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Chapter – 1 Preparation and Yield optimization.....
1.8 RESULTS AND DISCUSSION
In this chapter, known methods were adopted for the preparation of 2methyl
indole as well as 2-methyl indoline with slight modifications in the
previously reported methods. 2-methyl indole was reduced to 2-methyl
indoline using trifluoroacetic acid and 1 M BH3.THF in tetrahydrofuran
(Method – A) along with its yield optimization. In this preparation method use
of trifluoroacetic acid was essential because the TLC analysis of a sample
obtained by mixing 2-methyl indole and 1 M BH3.THF in tetrahydrofuran under
nitrogen atmosphere with cooling and then worked up without addition of
trifluoroacetic acid, showed only the presence of unreacted 2-methyl indole. In
and another reduction method, indole was reduced using zinc dust and 85%
phosphoric acid (Method – B) where % yield was comparatively low as
compare to Method – A. Reduction of indole was carried out under nitrogen to
prevent the aerial oxidation as indole is a unstable compound. Its aerial
oxidation results into dimerization or polymerization.
Abonia et. al. a reported preparation method for the preparation of N-
Mannich bases of 2-methyl indoline where they used benzotriazole as
secondary amine and formaldehyde (37-41% w/w solution). They mixed all
the three reagents in diethylether and stirred the reaction mixture at the room
temperature and obtained solid product. While the same method was adopted
in this chapter also using different liquid secondary amines and primary
aromatic amines were used to obtain N-Mannich bases and oily liquid type
products were obtained in all the cases, but solid product was obtained in
case of piperazine. The same was not happened in case of diphenylamine.
Thus it may be concluded that the physical state of the product may depend
upon the secondary / primary amine used.
Department of Chemistry, Saurashtra University, Rajkot-360 005 58