Organic Syntheses, Coll. Vol. 4, p.700 (1963); Vol. 36, p.56 (1956).
In a 500-ml. round-bottomed flask
fitted with a reflux condenser
are placed 16.2 g. (0.08 mole) of dry α-naphthylthiourea (Note 1)
and 180 ml. of redistilled chlorobenzene
. The flask is heated at the reflux temperature by means of an electric heating mantle
. Evolution of ammonia
begins almost at once, and all of the solid dissolves after 30–45 minutes. The solution is maintained at reflux for 8 hours (Note 2)
and then is evaporated on a steam bath
at water-pump pressure to remove all of the chlorobenzene
. The residue crystallizes on cooling and is extracted with four 30-ml. portions of boiling hexane (Note 3)
. Removal of solvent from the combined hexane
extracts affords pale yellow crystals of α-naphthyl isothiocyanate
, m.p. 58–59°.
The yield is 12.7–13.0 g.
). Recrystallization from hexane (9 ml. of hexane for 1 g. of solute)
gives colorless needles, melting point unchanged (Note 4)
may be prepared by the method of Frank and Smith, Org. Syntheses Coll. Vol. 3, 735 (1955)
, or by the method of de Clermont, Ber.
, 446 (1876), and Bertram, Ber.
, 48 (1892).
A fifth extraction yields no further product. The residue insoluble in hexane
was found by the submitters to consist of 1.3–1.9 g. of a mixture of equal parts of di-α-naphthylthiourea
, m.p. 178–181°
The method is generally applicable to the preparation of aryl isothiocyanates. Using this procedure, the submitters have prepared the following isothiocyanates, with the yields and times of refluxing indicated: phenyl
, 8 hours; o-chlorophenyl
, 8; p-bromophenyl
, 8; p-biphenylyl
, 6; β-naphthyl
, 10; 9-phenanthryl
, 10; 1-pyrenyl
Aryl isothiocyanates can be prepared by the action of thiophosgene
on the arylamine2
(this reaction fails with naphthyl compounds),3
by fission of a sym
-diarylthiourea with acidic reagents4
(this reaction involves the loss of half the amine used), and by the decomposition of an ammonium aryldithiocarbamate5
(low yields are reported for naphthyl and other compounds).5,6
The procedure described here is that of Baxter, Cymerman-Craig, Moyle, and White.7
Copyright © 1921-, Organic Syntheses, Inc. All Rights Reserved