Preparation
STEP A:
Preparation of 7-chloro-3-hydrazono-oxindole.
A solution of 25.0 g of 7-chloro-isatin in 250 ml of
ethanol is refluxed for 24 hours, cooled, and precipitate
recovered by filtering and washed once with ethanol
and twice with pentane to obtain 7-chloro-3-hydrazono
oxindole, m.p. 217-219℃. (decomp.). STEP B:
Preparation of 7-chloro-oxindole.
To a solution of sodium ethoxide prepared by heating
5.5 g of sodium in 200 ml. of ethanol at 70°℃. is added
17 g of 7-chloro-3-hydrazono-oxindole over a period of
3.5 hours, and the resulting solution is heated at 70℃.
for 24 hours. The solvent is evaporated in vacuo, the
residue dissolved in water, acidified with 6 N-hydro
chloric acid and the resulting precipitate recovered by
filtering, washed three times with water, dried by suc
tion and crystallized from methylene chloride/ether to
obtain 7-chlorooxindole, 28-220℃.
