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Schiff base condensation with bulky amine; (E)-2,6-diisopropyl-N-(pyridin-2-ylmethylene)aniline

SyntheticPage 719
DOI: 10.1039/SP719
Submitted Feb 11, 2014, published Feb 27, 2014
Leonardo ALVAREZ (leonardo.alvarezgalan@ucr.ac.cr)
Reaction Scheme: <IMG src="/images/empty.gif">Schiff base condensation with bulky amine<IMG src="/images/empty.gif">

Chemicals Used

Piconilaldehyde 99% (Aldrich)
2,6-diisopropylaniline 97% (Aldrich)
Ethanol anhydrous (Sigma-Aldrich)
n-pentane 98% (Sigma-Aldrich)

Procedure

An oven dried  50 ml round bottom  two necked flask, equipped with a spin bar, a septa, a water condenser and a Nitrogen inlet at the top,  was charged  with 12.5 mL of anhydrous ethanol and 1.03 g (9.6 mmole) of freshly distilled piconilaldehyde. After mixing, 2.0 mL (10.6 mmole) of 2,6-diisopropylaniline were added through the septa with the aid of an hypodermic syringe and  the reaction mixture was brought to reflux using a heating mantle.  Reflux was kept for an hour and then the system was let to cool down to room temperature. Solvent and reagent excess were removed by means of a rotatory evaporator to give a yellow solid in quantitative yield.  The product is sufficiently pure for most purposes but it may be recrystallized from n-pentane at -25oC to give yellow crystals with yields oscillating from  80-85%. 

Author's Comments

  • Piconilaldehyde must be distilled prior to use.  New bottles of this compound contain a colored product with colors going from yellow to dark orange. The colored impurities can be easily removed by means of a distillation under reduced pressure.  After distilled, this aldehyde must be protected fron light by means of Al foil in order to keep it colorless. 
  • 2,6-diisopropylaniline can be used directly from the bottle if the bottle is less than 6 months old.  For older bottles a fast disitllation under reduced pressure removes all impurites.
  • It is noteworthy to mention that in this particular reaction, there is no need for an acidic catalyst and water does not need to be removed.  This particular feature becomes handy when the reaction needs to be performed at a small scale and a micro  Dean-Stark trap is not at hand.
  • Refux time should me monitored.  As metioned before, when reaching the reflux temperature, the reaction must not be heated more than an hour.  Longer heating times have shown to decrease the amount of desired products and in sometimes give complex mixtures.

Data

H-NMR (CDCl3, 400 MHz):  8.82 (d, 1H, J = 4.0 Hz), 8.41 (s, 1H), 8.36 (d, 1H, J = 8.0 Hz), 7.94 (t, 1H, J = 8.0 Hz), 7.50 (ddd, 1H, J = 12.0, 4.0, 1.2 Hz), 7.28-7.20 (m, 3H), 3.06 (heptuplet, 2H, J = 6.8 Hz), 1.27 (d, 12H, J = 6.87 Hz). C-NMR (CDCl3, 100 MHz): 163.1, 154.5, 149.8, 148.5, 137.4, 136.9, 125.4, 124.6, 123.2, 121.5, 28.1, 23.6.

Lead Reference

L. X. Alvarez, PhD Thesis, Université Joseph Fourier, 2009.

Other References

(1) Y. Dong, R. Fan, P. Wog, Y. Yang, Acta Cryst., 2012, 01427. DOI: 10.1107/S1600536812015905
(2)  J. Wu, B. N.  Stanzl, T. Ritter, J. Am. Chem. Soc., 2010, 138, 13214. DOI:10.1021/ja106853y
(3) S. Zai, F. Liu, H. Gao, C. Li, G. Zhou, S. Cheng, L. Guo, L, Zhang, F. Zhu, Q. Wu, Chem. Commun., 2010, 46, 4321. DOI: 10.1039/c000176g

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Keywords: addition, aldehydes, amination, amines, Bi-dentate ligand, Imine Formation, nucleophilic