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Org. Synth. 1945, 25, 51
DOI: 10.15227/orgsyn.025.0051
FURYLACRYLIC ACID
[2-Furanacrylic acid]
[I. METHOD A]
Submitted by S. Rajagopalan and P. V. A. Raman.
Checked by C. S. Hamilton and R. A. Alberty.
1. Procedure
In a 1-l. round-bottomed flask fitted with a reflux condenser are placed 192 g. (166 ml., 2 moles) of freshly distilled furfural (Note 1), 208 g. (2 moles) of malonic acid (Note 2), and 96 ml. (1.2 moles) of pyridine (Note 3). The flask is heated on a boiling water bath for 2 hours, and the reaction mixture is cooled and diluted with 200 ml. of water. The acid is dissolved by the addition of concentrated aqueous ammonia, the solution is filtered through a fluted filter paper, and the paper is washed with three 80-ml. portions of water. The combined filtrates are acidified with an excess of diluted (1:1) hydrochloric acid with stirring. The mixture is cooled by running water and then allowed to stand in an ice bath for at least 1 hour. The furylacrylic acid is filtered, washed with four 100-ml portions of water, and dried. The yield of practically colorless needles melting at 141° is 252–254 g. (91–92%). If a purer product is desired, recrystallization is best effected from dilute alcohol (Note 4). On slow cooling of the solution, needles melting at 141° separate.
2. Notes
1. Commercial furfural is subjected to a single distillation; b.p. 160–161°.
2. Commercial malonic acid is dried at 100° for 2 hours and stored in a stoppered bottle.
3. The pyridine, which may be a commercial grade, is dried over sticks of potassium hydroxide for a few hours and filtered.
4. A convenient procedure is to dissolve the acid in a slight excess of 50% ethanol, reflux the solution with charcoal (5 g. per 100 g. of acid) for 5–10 minutes, and filter through a fluted filter in a preheated funnel. Any solid material that separates toward the later stages is redissolved by the addition of a few drops of ethanol. The residue is thoroughly washed with boiling water. The hot solution is then diluted with cold water until crystals separate, heated to boiling, cooled slowly, and allowed to stand in a refrigerator for several hours. When the mother liquors are used for subsequent batches, the usual loss (2–3%) by recrystallization is more than halved.
[II. METHOD B]
Submitted by John R. Johnson
Checked by R. L. Shriner and C. M. Stevens.
1. Procedure
In a 3-l. round-bottomed flask provided with a mechanical stirrer and a 90-cm. air-cooled condenser are placed 288 g. (3 moles) of freshly distilled furfural, 460 g. (425 ml., 4.5 moles) of acetic anhydride, and 294 g. (3 moles) of dry, pulverized, freshly fused potassium acetate (Note 1). The ingredients are mixed thoroughly, stirring is started, and the flask is heated in an oil bath at 150° (bath temperature) for 4 hours, without interruption (Note 2). It is well to make provision for acetic acid vapor which escapes through the air condenser.
After cooling slightly, the reaction mixture is transferred to a large flask and treated with 3.5 l. of water. Part of this is used to rinse out the reaction flask. The mixture is boiled with 30 g. of Norit for about 10 minutes and is filtered while still hot with suction, using a preheated Büchner funnel. Furylacrylic acid tends to separate quickly and sometimes offers trouble in clogging the funnel. The filtrate is acidified to Congo red by the addition of a 1:1 solution of concentrated hydrochloric acid in water. After being cooled to 20° or below, preferably with stirring, and being allowed to stand for at least 1 hour, the acid is filtered with suction and washed with a small quantity of ice water. The yield is 270–290 g. (65–70%). The light tan crude acid melts at 138–139° (Note 3)
2. Notes
1. If fused sodium acetate is used the reaction is slower and 6–8 hours' heating is required.
2. When the temperature of the bath approaches 145–150° a rapid exothermic reaction sets in. This must be controlled (by application of cold, wet towels to the flask) to avoid too vigorous ebullition.
3. Furylacrylic acid melting at 138–139° is sufficiently pure for most purposes. The acid is perfectly white when pure, but many recrystallizations are required to attain that state. It may be recrystallized from benzene or ligroin (90–100°) with the addition of Norit. The loss is about 20–25%, and the product melts at 139–140° (sometimes 140–141°).
3. Discussion
This acid is usually prepared by the condensation of furfural with malonic acid in the presence of pyridine.1 It may also be prepared from furfural by the Perkin reaction.2 The use of potassium acetate is advantageous since it allows the reaction to proceed rapidly at relatively lower temperatures. A preparation from furfuralacetone by oxidation has also been reported.3
This preparation is referenced from:

References and Notes
  1. Dutt, J. Indian Chem. Soc., 1, 297 (1925); Kurien, Pandya, and Surange; J. Indian Chem. Soc., 11, 824 (1934) [C. A., 29, 3325 (1935)].
  2. Marckwald, Ber., 10, 357 (1877); Gibson and Kahnweiler, Am. Chem. J., 12, 314 (1890).
  3. Hurd and Thomas, J. Am. Chem. Soc., 55, 1646 (1933).

Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

ligroin

ethanol (64-17-5)

hydrochloric acid (7647-01-0)

acetic acid (64-19-7)

ammonia (7664-41-7)

Benzene (71-43-2)

acetic anhydride (108-24-7)

sodium acetate (127-09-3)

Norit (7782-42-5)

pyridine (110-86-1)

potassium hydroxide (1310-58-3)

Furfural (98-01-1)

furfuralacetone

Furylacrylic acid,
2-Furanacrylic acid (539-47-9)

Malonic acid (141-82-2)

potassium acetate (127-08-2)