Manufacturing Process
To a solution of 106 g (0.74 mol) of 2-amino-4-chlorophenol in 500 ml of
water containing 69 ml of concentrated hydrochloric acid (29.2 g, 0.8 mol) are
added 60.8 g (0.8 mol) of ammonium thiocyanate. The solution is placed in
an evaporating dish and heated on a steam bath for 5 hours. The solid which
results is then removed from the concentrated solution by filtration, washed
with a small amount of water and dried. The filtrate is placed in an
evaporating dish and heated on a water bath for 2 hours. At the end of this
time, the mixture is cooled, and the solid which precipitates out is removed by
filtration. Both solid products are 5-chloro-2-hydroxyphenylthiourea melting at
157°C, and may be combined. The calculated N content for C 7 H 7 ClN 2 OS is
13.8; that found is 13.6.
To a solution of 10 g (0.05 mol) of 2-hydroxy-5-chlorophenylthiourea in 50 ml
of methanol is added a solution of 11 g (0.04 mol) of ferric chloride
hexahydrate in 50 ml of methanol. The initial purple-red color changes in a
few minutes to amber. After stirring for one half hour, the solution is treated
with 16.5 ml of 57% ammonium hydroxide solution (0.24 mol). A brown,
flocculent precipitate of ferric sulfide appears. The mixture is then refluxed
with stirring for one hour, cooled and centrifuged. The centrifugate is
evaporated to dryness, and the residue is shaken with ether and water to
separate the organic material from the ammonium chloride. The ether layer is
extracted three times with 25 ml portions of 1 N hydrochloric acid. The acid
solution is then poured into excess ammonium hydroxide, and the resulting
solid collected, washed with water and dried. This gives a light tan solid
melting at 183°C to 185°. The material is then dissolved in 25 ml of acetone
and 50 ml of benzene are added. After treatment of the solution with
activated charcoal, the light yellow solution is evaporated to 25 ml and cooled.
The white crystals of 2-amino-5-chlorobenzoxazole which separate melt at
185°C to 186°C.
