A Publication
of Reliable Methods
for the Preparation
of Organic Compounds
Annual Volume
Org. Synth. 1929, 9, 32
DOI: 10.15227/orgsyn.009.0032
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.
4. The gas-absorption trap shown in Fig. 7 on p. 97 may be 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
n-Butyryl chloride can be prepared from n-butyric acid with phosphorus trichloride,1 with phosphorus pentachloride,1 with benzotrichloride and zinc chloride,2 with phthaloyl chloride,3 and with benzoyl chloride.4 A study has been made of the preparation of butyryl chloride using phosphorus pentachloride, phosphorus trichloride, and thionyl chloride.5
This preparation is referenced from:

References and Notes
  1. Burcker, Ann. chim. phys. (5) 26, 468 (1882).
  2. Rabcewicz-Zubkowski, Roczniki Chem. 9, 523 (1929) [C. A. 24, 61 (1930)].
  3. Kyrides, J. Am. Chem. Soc. 59, 208 (1937).
  4. Brown, ibid. 60, 1325 (1938).
  5. Clark and Bell, Trans. Roy. Soc. Canada, III, 27, 97 (1933) [C. A. 28, 3053 (1934)].

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

phosphorus pentachloride (10026-13-8)

thionyl chloride (7719-09-7)

benzoyl chloride (98-88-4)

benzotrichloride (98-07-7)

phosphorus trichloride (7719-12-2)

butyric acid,
n-butyric acid (107-92-6)

zinc chloride (7646-85-7)

butyric anhydride (106-31-0)

phthaloyl chloride (88-95-9)

Butyryl chloride,