C. G. ADAM, G. G. FORTUNATO AND P. M. MANCINI
Scheme 3.
spectrum corresponding to the aldehyde in pure AcN
General methods
([aldehyde] ¼ 10ꢁ4 M) (dot line); (b) the spectra obtained as
EAN is added to the aldehyde solution, at different concen-
trations of the IL (solid line), and (c) the spectrum corresponding
to the pure imine product in AcN. (dash-dot line). From the
analysis of the plots, it can be concluded that, as EAN
concentration in the media is increased, a new species appears
at lmax near to 400 nm, corresponding to the formation of the
imine product.
All the products were obtained stirring the reaction mixture over
night at room temperature. Yields were determined by weight,
purity by 1H and 13CNMR and mass spectroscopy. All NMR spectra
were taken at a 500 MHZ Bruker Unity instrument in CDCl3. These
values were verified with those previously reported.[41,42]
The spectrophotomectric measurements and kinetic exper-
iments were preformed on PerkinElmer Lambda 40 UV/Vis
spectrophotometer, equipped with a thermostatic cell holder.
The kinetics of the reactions was run under pseudo-first order
conditions with the substrate (FDNB) as a minor component at
258C.
In the light of these results, a simplified reaction scheme is
presented in Scheme 3.
N-(2,4-dinitrophenyl) ethylamine was obtained by the reac-
tion of FDNB, PIP, and EAN (1:10:20, respectively). The reaction
was followed by TLC (Hexane/EtOAc, 10:1). The reaction mixture
was cleaned up by chromatography silica gel column.
4-[(Ethylimino) methyl]-N,N-dimethylbenzenamine was
obtained as yellow solids by the reaction of 4-(dimethyl)-
aminobenzaldehyde and with EAN (1:7), measured pH value for
this mixture was about 6. The solid obtained was washed
repeatedly with diethyl ether (2 ꢀ 5 ml) to give a 97% yield.
4-[(ethylimino) methyl] phenol was obtained by the reaction
of 4-(hydroxy)benzaldehyde and with EAN (1:8) measured pH
value for this mixture was about 6. The imine was extracted from
the reaction mixture with dichlomethane, and purified by
chromatography silica gel column. This product was obtained
with a 64% yield.
CONCLUSIONS
Based on the overall results presented in this work, we can
conclude the following:
ꢅ For the SNAr reactions studied, it was possible to confirm that
EAN can take part in an acid–base equilibrium with amines,
even at very low concentrations ([EAN] ꢂ 0.05 M), generating a
nucleophile species which can participate in the reaction. The
substitution product, N-(2,4-dinitrophenyl) ethylamine was
obtained and therefore the kA second-order rate constant
for ethylamine could be determinated.
ꢅ For the nucleophilic addition reactions of amines to substi-
tuted aromatic aldehydes, where acid catalysis is required, the
use of EAN seems to be convenient. The EAN can take part in an
acid–base equilibrium with aromatic aldehydes substituted by
electron-donating group. The imine products from the
selected aldehyde could be obtained, confirming the dual
Acknowledgements
¨
behavior of EAN as Bronsted acid and potential nucleophile.
The participation of these salts as potential nucleophiles in this
type of process allows developing new synthesis routes.
Financial support form Universidad Nacional del Litoral (U.N.L),
C.A.I R D 2006 (projects: 33-183 and 33-182) and Agencia Nacio-
´
´
nal de Promocion Cient´ıfica y Tecnica-U.N.L (Project PIC-TO:
The model reactions presented in this work constitute suitable
examples of how the microscopic feature of a reactive system can
be modified by adding aliquots of a protic ionic liquid to a
molecular solvent. The acidity of the resultant binary mixtures
plays a key role in acid-catalyzed reactions with the possibility of
replacing traditional acid reagents. Moreover, the whole reactive
system can be modulated with the aim of not only to promote
acid-catalyzed reactions but also to generate nucleophilic species
in situ. In connection with this, the design of ionic liquids can be
formulated according to the particular requirements of a reactive
system.
36189) is gratefully acknowledged.
REFERENCES
[1] J. D. Holbrey, K. R. Seddon, Clean Products and Processes 1999, 1,
223–236.
[2] T. Welton, Chem. Rev. 1999, 99, 2071–2083.
[3] P. Wassercheid, W. Keim, Angew. Chem. Int. Ed. Engl. 2000, 39,
3772–3789.
[4] H. Olivier-Bourbigou, L. Magna, J. Mol. Catal. A: Chem. 2002, 182–183,
419–437.
[5] H. Z. Zhao, Phys. Chem. Liq. 2003, 41, 545–557.
[6] C. F. Poole, J. Chromatgr. A 2004, 1037, 49–82.
[7] C. T. Martins, B. M. Sato, O. A. El Seoud, J. Phys. Chem. B 2008, 112,
8330–8339.
[8] P. Wasserchied, T. Welton, Ionic Liquids in Synthesis, Wiley-VCH,
Weinheim, 2007.
[9] R. Rogers, K. R. Seddon, Ionic liquids as Green Solvents: Progress and
Prospects, ACS, Washington DC, 2003.
[10] C. Reichardt, Pure Appl. Chem 2004, 76, 1903–1919.
[11] C. Reichardt, Green Chem. 2005, 7, 339–351.
EXPERIMENTAL
Materials
All the amines, reagents and the solvents were prepared and/or
purified as reported previously.[30–34] The EAN was prepared from
a concentrated aqueous solution of ethylamine (70%) and nitric
acid (70%).[12,13]
Copyright ß 2008 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2009, 22 460–465