate unit is styrene [Lee et al., 1963]. 

The complex participation model has been tested in the radical copolymerizations of 1,1-diphenylethylene-methyl acrylate, styrene-P-cyanoacrolein, vinyl acetate-hexafluoroace-tone, A-vinylcarbazole diethyl fumarate, A-vinylcarbazole funiaronitrile, maleic anhydride-vinyl acetate, styrene-maleic anhydride [Burke et al., 1994a,b, 1995 Cais et al., 1979 Coote and Davis, 2002 Coote et al., 1998 Dodgson and Ebdon, 1977 Fujimori and Craven, 1986 Georgiev and Zubov, 1978 Litt, 1971 Lift and Seiner, 1971 Yoshimura et al., 1978]. 

Some monomers with no tendency toward homopolymerization are found to have some (not high) activity in copolymerization. This behavior is found in cationic copolymerizations of tetrahydropyran, 1,3-dioxane, and 1,4-dioxane with 3,3-bis(chloromethyl)oxetane [Dreyfuss and Dreyfuss, 1969]. These monomers are formally similar in their unusual copolymerization behavior to the radical copolymerization behavior of sterically hindered monomers such as maleic anhydride, stilbene, and diethyl fumarate (Sec. 6-3b-3), but not for the same reason. The copolymerizability of these otherwise unreactive monomers is probably a consequence of the unstable nature of their propagating centers. Consider the copolymerization in which M2 is the cyclic monomer with no tendency to homopolymerize. In homopolymerization, the propagation-depropagation equilibrium for M2 is completely toward... 

A special case of asymmetric enantiomer-differentiating polymerization is the isoselective copolymerization of optically active 3-methyl-1-pentene with racemic 3,7-dimethyl-1-octene by TiCl4 and diisobutylzinc [Ciardelli et al., 1969]. The copolymer is optically active with respect to both comonomer units as the incorporated optically active 3-methyl-l-pentene directs the preferential entry of only one enantiomer of the racemic monomer. The directing effect of a chiral center in one monomer unit on the second monomer, referred to as asymmetric induction, is also observed in radical and ionic copolymerizations. The radical copolymerization of optically active a-methylbenzyl methacrylate with maleic anhydride yields a copolymer that is optically active even after hydrolytic cleavage of the optically active a-methylbenzyl group from the polymer [Kurokawa and Minoura, 1979]. Similar results were obtained in the copolymerizations of mono- and di-/-menthyl fumarate and (—)-3-(P-styryloxy)menthane with styrene [Kurokawa et al., 1982],... 

Ethyl maleate from Commercial Solvents Corporation, Terre Haute, Indiana, was distilled before use. Ethyl fumarate can be used also, but the yield of product is lower since a much greater proportion of high-boiling compounds is obtained. Aldehydes do not undergo free-radical addition to maleic anhydride under these conditions. 

The mercurio ketone 4 upon reduction with NaBH4 yields a radical which is trapped in situ by reactive acceptors such as vinyl ketones [37]. Treatment of a 1 3 mixture of mercurio ketone 4 and electron deficient terminal alkenes (or fumarate) in CH2C12 with a concentrated solution of NaBH4 in water gives conjugate adducts, Eq. (36). 

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