Green Method For Synthesis Of 2-Methyl-1,4-naphthoquinone And Its Technology

2-Methyl-1,4-naphthoquinone（2-MNQ）and sodium bisulfite menaquinone（2-MSB）belong to vitamin K₃.2-MSB is water-soluble and has the functional properties of vitamin K₃.As a kind of fat-soluble vitamin K₃,2-MNQ is an important intermediate of K vitamins,which has a lot of value.In the animal husbandry,it is often used as a feed additive.In medicine,it has a coagulation effect,and mixed with a certain amount of vitamin C can effectively treat tumors.Vitamin K₃ in the market is generally synthetic by human in that it is difficult to obtain in nature.In industry,vitamin K₃ is prepared from 2-methylnaphthalene（2-MN）as raw material and chromic anhydride as oxidant,but this process will generate a large amount of chromium-containing waste-water,causing irreversible pollution to the environment,threaten human health because of trace amounts of chromium in products.Therefore,it is important to design a green and environment friendly method for preparing vitamin K₃.In this paper,we prepared 2-MNQ and 2-MSB by chromium-free oxidation firstly,then the purity of the product was tested by HPLC（area normalization method）and the synthesis process was optimized finally.The main research contents are as follows:（1）2-MNQ was prepared using 2-MN as raw material,ammonium persulfate as initiator,30%hydrogen peroxide as oxidant,and glacial acetic acid as solvent.The structure of2-MNQ was confirmed by IR,MS,and NMR spectra.By optimizing the synthesis method,the best synthesis conditions were obtained:reaction temperature was 85^oC,reaction time was 3 h,and raw material ratio n（CH₃COOH）:n（H₂O₂）:n（2-MN）=50:11:1.Finally,the yield of 2-MNQ was 61%and the purity was 87.7%（HPLC area normalization method）in the optimal condition.（2）HPLC（area normalization method）was used to confirm the composition and content of impurities in the raw 2-MNQ,a gradient elution method was established to separate 2-MNQ from its isomer 6-methyl-1,4-naphthoquinone（6-MNQ）.The crude 2-MNQ is treated with a saturated aqueous solution of sodium bicarbonate and an aqueous solution of sodium bisulfite to obtain pure 2-MNQ.By optimizing the purification reaction,the best optimization conditions were obtained:reaction time was 20 min,reaction temperature was20℃,and n（6-MNQ）:n（NaNSO₃）=1:1.2,which reduced the loss of target products during the impurity removal process.The recovery rate of 2-MNQ was 91.9%,the total yield was56.2%,and the purity was 97.7%（HPLC area reduction One method）in the optimal condition.（3）The synthesis of 2-MSB was used 2-MNQ and sodium bisulfite as raw materials.The optimal reaction process was:reaction temperature was 50℃,reaction time was 2 h,n（2-MNQ）:n（NaHSO₃）=1:2.The yield of 2-MSB was 85.2%,and the purity reached 98.1%（HPLC area normalization method）in the optimal condition.