Study On Hydroesterification Hydrogenation Catalyzed By 1-Butyl-3-Methylimidazolium Cobalt Tetracarbonyl Ionic Liquids From Ethylene Oxide

1,3-propanediol (1,3-PDO) has recently attracted considerable industrial interest as a key component for polyester and as a pharmaceutical intermediate. In this paper, functional ionic liquid 1-butyl-3-methylimidazolium cobalt tetracarbonyl [Bmim][Co(CO)₄] was prepared and used for preparation of 1,3-propanediol (1,3-PDO) by hydrogenation of the intermediate methyl 3-hydroxypropionate (3-HPM) which was synthesized by hydroesterification of ethylene oxide (EO). Liquid/liquid biphase systems which is superior to traditional catalysts in the catalytic activity, selectivity was contrived. According to experimental result, a possible reaction mechanism has also been proposed.At first, several kinds of 1-butyl-3-methylimidazolium ionic liquids [Bmim]Cl,[Bmim]BF₄,[Bmim]PF₆ were prepared in this paper, [Bmim][Co(CO)₄] was prepared in a metathesis reaction between [Bmim]Cl and KCo(CO)₄. The structure of ionic liquids was illustrated by FT-IR and ¹H NMR. The solubility of ionic liquids in common organic solvents was investigated, it was an essential prerequisite for application in liquid/liquid biphase systems.In this paper, the synthesis of 3-HPM by hydroesterification of EO catalyzed by [Bmim][Co(CO)₄] was studied. The optimum reaction conditions of the hydroesterification of EO were obtained by single-factor experiments. Under a pressure of 3.7 MPa and at temperature of 75 oC, the conversion of EO reached 98.1%, while the yield of 3-HPM up to 90.8% in 10 h. Even after the catalyst is recycled three times, a yield of more than 80% can be obtained. Using [Bmim]PF₆ as solvent, the hydrogenation of 3-HPM in the presence of [Bmim][Co(CO)₄] catalyst was studied. The optimum conditions were obtained as follows: imidazole as promoter, reaction temperature 165 oC, hydrogen pressure 10.5 MPa for 10 h, the best conversions of 3-HPM were up to 99.2% with selectivity in the 1,3-PDO up to 83.6%, the catalyst could be recycled three times with the yield of 1,3-PDO not less than 70%.The activity of the catalytic system was better than organic catalytic system and the catalytic system can be reused several times after the product was separated by extraction with deionized water. It is well established that the active species was an ionic species, [L_n]⁺[Co(CO)₄]^-, when a Lewis base (L) was used as a promoter. The Lewis acidic cationic species [L_n]⁺ was thought to be responsible for the coordination and activation of EO or 3-HPM, while anionic species [Co(CO)₄]^- was accountable for nucleophilic attack on the less hindered carbon atom of the coordinated EO or 3-HPM and CO or H₂ insertion.