Naphthalene Selective Carbonylation

2, 6-naphthalenedicarboxylic acid is the main raw material to produce the novel polyester PEN. It is a advanced route to synthesize 2, 6-naphthalenedicarboxylic acid from naphthalene in 3 steps: 2-position selected acylation, 6-position oriented acylation and controlled oxidation. The selective Friedel-Crafts acylations of naphthalene in ionic liquid [bmim]Br/AlCl3 and the [bmim]Br/AlCl3-zeolite composite system were investigated.Firstly, ionic liquids ([bmim]Br) were synthesized and the influence of the reaction temperature on the reaction yield was studied. Secondly, the influence of temperature, pressure and ionic liquid composition on the solubility of carbon monoxide in ionic liquids ([bmim]Br/AlCl₃) were investigated. Finally, the Friedel-Crafts acylations of naphthalene in ionic liquid [bmim]Br/AlCl₃ and the [bmim]Br/AlCl₃-zeolite composite system were proceeded at room temperature under CO pressure of 1.5 MPa.The optimal yield over 96% can be achieved in the synthesis of [bmim]Br at 100-110℃. Carbon monoxide has higher solubility in ionic liquid [bmim]Br/AlCl₃ than in [bmim]BF₄. Its solubility increased as the fraction of AlCl₃ and the pressure increased, but decreased as the temperature increased. In the presence of ionic liquid [bmim]Br/AlCl₃, naphthalene can convert into 100%α-naphthaldehyde with a conversion over 40% under the optimum condition (CO pressure was 1.5 MPa, room temperature, [bmim]Br/AlCl₃(1:2) was used as catalyst, 2 hours). When the reaction was carried out in the composite system of [bmim]Br/AlCl₃(1:2) and ZSM zeolite, also under CO pressure of 1.5 MPa and at room temperature,β-naphthaldehyde can be obtained with a selectivity over 50%.Combined the expeimental results with the simulation using HyperChem, we can draw the following conclusions: Al₂Cl₆ is the active group in [bmim]Br/AlCl₃, which can activate not only the acylation agent (CO) but the aromatic ring (naphthalene) as well. As a result, the conversion of naphthalene can be greatly increased. Apart from the high activity, Ionic liquid is a green Friedel-Crafts catalyst compared with the traditional anhydr-AlCl₃. Ionic liquid catalyst leads to 100%α-naphthaldehyde, but when it is mixed with ZSM zeolite,halfα-naphthaldehyde and halfβ-naphthaldehyde can be obtained.