Organic Syntheses, CV 5, 545
Submitted by J. Lavety and G. R. Proctor
1.
Checked by Ian Morrison and Virgil Boekelheide.
1. Procedure
A solution of
200 g. (2.33 moles) of γ-butyrolactone (Note
1) in
375 ml. of absolute ethanol is cooled to 0° in an
ice bath while a stream of dry
hydrogen bromide (Note
2) is introduced. The passage of gas is discontinued 1 hour after
hydrogen bromide is seen to pass through the reaction mixture unchanged (Note
3).
The alcoholic solution of the product is kept for 24 hours at 0° and then poured into 1 l. of ice-cold water. The oily layer is separated, and the aqueous layer is extracted with two
100-ml. portions of ethyl bromide (Note
4). The combined oil and extracts is washed with ice-cold
2% potassium hydroxide solution, then with very dilute
hydrochloric acid, and finally with water. The organic layer is dried over
sodium sulfate, the solvent is removed under reduced pressure, and the residual crude ester is purified by distillation. The yield of
ethyl γ-bromobutyrate, obtained as a colorless oil, b.p.
97–99° (25 mm.),
n25D 1.4543, is
350–380 g. (
77–84%) (Note
5) and (Note
6).
2. Notes
2. The
hydrogen bromide is made by burning together
hydrogen and
bromine. The apparatus is essentially that described previously.
2,3 The submitters found that standard ground-glass fittings can be used throughout, connected where necessary by Neoprene
® tubing. The combustion tube is made by "butt-joining" two ground-glass sockets. The checkers used commercial
hydrogen bromide from a cylinder which was connected to the reaction flask through a safety
trap.
3. The time varies from 6 to 8 hours, and the increase in weight from 450 g. to 480 g. Using the commercial
hydrogen bromide, the checkers found the time for saturation to be 3.5–4 hours.
4. The aqueous layer may be kept and used again in repeating the reaction.
5. In smaller runs, yields as high as 95% have been obtained.
4
6. The product is best stored in dark bottles at 0°.
3. Discussion
The ester has been made from the corresponding acid which was obtained from the nitrile,
5 but the present method is the more practicable.
4,6 This procedure is an adaptation of the method used for the preparation of
ethyl 2-bromocyclopentaneacetate.
7
4. Merits of the Preparation
Copyright © 1921-2002, Organic Syntheses, Inc. All Rights Reserved