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The general procedure for the synthesis of 1,4:3,6-bis-anhydromannitol from D-mannitol was as follows: 1350 g of crystalline D-mannitol was added to a reduced-pressure reactor equipped with a stirrer and heated to 170 °C to melt it. Subsequently, 10 g of 98% concentrated sulfuric acid was added to the melt, and the reaction lasted for 20 h at 170 °C and 2 kPa with nitrogen gas being passed at a flow rate of 200 mL/min. Upon completion of the reaction, the product was cooled to 90 °C and 30 g of 48% (w/w) aqueous sodium hydroxide solution was added to give crude 1,4:3,6-bis-anhydromannitol. Next, 39 g of horseshoe-based wood activated carbon (trade name: Tyco K, produced by Futamura Chemical Co., Ltd.) was added to the crude product and stirred for 3 h for decolorization to obtain a mixture to be distilled. Water was distilled from the mixture at 120 °C and 5 kPa. Subsequently, a reduced pressure distillation was carried out at 170 °C and 0.3 kPa under reduced pressure by passing nitrogen at a flow rate of 200 mL/min, resulting in 491 g of product. A portion of the distilled product was taken and the pH of the mixture was determined to be 10 according to the method of Example 1.