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.
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%
A pressure outlet may be used, but the arrangement outlined here is quite sufficient. Citral
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.
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.
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.
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.