Faculty of Pharmacy, Medical University of Sofia, Dunav 2, BG-1000 Sofia,
Bulgaria
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Received: 20 January 2001 / Accepted: 15 May 2001 / Published: 25 May 2001
Keywords: Mannich base, cyclohexanone, aminoketones, aminomethylation, primary amine
The Mannich bases of cyclohexanone with benzylamine and 3,4-methylenedioxybenzylamine
hydrochlorides have been prepared in moderate yields using aqueous formaldehyde
solution [1]. We report now the synthesis of an analogous product from
2-phenylethylamine. A mixture of cyclohexanone (2.00 g, 0.02 mol), paraformaldehyde
(1.20 g, 0.04 mol) and 2-phenylethylamine hydrochloride (3.18 g, 0.02 mol)
was refluxed under stirring in anhydrous ethanol (15 ml) for 5 h (TLC monitoring).
The reaction mixture gradually turned into a solution. The solvent was
then removed under reduced pressure and the residue was triturated with
ice-cooled acetone (20 ml). The separated crystals were filtered, washed
with cold acetone, recrystallized from n-butanol and air-dried.
Yield: 3.00 g (52 %) of colorless crystals.
TLC homogeneous product (TLC: silica gel Merck GF254 Al-sheets,
eluted by chloroform-ethanol 3:1).
Mp. 155-156 ºC (n-butanol).
1H NMR (300 MHz, d6-DMSO): 1.23-1.42 (m, 1H), 1.50-1.84 (m, 3H), 1.88-2.05 (m, 1H), 2.09-2.35 (m, 2H), 2.35-2.47 (m, 1H), 2.75-2.83 (m, 1H), 2.92-3.06 (m, 3H), 3.06-3.18 (m, 2H), 3.18-3.29 (m, 1H), 7.20-7.38 (m, 5Harom.), 9.15 (br. s, N+H2).
FT IR (fluorolube): 3023, 2936, 2861, 2750, 2705, 1705 (C=O), 1593, 1455, 1424, 1390.
FAB-MS [glycerol; m/z (%)]: 499 (2M + HCl + H+(super)), 463 (2; 2M + H+), 324 (6; MH+ + glycerol), 232 (100; MH+= C15H22NO+), 140 (6), 134 (25), 105 (13).
Anal. calcd. for C15H22NOCl (267.80): C 67.28, H 8.28, N 5.23, Cl 13.24; found C 67.24, H 8.27, N 5.23, Cl 13.36.
Reference
1. Mannich C.; Hieronimus O. Ber. Dtsch. Chem. Ges. 1942, 75, 49-55.
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