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04
2021
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03
Preparation of UV absorbers
UVA ultraviolet absorber is a kind of light stabilizer. It is a substance that can absorb ultraviolet rays in sunlight or fluorescent light sources without changing its own structure. It converts the high-energy ultraviolet light energy into heat energy or releases longer, non-destructive light waves, thus protecting the substance containing the ultraviolet absorber from ultraviolet damage. It is mainly used as a light stabilizer for plastics, rubber, coatings, and dyes to prevent their photodegradation under long-term exposure to sunlight. Generally, it is required to have light color, good miscibility, heat resistance, chemical stability, low volatility, etc. When used in food packaging materials, it must also be non-toxic and non-migratory. Different substances have different sensitive wavelengths to ultraviolet rays, and different ultraviolet absorbers have different absorption ranges of light waves. Only with appropriate selection can satisfactory light stabilization effect be achieved. UVA ultraviolet absorber is one of them.
Features
UVA ultraviolet absorber is a broad-band oil-soluble ultraviolet absorber. This product has strong absorption of ultraviolet rays in the entire UVA band (320-400nm), with a maximum absorption peak at 354nm. It is one of the best ultraviolet absorbers in the UVA band currently available. Compared with UV1789 (Avobenzone), it has better photostability. Avobenzone, due to its structural limitations, will significantly reduce its ultraviolet absorption performance under ultraviolet irradiation. Therefore, in the application process, it has to be protected by MC80 (octyl methoxycinnamate) and HMS (homosalate). However, the molecular structure of UVA ultraviolet absorber has good resonance and hydrogen ion transfer effects. The molecular structure will not be destroyed during the absorption of ultraviolet rays by the absorber, so it can provide long-term protection.
Preparation
1) Preparation of 2-(4-N, N-diethylamino-2-hydroxybenzoyl)benzoic acid
Under a nitrogen atmosphere, 99g (0.60mol) 3-diethylaminophenol, 93.2g (0.63mol) phthalic anhydride and 460ml toluene were introduced into a 500ml four-necked flask equipped with a Teflon stirrer, thermometer and reflux condenser, and heated to reflux temperature. After reacting for 2 hours, 300g of toluene was distilled off in 30 minutes, and then the mixture was stirred under reflux for 3 hours. The mixture was cooled to room temperature and filtered. The filter cake was washed with 90ml toluene and 2×90ml hexanol. The hexanol-wetted acid can be directly used in the second step. Yield: 169g (90%) pink 2-(diethylamino-2-hydroxybenzoyl)benzoic acid.
2) Preparation of 2-(4-N, N-diethylamino-2-hydroxybenzoyl)benzoic acid hexyl ester (UVA ultraviolet absorber)
313g (1.0mol) hexanol-wetted 2-(4-diethylamino-2-hydroxybenzoyl)benzoic acid (based on 100%) and 750ml n-hexanol were introduced into a 1L shallow flanged flask equipped with an anchor stirrer, nitrogen inlet tube, thermocouple and water separator, mixed with 53g (519mmol) 96% sulfuric acid and heated to an internal temperature of 105-110℃. After heating, the water formed by the reaction was azeotropically removed at an internal temperature of 105-110℃ and a pressure of about 200 mbar for 6-8 hours. After cooling to about 70℃, the mixture was mixed with 830ml water and neutralized with 25% NaOH solution at a temperature of 52-58℃. The aqueous phase was separated and the organic phase was extracted with 500ml water (temperature: 52-58℃). The aqueous phase was separated, the organic phase was cooled to 20℃ and the ester was allowed to crystallize. After maintaining for 1 hour to mature the seed crystals produced, the mixture was cooled to 0-5℃ at 5K/h, stirred at this temperature for 2 hours and filtered. The filter cake was washed with 2×85ml cold hexanol. The hexanol-wetted pink crude product UVA ultraviolet absorber (407g) was thoroughly dried and purified by adsorption on activated carbon.
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Tel: 18857019806;13665709588
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