The liquid phase products were analyzed using GC equipped with a capillary chromatography column (HP-5, 30 m×250 mm×0.25 μm) and a flame ionization detector (FID). The temperature program is set as follows: injection temperature is 260°C, the column temperature is maintained at 50°C for 2 min and then raised to 250°C at a heating rate of 5°C•min -1 and maintained at this temperature for 3 min, the detector temperature is 280°C. Methanol is a solvent. The injection volume: 1 μL. The separation ratio is 20: 1.