Hypophosphorous acid is a colorless oily liquid or deliquescent crystal, easily soluble in hot water, ethanol, ether, soluble in cold water, strong reducing agent. Hypophosphite is generally prepared by sodium hypophosphite through ion exchange resin treatment, adsorption, desorption, filtration, evaporation and concentration. It can be used as a bactericide, a strong agent for the nervous system, a treatment agent for the metal surface, and a catalyst and hypophosphite for manufacturing. When heated to 130 ° C, it is decomposed into orthophosphoric acid and phosphine. The concentration of hypophosphoric acid is greatly limited due to the highly toxic phosphine gas generated by the decomposition of hypophosphoric acid.
Hypophosphorous acid is used as：
1. In organic chemistry, hypophosphoric acid can reduce aromatic diazonium salt Ar-N2+to aromatic hydrocarbon Ar-H. By combining this reaction with nitration of aromatics, reduction of nitro groups and diazotization reaction, an amino group can be introduced to the aromatic ring first, and a certain group can be introduced to a certain position of the aromatic ring by virtue of the localization effect of the amino group. Then the amino group is removed by diazotization-reduction.
2. Sodium hypophosphite hydrate is used as a reducing agent in industry, especially for electroless nickel plating on metal, non-metal and plastic surfaces. The surface nickel layer is generally amorphous or metallic nickel containing about 10% phosphorus. When heated, Ni3P can be produced to enhance the hardness of the coating. In addition to hypophosphite, the plating solution also contains nickel chloride (or nickel sulfate), lactic acid (coordination agent), malate or succinate (accelerated deposition) and lead salt (stabilizer).
3. Hypophosphoric acid can reduce iodine to hydroiodic acid, and hydroiodic acid can reduce ephedrine or pseudoephedrine to methamphetamine, which is also known as methamphetamine. Therefore, hypophosphite/hypophosphite is listed as the first category of precursor chemicals by the Drug Enforcement Administration of the United States Department of Justice, and its purchase and use are strictly controlled. The classification and variety list of precursor chemicals in Chinese Mainland does not include hypophosphite and hypophosphite, but "ephedrine, pseudoephedrine, racemic ephedrine, norephedrine, methylephedrine, ephedrine extract, ephedrine extract powder and other ephedrine substances" are listed. These are classified as the first category of precursor chemicals and are subject to strict control.
The current concentration method of hypophosphoric acid:
1. Vacuum distillation method: Due to the characteristics that hypophosphoric acid is very easy to decompose when heated, its heating temperature is greatly limited during the concentration process, making the general concentration temperature not higher than 80 ° C. The water in hypophosphoric acid is evaporated by vacuum distillation method. When the temperature is 80 ° C, it can only be concentrated to about 90wt%. Due to the characteristics of easy sublimation of hypophosphoric acid, if the vacuum is too high, the concentration of hypophosphoric acid by vacuum distillation method will have a great loss.
2. Oil-water separator azeotropic distillation method: use oil-water separation method to concentrate hypophosphoric acid, which can be concentrated to about 95wt% at 80 ° C, but it is extremely difficult to concentrate to more than 95wt%. It takes a very long time to obtain a higher concentration, and the longer the heating time of hypophosphoric acid is, the more dangerous it is. Among them, azeotropic distillation is extremely difficult to concentrate to more than 95wt%, because when the amount of organic solvent used for azeotropic distillation is small, the concentration temperature will be high, which is not desirable; When the amount of organic solvent used for azeotropic distillation is large, the organic solvent after condensation and reflux in the oil-water separator will mix and dissolve part of the water back to the system, resulting in that the azeotropic distillation method is extremely difficult to concentrate hypophosphoric acid to a higher concentration after it is concentrated to 95wt%. The invention also relates to the application of oil-water separator structure in azeotropic distillation.
Preparation method of hypophosphoric acid:
Take 400. 3g of 50wt% hypophosphoric acid and 250mL of cyclohexane, add them into the reaction bottle equipped with an oil-water separator and condenser, fill the oil-water separator with cyclohexane, heat and stir it under nitrogen protection until it is azeotropic for 4 hours, and discharge the water separated at the bottom of the oil-water separator in stages in the middle; Add the solution in the reaction bottle to the lower liquid 212 separated by the separating funnel 1g, the acid content titrated by acid-base titration is 94 12wt% ;
Take 94.12wt% hypophosphite 200 1 g and 200 mL methanol are added into the reaction bottle equipped with oil-water separator and condenser, in which the oil-water separator and condenser are equipped with fixed solid silica gel desiccant, and the oil-water separator is filled with methanol, heated and stirred under nitrogen protection until azeotropic for 4 hours; Put the solution in the reaction bottle on the rotary evaporator at 60 ° C, - 0 Concentrate under reduced pressure for 4 hours at 098 KPa, cool to room temperature, and vent to obtain 198 9g hypophosphoric acid; The acid content dropped by acid-base titration is 99 76wt% ; The content of hypophosphoric acid dropped by oxidation-reduction method is 99 48wt%, phosphite content is 0 22wt%.