Natural vitamin A is extracted from cod liver oil. The liver of the marine fish was extracted with retinol (Vitamin A1). The liver of freshwater fish was extracted with 3-dehydroretinol, vitamin A2.
There are many routes for the synthesis of retinol and its derivatives. The Isler route is commonly known as C13-C14-C20.
Condensation of βionone with monochloroacetic acid ethyl ester, followed by hydrolysis and decarboxylation to give tetradecanal; and condensation of sodium acetylide with methylketene, the resulting material is then reacted with ethylmagnesium bromide to give magnesium dibromide. Chemicals. Condensation of bisbromomagnesium compounds with tetradecanal, hydrolysis, catalytic hydrogenation to obtain hydroxyl vitamin A, acetyl chloride and hydroxy vitamin acetate, rebromination, debromination to obtain vitamin acetate.