Electrolytic synthesis method of 2-picolinic acid_Industrial additives

Background and overview of the electrolytic synthesis method of 2-pyridinecarboxylic acid

2-pyridinecarboxylic acid is an important organic synthesis intermediate in the medical trifluoromethylpyridine pharmaceutical industry. It is used to prepare carbocaine drugs and neurotropic drugs, and is widely used in neurosuppression and local anesthesia; 2-picolinate is an essential raw material for the synthesis of various 2-picolinates, of which chromium 2-picolinate is the human Heavy propyl carbonate is an important health-care drug and is widely used in human chromium supplements, feed additives, diabetes treatment, etc.; 2-picolinic acid can also be used to prepare herbicides.

Preparation of 2-picolinic acid by electrolytic synthesis

Electrolytic synthesis method of 2-picolinic acid 1. Ingredients

(1) Preparation of alkali solution: Put 1125L pure water into the preparation kettle; turn on the stirring paddle, and then add 375 kg of lye at a constant speed Dissolve sodium hydroxide completely and prepare 25% alkali solution; turn on the cooling circulating water to reduce the temperature of the alkali solution to 25-30°C, turn on the prepared liquid pump, and send the alkali solution to the alkali solution metering tank for later use.

(2) Preparation of initial electrolyte material: Put 3600L pure water into the preparation kettle, start stirring, then add kilograms of 25% alkali solution from the alkali solution metering tank, stir evenly; then add 103 kilograms at a constant speed Polychlorides of 2-picolinic acid (6-chloro-2-picolinic acid 18 wt%, 3,6-dichloro-2-picolinic acid 70 wt %, 3,5,6-trichloro-2-picolinic acid 9 wt %, 3,4,5,6-tetrachloro-2-pyridinecarboxylic acid 3 wt %), stop stirring after complete dissolution, start the prepared solution pump, and send it to the electrolyte circulation tank for later use.

Electrolytic synthesis method of 2-picolinic acid 2. Electrolysis

(1) Turn on the circulating liquid pump, and the initial electrolytic material enters the diaphragm-free electrolysis through the cooler in the trough.

(2) Turn on the electrolysis control system and control the current density between 200 and 1000A/m2.

(3) Open the cooling water valve of the cooler and control the temperature of the reaction solution to 20°C.

(4) During the electrolytic reduction reaction, continuously replenish the polychloride of solid 2-picolinic acid (same ratio as above), and add it to the electrolyte circulation tank at a constant rate of 27 kg/hour. The total amount added Amount is in kilograms. At the same time, the flow of alkali solution is controlled to keep the pH of the system within the range of 8.5 to 13.4. After liquid chromatography tracking analysis, the end point of the electrolysis reaction is when the content of the target product 2-picolinic acid is ≥98%.

(5) When the electrolysis reaction reaches the end point, turn off the electrolysis control system, cooling water valve, and circulation pump switch in sequence. The electrolyte is placed in the circulation tank for later use.

Electrolytic synthesis method of 2-picolinic acid 3. Separation and crystallization

1) Neutralization: Turn on the circulating liquid pump to circulate the electrolyte in the tank Pump the liquid into the neutralization kettle, start stirring and pour in cold water; add an appropriate amount of concentrated hydrochloric acid at a constant speed to make the pH value of the reaction solution 3 to 4.

2) Evaporation: Put the materials in the neutralization kettle into the three-effect crystallization evaporator, evaporate the condensed water and use it as water for the next batch of electrolysis ingredients. The precipitated crystals settle into the lower crystal tank of the three-stage evaporation crystallizer. It is sent to the centrifuge by the three-stage discharging reflux pump. The solid materials go to the next step for solvent extraction, and the liquid materials return to the evaporator.

3) Extraction: Add about 780 kilograms of the solid material from the previous step into the extraction kettle, then add 1500L ethanol into the extraction kettle, start stirring; open the steam jacket and heat to 90~95°C. Reflux for 1 hour, close the jacket steam valve to stop heating, turn on the cold water in the jacket, cool to 20-30°C, and then filter to remove sodium chloride. The filtrate is sent to the concentration kettle to recover ethanol, the concentrated liquid is cooled and crystallized, and centrifuged to obtain crude 2-picolinic acid. The mother liquor is returned to the concentration kettle, and the crude product enters the crystallization kettle and is recrystallized with ethanol to obtain 280 kilograms of 2-picolinic acid crystals with HPLC purity ≥ 99.60%. The total yield is ≥87.5%, and the recrystallization mother liquor is returned to the extraction kettle.

References

[1] [Chinese invention] CN201110099198.X An electrolytic synthesis method of 2-pyridinecarboxylic acid