Org. Synth. 1944, 24, 96
DOI: 10.15227/orgsyn.024.0096
VINYLACETIC ACID
[3-Butenoic acid]
Submitted by Edward Rietz
Checked by C. F. H. Allen and James VanAllan.
1. Procedure
In a
500-ml. flask attached to a reflux condenser is placed a mixture of
67 g. (80 ml., 1 mole) of allyl cyanide1 (Note 1) and
100 ml. (1.2 moles) of concentrated hydrochloric acid (sp. gr. 1.19). The mixture is heated by a small flame and is shaken frequently. After 7–8 minutes, the reaction begins, a voluminous precipitate of
ammonium chloride appears, the temperature rises rapidly, and the mixture refluxes. After 15 minutes the flame is removed, 100 ml. of water is added, and the upper layer of the acid is separated
(Note 2). The aqueous layer is extracted with two
100-ml. portions of ether. The extracts and the acid are combined and distilled. Most of the
ether is removed at atmospheric pressure
(Note 3),
(Note 4), and
(Note 5), and the remainder is removed as the pressure is diminished. The acid is collected at 70–72°/9 mm. after a fore-run of approximately
40 g. The yield of crude acid is
50–53 g. (
52–62%)
(Note 5).
Although this product is pure enough for most purposes, it contains small amounts of by-products which cannot be removed by distillation. Further purification is accomplished by the following procedure: In a 250-ml. three-necked round-bottomed flask fitted with a stirrer, a small dropping funnel, and a thermometer for reading low temperatures, 24 g. of sodium hydroxide is dissolved in 80 ml. of water. While the temperature of of the solution is maintained at 8–15° by external cooling, 45 g. (40.5 ml.) of the impure vinylacetic acid is added; this operation requires 25 minutes. This solution is transferred to a 600-ml. conical separatory funnel and extracted with 50 ml. of chloroform (Note 6) and (Note 7). The alkaline solution is immediately transferred to a 1-l. beaker, and 300 ml. of dilute sulfuric acid (Note 8) and (Note 9) is added with stirring. This acid solution is at once extracted with three 100-ml. portions of chloroform (Note 7) and (Note 10). The solvent is then removed by distillation, first at atmospheric pressure and then at reduced pressure, from a 200-ml. modified Claisen flask. The residue is distilled under reduced pressure. Almost all the material boils at 69–70°/12 mm. (163°/760 mm.). The recovery is 30–33 g. (75–82%) (Note 11).
2. Notes
1.
An improved procedure for preparation of
allyl cyanide (3-butenenitrile) is as follows: In a dry (washed with absolute
ethanol and absolute
ether)
500-ml. three-necked flask, equipped with a sealed mechanical stirrer and a 90-cm. bulb condenser set vertically and protected by a calcium chloride tube, are placed
85 g. of dry cuprous cyanide (commercial, or prepared as previously described;
1 dried for 72 hours in an
oven at 110° just before use),
0.25 g. of potassium iodide, and
72.5 g. of allyl chloride (dried over
calcium chloride and freshly distilled; b.p.
45–47°). The stirrer is started, and the mixture is heated on a
water bath. After about 6 hours the reaction is substantially complete, as indicated by cessation of the refluxing; heating is continued for 1 hour beyond this point. With larger runs it may be necessary to moderate the reaction by removing the water bath when vigorous refluxing sets in. This usually occurs about 3–5 hours after heating is started. Runs of the size described do not require any special attention. The water bath is replaced by an
oil bath, the condenser is set downward for distillation, and stirring is continued while the
allyl cyanide is distilled into a
100-ml. distilling flask. Near the end of the distillation it may be necessary to discontinue stirring, and it is advisable to reduce the pressure somewhat to aid in the removal of the last portion of the product. The distillate is redistilled, and
50–53 g. (
79–84%) of
allyl cyanide boiling at
116–122° is collected. (Private communication from Curtis W. Smith and H. R. Snyder; checked by W. E. Bachmann and G. Dana Johnson.)
2.
This amounts to 90–95 g. A
separatory funnel of about 600-ml. capacity is the most convenient size.
3.
The first
ether extract contains 10 g. of nitrile; the second extract contains 4.5 g.
4.
This procedure is shorter and less tedious than the more common method of drying and fractionating the ethereal solution.
5.
A
Dry Ice trap, inserted between the oil pump and the apparatus, condenses
5–10 g. of unchanged allyl cyanide. The yield of crude acid, after allowing for the recovered nitrile, is 62–72%.
6.
This extraction removes about 1 g. of non-acidic impurity.
7.
Ether can be substituted for
chloroform without materially decreasing the yield.
8.
This is prepared by diluting
16.5 ml. of concentrated sulfuric acid to 300 ml.9.
Contact with alkali results in the isomerization of
vinylacetic acid to
crotonic acid.
10.
The first two extractions remove 27–28 g.; the last one, 3–4 g.
11.
When cooled in a
Dry Ice-acetone bath the acid should remain clear until it crystallizes at −36° to −35°. This indicates freedom from
crotonic acid.
2
3. Discussion
The only practical methods for the preparation of
vinylacetic acid involve hydrolysis of
allyl cyanide;
3,4 carbonation of
allylmagnesium bromide5,6 or an alkali salt of propylene.
7 The
malonic acid synthesis is less satisfactory than the hydrolysis of
allyl cyanide.
4
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
allyl cyanide (3-butenenitrile)
ethanol (64-17-5)
calcium chloride (10043-52-4)
sulfuric acid (7664-93-9)
hydrochloric acid (7647-01-0)
ether (60-29-7)
ammonium chloride (12125-02-9)
sodium hydroxide (1310-73-2)
chloroform (67-66-3)
potassium iodide (7681-11-0)
Allyl cyanide (109-75-1)
Cuprous Cyanide (544-92-3)
allyl chloride (107-05-1)
Malonic acid (141-82-2)
crotonic acid (3724-65-0)
Vinylacetic acid,
3-Butenoic acid (625-38-7)
Allylmagnesium bromide (1730-25-2)
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