Views: 3 Author: Site Editor Publish Time: 2023-03-14 Origin: Site
Salicylic acid, also known as 2-hydroxybenzoic acid and o-hydroxybenzoic acid, CAS 69-72-7, is an important intermediate in the pharmaceutical, food, fragrance, dye and pesticide industries. Salicylic acid is mainly divided into Salicylic Acid industrial grade, Salicylic Acid sublimed grade and Salicylic Acid Pharmaceutical grade. The most important downstream products are aspirin, methyl salicylate and sodium salicylate. It is also used in the synthesis of pesticide species such as hydantoin and methylisophos, and in the synthesis of direct dyes and acid mordant dyes. With the wide application of salicylic acid in many fields, the demand for salicylic acid has increased greatly. Salicylic acid is white needle-like crystals with a melting point of 157-1590C, slightly soluble in water and easily soluble in ethanol. Salicylic acid is a phenolic acid and has the general properties of phenols and carboxylic acids. For example, it reacts with ferric chloride reagent to show purple color, is easily oxidized in air, shows acidity in aqueous solution, and can form salt and ester, etc.
Synthesis method of salicylic acid
Atmospheric pressure method
Using phenol as raw material, we can obtain 99 % of finished salicylic acid with a yield of 50-70%. The advantage of this method is the atmospheric pressure operation, better safety, more suitable for small enterprises, equipment investment is also small; disadvantage is the high consumption of phenol, low conversion rate per consumption, phenol recycling energy consumption is also high. At present, this method is not used for production.
Medium pressure method
Using phenol as raw material, the content of this method is 99%, with a yield of 98% or more. The advantage of this method is the high one-way conversion of phenol, low cost, good product quality; the disadvantage is that with 0.7 to 0.8 MPa reaction pressure, the equipment input is large, there is a certain degree of danger. This method is the main method currently used in industry and has strong competition.
2. o-nitrotoluene method
With o-nitrotoluene as raw material, the process is long, high cost and many side reactions, not suitable for industrial production.
3.o-Toluenesulfonic acid method
Using o-methylbenzenesulfonic acid as raw material, this method has only theoretical academic significance, no industrial significance, extremely low efficiency, and difficult sources of raw materials.
This method is based on o-cresol as raw material, which has some industrial value, but the cost is high and the process is long. No manufacturer has adopted it yet.
Application of salicylic acid
1. Synthesis of fragrances
Salicylic acid can be used to synthesize methyl salicylate, ethyl salicylate, isoamyl salicylate, isobutyl salicylate, benzyl salicylate, phenyl salicylate and phenyl ethyl salicylate and other fragrances.
Salicylic acid can be used to synthesize acetylsalicylic acid (aspirin), salicylic acid, glibenclamide, tribromoxalen, salazosulfapyridine, clonidine and salicylamide, etc.
3. Synthetic pesticides
Salicylic acid can be used to synthesize hydromorphone, methylisophos and ethylisophos and other pesticides.
4. Synthetic dyes
Salicylic acid can be used to synthesize direct yellow-brown D3G (C.I.30045), direct dark brown M (C.I.22311), direct yellow-brown 3G (C.I.30050), direct sun-resistant brown BRL (C.I.30145), acid mordant dark yellow GG (C.I.14010) and acid mordant yellow 3G (C.1.13990) and other dyes. 1.2.5 Synthesis of fine chemical intermediates
Salicylic acid can be used to synthesize 5-chlorosalicylic acid, 3,5-dichlorosalicylic acid and salicylanilide and other products.
It can be seen that salicylic acid is a chemical intermediate with a wide range of applications. At present, the international research on its application is not yet in-depth, but only in the pharmaceutical and pesticide usage is large. Therefore, its derivatives should be developed vigorously, and the quality of salicylic acid should be continuously improved and the production cost reduced to meet the needs of the fine chemical industry.