Organic Syntheses, Coll. Vol. 2, p.258 (1943); Vol. 10, p.44 (1930).
[Hydrolysis of Rape-Seed Oil]
In a 5-l. flask
fitted with a reflux condenser
are placed 2.5 l. of 95 per cent ethyl alcohol
and 340 g. (4.5 moles) of commercial (73–75 per cent) potassium hydroxide
. The mixture is gently shaken until the hydroxide is dissolved, 1330 g. (1.5 l., approximately 4 equivalents) of rape-seed oil is added with shaking (Note 1)
, and the mixture is refluxed on a steam bath
for twenty-five to thirty hours.
The hot mixture is poured, with stirring, into 15 l. of warm water (50–60°), and is followed by 700 cc. (8.2 moles) of concentrated (36 per cent) hydrochloric acid (Note 2)
. After standing until the layers are distinct (ten to fifteen minutes), the lower layer is siphoned off as completely as possible and the oil is washed with two 1-l. portions of warm water.
The oil thus obtained, which should amount to 1460–1600 cc., is dissolved in three times its volume of 95 per cent ethyl alcohol
and the mixture cooled to −10 to 0°, when the erucic acid
crystallizes (Note 3)
. After six to eight hours at this temperature, the crude erucic acid
is collected on a basket centrifuge (Note 4)
. The mother liquor, on chilling, yields a second crop of erucic acid
. The combined product (800–1100 g.
) melts either partially or wholly at room temperature, owing to the presence of oleic acid
. It is dissolved in an equal volume of alcohol, chilled for six hours at 0°, and centrifuged as before, when it is obtained in well-defined crystalline form. The second crop of this recrystallization resembles that of the first crystallization and must again be recrystallized. The product is finally recrystallized once again from an equal volume of 95 per cent alcohol
. The recrystallized acid contains alcohol, which is removed by heating to constant weight on the steam bath
under diminished pressure. The yield of acid is 260–360 g. (Note 5)
; the acid melts at 31–32° (Note 6)
If the solution is mixed in this manner, the rape-seed oil emulsifies on being poured into the alkali and refluxing begins more smoothly.
If the acid is added before the water, esterification occurs to an appreciable extent, and the yield may fall to less than 200 g.
The crystallization is best accomplished by cooling for several hours at 0°. Cooling in an ice-salt mixture is much quicker but the erucic acid
so obtained contains more oleic acid
The centrifuge affords an easy way of filtering the erucic acid
, since if the acid is not quickly separated from the mother liquor it melts and makes separation impossible. If a centrifuge is not available, the acid must be filtered at 0°, which is inconvenient except during cold weather.
The mother liquors from the recrystallizations may be combined, evaporated, and distilled under reduced pressure, taking two equal fractions. The lower (b.p. 200–220°/5 mm.) consists mainly of oleic acid
; the higher (b.p. 220–230°/5 mm.
) is solid at 20° and yields a further quantity of erucic acid
The acid obtained contains a small percentage of arachidic acid
and other higher saturated fatty acids, and has an iodine number of 66.9 (instead of about 75). If not entirely colorless, the product may be distilled under reduced pressure, when it boils at 241–243°/5 mm.
or 252–254°/12 mm.
; there is practically no loss, only a minute amount of higher-boiling material remaining in the flask.
is a constituent of various natural oils but is most conveniently obtained from rape-seed oil. The process described above is essentially that of Reimer and Will.1
Methods have been developed for obtaining pure erucic acid
free from saturated acids,2
but these involve time-consuming procedures of fractional precipitation and crystallization, and necessarily give poor yields. The product obtained above is satisfactory for most purposes.
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