Adipic methyl acrylate dimerization

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]. 

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. 

In a further example using SCCO2 as the extrachng solvent, methyl acrylate was dimerized to dimethyl dihydromuconate derivatives [34], This novel approach could open an altemahve route for the manufacture of adipic acid. In this palladium-catalyzed reachon using the IL [BMIM][BF4], the catalyst showed a higher activity than under the convenhonal monophasic reaction conditions. 

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%... 

Protonation of Cp Rh(C2H4)2 gives a related catalyst that dimerizes methyl acrylate with tail-to-tail regiochemistry to give hexenedioates that can be hydrogenated to the nylon precursor, adipic acid (HOOC(CH2)4COOH). ... 

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