2021

Preparation of ultraviolet absorber

The ultraviolet absorber UVA is a light stabilizer. It is a kind of material that can absorb the ultraviolet part of sunlight or fluorescent source, but its structure does not change. It can convert high-energy ultraviolet light energy into heat energy or non-destructive longer light waves to release, thereby protecting substances added with ultraviolet absorbers from ultraviolet damage. It is mainly used as a light stabilizer for plastics, rubber, coatings, dyes, etc. to prevent their photodecomposition in long-term exposure to sunlight. General requirements of light color, good miscibility, heat resistance and chemical stability, low volatility. When used in food packaging materials, it is also non-toxic and non-migratory. Various substances are sensitive to different wavelengths of ultraviolet light, and the light wave range that various ultraviolet absorbers can absorb is also different. Appropriate selection can achieve satisfactory light stabilization effect. The ultraviolet absorber UVA is one of them.

　Features

UV absorber UVA is a broadband oil-soluble UV absorber, the product of the entire UVA band (320-400nm) UV has a strong absorption, the maximum absorption peak of 354nm. It is one of the best UV absorbers in UVA band. Compared with UV1789 (avobenzone), it has more excellent light stability. Avobenzone is limited by its own structure, and its ultraviolet absorption performance will be greatly reduced under ultraviolet light irradiation. Therefore, MC80 (octyl p-methoxy cinnamate) and HMS (humoryl ester) have to be used for protection during application. The molecular structure of the ultraviolet absorber UVA has good resonance and hydrogen ion transfer effect, and the molecular structure will not be destroyed during the absorption of ultraviolet rays, so it can play a long-term protection.

　Preparation

1) Preparation of 2-(4-N, N-diethylamino-2-hydroxybenzoyl) benzoic acid

99g(0.60mol) of 3-diethylaminophenol, 93.2g(0.63mol) of phthalic anhydride and 460ml of toluene were introduced under a nitrogen atmosphere into a 500ml four-necked flask equipped with a Teflon stirrer, a thermometer and a reflux condenser and heated to the reflux temperature. After a reaction time of 2 hours, a total of 300g of toluene were distilled off within 30 minutes, and the mixture was then stirred under reflux for 3 hours. The mixture was cooled to room temperature and filtered with suction. The filter cake was washed successively with 90ml of toluene and 2 x 90ml of hexanol. The ethanol-wet acid can be used directly in the second step. Yield: 169g(90%) of pink 2-(diethylamino-2-hydroxybenzoyl) benzoic acid.

2) Preparation of 2-(4-N, N-diethylamino-2-hydroxybenzoyl) benzoic acid n-hexyl ester (UV absorber UVA)

313g(1.0mol) of 2-(4-diethylamino-2-hydroxybenzoyl) benzoic acid moistened with hexanol (based on 100%) and 750ml of n-hexanol are introduced into a 1 l shallow flange flask equipped with anchor stirrer, nitrogen conduit, thermocouple and water separator, mixed with 53g(519mmol) of 96% strength sulfuric acid and heated to an internal temperature of 105-110°C. After heating, the water of reaction formed is distilled off azeotropically at an internal temperature of 105 to 110 ° C. and a pressure of about 200 mbar over a period of 6 to 8 hours. After cooling to about 70°C, the mixture is admixed with 830ml of water and neutralized at a temperature of 52-58°C with 25% strength NaOH solution. The aqueous phase is separated off and the organic phase is extracted with 500ml of water (temperature: 52-58°C). The aqueous phase is separated, the organic phase is cooled to 20°C and the ester is allowed to crystallize. After a 1 hour hold to ripen the seed material generated in situ, the mixture is cooled to 0-5°C at 5 K/h, after-stirred at this temperature for 2 hours and filtered off with suction. The filter cake was washed with 2 x 85ml of cold hexanol. The hexanol-wet pink crude product UV absorber UVA(407g) was thoroughly sucked dry and purified by adsorption on activated carbon.