Organic Syntheses, Coll. Vol. 4, p.739 (1963); Vol. 37, p.66 (1957).
Seventy grams (0.25 mole) of oleic acid (Note 1)
is placed in the dropping funnel H
of the tangential apparatus (Fig. 13
; (Note 2)
). The thionyl chloride
distillation is started and regulated (Note 2)
; the upper part of the column
should be filled with the vapor, and reflux should be constant and steady. The acid is dropped in at the top of the column over a period of 35 minutes (120 g. per hour). The product that collects in the receiver I
contains about 25–27% of thionyl chloride (Note 2)
if the heated lower leg K
is employed. The product in receiver I
is heated on a steam bath
under reduced pressure until the more volatile components are completely removed. The residue of crude acid chloride weighs 72–74 g.
yield). The infrared spectrum of this product shows no trace of a carboxyl band (Note 1)
, (Note 3)
, and (Note 4)
The crude acid chloride will serve for most purposes. It can be distilled at very low pressures (b.p. 99–109°/25 μ
) to yield a water-white product; nD25
1.4580–1.4613 (Note 5)
. Small amounts of oleoyl chloride
may be distilled at higher pressures; b.p. 180–185°/1–2 mm.
The infrared absorption curve of the oleic acid
obtainable by hydrolysis is the same as that of the oleic acid
used; thus no isomerization during the reaction is indicated.
The oleic acid
used by the submitters had a freezing point of −2° to +13° and a boiling point of 182–187°/1–2 mm.
It was a 90% middle cut from Emerson 233 as obtained from Emery Industries, Inc., Cincinnati, Ohio. The checkers found that the amount of color in the product was a function of the purity of the oleic acid
. The product from distilled Emerson 233 was dark red-brown, whereas that from a purified grade of oleic acid
was pale yellow.
The tangential apparatus2
is built from stock pieces of glassware having 24/40 standard taper glass joints, and it is clamped to two ring stands. The reactor consists of a column 50 cm. long and 2 cm. inside diameter, packed with 1/8-in. glass helices of the type used for packing distillation columns, and wrapped with a 275-watt flexible heating tape A
, 6 ft. long and
in. wide, with lead wires connected to a variable transformer such as the Powerstat or Variac, which is attached to a source of 110-volt power. Near the bottom of the column is a heated side arm connection B
to a three-necked flask
. The use of the leg K
, wrapped with a heating tape, removes much of the excess of thionyl chloride
and is particularly advantageous with acid chlorides (such as oleoyl chloride
) that are sensitive to heat. The crude effluent from the reactor ordinarily contains 40–50% of thionyl chloride
, which is reduced one-half or more by this leg. It is not essential for use with chlorides insensitive to heat. Vapor supplied by boiling the liquid in the reservoir is forced to circulate via B
through the column by sufficient heat input to the column and the lower leg K
; the excess escapes at the top through the side arm D
which is connected to a Friedrichs condenser E
. The bottom of the condenser is connected to a Y-shaped section with an outlet F
for effluent gas and a return G
which extends below the surface of the liquid in the reservoir. At the top of the column is a 250-ml. dropping funnel H
for admitting reactants to the column. Since oleic acid
is a liquid at room temperature, heating of this funnel is not required in the present preparation. At the bottom of the column is a 500-ml. flask I
for receiving the product.
Other acid chlorides can be prepared similarly. (a
) Palmitoyl chloride
: Palmitic acid
is a solid at room temperatures (m.p. 61–62°
) and is not sufficiently soluble in palmitoyl chloride
or thionyl chloride
, and so these cannot be used as solvents. It is admitted to the reactor in the melted condition by warming the acid in the dropping funnel H
. The quality of the chloride naturally depends on the homogeneity of the starting acid; palmitic acid
usually contains a little stearic acid
, which does not affect the melting point. Palmitoyl chloride
1.4489, can be obtained as a water-white product by distillation at very low pressures (b.p. 110°/15–24 μ
), or with negligible decomposition at boiling points as high as 165°.
) Ricinoleoyl chloride
: b.p. 205–210°/8 mm.
, 125–130°/25 μ
1.4759; this substance decomposes significantly at the higher distillation temperature.
) 2,4-Di-tert-amylphenoxyacetyl chloride
: In this instance, the corresponding solid acid (20 g.) is dissolved in the acid chloride (80 g.) as a solvent and admitted at the rate of 70 g. of acid per hour. The crude acid chloride, after removal of the excess thionyl chloride
, contains about 1% of unchanged acid (infrared determination). The yield of distilled acid chloride, b.p. 143–146°/2 mm.
1.5062, is 85%.
The described procedure is not suitable for all acids. For instance, the acid chloride must not have a boiling point so near that of thionyl chloride
that they are inseparable by distillation. Certain high-molecular-weight acids give dehydration products, presumably diketenes: e.g., behenic and dihydroxystearic acids.
The refractive index will vary with the purity of the oleic acid
. Oleic acid
purified by low-temperature crystallization and by conversion to the oleic acid-urea complex (95.3% oleic, 0.7% linoleic)
yielded a product with nD25
This modification of the continuous reactor (cf. benzoylacetanilide
, p. 80
) with countercurrent distillation is preferred for reactions in which a large amount of solvent or excess of one reactant is essential, but increase of total volume is undesirable. It is especially useful if the substances involved are heat-sensitive; with this apparatus the reactants are heated for only a few minutes at most. It is particularly applicable to the preparation of acid chlorides from carboxylic acids and thionyl chloride
(cf. (Note 3)
and (Note 4)
). An indefinite amount of product can be prepared by replenishing the reactants as they are consumed.
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