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Schiff base formation by condensation of a diketone with amine; 2,6-bis[1-(2-isopropylphenylimino)ethyl]pyridine

SyntheticPage 436
DOI: 10.1039/SP436
Submitted Jul 06, 2010, published Jul 09, 2010
Giles Theaker (g.w.theaker@warwick.ac.uk)
A contribution from Scott group, Warwick University
Reaction Scheme: Schiff base formation by condensation of a diketone with amine

Chemicals Used

2,6-diacetylpyridine, 98% (Sigma-Aldrich)
2,6-diisopropylaniline, 98% (Sigma-Aldrich)
glacial acetic acid
ethanol

Procedure

2,6-diacetylpyridine (1.50 g, 9.19 mmol) was dissolved in ethanol (25 ml) in a 50 ml round bottom flask. To this was added 2,6-diisopropylaniline (3.50 ml, 3.25 g, 18.38 mmol, 2 eq.) and 2 drops of glacial acetic acid. The solution was heated to reflux for ca 20 h. After this time, a crude sample was taken and shown by NMR to be monosubstituted 2,6-diacetylpyridine. A further 1 ml of 2,6-diisopropylaniline was added, and reflux continued for a further 24 h. Upon cooling light yellow crystals were formed. These were collected by filtration and recrystallised from ethanol. (1.84 g, 41 %).

Author's Comments

Secondary ketimines generally require longer reaction times and a small amount of acid catalyst, unlike secondary aldimines (though in both cases, substituants on either reactant may have significant effects on reaction rate).
These compounds are used as ligands for Brookhart/Gibson olefin polymerization catalysts; see page 437.

Data

 1H NMR (400 MHz, CDCl3): δ 8.41 (2H, d, 3J = 8 Hz, Ar), 7.86 (1H, t, 3J = 8 Hz, Ar), 7.11 (4H, d, 3J = 7 Hz, Ar), 7.03 (2H, t, 3J = 7 Hz, Ar), 2.70 (4H, sept., 3J = 7 Hz, CHMe2), 2.20 (6H, s, NCMe), 1.19 (24H, d, 3J = 7 Hz, CHMe2).

13C NMR (100 MHz, CDCl3): δ 166.9 (CN), 155.2, 146.5 (Ar q), 136.9 (Ar), 135.8 (Ar q) 123.6, 123.0, 122.2 (Ar), 28.3 (CMe2), 23.2 (Me), 22.9 (CMe2).

Lead Reference

G. J. P. Britovsek, V. C. Gibson, B. S. Kimberley, P. J. Maddox, S. J. McTavish, G. A. Solan, A. J. P. White and D. J. Williams, Chem. Commun., 1998, 849-850 doi:10.1039/a801933i
B. L. Small, M. Brookhart and A. M. A. Bennett, J. Am. Chem. Soc., 1998, 120, 4049-4050 doi:10.1021/ja9802100

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Keywords: amination, amines, Condensation, heterocyclic compounds, imines, ketones, Schiff base