Dimerization of methyl acrylate

Methyl acrylate can be dimerized to give a molecule that can be hydrogenated to dimethyl adipate the latter, in turn, can be hydrolyzed to yield AA. Methyl acrylate is synthesized by esterification of acrylic acid, which is obtained by the two-step oxidation of propylene. However, the overall scheme requires several reaction steps, and investment requirements may be large. 

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Bronsted acidic ionic liquids [HMIM]BF4, [HMIM]TfO, and [HMIM]TsO are effective for proton- and metal-assisted catalytic processes such as the dimerization of methyl acrylate and ring-closure metathesis (Scheme 3) (72J). For example, the acidic [HBIM]BF4 in association with the [Ru( = C = C = CPh2)(/ -cymene) (PCy3)Cl][OTf catalyst afforded a dramatic increase in the activity (100%) and selectivity (100%) for the ring-closure metathesis of A,A-diallyltosylamide. 

Several catalyst systems have been described for the tail-to-tail dimerization of methyl acrylate.7 -7 Advantages of the dimerization procedure described here are its mild conditions, efficient use of the catalyst, and high selectivity for the b isomer. Tetrakis(aceto-nitnle)palladium tetrafluoroborate, Pd (NCMe)4(BF )2, also efficiently catalyzes dimerization of ethyl acrylate and methyl methacrylate. The presence of lithium tetrafluoroborate in the reaction mixture increases the rate of the reaction and prolongs catalyst life. Dimerization of methyl acrylate can be effected without lithium tetrafluoroborate if the reaction is performed in mtromethane. 

The efficiency of the tail-to-tail dimerization of methyl acrylate has been further improved, based on a detailed study of the role of the Rh(III)-catalyst, the resting state and the mechanism of the catalyst deactivation477. 

Ruthenium-catalyzed hydrodimerization of acrylonitrile under hydrogen atmosphere to give adiponitrile (393) is a useful coupling reaction [154], Dimethyl hexenedioates (394a and 394b) are formed by dimerization of methyl acrylate by Pd, Ru and Rh catalysts. In particular the catalyst prepared by the treatment of RuC12 with Zn and... 

For example, the tail-to-tail dimerization of methyl acrylate was catalyzed by ruthenium complexes such as RuHCl(C0)(Pz-Pr3)2/CF3S03Ag or even RuC13 and gave dimethyl hexenedioate isomers. Efficient catalytic systems such as Ru(rf-naphthalene)(COD)/CH3CN, where COD is cyclooctadiene, selectively led to the diester 2 in 75% yield [1] (Eq. 1). 

Both nickel and palladium monophosphine complexes catalyze the dimerization of methyl acrylate the tail-to-tail dimer is a nylon-6,6 precursor. The cycle involves... 

Ruthenium carbonyl, Ru3(CO)i2, has been found to be active for the catalytic dimerization of methyl acrylate to give predominantly the transisomer of 91... 

RhCp (C2H4)(CH2CH2- -H)] which is prepared by protonation of RhCp (C2H4)2, is a highly active catalyst for tail-to-tail dimerization of methyl acrylate to dimethyl hexenedioates (eq (51)) [61]. 

The palladium-catalyzed dimerization of methyl acrylate was found to proceed smoothly in a [BMIM][BF4]/scC02 biphasic system [42] (BMIM = l-butyl-3-methyl-imidazolium). The catalytic system comprises phosphonium salts and HBF4 as cocatalysts, making the IL environment particularly attractive. The partitioning of substrates and products between the IL and scC02 was investigated and the data were used for planning of the reaction conditions. Turnover numbers up to 560 and turnover frequencies up to 195 h-1 were obtained under optimized conditions. 

Other reactions studied by these authors include the thermal dimerization of methyl acrylate and the reaction of benzene with certain alkynes in a Diels-Alder reaction. Supercritical extraction in coal processing may also be classified under this scheme. This subject is reviewed by Williams (1981) it is not included in this chapter. 

The separation of the products from the IL catalytic mixture can be performed in various cases by simple decanting and phase separation or by product distillation. In this respect, a continuous-flow process using toluene as extractant has been appHed for the selective Pd-catalyzed dimerization of methyl acrylate in ILs [136]. However, in cases where the products are retained in the IL phase, extraction with supercritical carbon dioxide can be used instead of classical liquid-liquid extractions that necessitate the use of organic solvents, which may result in cross-contamination of products. This process was successfully used in catalyst recycling and product separation for the hydroformylation of olefins employing a continuous-flow process in supercritical carbon dioxide-IL mixtures [137]. Similarly, free and immobilized Candida antarctica lipase B dispersed in ILs were used as catalyst for the continuous kinetic resolution of rac-l-phenylethanol in supercritical carbon dioxide at 120°C and 150°C and 10 Mpa with excellent catalytic activity, enzyme stability and enantioselectivity levels (Fig. 3.5-11). 

By using scCOz instead of toluene as second phase, Pd-leaching could be avoided, even without additional ammoniumphosphine ligand and the TOF and selectivity was increased to 195 h and >98% respectively [253]. In another publication Tkachenko and coworkers demonstrated that the selective taQ-to-tad dimerization of methyl acrylate can also be carried out with very good results in protonated N-butyl-imidazole, [H-BIM][BF4], giving a first example of the versatility of such simple acid-base ionic liquids in continuous catalytic processes [254]. 

Later, Ballivet-Tkatchanko and coworkers compared the palladium catalyzed dimerization of methyl acrylate in ionic liquids (monophasic) and IL/SCCO2 (biphasic) [20]. They found that both reactions exhibited similar selectivities for tail-to-tail... 

The head-to-head dimerization of methyl acrylate (MA) to dimethyl A2- and A3-dihydromuconate (DHMs) [Eq. (11)] leads to an intermediate which can be transformed to nylon-6,6 via adipic acid. An scC02-[BMIM][BF4] biphasic system for methyl acrylate dimerization using a catalyst formed from [Pd(acac)2], [Bu3PH][BF4], and [Et20H][BF4] has recently been reported [59]. 

Jenner " has reported phosphine-catalyzed dimerization of methyl acrylate and acrylonitrile under MBH conditions at ambient pressure (Scheme 2.96). He also noticed that the p-substituted derivatives generally require high pressures. However, cyclohex-2-en-l-one underwent dimerization smoothly under these conditions with 100% yield (Scheme 2.97). 

Methyl acrylate [30,31], methyl methacrylate and acrylonitrile [31,33] can be dicarboxylated with yields up to 60 %. The electrocarboxyla-tive dimerization of methyl acrylate leads to 1,1,4,4-tetracarboxy-butane. Dicarboxylation of stilbenes yields 2,3-diphenylsuccinic acid [33,34]. Styrene can be carboxylated to 2-phenylsuccinic acid or to 3-phenylpropionic acid [35] and ethene reacts to succinic acid [36]... 

Scheme 22.15 shows a mechanism for this taU-to-tail dimerization of methyl acrylate catalyzed by [Cp Rh(ethylene)(ethyl)]. 285 Addition of acrylate converts the starting... 

Dimerization of methyl acrylate may open up a new way to production of adipic acid. The reaction was carried out in a continuous flow biphasic system where the catalyst (obtained from [Pd(acac)2] and the hemilabile (C4H9)2P-CH2-CH2-N(CHs)2 ligand) was dissolved in [bmim][BF4] together with some HBF4, and the substrate methyl acrylate was applied in toluene solution. At 80°C, no sign of catalyst deactivation was seen for 10 h, and the overall TON after 50 h was more than 4000, with a selectivity to A -dihydromuconate more than 90%... 

Finally, the involvement of deoxy-Breslow species as intermediates and related to the reactivity profile of acrylates under NHC catalysis has been reported twice. The first report dealt with detailed mechanistic studies of the well-known tail-to-tail dimerization of methyl acrylate. By means of complementary and robust experiments (including kinetic isotope effects, deuterium-labelling studies and competitive reactions), the formation of the dimer (148) has been unambiguously rationalized. The second report has described/or the first time the NHC-catalysed cyclotetramerization of acrylates. Using imidazolium chloride (135) as NHC source, various trisubstituted cyclopen-tenones (149), thus resulting from the cyclotetramerization of acrylates, have been obtained in moderate yields. 

Also the dimerization of acrylates has found great interest in munerous academic and industrial research groups. Alderson and co-workers of Du Pont [48] investigated the dimerization of methyl acrylate in the presence of rhodium chloride. By heating a solution of methyl acrylate in methanol to 140 °C some dimethyl 2-hexenedioate (= dimethyl-a-dihydromuconate) was formed (Equation 42). 

Effect of Lewis Acids on Dimerization of Methyl Acrylate by PdCl2(NCPh)2"... 

Tkatchenko and coworkers reported that cationic palladium complexes are very effective in the dimerization of methyl acrylate [53], as it has been already observed for other oligomerization and telomerization reactions... 

Dimerization of Methyl Acrylate with Different Ionic Nickel Catalysts ... 

Dimerization of methyl acrylate gave a mixture of ( )-A -dimethyl and ( )-A -dimethyl dihydromuconates possibly via oxidation addition of the terminal olefinic C-H bond, insertion, and reductive elimination (eq 39). ... 

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