Abstract
Conditions of esterification of vitamin A concentrate with acid chloride were examined.
I. Acetylation
Method. Acetyl chloride in benzene was added slowly with stirring to vitamin A concentrate in benzene and pyridine under a stream of inert gas. After standing, water was added with vigo-tous stirring to dissolve pridine hydrochloride. The reaction mixture was then poured into a separating funnel and washed with 3% HCl, water, 2% KOH and finally with water. Acetate of vitamin A concentrate was obtained after evaporating benzene off.
Result. The rate of acetlylation was examined by means of refractive index. Acetylation was performed so rapidly that reaction time for 5min, was enough to complete esterification. More than 1.8 mole of acetyl chloride per 1 OH of vitamin A concentrate and 1.5 mole of pyridine per 1 mole of acetyl chloride were needed for perfect esterification (table 1).
Vitamin A recovery in the process of acetylation was almost 100% except for cases such as vitamin A concentrate contaminated with fatty acid or impure acetyl chloride was used (tables 3, 4 and 5).
Change of vitamin A to anhydrovitamin A was not occurred in acetylation (table 2).
II. Palmitylation.
Method. Palmityl chloride in benzene was run into benzene dissolving vitamin A concentrate and pyridine. Water was added after stadding for some time. The reaction mixture transferred into a separating funnel was washed with 3% HC1, water, then with 30-50% methanol containing 2% KOH. Methanol used for washing was extracted several times with fresh benzene. Both the initial benzene and the extracts were combined and washed with 30 % methanol and finally with water. Benzene was distilled. Acetone was added to the remainings and heated. After cooling for a night in a refrigerator, the acetone solution was filtered to remove the precipitate. Benzene was added into the remainings from which acetone had been distilled, and the benzene solution was washed with methanol containing KOH and then with water. After benzene had been driven off, palmitate of vitamin A concentrate was obtained.
The author assumed that the above precipitate was palmityl anhydride, because its m. p. was 62°C. molecular weight (observed) 475 and because it was very slowly hydrolyzed with alkali solution.
Result. Reaction time for 10min., 1.5 mole of palmityl chloride per 1 OH of vitamin A concentate and 1 mole of pyridine per 1 mole of palmityl chloride were enough to complete esterification (table 6).
Vitamin A recovery by palmitylating process was almost 100% (table 7). But if the washing with alkali before acetone treatment had been omitted, vitamin A recovery decreased to about 90% (tables 8 and 9). Therefore, washing with alkali before and after actone treatment may be needed for good recovery.
