Organic Syntheses, Coll. Vol. 3, p.394 (1955); Vol. 26, p.34 (1946).
In a 2-l. round-bottomed flask
are placed 120 g. (1.83 moles) of 92% ethylenediamine (Note 1)
, 300 ml. of 95% ethanol
, and 300 ml. of water. The flask is attached to an efficient reflux condenser
, and 121 ml. of carbon disulfide
is placed in a separatory funnel
attached to the top of the condenser by means of a notched cork
. About 15 to 20 ml. of the carbon disulfide
is added, and the flask is shaken to mix the contents. A vigorous reaction takes place (Note 2)
, and it may be necessary to cool the flask. After the reaction has started, a water bath
at 60° is placed under the flask and the balance of the carbon disulfide
is added at such a rate that the vapors reflux about one-third the way up the condenser. About 2 hours is required for the addition of the carbon disulfide
. At this time the bath temperature is raised to about 100°, and the mixture is allowed to reflux for 1 hour. Then 15 ml. of concentrated hydrochloric acid
is added, and the mixture is refluxed under a good hood
(bath at 100°) for 9–10 hours. The mixture is cooled in an ice bath
, and the product is filtered by suction on a Büchner funnel
and washed with 200–300 ml. of cold acetone (Note 3)
. A yield of 156–167 g.
) of white crystals is obtained melting at 197–198° (Note 4)
and (Note 5)
If commercial ethylenediamine
is used, it should be redistilled. The concentration of the ethylenediamine
may be determined by titration with standard acid and the proper amount taken.
Care should be exercised to make certain that the reaction starts, before an additional quantity of carbon disulfide
is added. In one experiment in which the carbon disulfide
was added all at once, a very violent reaction occurred.
Since all the likely contaminants are readily volatile, extensive washing is unnecessary.
This product is pure enough for most purposes. It gives no precipitate with copper sulfate
solution, indicating the absence of the open-chain acid.1
It has been reported (J. VanAllan) that this procedure may also be used for the preparation of 2-thio-3,4,5,6-tetrahydropyrimidine
; in this case 130 g. (150 ml., 1.76 moles) of propylenediamine
is used in place of ethylenediamine
. The yield is 160 g.
) of colorless product, m.p. 207–208°
, after recrystallization from water.
The only practical method for preparing alkylene thioureas is by the action of the diamines upon carbon disulfide
in aqueous alcohol.1,2,3,4,5
The final heating is essential to convert the thiocarbamic acid
into the cyclic compound, the addition of hydrochloric acid
being beneficial. Alkylene thioureas have also been prepared by heating N-formylalkylenediamines with sulfur
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