Pure isophthalaldehyde bisulfite adduct and novel preparation method thereof
Disclosed are a method for preparing a pure isophthalaldehyde bisulfite adduct free from impurities through a specific purification process, and use thereof as a starting material for polymerizing polybenzimidazole under a mild condition. According to the present disclosure, it is possible to obtain a pure isophthalaldehyde bisulfite adduct free from impurities, such as unreacted materials or byproducts. In addition, it is possible to accomplish industrial mass production of a high-molecular weight polybenzimidazole by using the adduct as a starting material for polymerizing polybenzimidazole under a mild condition in an organic solvent.
1. A method for preparing a pure isophthalaldehyde bisulfite adduct free from impurities, the method comprising:
I) dissolving sodium bisulfite into distilled water and dissolving isophthalaldehyde into methanol, mixing the two solutions to carry out a reaction at 10-30° C., and filtering and drying the reaction mixture to obtain an isophthalaldehyde bisulfite adduct;
II) dissolving the resultant adduct into water with sodium bisulfite to further carry out a reaction and adding methanol thereto to precipitate the adduct, followed by filtering and drying to carry out preliminary purification; and
III) dissolving the preliminarily purified adduct into an organic solvent, filtering the non-dissolved unreacted starting materials and an inorganic salt, further precipitating the filtrate, and further filtering and drying the precipitate to carry out secondary purification.
2. The method for preparing a pure isophthalaldehyde bisulfite adduct free from impurities according to claim 1 , wherein sodium bisulfite is used in a ratio of 2-3 equivalents to 1 equivalent of isophthalaldehyde, in step I).
3. The method for preparing a pure isophthalaldehyde bisulfite adduct free from impurities according to claim 1 , wherein the organic solvent is any one selected from the group consisting of dimethyl sulfoxide (DMSO), dimethyl acetamide (DMAc), dimethylformamide (DMF), N-methylpyrrolidone (NMP) and a mixture thereof, in step III).
4. The method for preparing a pure isophthalaldehyde bisulfite adduct free from impurities according to claim 1 , wherein the filtrate is further precipitated with acetone, isopropyl alcohol or hexane, in step III).