Organic Syntheses, CV 6, 268
Submitted by E. L. Martin
1
Checked by R. Kottke and W. D. Emmons.
1. Procedure
A
500-ml., three-necked flask equipped with a
magnetic stirring bar, a
pressure-equalizing dropping funnel, a
thermometer, and a
25-cm. Vigreux column attached to a
trap cooled in an acetone–dry ice mixture is charged with
100 ml. of diethyl phthalate (Note
1) and
43 g. (0.30 mole) of tetracyanoethylene oxide (Note
2). The dropping funnel is charged with
44 g. (0.30 mole) of distilled n-butyl sulfide, the pressure is reduced to 5–20 mm. with a
water aspirator, and the reaction flask is warmed with a 50°
water bath. The
n-butyl sulfide is added dropwise with stirring over 20–25 minutes, and the internal temperature is maintained at 50 ± 2° by controlling the temperature of the water bath. The reaction is exothermic at the start, but it is necessary to supply heat toward the end of the addition. The internal temperature is increased to 80° over 10–15 minutes after the sulfide has been added. The vacuum on the system is released by the introduction of
nitrogen. The solid
carbonyl cyanide that has collected in the trap is allowed to warm to room temperature under
nitrogen, and
2 g. of tetracyanoethylene oxide (Note
3) and a boiling stone are added. The mixture is then warmed to 50°, and the product is distilled under reduced pressure (5–20 mm.) into a second trap cooled in an acetone–dry ice mixture. Another portion of
tetracyanoethylene oxide (1 g.) is added to the distillate, and the
carbonyl cyanide is distilled, again under reduced pressure (5–20 mm.), into a distillation flask cooled in acetone–dry ice mixture. Fractionation of the distillate through a
20-cm. column packed with glass helices gives
20.8–21.8 g. (
86–91%) (Note
4) of faintly yellow
carbonyl cyanide, b.p.
65–66° (Note
5), (Note
6), and (Note
7).
2. Notes
1. The
diethyl phthalate is freed of traces of water and
ethanol by distilling about 5% of it under reduced pressure, b.p.
185° (20 mm.) and then cooling the residue with protection from moisture. Moisture must be excluded because
carbonyl cyanide reacts vigorously with water.
5. There is very little if any low-boiling material when the reaction is carried out as described and care is taken to have the apparatus dry and exclude moisture.
3. Discussion
The procedure described is that of Linn, Webster, and Benson.
3 Carbonyl cyanide has previously been prepared by the pyrolysis of the diacetyl derivative of
diisonitrosoacetone, a multistep process that suffers from low yield, lack of reproducibility, and risk of explosion.
2 The present procedure provides a convenient high-yield synthesis of
carbonyl cyanide.
Carbonyl cyanide reacts with alcohols and phenols, giving cyanoformate esters;
4 with primary and secondary amines, giving cyanoformamides; with
N,N-dimethylaniline, giving
bis[4-(dimethylamino)phenyl]malononitrile; and with
pyrrole, giving
2-(cyanoformyl)pyrrole.
5 With olefins of the type C=C-CH, products with structures C=CC-C(CN)
2OH, C=CC-COCN, and C=CC-C(CN)
2OCOCN are obtained, depending on the nature of the olefin and the reaction conditions.
6 Carbonyl cyanide also undergoes Diels-Alder reactions with some conjugated dienes, yielding dicyanodihydropyrans.
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