Synthesis Of P-Hydroxybenzaldehye By Indirect Electrooxidation Methode

P-hydroxybenzaldehyde is extensively used in medicine, pesticide, spice, petrochemical industry, liquid crystal and electric plating. Synthesis of p-hydroxybenzaldehye by indirect electrooxidation method has outstanding commercial prospect, for its few processes, simple operations, high selectivity, few three wastes and recycle application of electrolyte. Optimum process for heterogeneous electrolytic oxidation of MnSO₄ was studied through orthogonal test. The best catalyst was choosed then the mechanism of catalyst was studied using cyclic voltammetry. Hydroxyl was under protection through the etherification of p-cresol and dissolution loss of P-hydroxybenzaldehyde could be controlled. P-hydroxybenzaldehyde were obtained through the strongly oxidation of p-cresol by Mn³⁺ which were regeneration.The homogeneous and heterogeneous electrolytic oxidation of MnSO₄ in H₂SO₄ solution were investigated. Results show that the anode current efficiency of heterogeneous electrolytic oxidation is better. Optimum process were obtained through orthogonal test: concentration of MnSO₄ and H2SO₄ were 0.50mol/L and 40% respectively, electrolysis time was 30min, temperature was 60℃, stirred rate was 1000r/min, anode current efficiency was 55%, productivity was 20%.The influence of catalyst of Ag₂SO₄ and CoSO₄ on current efficiency was also studied. The anode current efficiency increases rapidly when the concentration of Ag2SO₄ is between 0 mol/L and1.5 mmol/L, then decreases at 1.5 mmol/L under which anodic current efficiency of 60% and productivity of 22% are obtained after 30 minutes. The trend of anode current efficiency for CoSO₄ is the same and reach max value at 7 mmol/L ,under which condition anodic current efficiency of 84% and productivity of 30% for Mn³⁺ are obtained after 30 minutes. Results show that catalytic effect of CoSO₄ is better than Ag2SO₄. The mechanism of catalysis of CoSO₄ was studied using cyclic voltammetry. Results show that chemical and electrochemical oxidation of Mn2+ proceed at the same time, which improves the current efficiency. The influence of mole ratio of the material and Mn³⁺, concentration of H₂SO₄, stirring speed, temperature, time, PTC, dditional mode of electrolyte and lacquer solvent CHCl3 to synthesis of p-Hydroxybenzaldehye by indirect electrooxidation methode were investigated. Results show that influence of time on the productivity and influence of H2SO₄ concentration on conversion is great. Optimum process of synthesis of p-hydroxybenzaldehye by indirect electrooxidation methode were obtained: mole ratio of the material and Mn³⁺ was 1:4, concentration of H2SO₄ was 40%, stirring speed was 600r/min, temperature was 50℃, time was 4h, quality of PTC was 0.3g, dditional mode of electrolyte was constant rant and capacity of lacquer solvent CHCl3 was 40ml, productivity is 74.5%, and conversion is 86.3%. P-Hydroxybenzaldehye was obtained by distillation,with the overall yield of 71%.The programme"hexane+activated carbon"was selected from five programmes for electrolyte recycle regeneration. The anode current efficiency was keeped above 65% after 30st reproduction of electrolyte.