NOVELTY - Vitamin K2 is chemically synthesized by performing catalytic hydrogenation reduction reaction on 2-methyl-1,4-naphthoquinone and isopropyl ether in presence of palladium on carbon (Pd/C) catalyst to obtain 2-methyl-1,4-hydronaphthoquinone; adding 2-methyl-1,4-hydronaphthoquinone product, isopropyl ether and water-resistant Lewis acid catalyst, then dripping geraniol, and performing Friedel Crafts alkylation reaction for 3-6 hours to obtain long-chain hydroquinone; and preparing vitamin K2 crude product by oxidizing the long-chain hydroquinone with ferric trichloride.    USE - Method for chemical synthesis of vitamin K2 (claimed) used in medicine or health product.    ADVANTAGE - The method high yield, high production efficiency and high recycling rate, low production cost and energy consumption, and simple operation, and is environment-friendly and suitable for industrial production of vitamin K2.    DETAILED DESCRIPTION - Chemical synthesis of vitamin K2 comprises:    (A) adding 2-methyl-1,4-naphthoquinone and isopropyl ether and uniformly stirring and mixing in a dry reflux reactor with a stirring device, introducing nitrogen for protection, and heating the reaction solution to reflux, keeping reflux condition by filling nitrogen and hydrogen into the reactor, then adding 5% Pd/C catalyst with stirring, continuously introducing hydrogen to perform catalytic hydrogenation reduction reaction until a yellow reaction liquid is totally faded and is colorless, cooling the reaction liquid to room temperature, filtering, collecting filtrate and filter residue, distilling filtrate and recycling solvent isopropyl ether at constant temperature of 70-72 degrees C, and vacuum drying distilled product at 90-100 degrees C for 0.5-1 hour to obtain 2-methyl-1,4-hydronaphthoquinone, where mass ratio of 2-methyl-1,4-naphthoquinone to isopropyl ether to Pd/C is 1 mol:4000-6000 ml:15-25 g;    (B) filling a reactor with nitrogen gas, adding the 2-methyl-1,4-hydronaphthoquinone product, isopropyl ether solvent and water-resistant Lewis acid catalyst comprising samarium triflate and scandium triflate, stirring and mixing uniformly until 2-methyl-1,4-hydronaphthoquinone is completely dissolved, continuously introducing nitrogen gas at constant temperature of 40-60 degrees C, stirring, then dripping geraniol, performing Friedel Crafts alkylation reaction for 3-6 hours, and then cooling reaction liquid to room temperature under protection of nitrogen, diluting the solution with distilled water, washing the reaction liquid, collecting water layer and organic layer, washing the organic layer, and then collecting water layer and organic layer, repeating for 1-2 times, combining and collecting the water layer and heating the mixture at 105-115 degrees C to distill, collecting distillate and distilling the product, vacuum drying distilled product at 180-200 degrees C for 2-4 hours, placing the collected organic layer in a sealed container filled with nitrogen, and then adding anhydrous sodium sulfate to dry for 0.5-1 hour, placing dried product again to the reactor at 55-65 degrees C and 0.03-0.05 MPa for reduced pressure distillation, and collecting distilled liquid and distilling the product, and then vacuum drying distilled product at 30-50 degrees C for 0.5-1 hour to obtain long-chain hydroquinone, where mass ratio of finally collected organic layer to volume of anhydrous sodium sulfate is 10 mol:2-5 g;    (C) preparing vitamin K2 crude product by adding ferric trichloride oxidant into isopropyl ether solvent, stirring ferric trichloride until completely dissolving to prepare oxidant solution, and then drying in a reactor, adding residue from the second step, the long-chain hydroquinone and oxidant solution while stirring to oxidize for 2-4 hours, adding distilled water, and stirring the oxidation reaction liquid to dilute, standing for 20-40 minutes, collecting upper layer of organic layer and lower layer of water layer, collecting the organic layer, adding anhydrous sodium sulfate to dry for 0.5-1 hour, and then performing reduced pressure distillation at 55-65 degrees C and 0.03-0.05 MPa, collecting distilled liquid and distilling the product; and    (D) adding n-butanol into the vitamin K2 crude product at constant temperature of 64-67 degrees C, stirring until vitamin K2 crude product is completely dissolved, standing and cooling to 28-31 degrees C, collecting upper clear liquid and lower oil layer and cooling to - 2 to 0 degrees C after crystallizing, filtering, collecting filtrate and filter residue, adding n-butanol again into the filter residue at constant temperature of 64-67 degrees C, stirring until the filter residue is completely dissolved, standing and cooling to 28-31 degrees C, collecting upper clear liquid and lower oil layer, and then standing and cooling the upper layer clear liquid to - 2 to 0 degrees C, crystallizing, then filtering and respectively collecting filtrate and filter residue, repeating steps for 1-2 times, and collecting the filter residue, combining the collected lower oil layers, and finally combining the filtrate collected in each time.