CN117164444A  *  2023-09-01  Synthesis method of salicylaldehyde   Current Assignee    Zhejiang Hongda Chemicals Co ltd 
  
  
  a method for synthesizing salicylaldehyde includes the following steps:
s1, synthesizing magnesium methoxide: adding 320g of absolute methanol into a 2000mL four-necked flask 1, heating to 40 ℃, adding 27g of magnesium chips in batches, and feeding for 4 hours; after the addition, the mixture is stirred for 4 hours at the temperature of 50 ℃ until the bubbles are completely discharged; 10.75g of methanol vapor and 2.25g of hydrogen are discharged from the reaction, and 334g of mixed solution containing magnesium methoxide and methanol is finally obtained;
the reaction equation for synthesizing the magnesium methoxide in the step S1 is as follows:
CH 3 OH+Mg→CH 3 O-Mg-OCH 3 +H 2 ↑；

s2, synthesizing magnesium phenoxide: 150g of phenol is put into the mixed solution, 174g of toluene is added, and the mixture is stirred for 1h at 55 ℃; continuously adding 609g of toluene, heating and distilling for 3 hours, and distilling 702g of toluene-methanol azeotrope to obtain 565g of mixed solution containing magnesium phenoxide and toluene;
the reaction equation for synthesizing the magnesium phenoxide in the step S2 is as follows:

s3, synthesizing salicylaldehyde magnesium: when the temperature is steamed to 95 ℃, 167g of paraformaldehyde is slowly added, the process of adding paraformaldehyde is carried out for 6 hours, the temperature is kept at 95 ℃ during the period, and simultaneously, toluene-methanol azeotrope is continuously steamed; heating to 105 ℃ after the addition of paraformaldehyde is completed, stirring for 1h, and reacting to obtain 732g of mixed solution containing salicylaldehyde magnesium and toluene;
the reaction equation for synthesizing the salicylaldehyde magnesium in the step S3 is as follows:

s4, acidizing: cooling to below 60 ℃, adding 625g of 20% sulfuric acid into the four-neck flask 1, continuously cooling to 40 ℃ and stirring for 4 hours to obtain 1357g of reaction liquid containing salicylaldehyde and magnesium sulfate;
the reaction equation for obtaining salicylaldehyde by acidification in the step S4 is as follows:

s5, separating: after stirring, transferring the reaction solution to a 2000mL separating funnel, standing for separating liquid, and separating 685g of upper oil phase and 672g of lower water phase, wherein the lower water phase is used as waste liquid; washing the oil phase with 300mL of water, continuing separating liquid, separating 680g of the upper oil phase and 305g of the lower water phase, and recycling the lower water phase;

s6, distilling: adding the oil phase obtained by the secondary liquid separation and 400mL of water into a 2000mL three-neck flask, wherein the water is taken as an entrainer, the three-neck flask is taken as a distillation flask 3, and the stirring distillation process is carried out, so that a first fraction is distilled out at the temperature of 85-101 ℃ to obtain a water-toluene azeotrope, and the water-toluene azeotrope contains 495g of toluene; after the distillation of the first fraction is finished, water-salicylaldehyde azeotrope is distilled out through a water separator 4 at the temperature of 101-102 ℃ until the entrainer is completely distilled out, 156g of salicylaldehyde is received from the bottom of the water separator 4, the content is 97.49%, and the yield is 80.13%; the water at the upper part of the water separator 4 is reused.

raw material usage for 156 gr of salicylaldehyde:
Mg 27 gr/Phenol 150 gr/paraformaldehyde 167 gr/H2SO4 100% 125 gr