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Chapter – 1 Preparation and Yield optimization.....
over about 30 minutes. Thereafter, 50 ml of water was added, the resulting
solution was stirred at room temperature for about 90 minutes. The progress
and the completion of the reaction were checked by silica gel-G F254 thin layer
chromatography using toluene : ethyl acetate (7 : 3) as a mobile phase. After
the reaction to be completed the mixture was then evaporated under reduced
pressure to about 30 ml of semi-solid viscous oil. The oil was partitioned
between methylene dichloride and aqueous sodium hydroxide solution
(pH>10). The organic layer was dried over anhydrous potassium carbonate,
filtered and evaporated under reduced pressure to obtain 5.65 gm of a slightly
greenish transparent oily 2-methyl indoline product. Yield - 85%, BP – 224-
226 °C (225-227°C d )
REVERSE ADDITION METHOD:
0.05 mole 2-methyl indole was dissolved in 90 ml of 1 M BH3.THF
solution in tetrahydrofuran by stirring under nitrogen atmosphere while cooling
in an ice bath and the stirring was continued for about 15 minutes. Thereafter,
110 ml of trifluoroacetic acid was added drop-wise with continued stirring,
cooling and maintaining a nitrogen atmosphere. 50 ml of water was added to
the mixture, followed by methylene dichloride and aqueous sodium hydroxide
solution (pH>10). The solution then was stirred about 30 minutes and a
sample was taken for TLC, the progress and the completion of the reaction
were checked by silica gel-G F254 thin layer chromatography using toluene :
ethyl acetate (7 : 3) as a mobile phase. The organic layer was dried over
anhydrous potassium carbonate, filtered and evaporated under reduced
pressure to obtain 5.70 gm of a slightly greenish transparent oily 2-methyl
indoline product. Yield - 86%, BP – 224-226 °C (225-227°C d )
METHOD – (B)
To 0.36 mole of untreated zinc dust in a nitrogen atmosphere was
added all at once 200 ml of 85 % phosphoric acid. The mixture was rapidly
heated to 70-80°C on a steam bath and 0.12 mole of 2-methyl indole was
added in portions during 30 minutes with vigorous mechanical stirring
d J. T. Shaw and F. T. Ryson; J. Am. Chem. Soc., 1956, 78, 2538.
Department of Chemistry, Saurashtra University, Rajkot-360 005 41