Salicylic acid

Salicylic acid, whose molecular formula is C7H6O3, is an extract of plant willow bark and a natural anti-inflammatory drug. The commonly used cold medicine aspirin is the derivative of salicylic acid, sodium acetylsalicylate, and sodium para-aminosalicylate (PAS) is a commonly used anti-tuberculosis drug. Salicylic acid is commonly used in dermatology to treat various chronic skin diseases such as acne (acne) and ringworm. Salicylic acid can exfoliate, sterilize, and reduce inflammation, so it is very suitable for treating acne caused by clogged pores. The international mainstream anti-acne products are all salicylic acid, and the concentration is usually 0.5 to 2%.

 

Basic Information

Chinese name: Salicylic acid

English name: Salicylic acid

Chinese aliases: 2-hydroxybenzoic acid; salicylic acid; o-hydroxybenzoic acid; sublimated salicylic acid; o-hydroxybenzoic acid

English alias: 2-Hydroxybenzoic Acid; 2-hydroxy benzoic acid; o-hydroxybenzoic acid; ortho-hydroxybenzoic acid

CAS number: 69-72-7

Molecular formula: C7H6O3

Molecular weight: 138.12

 

Physical data

1. Properties: white needle-like crystals or monoclinic prisms, with special phenol sour taste. It is stable in the air, but gradually changes color when exposed to light.

2. Relative density (g/mL, 20/4℃): 1.443

3. Relative vapor density (g/mL, air=1): 4.8

4. Melting point (℃): 158～161

5. Boiling point (℃, 2.67KPa): 210 (2666pa)

6. Relative density (25℃, 4℃): 0.9438159

7. Refractive index (n20D): 1.565

8. Flash point (℃): 157

9. Standard heat of combustion in gas phase (enthalpy) (kJ·mol-1): -3117.2

10. The gas phase standard claims heat (enthalpy) (kJ·mol-1): -494.8 molecular structure

11. Vapor pressure (114℃): 1mmHg

12. Standard combustion heat of crystal phase (enthalpy) (kJ·mol-1): 3022.1

13. The crystal phase standard claims heat (enthalpy) (kJ·mol-1): -589.9

14. Critical temperature (℃): uncertain

15. Critical pressure (KPa): uncertain

16. The logarithm of the partition coefficient of oil and water (octanol/water): uncertain

17. Upper explosion limit (%, V/V): Uncertain

18. Lower explosion limit (%,V/V): Uncertain

19. Solubility: slightly soluble in cold water, soluble in hot water, ethanol, ether and acetone, and soluble in hot benzene. 1 g of this product can be dissolved in 460 ml of water, 15 ml of hot water, 2.7 ml of alcohol, 3 ml of acetone, 42 ml of chloroform, 3 ml of ether, 135 ml of benzene, 52 ml of turpentine.

 

Storage method

1. It should be stored in a cool, ventilated and dry warehouse, away from fire and heat, and stored separately from explosives and oxidants.

2. The packaging is packed in plastic bags lined with burlap bags or polypropylene woven bags or fiberboard drums.

3. Isolate from explosives and oxidants. Keep away from light.

 

resolve resolution

1. Phenol reacts with sodium hydroxide to produce sodium phenate. After distillation and dehydration, the carboxylation reaction is carried out through carbon dioxide to obtain sodium salicylate, which is then acidified with sulfuric acid to obtain a crude product. The crude product is refined by sublimation to obtain a finished product. Raw material consumption quota: phenol (98%) 704kg/t, caustic soda (95%) 417kg/t, sulfuric acid (95%) 500kg/t, carbon dioxide (99%) 467kg/t. The method is divided into normal pressure method and medium pressure method.

(1) Atmospheric pressure method The phenol and 50% sodium hydroxide solution are prepared into sodium phenate, so that the free alkali is within 1%, and after dehydration under reduced pressure, phenol is added as a solvent for azeotropic dehydration. Then sodium phenolate is carboxylated with dry carbon dioxide in the solvent phenol, and then acidified with sulfuric acid to obtain the finished product.

Phenol and 50% sodium hydroxide are added into the reactor at a ratio of 1:1.02 (mol) for reaction dehydration, and the free alkali is controlled to be ≤1%. After dehydration under reduced pressure, phenol is added as a solvent for azeotropic dehydration. Then, dry carbon dioxide gas is passed through the sodium phenate in the phenol, and after the carboxylation reaction is carried out for 3 hours, carbon dioxide is passed in for the second time for 2 hours, and then the phenol is recovered under reduced pressure, that is, the carboxylation is completed. Then add water to the above sodium salicylate solution to dissolve into a 50% solution, add 7%-8% sulfuric acid under stirring to acidify to pH 1-2, then cool and filter, and vacuum dry to obtain salicylic acid The crude product, then the crude product is sublimated under reduced pressure to obtain the finished product salicylic acid with a content of 99%, and the yield is 50%-70%.

(2) The medium pressure method still uses phenol as the raw material, and first makes sodium phenate, then carboxylates it with carbon dioxide under medium pressure to produce phenol carbonate, and then presses for molecular rearrangement to produce sodium salicylate, which is then acidified After treatment, salicylic acid is obtained. The phenol is neutralized with 50% liquid caustic soda, dried in vacuum, then the temperature of the kettle is cooled to 100℃, and dry carbon dioxide is slowly introduced. When the pressure in the kettle reaches 0.7-0.8Mpa, the carbon dioxide is stopped, and phenol carbonate is generated at this time. Sodium ester, then undergoes intramolecular rearrangement and isomerization at 130-140°C to become sodium salicylate, which is then acidified with sulfuric acid to obtain crude salicylic acid. The crude product is sublimated under reduced pressure to obtain a fine-quality salicylic acid with a content of 99% and a yield of over 98%. Consumption quota (kg/t): phenol (98%) 704, caustic soda (95%) 417, sulfuric acid (95%) 500, carbon dioxide (99%) 467.

(3) Preparation method Phenol reacts with sodium hydroxide to form sodium phenolate, and then synthesizes sodium ortho-hydroxybenzoate with carbon dioxide, and then obtains salicylic acid by acidification: the crude product is dissolved in water, decolorized by activated carbon, and purified by recrystallization.

(4) The phenol of the same substance and 50% sodium hydroxide are reacted at 105～130℃ to generate sodium phenoxide, and the free alkali is controlled within 1%. After the reaction, it is dehydrated under reduced pressure, and then azeotropically dehydrated with phenol as a solvent. After cooling to 100°C, dry carbon dioxide was introduced to carry out 3h carboxylation reaction, and the temperature rose from 128°C to 200°C. After the temperature drops, the solvent phenol is recovered. After 2 to 3 hours, carbon dioxide is introduced for carboxylation for 2 hours, and the phenol is recovered under reduced pressure. (Another method of carboxylation is to pass carbon dioxide at 140～180℃, control the reaction pressure to 0.7～0.8MPa and carry out carboxylation reaction for 12h.) After the carboxylation reaction, add water to dissolve the sodium salicylate and adjust it to 50% The solution, while stirring, add 7%-8% sulfuric acid solution to make the pH value 1-2, cool, filter, spin dry, wash several times with water, after spin dry, then heat it with distilled water to dissolve, add a small amount of activated carbon, and boil , Filter while it is hot, cool the filtrate repeatedly to dissolve it with distilled water, filter and spin dry several times to obtain pure salicylic acid. The resulting crude salicylic acid can also be refined by sublimation under reduced pressure. The process reaction formula is: 2. Tobacco: OR, 44; OR, 26; FC, 9; FC, 54; BU, 26; FC, 40.

 

The main purpose

1. Mainly used as a raw material in the pharmaceutical industry to prepare aspirin, sodium salicylate, salicylamide, Zhitongling, phenyl salicylate, schistosomiasis-67 and other drugs. The dye industry is used to prepare mordant pure yellow, direct brown 3GN, acid chrome yellow, etc. It is also used as rubber vulcanization retardant and disinfectant and antiseptic.

2. Used as an accelerator for epoxy resin curing and also as a preservative. It can be used to prepare synthetic fragrances such as methyl salicylate and ethyl salicylate. The dye industry is used as a raw material for the preparation of direct dyes and acid dyes. It can also be used as rubber antiscorching agent, disinfectant, etc.

3. Standards for alkalimetry and iodometric titration. Fluorescent indicator. Complexing indicator.

4. This product is used as an anti-scorching agent in the rubber industry and the production of ultraviolet absorbers and foaming agents.

5. Used as a fluorescent indicator, a matching indicator, and a matching masking agent. Titanium, zirconium, tungsten paraben sodium salt plasma color developer and preservative.

6. Salicylic acid is used as an additive in some weakly acidic electrolytes, and also as a complexing agent for electroplating or electroless plating.

7. Cosmetic preservatives. Mainly used for toilet water, prickly heat water, quinine head water and other water cosmetics. In addition to antiseptic and bactericidal effects, it also has the functions of removing sweat and odor, relieving itching and swelling, relieving pain and inflammation.

8. A small amount is used to formulate animal flavors and other daily flavors. Used in small amounts in food, it acts as a preservative. It is an important raw material for the pharmaceutical industry.