Checked by S. C. Welch, P. Bey, and Robert E. Ireland.
1. Procedure
A
tared, 500-ml., round-bottomed flask is fitted with a vacuum take-off, and the entire assembly is connected through an
adaptor containing a stopcock to an inverted cylinder of triethylaluminum, as shown in
f.htmigure 1. The assembly is connected to a
nitrogen source (Note
1) through the vacuum take-off, and with the cylinder valve closed but the stopcock open, the system is alternately evacuated and filled with
nitrogen four times. With the system filled with
nitrogen the cylinder valve is opened and approximately
55 ml. (46 g; 0.40 mole) of triethylaluminum (Note
2) is allowed to flow into the reaction flask. The cylinder valve is then closed; the system is evacuated and filled three times with
nitrogen, and the adaptor stopcock is then closed (Note
3). The reaction flask is then quickly removed, stoppered, and weighed to determine the exact amount of
triethylaluminum collected. A
magnetic stirring bar is added and the flask is fitted with a vacuum take-off and
250-ml., pressure-equalizing dropping funnel. The system is again placed under a
nitrogen atmosphere, and the
triethylaluminum is dissolved in
150 ml. of anhydrous benzene, added through the dropping funnel. The dropping funnel is charged with a solution of
11.9 g. (0.441 mole) of hydrogen cyanide (Note
4) in
100 ml. of anhydrous benzene, which is added dropwise to the solution of
triethylaluminum, with stirring and cooling. Preferably, the addition is carried out at a constant rate such that the
hydrogen cyanide solution is added in about 2 hours. The evolution of
ethane becomes slow suddenly after one molar equivalent of
hydrogen cyanide is added (Note
5). After the addition is complete, the reaction mixture is allowed to stir overnight (Note
6).

After this period, the dropping funnel and the vacuum take-off are replaced by the short-path distillation assembly shown in
f.htmigure 2. The system is protected with a Drierite tube, and the
benzene is distilled under reduced pressure (
water aspirator). After the
benzene is removed, the
benzene-containing receiver is replaced with a clean, dry flask, and the system is connected to an
efficient vacuum pump. The pressure in the system is reduced to 0.02 mm., and the flask is immersed deeply in an
oil bath (
f.htmigure 2) heated to about 200°. After about 1 ml. of forerun is collected,
diethylaluminum cyanide distils at
162° (0.02 mm.) (Note
7) and is collected in a tared,
200-ml. receiver by heating the side arm and the adaptor with a stream of hot air or an IR lamp (Note
8). After all the distillate is collected in the receiver (Note
9), dry
nitrogen is admitted to the evacuated apparatus, and the receiver is stoppered, giving
26.7–35.6 g. (
60–80%) of
diethylaluminum cyanide, usually as a pale, yellow syrup (Note
10) and (Note
11).
>Figure 2. Short-path distillation apparatus.
The stopper of the flask is quickly replaced with the
nitrogen adaptor, and after placing the system under a
nitrogen atmosphere, the
diethylaluminum cyanide is treated with
130 ml. of dry benzene. The resulting mixture is allowed to stand with occasional swirling under
nitrogen until the syrup goes into solution (Note
12). Sufficient dry
benzene is then added to make the total volume of the solution 200 ml. After thorough mixing with a magnetic stirring bar, the resulting
diethylaluminum cyanide solution (
13.4–17.8%; 1.2–1.6
M) may be divided and stored in sealed ampoules (Note
13).
2. Notes
2. The exact volume of the
triethylaluminum added at this point is not critical, since the exact weight is determined later. The use of a
25% solution of triethylaluminum in benzene, available from the Stauffer Chemical Company, 299 Park Avenue, New York, eliminates the tedious preparation of the
triethylaluminum solution described in this procedure.
3. These precautions will ensure the removal of any adhering
triethylaluminum that will flame when the apparatus is disassembled.
5. The change in the rate of gas evolution is sometimes not clear, especially when the temperature of the hood is high. When the change is recognized distinctly, the addition of
hydrogen cyanide solution may be stopped.
8. Heating of the glassware above 150° with a hot air stream or IR lamp is needed to make the viscous product run into the receiver.
11. The yield depends on the efficiency of the collection of the viscous distillate in the receiver.
12. It takes considerable time (5–10 hours) to dissolve
diethylaluminum cyanide. Magnetic stirring is not effective unless most of the material goes into solution.
3. Discussion
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