Study On Preparation Of 2-methylnaphthoquinone-1, 4 By "In-Cell" Indirect Electrooxidation

2-methylnaphthoquinone-1,4 (2-MNQ) is a lipid-soluble vitamin drug with hemostatic function, and also an important medical intermediate when synthesizing vitamin K series, which has extensive functions in pharmaceutical and feed additives. Traditional synthetical methods of 2-MNQ generally had defects, such as serious pollution, complex techniques and high cost. Indirect electrochemical synthesis which was called "Green Technology" has advantages of fewer investment, lower cost, less pollution and better quality of products. It becomes the research hotspot in the world. Funded by Henan Natural Science Foundation (No.0611023300), this dissertation studied "In-Cell" indirect electrochemical oxidation of 2-MN to prepare 2-MNQ with Cr⁶⁺/Cr³⁺ as oxidation medium. Analysis method for electrolyte, electro-catalytic capability of electrodes and the synthesis technology had also been discussed in this dissertation.The reaction solutions of "In-Cell" indirect electro-synthesis of 2-MNQ contained the product 2-MNQ, byproduct 6-MNQ, unreacted material 2-MN, and H2SO4. Thus, a new analysis method for the determination of 2-MN and 2-MNQ in reaction solution by gas chromatography using an internal standard was developed with recovery as 98%～102% and RSD less than 2%.Based on the characteristics of "In-Cell" indirect electro-synthesis process of 2-MNQ, electro-catalytic activities of PbO₂/Ti,IrO₂/Ti,Pt and Pt/Ti electrods in 2-MN oxidizing process were studied by steady-state polarization curve, results of which showed that PbCVTi had higher overpotential, better electro-catalytic activity, and could be a relatively perfect electrode in indirect electro-synthesis of 2-MNQ. In Cr₂(SO₄)₃+H₂SO₄+H₂O system, kinetic parameters and apparent activation energy of PbO₂/Ti anode in 2-MN oxidizing process were determined under different temperatures.2-MNQ was prepared from 2-MN through "In-Cell" indirect electro-synthesis process in the plate and frame electrolyzer with cation-exchange membrane, using PbO₂/Ti as anode, Pb as cathode, H₂SO₄ as supporting electrolyte, Cr⁶⁺/Cr³⁺ as oxygen medium and tetrabutyl-ammonium bromide as phase transfer reagent. Through mono-factor experiments, influences of 2-MN concentration, Cr₂O₇^2- concentration, H₂SO₄ fraction, electrical charge, current density and reaction temperature on the selectivity and current efficiency of synthesizing 2-MNQ were studied, and technologic conditions were optimized as followed: 2-MN concentration was 0.02 mol/L, Cr₂O₇^2- concentration was 0.03mol/L, the mass fraction of H₂SO₄ was 20%, current density was 110 A/m², reaction temperature was 50°C, and the electrical charge was 20% of theoretical value. Under the optimized technological conditions, the average selectivity and superficial current efficiency of 2-MNQ were respectively 71.9% and 69.7%, the structure of 2-MNQ was identified by infrared spectrogram.