1. Unless a pure
pseudoionone free from isomers is wanted, it is not necessary to perform the elaborate purification of
citral, or the elaborate purification of
pseudoionone. The checkers, using commercial
citral obtained from the Florasynth Laboratories, Inc., New York, found 90% of it to boil over a 3° range between 100° and 103°/7 mm. Using a solution of
203 g. of this distilled citral in
1 l. of commercial acetone, the checkers proceed as follows: The
citral solution is cooled in an ice-salt bath to −10°, and one-fourth of the solution is forced, by dry compressed air, into a
500-ml. round-bottomed three-necked flask, fitted with a stirrer, dropping funnel, and an adjustable outlet tube long enough to reach to the bottom of the flask. The temperature is maintained at 0° to −5° while one-fourth of a solution of
9.2 g. of sodium in 200 ml. of absolute ethanol is added dropwise. After all the base is added, stirring is continued for 3 minutes, and then the reaction mixture is forced over into one-fourth of a solution of
33 g. of tartaric acid in 200 ml. of water. The elapsed time, from the addition of the first drop of base until the mixture is forced into the acid, is 14 minutes. The condensation is repeated three times more, and the combined acidified mixture is steam-distilled until 1 l. of distillate is obtained. It is important that the solution should remain slightly acid during steam distillation. The material remaining in the flask is cooled, the layers are separated, and the aqueous layer is extracted with
ether. The combined organic layers are dried over
sodium sulfate and then distilled. The yield of
pseudoionone boiling at
123–124°/2.5 mm. is
177.8 g. (
70% based upon the
citral). By carrying out the condensation in small batches, the temperature is much more easily controlled and the yields are greatly improved. This
pseudoionone, when catalytically reduced in a bomb, gave
hexahydro-pseudoionol, boiling at
124–128°/10 mm., in a yield of more than
90%.
3. A pressure outlet may be used, but the arrangement outlined here is quite sufficient.
Citral and
pseudoionone are both rapidly polymerized by contact with aqueous
sodium hydroxide. This apparatus continuously provides an intimate mixture of the sulfite solution with the
ether. On decomposition, the free carbonyl compound is immediately extracted and prolonged contact with
sodium hydroxide is thus avoided.
4. From the completion of addition of the
sodium ethoxide solution to the steam distillation, fast work is advantageous, and all equipment should be in readiness before the addition is started. Allowing the solution to stand before addition of the
tartaric acid may cause darkening and formation of gummy material. It is important that the solution should remain slightly acid during the steam distillation.
5. The
pseudoionone bisulfite addition product, unlike that of
citral, apparently decomposes rather slowly; if the separation is made too soon, some undecomposed bisulfite compound is left in solution. This is later decomposed and, in contact with the alkali, polymerizes to a dark red gum.
6. The checkers obtained three layers at this point—a lower aqueous layer, a dark red oily layer, and the upper
ether layer. The
ether layer was removed and the other two layers were returned for further treatment. The dark oily layer gradually disappeared during the subsequent extractions.