Dry eye occurs due to dryness, desquamation, hyperkeratosis and decreased lacrimal gland secretion of epithelial cells of epidermis and mucosa, and severe corneal softening and perforation lead to blindness. Respiratory epithelial cells keratinize, cilia fall off, their resistance drops, and they are susceptible to infection. The recommended intake (RNI) of vitamin A for adults in China is 800 micrograms of retinol equivalent per day for men and 700 micrograms of retinol equivalent per day for women.
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Synthesis of vitamin a
Although vitamin A can be extracted from animal tissues, the resources are relatively scattered, the steps are complicated and the cost is high, so commercial vitamin A is a chemical synthetic product. The industrial synthesis of vitamin A at home and abroad mainly includes Roche in Switzerland and BASF in Germany.
The former takes β -ionone as the starting material and is characterized by Grignard reaction. The synthesis of vitamin A acetate was completed by Dazens reaction, Grignard reaction, selective hydrogenation, hydroxyl bromination and debromination.
The typical feature of the latter is Wittng reaction, in which β-ionone is used as the starting material to react with acetylene to generate acetylene-β-ionol, and then ethylene-β-ionol is obtained by selective hydrogenation. After Wittng reaction, sodium alkoxide was used as catalyst to condense with C 5 aldehyde to form vitamin A acetate.
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