Org. Synth. 1949, 29, 44
DOI: 10.15227/orgsyn.029.0044
ETHYL 2-PYRIDYLACETATE
[2-Pyridineacetic acid, ethyl ester]
Submitted by R. B. Woodward and E. C. Kornfeld.
Checked by Arthur C. Cope and William R. Armstrong.
1. Procedure
A 2-l. round-bottomed three-necked flask is fitted with a reflux condenser, a dropping funnel, and an efficient mechanical stirrer. A calcium chloride tube is attached to the condenser to protect the apparatus from moisture. To the flask are added 800 ml. of absolute ether and 13.9 g. (2 gram atoms) of lithium chips or shavings (Note 1). The stirrer is started, and 105 ml. (157 g., 1 mole) of dry bromobenzene is placed in the dropping funnel. About 5–15 ml. of the bromobenzene is added to initiate the reaction; when the ether begins to reflux, the balance is added at such a rate that the solvent refluxes continuously (1 hour) (Note 2). The mixture is then stirred and refluxed until most of the lithium disappears (45–90 min.). While stirring is continued, 97 ml. (93.1 g., 1 mole) of α-picoline is added dropwise in about 5–10 minutes. The dark red-brown solution of picolyllithium is stirred for an additional 30 minutes and is then poured slowly and with shaking onto 500–750 g. of crushed Dry Ice contained in a 3-l. round-bottomed flask (Note 3). The mixture is stirred well until the dark color of the picolyllithium is discharged, and the excess of Dry Ice is allowed to evaporate. The ether is removed by distillation under reduced pressure at room temperature. The lumpy residue of lithium salts is broken up, and to it is added 750 ml. of commercial absolute ethanol. The solution is saturated with dry hydrogen chloride while cooling in an ice bath. The esterification mixture is allowed to stand overnight, after which the solvent is removed as completely as possible by distillation under reduced pressure on a steam bath. The syrupy residue is dissolved in 750 ml. of chloroform, and a paste prepared from 225 g. of potassium carbonate and 135 ml. of water is slowly added to the solution with mechanical stirring. After the paste has been added, the solution is stirred vigorously and is kept just below the boiling point for 1 hour. The chloroform solution is decanted from the inorganic salts, and the chloroform is removed by distillation. The residue is fractionated under reduced pressure from a modified Claisen flask with a fractionating side arm. About 40 g. of α-picoline is recovered in the fore-run, and the ethyl 2-pyridylacetate is obtained as a light yellow liquid, b.p. 135–137° /28 mm., 142–144° /40 mm., 109–112° /6 mm.; n25D 1.4979. The yield is 58–66 g. (35–40% based on lithium) (Note 4) and (Note 5).
2. Notes
1.
The most convenient method of preparing the
lithium chips is as follows. Pieces of
lithium several grams each in size and slightly moist with paraffin oil are pounded with a hammer into thin sheets on a dry surface. The sheets are quickly cut into small chips by means of a pair of scissors and are added immediately to the absolute
ether.
2.
The use of a
nitrogen atmosphere is not essential if the solution is kept protected from
oxygen by an atmosphere of
ether vapor. For this purpose the solution is kept at the reflux point throughout.
3.
Rapid filtration of the
picolyllithium solution onto the Dry Ice through a thin layer of glass wool is useful in removing unreacted
lithium at this point.
4.
Runs twice the size of the one described give comparable yields.
5.
Methyl 2-pyridylacetate, b.p.
122–125° /21 mm., can be obtained in similar yield by use of
methanol in the esterification.
3. Discussion
2-Pyridylacetic esters have been obtained by the alcoholysis of
2-pyridylacetanilide, in turn prepared by Beckmann rearrangement of the
oxime of 2-phenacylpyridine,
1 and by the carbethoxylation of
α-picoline in the presence of
potassium amide.
2
This preparation is referenced from:
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
oxime of 2-phenacylpyridine
ethanol (64-17-5)
potassium carbonate (584-08-7)
hydrogen chloride (7647-01-0)
methanol (67-56-1)
ether (60-29-7)
chloroform (67-66-3)
oxygen (7782-44-7)
nitrogen (7727-37-9)
bromobenzene (108-86-1)
lithium (7439-93-2)
potassium amide
Ethyl 2-pyridylacetate,
2-Pyridineacetic acid, ethyl ester (2739-98-2)
picolyllithium
Methyl 2-pyridylacetate (1658-42-0)
2-pyridylacetanilide
α-picoline (109-06-8)
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