Organic Syntheses, CV 1, 147
Submitted by B. Helferich and W. Schaefer.
Checked by Henry Gilman and S. A. Harris.
1. Procedure
In a
125-cc. distilling flask, provided with a water-cooled side arm to act as reflux condenser (Note
1), is placed
56 g. (33.4 cc., 0.47 mole) of thionyl chloride (Note
2). This is heated on a
water bath, and to it is added during the course of one hour
35.2 g. (0.4 mole) of n-butyric acid (Note
3) by means of a
separatory funnel attached to the neck of the flask. The evolved gases are absorbed in water (Note
4).
When all the acid has been added, the mixture is heated for one-half hour on the water bath and then distilled directly from an
oil bath into a second distilling flask. The crude acid chloride thus obtained boils between 70° and 110°; it is purified by distillation through a column and boils almost entirely at
100–101°, only a few drops of forerun being obtained. The yield is
36 g. (
85 per cent of the theoretical amount) (Note
5).
2. Notes
1. If a
Claisen distilling flask is used for the preparation of the acid chloride the side arm is plugged by a
small cork; the short neck holds the reflux condenser, and the long neck the separatory funnel.
2. The yield is influenced by the purity of the
thionyl chloride; the results reported above were obtained with a pure product which boiled over a two-degree range.
3. The presence of traces of water in the
butyric acid is of no disadvantage if a correspondingly larger quantity (1 mole for 1 mole of water) of
thionyl chloride is used.
5. It is reported that the major loss in this preparation is due to the formation of
butyric anhydride and that, if the
thionyl chloride is kept cool by means of a water bath during the addition of the acid, the formation of anhydride is suppressed with a consequent improvement in the yield of the acid chloride (R. R. Read, private communication).
3. Discussion
This preparation is referenced from:
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