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Chapter – 3 Preparation of small library…..
secondary amine, drop wise, with cooling and shaking. The reaction mixture
was allowed to stand at room temperature for one hour with occasional
shaking after which it was warmed on a steam bath for 15 minutes. At the end
of this period the contents were cooled and the product thus separated was
filtered and recrystallized from ethanol.
Code
Substitution
R1 & R2
Department of Chemistry, Saurashtra University, Rajkot – 360 005 155
MF
MW
(g/m)
MP
(°C)
%
Yield
IMB-01 Morpholine C13H14N2O3 246 202-204 b 70
IMB-02 Piperidine C14H16N2O2 244 146-148 c 65
IMB-03 1-Methyl Piperazine C14H17N3O2 259 178-180 67
IMB-04 1-Ethyl Piperazine C15H19N3O2 273 192-194 63
IMB-05 1-Benzyl Piperazine C20H21N3O2 335 128-130 d 60
3.4.4 PREPARATION OF 2-AMINO BENZOTHIAZOLES
It was prepared according to the method described by Stuckwisch. e To
a solution of 0.2 mole of an appropriate amine and 0.8 mole of potassium
thiocyanate in 360 ml of glacial acetic acid was added drop wise, with stirring,
0.2 mole of bromine dissolved in 150 ml of glacial acetic acid while the
temperature was kept below 35 °C. After all the bromine solution had been
added, the mixture was stirred for ten hours and was then filtered and the
residue washed with water. The combined filtrate and washings were
neutralized with ammonium hydroxide. The precipitate was collected on a
filter and dried. This material was pure enough for subsequent reactions.
Further purification was most readily carried out by recrystallization from a
mixture composed of equal volumes of concentrated hydrochloric acid and
95% ethanol. The hydrochloride thus obtained was dissolved in water and the
free base was precipitated with sodium carbonate. The recovery of 2-amino
benzothiazole was nearly quantitative.
b Reported : 203-205°C; A. A. Esmaeili, S. Amini and A. Bodaghi; Synlett, 2007, 9, 1452.
c Reported : 147-148°C; R. S. Varma and I. A. Khan; Nat. Acad. Sci. Lett., 1979, 2(4), 137.
d Reported : 128-129°C; F. Collino and S. Volpe; Boll. Chim. Farmace., 1982, 121(5), 221.
e C. G. Stuckwisch; J. Am. Chem. Soc., 1949, 71, 3417.