A Publication
of Reliable Methods
for the Preparation
of Organic Compounds
Annual Volume
Org. Synth. 1931, 11, 92
DOI: 10.15227/orgsyn.011.0092
[Thiocyanic acid, isopropyl ester]
Submitted by R. L. Shriner
Checked by C. R. Noller
1. Procedure
In a 3-l. round-bottomed flask, fitted with a very efficient mechanical stirrer (Note 1), a reflux condenser, and a 500-cc. separatory funnel, are placed 445 g. (5.5 moles) of sodium thiocyanate (Note 2) and 1250 cc. of 90 per cent ethyl alcohol. The stirrer is started and the mixture is heated to boiling. Then 615 g. (5 moles) of isopropyl bromide (p. 359; Org. Syn. Coll. Vol. I, 1941, 37) is added slowly during the course of one hour. The mixture is refluxed with stirring for six hours. At the end of this time the precipitated sodium bromide is removed by filtration and washed with 250 cc. of 95 per cent alcohol. As much of the alcohol as possible is then removed by distillation on the steam bath. To the residue in the flask is added 500 cc. of water, and the upper layer of isopropyl thiocyanate is separated. The aqueous layer is extracted with two 100-cc. portions of ether (Note 3). The ether extracts are added to the crude thiocyanate, and the combined product is dried over anhydrous sodium sulfate (Note 4). The dried material is fractionated twice from a modified Claisen flask with a 25-cm. fractionating column. The following fractions are collected: up to 60°; 60–100°; 100–130°; 130–146°; and 146–151°. The last fraction contains the pure product. The yield is 320–345 g. (63–68 per cent of the theoretical amount). By redistilling the alcohol that was removed on the steam bath through an efficient fractionating column (Note 5) until all the alcohol is removed (Note 6), separating the water, and distilling, there is obtained an additional 55–65 g. of product boiling at 146–151°. The total yield is 385–400 g. (76–79 per cent of the theoretical amount). On redistillation of the combined fractions boiling at 146–151°, practically the entire amount distils at 149–151°.
2. Notes
1. A vigorous mechanical stirrer must be used to prevent the precipitated sodium bromide from settling to the bottom and causing bumping.
2. A technical grade of sodium thiocyanate was used. Potassium thiocyanate does not possess any advantages over the sodium salt.
3. If benzene is used to extract the aqueous layer, three fractionations are necessary to obtain the same yields.
4. The sodium sulfate does not remove the water entirely, and in the subsequent fractionation the water layer should be removed by means of a separatory funnel wherever it appears.
5. An eight-bubbler fractionating column of the type described by Clarke and Rahrs1 was used.
6. Distillation was continued until water began to appear in the lowest bubbler.
3. Discussion
Isopropyl thiocyanate has been prepared by the action of isopropyl iodide on potassium thiocyanate.2

References and Notes
  1. Clarke and Rahrs, Ind. Eng. Chem. 18, 1092 (1926).
  2. Henry, Ber. 2, 496 (1869); Gerlich, Ann. 178, 80 (1875).

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

ethyl alcohol,
alcohol (64-17-5)

Benzene (71-43-2)

ether (60-29-7)

sodium bromide (7647-15-6)

Isopropyl bromide (75-26-3)

sodium sulfate (7757-82-6)

potassium thiocyanate (333-20-0)

isopropyl iodide (75-30-9)

Isopropyl thiocyanate,
Thiocyanic acid, isopropyl ester (625-59-2)

sodium thiocyanate (540-72-7)