86
J. M. Khurana et al.
Experimental
Potassium hydroxide (Qualigens) and methanol (SD Fine) were used. The esters obtained from
commercial sources were distilled=recrystallized before use and others were prepared by known
procedures. The IR spectra were recorded on a Perkin Elmer FT-IR and NMR spectra were recorded
on a FT-NMR model R-600 (60 MHz) with TMS as internal standard.
General Procedure
In a typical experiment, 1 g of ester and 3 cm3 of methanol were placed in a 25 cm3 round-bottomed
flask mounted over a magnetic stirrer and maintained at ꢁ35ꢂC. KOH (see Table 1) was added and the
contents were stirred. The reactions were quenched invariably after 60min by addition of 10cm3 of
water. Unreacted ester, if any, was removed by ether extraction (2ꢃ 5 cm3) and the carboxylic acid was
recovered by one of the methods given below. The carboxylic acids were characterized by their mp,
mixed mp, and NMR spectra.
Method A: The aqueous portion was acidified to pH¼ 2 with 6 N hydrochloric acid and extracted
with ether (3ꢃ 5 cm3). The combined ether extracts were dried with Na2SO4 and concentrated on a
Buechi rotavapor. The carboxylic acid was obtained after drying under vacuum.
Method B: The aqueous portion was acidified to pH ¼ 2 with 6 N hydrochloric acid. The carboxylic
acid precipitated on standing, was filtered off, and dried under vacuum.
Method C: The aqueous portion was acidified to pH¼ 2 with 6 N hydrochloric acid and treated
with aq. sodium bicarbonate solution (ꢁ5%) with stirring till basic to litmus. The phenol was removed
by extraction with ether (2ꢃ 5 cm3). The aqueous layer was acidified with 6 N hydrochloric acid and
the acid was extracted with ether (3 ꢃ 5 cm3). The combined ether extracts were dried with Na2SO4
and concentrated on a Buechi rotavapor. The carboxylic acid was obtained after drying under vacuum.
Method D: The aqueous portion was acidified to pH¼ 2 with 6 N hydrochloric acid and treated
with aq. sodium bicarbonate solution (ꢁ5%) with stirring till basic to litmus. A saturated solution of S-
benzyl isothiouronium chloride was added and the carboxylic acid was recovered as S-benzyl iso-
thiouronium salt from the solution.
Acknowledgements
SC and GB are thankful to CSIR, New Delhi, India, for grant of Junior and Senior Research Fellowships.
References
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