Organic Syntheses, Coll. Vol. 1, p.447 (1941); Vol. 6, p.72 (1926).
In a 500-cc. round-bottomed flask (Note 1)
, fitted with a mechanical stirrer
and surrounded by an ice-salt cooling bath
, are placed 54 g. (43 cc., 0.71 mole) of carbon disulfide
and 90 cc. (1.3 moles) of concentrated aqueous ammonia
(sp. gr. 0.9). The stirrer is started, and 56 g. (0.6 mole) of aniline (Note 2)
is run into the mixture from a separatory funnel
at such a rate that the addition is complete in about twenty minutes. The stirring is continued for thirty minutes after all the aniline
has been added, and then the reaction mixture is allowed to stand for another thirty minutes. During this time a heavy precipitate of ammonium phenyldithiocarbamate
separates and may even stop the stirrer.
The salt is dissolved in 800 cc. of water (Note 3)
and transferred to a 5-l. round-bottomed flask
. To the solution is added with constant stirring a solution of 200 g. (0.6 mole) of lead nitrate
in 400 cc. of water. Lead sulfide
separates as a heavy brown precipitate which soon turns black. The mixture is then distilled with steam into a receiver
containing 5–10 cc. of 1 N sulfuric acid
as long as any oil comes over (Note 4)
. About 2–3 l. of distillate is collected. The product is separated from the water and weighs 63–66 g.
If the reaction is carried out in a beaker
, so much ammonia
is lost by volatilization that the crystalline ammonium phenyldithiocarbamate
is not formed. The temperature should be from 0° to 10° to avoid loss of ammonia
Ordinary technical aniline
was used in these experiments.
The transfer of the salt to the 5-l. flask is conveniently made by the addition of four successive 200-cc. portions of water to the flask containing the salt.
Larger runs give somewhat lower percentage yields; thus 280 g. of aniline
gives about 250 g.
per cent of the theoretical amount) of redistilled phenyl isothiocyanate
The following slightly modified procedure is generally applicable to the preparation of aryl isothiocyanates.
To a solution of 90 g. (0.50 mole) of p-bromoaniline
, 60 g. (0.78 mole) of carbon disulfide
and 90 cc. of 95 per cent alcohol
at 10–15° is added 81.6 g. (0.63 mole) of concentrated aqueous ammonia
. The milky suspension, in a stoppered flask
covered with a towel, is shaken occasionally until a clear solution is obtained. Considerable heat is evolved, and crystals of the intermediate dithiocarbamate
soon separate. After standing overnight the crystals are filtered, washed with ether
, dissolved in 3 l. of cold water, and stirred while a solution of 174 g. (0.5 mole) of lead nitrate
is slowly added. Stirring is continued for fifteen to twenty minutes, and then the p-bromophenylisothiocyanate
is steam-distilled into a flask acidified with sulfuric acid
. The product, which solidifies, is separated and dried. It weighs 30.5 g.
(a yield of 27
per cent) and melts at 60–61°
In this procedure the use of alcohol is essential; without it no isothiocyanate is obtained. It is also advisable with very reactive aromatic amines to add the ammonia
in small portions so as to avoid a too vigorous reaction and to keep the temperature of the contents of the stoppered flask below 35°. With some substituted anilines the intermediate dithiocarbamate
does not crystallize although the heat evolved indicates that a reaction has taken place. When this happens the solution can be diluted with water and treated with lead nitrate
, but the yield will usually be small.
can be prepared from thiocarbanilide
by the action of phosphorus pentoxide
,1 hydrochloric acid
,3 phosphoric acid
,4 acetic anhydride
and dilute sulfuric acid;6
from ammonium phenyldithiocarbamate
by the action of ethyl chlorocarbonate
,7 copper sulfate
,9 ferrous sulfate
and zinc sulfate
and from methylene aniline
by heating with sulfur
This preparation is referenced from:
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