Synthesis of (2E,4E,6E,8E)-3,7-dimethyl-9-(2,6,6-trimethylcyclohex-1-en-1-yl)nona-2,4,6,8-tetraen-1-yl acetate from methyl palmitate and (2E,4E,6E,8E)-3,7-dimethyl-9-(2,6,6-trimethylcyclohex-1-en-1-yl)nona-2,4,6, 8-tetraen-1-yl palmitate in the following general procedure: 3000 kg of vitamin A acetate (compound of formula Ia) in crystalline form and 2750 kg of methyl palmitate (compound of formula Ia) were added to the reactor. Subsequently, 10 kg of sodium hydroxide was dissolved in about 60 liters of methanol and this solution was added to the above mixture. The reaction mixture was heated to 55°C and the system pressure was reduced to 1500-2200 Pascal. The reaction lasted for about 3 hours, during which time the main by-product, methyl acetate, was continuously removed by distillation. Reaction termination was achieved by addition of water and carbon dioxide. Finally, the target product vitamin A palmitate (compound of formula IIIa) was isolated from the reaction solution by extraction in 96% yield.
