Organic Syntheses, Coll. Vol. 3, p.846 (1955); Vol. 24, p.94 (1944).
In a 1-l. three-necked flask
, equipped with a stirrer
and a thermometer
and immersed in an ice bath
, is placed 46 g. (0.7 mole) of sodium azide (Note 1)
in 150 ml. of water. A mixture of 109 g. (0.5 mole) of lauroyl chloride
(b.p. 134–137°/11 mm.
) and 150 ml. of acetone
is then added from a separatory funnel
to the well-stirred solution of the azide at such a rate that the temperature remains at 10–15°. After the mixture has been stirred at this temperature for an hour, the stirrer is stopped and, when the layers have separated, the lower water layer is removed carefully by suction through a glass capillary tube (Note 2)
. The upper layer is then added slowly to 500 ml. of benzene
which has been warmed to 60° (Note 3)
. A rather rapid evolution of gas results, and the mixture is kept at 60–70° (Note 4)
until no more nitrogen
is evolved; the conversion of azide to isocyanate requires about an hour. The solution is filtered to remove any insoluble matter, and the benzene
is removed by distillation from a modified Claisen flask
. Distillation of the residue yields 80–85 g. of ester (81–86%) (Note 5)
and (Note 6)
A practical grade of sodium azide such as that obtained from the Eastman Kodak Company
It is important that the water be removed as completely as possible before the azide is added to the warm benzene
. Failure to remove the water causes formation of the sym-disubstituted urea
during decomposition of the azide. If the water is separated carefully, there will be no need to filter the benzene
solution before the final distillation.
If the azide is added too rapidly, the solution may froth over; it is best to carry out this reaction in a 1-l. beaker
The heat of reaction is usually sufficient to maintain the temperature at 60–70°.
On redistillation all the product boils at 103°/3 mm. A second distillation is unnecessary; the original ester is pure enough for all practical purposes.
This method is a general one for the preparation of isocyanates.1
This procedure is one used by Schröter for preparing alkyl isocyanates.1
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