Crystal hydrates LnCl3?6H2O and Ln(NO 3)3?6H2O as catalysts in the synthesis of 2,3,5-trialkylpyridines by reaction of ammonia with aliphatic aldehydes

Full text of DOI:10.1134/S1070428007090291

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2007, Vol. 43, No. 9, pp. 1417–1418. © Pleiades Publishing, Ltd., 2007.
Original Russian Text © R.G. Bulgakov, S.P. Kuleshov, A.R. Makhmutov, U.M. Dzhemilev, 2007, published in Zhurnal Organicheskoi Khimii, 2007, Vol. 43,
No. 9, pp. 1420–1421.
SHORT
COMMUNICATIONS
Crystal Hydrates LnCl3·6H2O and Ln(NO3)3·6H2O as Catalysts
in the Synthesis of 2,3,5-Trialkylpyridines by Reaction
of Ammonia with Aliphatic Aldehydes
R. G. Bulgakov, S. P. Kuleshov, A. R. Makhmutov, and U. M. Dzhemilev
Institute of Petroleum Chemistry and Catalysis, Russian Academy of Sciences,
pr. Oktyabrya 141, Ufa, 450075 Bashkortostan, Russia
e-mail: ink@anrb.ru
Received May 10, 2007
DOI: 10.1134/S1070428007090291
sion of ammonia, and a catalytic amount of [Ln]
(2 mol %) is sufficient to catalyze the reaction.
Systems based on Zr, Fe, Cr, Co, Ni, Pd, and Mg
complexes and Et3Al are efficient catalysts in the syn-
thesis of alkyl-substituted pyridines [1]. Disadvantages
of these systems include high reaction temperature
(180–200°C) and pressure and the use of flammable
and explosive Et3Al. By contrast, trifluoromethanesul-
fonate lanthanide complexes Ln(OTf)3 ensure prepara-
tion of pyridine bases at room temperature in the ab-
sence of Et3Al [2–4]. However, almost stoichiometric
amounts (up to 50%) of Ln(OTf)3 are necessary to
attain the maximal yield (40–80%) of the target prod-
ucts. Therefore, search for new more effective catalysts
for the synthesis of alkyl-substituted pyridines is
an important problem. We previously found [5] that
LnCl3·6H2O crystal hydrates exhibit a high catalytic
activity in the synthesis of alkyl-substituted quinolines
and phenanthrolines at 20°C. In the present work we
examined the catalytic activity of LnCl3 ·6H2O and
Ln(NO3)3 ·6H2O ([Ln]) in the synthesis of 2,3,5-tri-
alkylpyridines I by reaction of ammonia with aliphatic
aldehydes.
Apart from the corresponding pyridines, the reac-
tion mixtures contained unidentified tarry materials
(18–26%) which remained in the still residue after
vacuum fractionation; presumably, they were formed
by crotonization of the initial aldehydes. With rise in
temperature, the yield of the target products decreased,
while the amount of tars increased. The aldehyde and
solvent nature only slightly influenced the selectivity
and the yield of compounds I. In the reaction of
ammonia with butyraldehyde, the examined lanthanide
catalysts can be arranged in the following series with
respect to the yield of pyridine Ia (%): PrCl3·6H2O
(82) > NdCl3 · 6 H2O (78) > TbCl3 · 6 H2O (61);
Pr(NO3)3 · 6 H2O (80) > Nd(NO3)3 · 6 H2O (77) >
Tb(NO3)3·6H2O (60). Thus PrCl3·6H2O possesses the
strongest catalytic activity. The catalytic activity weak-
ens as the lanthanide ionic radius decreases.
After addition of aldehyde to an aqueous ammonia
solution (before addition of catalyst), it is necessary to
separate the organic phase from aqueous, and the cata-
lyst should be added to the organic phase. Our attempts
to carry out the process in a one-pot mode, by mixing
in succession a solution of catalyst, aqueous ammonia,
and aldehyde, resulted in precipitation of Ln(OH)3, and
the catalysis became ineffective.
Compounds I were formed in up to 82% yield at
20°C (see Experimental) in polar solvents (dimethyl-
form-amide and dimethyl sulfoxide) in the presence of
[Ln]. The process is characterized by complete conver-
R
R
[Ln], 20°C
NH3
+ 3RCH2CHO
Thus lanthanide crystal hydrates LnCl3·6H2O and
Ln(NO3)3·6H2O make it possible to perform conden-
sation of ammonia with aldehydes under mild condi-
tions (20°C) and ensure preparation of trialkyl-substi-
tuted pyridines I in up to 82% yield. The examined
R
N
Ia–Ic
R = Et (a), Pr (b), Bu (c); [Ln] = LnCl3·6H2O, Ln(NO3)3·
6H2O; Ln = Pr, Nd, Tb.
1417

BULGAKOV et al.
1418
catalysts are more advantageous than Ln(OTf)3 due to
their low cost and accessibility; they exhibit catalytic
effect at much lower concentration and provide direct
formation of substituted pyridines rather than of the
corresponding pyridinium salts.
(C8), 31.46 t (C11), 34.30 t (C7), 133.23 d (C4), 135.54 s
(C3), 136.82 s (C5), 141.47 d (C6), 158.10 s (C2).
Found, %: C 81.93; H 11.55; N 6.52. C15H25N. Cal-
culated, %: C 82.19; H 11.42; N 6.39.
3,5-Dibutyl-2-pentylpyridine (Ic). Yield 74%
1
(DMF), bp 105–108°C (1 mm). H NMR spectrum, δ,
Substituted 2,3,5-trialkylpyridines. A glass finger
reactor equipped with a magnetic stirrer was charged
with 60 mmol of the corresponding aldehyde and
cooled to 0°C, 1.5 ml (20 mmol) of 25% aqueous
ammonia was added, and the mixture was vigorously
stirred for 1–2 min. The mixture was allowed to settle
down, the upper organic layer was withdrawn, a solu-
tion of 0.4 mol of the catalyst in 2 ml of DMF or
DMSO was added to the organic phase, and the mix-
ture was stirred for 24 h at 20°C. The product was
extracted into diethyl ether (3×50 ml), the extracts
were combined and dried over MgSO4, the solvent was
distilled off, and the residue was subjected to fractional
distillation under reduced pressure.
ppm: 0.92 m (9H, CH3), 1.32 m (14H, CH2), 2.50 q
(4H, CH2), 2.70 m (2H, CH2), 7.10–8.20 d (2H, 4-H,
6-H). 13C NMR spectrum, δC, ppm: 13.07 q (C19),
13.07 q (C15), 14.11 q (C11), 22.26 t (C18), 22.26 t
(C14), 22.49 t (C10), 28.40 t (C8), 30.44 t (C12), 32.64 t
(C17), 32.87 t (C9), 33.01 t (C13), 33.52 t (C16), 34.56 t
(C7), 135.22 d (C4), 136.28 s (C3), 136.55 s (C5),
145.89 d (C6), 159.06 s (C2). Found, %: C 82.27;
H 11.93; N 5.80. C18H31N. Calculated, %: C 82.76;
H 11.88; N 5.36.
1
The H and 13C NMR spectra were recorded on
a Jeol FX 90Q spectrometer using CDCl3 as solvent
and tetramethylsilane as internal reference. The ele-
mental compositions were determined on a Carlo Erba
106 analyzer.
3,5-Diethyl-2-propylpyridine (Ia). Yield 82%
1
(DMF), 80% (DMSO), bp 75–78°C (1 mm). H NMR
This study was performed under financial support
by the Federal Science and Innovation Agency (state
contract no. 02.434.11.2026).
spectrum, δ, ppm: 0.98 m (3H, CH3), 1.18 m (6H,
CH3), 1.32 m (2H, CH2), 2.54–2.66 m (4H, CH2),
2.72 q (2H, CH2), 7.25–8.21 d (2H, 4-H, 6-H).
13C NMR spectrum, δC, ppm: 14.06 q (C13), 14.70 q
(C11), 15.19 q (C9), 22.79 t (C12), 24.89 t (C8), 25.47 t
(C10), 36.30 t (C7), 135.29 d (C4), 136.07 s (C3),
136.36 s (C5), 145.83 d (C6), 157.04 s (C2). Found, %:
C 81.92; H 10.25; N 7.83. C12H19N. Calculated, %:
C 81.35; H 10.73; N 7.92.
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2-Butyl-3,5-dipropylpyridine (Ib). Yield 77%
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1
(DMF), bp 80–82°C (1 mm). H NMR spectrum, δ,
ppm: 0.90 m (9H, CH3), 1.40 m (2H, CH2), 1.53 m
(6H, CH2), 2.53 m (4H, CH2), 2.63 m (2H, CH2), 7.17–
8.15 d (2H, 4-H, 6-H). 13C NMR spectrum, δC, ppm:
13.11 q (C16), 13.60 q (C13), 14.25 q (C10), 22.90 t
(C15), 23.31 t (C12), 24.23 t (C9), 25.07 t (C14), 28.63 t
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RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 9 2007