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CYANOGEN IODIDE (Iodine cyanide)

NaCN + I2 => ICN + NaI

Organic Synthesis Collective volume IV, page 207-209.

Procedure:

Caution! Cyanogen iodide is relatively volatile and highly toxic. 
         Therefore, these operations should be conducted in a good hood.

A three-necked 500-ml. flask is surrounded by an ice-water bath and provided 
with a stirrer and thermometer. Twentyseven grams (0.55 mole) of sodium cyanide 
is dissolved in 100 ml. of water, added to the reaction flask, and cooled to 0°C. 
To this, in 3- to 4-g. portions, is added with good stirring a total of 127 g. 
(0.50 mole) of iodine over a period of 30-40 minutes. A given portion of iodine 
is not added until the preceding one has reacted almost completely. Ten minutes 
after the addition of iodine is completed, 120 ml. of peroxide-free ether is 
added and the mixture is stirred for a few minutes until the precipitated 
cyanogen iodide has dissolved in the ethereal layer. The entire contents are 
then transferred to a previously cooled separatory funnel, and the aqueous layer 
is separated. This aqueous solution is again extracted successively with 100-ml. 
and 80-ml. portions of cold, peroxide-free ether. The combined ethereal extracts 
are poured into a 500-m1. round-bottomed flask, and the ether is evaporated under 
reduced pressure at room temperature. To the slightly brown crude product, which 
weighs about 90 g., is added 120 ml. of water. A slightly diminished pressure 
(0.5 atm, 380 mmHg) is maintained while the contents in the closed flask are 
heated at 50°C for 15 minutes with occasional vigorous shaking (Note 1). The 
mixture is then cooled to 0°C, and the crystalline cyanogen iodide is separated 
from the light yellow mother liquor by suction a sintered-glass funnel or filter 
plate (Note 2). The crude product is washed with six 25-ml. portions of ice 
water, removed from the sintered-glass funnel, and air-dried (in a good hood) 
for 1 hour at room temperature. Colorless cyanogen iodide weighing gut 59 g. 
(77%) is obtained; m.p. 141-144°C (Note 3).

Cyanogen iodide of highest purity may be produced in the following way. The 
above crude product is dissolved in 150 ml. of boiling chloroform, and the 
solution is filtered through a plug of glass-wool on a hot-water funnel into a 
250-ml. Erlenmeyer flask. This solution, after being cooled at room temperature 
for 15 minutes, is placed in an ice-salt bath and cooled to -10°C (Note 4). 
By means of suction filtration, the crystalline product is collected on a 
sintered-glass funnel, washed with three 15-m1. portions of cold chloroform (0°C), 
and freed from the last traces of solvent by being placed on a watch glass and 
exposed to the atmosphere (in a good hood) at room temperature for 1 hour. 
Practically colorless needle-shaped crystals weighing 45 g. (59%) are obtained; 
m.p. 146-147°C (Notes 3 and 5).

Removal of 100 ml. of chloroform from the above filtrate by means of evaporation 
under reduced pressure at room temperature and subsequent cooling permits isolation 
of an additional 2 g. of cyanogen iodide; m.p. 146-147°C. The total yield thus 
becomes 47 g. (62% based on iodine).

Notes:

1. In this way sodium iodide, soluble in the solution of cyanogen iodide in ether 
   [complex formation of NaI2(CN)], is removed. The method adopted here is fast 
   and simple and gives almost the same yield of purified cyanogen iodide.

2. Contact with filter paper must be avoided.

3. Determinations of the melting point of cyanogen iodide must be made using a 
   sealed capillary which is kept totally immersed in the heating bath.

4. When the chloroform solution is cooled, a small aqueous layer is observed which 
   finally separates as ice. The ice is filtered with cyanogen iodide but melts on 
   the filter plate and is removed with the chloroform used as washing liquid.

5. Owing to the volatility of cyanogen iodide, the yield is slightly dependent on 
   the speed of operation. By the above method sublimation as a means of purification 
   is avoided. If, however, sublimation is desirable, it can be accomplished with 
   appreciable speed only under reduced pressure and at temperatures at which 
   cyanogen iodide is slowly decomposed into iodine and cyanogen. The vacuum must be 
   constantly renewed during the operation.




