Water → 2-Thiophen-2-yl-piperazine

Participants

Reaction Steps

A solution of ethylenediamine (4.1 g, 0.068 mol) in ethanol (25 ml) is added dropwise to a solution of 2-thienylglyoxal hydrate [prepared by the procedure of F. Kipnis and J. Ornfelt, J. Amer. Chem. Soc. 68, 2734 (1946)] (10.0 g, 0.063 mol) in ethanol (250 ml) at 0° C. under an atmosphere of dry nitrogen. The cooling bath is removed and the reaction mixture stirred for an additional 1.5 h. Sodium borohydride (4.5 g, 0.126 mol) is added all at once, and a cooling bath used to control the exothermic reaction. Stirring is continued for an additional 18 h. Water (25 ml) is added, and the ethanol removed under reduced pressure. The remaining aqueous solution is extracted with methylene chloride (3×100 ml) and the extracts dried with potassium carbonate. Removal of the solvent under reduced pressure gives 2-(2-thienyl)piperazine as an off-white solid. An analytical sample is obtained by addition of an ethereal solution of the base to an ethereal solution of oxalic acid dihydrate. The resulting precipitate is washed with diethyl ether and methanol, and the free base (m.p. 81°-83° C.) is obtained with a saturated solution of potassium carbonate.

Provenance & Evidence