Synthesis and molecular structure of the 1-phenyl-2-(2-pyridyl)ethanol intermediate obtained from the condensation reaction of 2-picoline and benzaldehyde

Article abstract of DOI:10.1007/s11164-013-1471-y

The 1-phenyl-2-(α-pyridyl)ethanol [or 1-phenyl-2-(2-pyridyl)ethanol] compound was obtained from the Knoevenagel condensation reaction between 2-methylpyridine with benzaldehyde without catalyst or solvent. The compound was characterized by IR, ¹H-NMR, and by single crystal X-ray diffraction. The X-ray structure clearly revealed that the compound crystallizes in a monoclinic system with centrosymmetric space group, P2₁/c, with Z′ = 1. The unit cell dimensions are a = 5.2481(3), b = 8.2862(4), c = 23.8498(14) ?, and β = 96.761(5). The crystal structure showed the formation of one intermolecular hydrogen bond O-H···N between the oxygen atom of the O-H and the nitrogen atom of the pyridine group of the adjacent molecule. The crystallography data gave evidence that the intermediate compound is a new stable 1-phenyl-2-(2-pyridyl)ethanol intermediate which presents an interesting relationship between stability and hydrogen bonds formation in the structure for obtaining similar compounds that have been proposed in the literature. Also, it is shown that it is just before the dehydration process which yields the trans double bond of the 1-phenyl-2-(2-pyridyl)ethene.

Full text of DOI:10.1007/s11164-013-1471-y

Res Chem Intermed (2015) 41:3563–3572
DOI 10.1007/s11164-013-1471-y
Synthesis and molecular structure of the 1-phenyl-2-
(
2-pyridyl)ethanol intermediate obtained
from the condensation reaction of 2-picoline
and benzaldehyde
M. Judith Percino
•
V ´ı ctor M. Chapela
Guillermo Soriano-Moro
•
Margarita Cer o´ n
M. Eugenia Castro
•
•
Received: 11 November 2012 / Accepted: 26 October 2013 / Published online: 14 November 2013
Ó Springer Science+Business Media Dordrecht 2013
Abstract The 1-phenyl-2-(a-pyridyl)ethanol [or 1-phenyl-2-(2-pyridyl)ethanol]
compound was obtained from the Knoevenagel condensation reaction between
2-methylpyridine with benzaldehyde without catalyst or solvent. The compound was
1
characterized by IR, H-NMR, and by single crystal X-ray diffraction. The X-ray
structure clearly revealed that the compound crystallizes in a monoclinic system with
0
centrosymmetric space group, P2 /c, with Z = 1. The unit cell dimensions are
1
˚
a = 5.2481(3), b = 8.2862(4), c = 23.8498(14) A, and b = 96.761(5)°. The crystal
structure showed the formation of one intermolecular hydrogen bond O–HÁÁÁN
betweenthe oxygen atom of the O–H and the nitrogen atom of the pyridine group of the
adjacent molecule. The crystallography data gave evidence that the intermediate
compound is a new stable 1-phenyl-2-(2-pyridyl)ethanol intermediate which presents
an interesting relationship between stability and hydrogen bonds formation in the
structure for obtaining similar compounds that have been proposed in the literature.
Also, it is shown that it is just before the dehydration process which yields the trans
double bond of the 1-phenyl-2-(2-pyridyl)ethene.
Keywords 1-Phenyl-2-(2-pyridyl)ethanol Á X-ray single crystal structure Á
Intermediate Á Stilbazole Á 2-Styrylpyridine
Introduction
The reaction of an aromatic aldehyde with a methylpyridine, classified as a
Knoevenagel condensation, gives stable products with trans configuration identified
M. J. Percino (&) Á V. M. Chapela Á M. Cer o´ n Á G. Soriano-Moro Á M. E. Castro
Lab. de Pol ´ı meros, Centro de Qu ´ı mica, Instituto de Ciencias, Universidad Aut o´ noma de Puebla,
Complejo de Ciencias, ICUAP, Edif. 103 H, 22 Sur y San Claudio,
C.P. 72570 Puebla, Puebla, Mexico
e-mail: judith.percino@correo.buap.mx
123

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M. J. Percino et al.
as styrylpyridines, also known as stilbazoles [1]. The Knoevenagel condensation has
been defined as the reaction between an aldehyde or ketone with any compound
having an active methyl and a methylene group being brought on an organic base,
ammonia or their salts [2]. The activation of the methylene group is due to the direct
attachment of one group such as a nitro, cyano, or acyl moiety, and, in most cases,
two such groups are required to provide sufficient activation [3].
In contrast, the identification of an intermediate from the condensation of
-methylpyridine with benzaldehyde to form 2-styrylpyridine has been reported to
2
proceed in two stages [4–6]. First is the formation of the alkine group (–CH2–
CHOH–), which is reversible [6]. When the reaction mixture of the benzaldehyde
and 2-picoline was boiled for 10 h, 1-phenyl-2-(2-pyridyl)-ethanol (the alkine) and
the corresponding stilbazole were formed as a mixture [6]. When intermediate
alcohols were heated in water between 140 and 200 °C, they were partly converted
into the picoline and the corresponding aldehyde. The second stage is the
dehydration of the intermediate alcohols by a condensing agent to yield the
stilbazoles (–CH=CH– group). The condensation of 2-picoline with p-nitrobenzal-
0
dehyde in N,N-DMF or DMSO in the presence of acetic acid gives the 1-(4 -
0
nitrophenyl)-2-(a-pyridyl)ethanol which is readily converted to 2-(4 -nitrosty-
ryl)pyridine by heating at 115 °C in acetic acid and acetic anhydride.
Taking into account previous investigations of methylpyridines with aromatic
aldehyde condensation reactions, and in order to synthesize new conjugated
compounds (styrylpyridines) with light emitting properties, we have applied the
Knoevenagel synthetic method under catalyst- and solvent-free conditions. The
method used has been important because is a straightforward and clean way to
obtain different styrylpyridines [7] and interesting intermediates such as the
1
-phenyl-2-(4-pyridyl)ethanol, 1-(p-fluorophenyl)-2-(a-pyridyl)ethanol, as well as
-(p-fluorophenyl)-2-(2-pyridyl)ethene, 2-styrylpyridine, and 2,6-distyrylpyridine,
1
which have been previously obtained and characterized by single crystal X-ray
diffraction [8–11].
Kinetic studies [12] on the reaction of 2-picoline and benzaldehyde under
catalyst- and solvent-free conditions, followed by HPLC and detection by UV-
spectroscopy, allowed us to detect the presence of the intermediate 1-phenyl-2-(2-
pyridyl)ethanol and 2-styrylpyridine just 20 min after the reaction began. However,
it was not possible to isolate the 1-phenyl-2-(2-pyridyl)ethanol compound because it
is readily converted into the corresponding 2-styrylpyridine. On the other hand, the
reaction of 4-picoline with benzaldehyde in the absence of a condensing agent
produced the compound 4-styrylpyridine, as well as the intermediate 1-phenyl-2-(4-
pyridyl)ethanol or (4-[2-(1-hydroxy-1-phenyl)ethyl]pyridine) [13], which was
separated and characterized by X-ray [8]. Furthermore, the 5-ethyl-2-(4-nitro-7-
ol-styryl)-pyridine intermediate may be obtained from 5-ethyl-2-picoline and
p-nitrobenzaldehyde, but only in the presence of benzoic anhydride as a condensing
agent [14].
Our group has pursued the syntheses of different styrylpyridines and stilbenes
with the Knoevenagel condensation, without catalyst and under solvent-free
conditions. Recently, that synthetic method was used to synthesize different
substituted phenylpyridylacrylonitrile-conjugated compounds [15, 16]. In the
1
23

1-Phenyl-2-(2-pyridyl)ethanol intermediary
3565
Scheme 1 The synthesis of the title compound by Knoevenagel condensation
present work, we used the Knoevenagel condensation under catalyst-free conditions
for the condensation reaction of 2-picoline and benzaldehyde which allowed us to
obtain the 1-phenyl-2-(2-pyridyl)ethanol compound and the dehydration compound
1
-phenyl-2-(2-pyridyl)ethene (Scheme 1). The determination of the type of product
was dependent on the reaction temperature used for each condensation reaction. To
the best of our knowledge, the crystal structure of the intermediate compound has
1
not been reported before. Also, the compound was characterized by IR and H-NMR
spectroscopy.
Experimental
Synthesis of 1-phenyl-2-(2-pyridyl)ethanol
The condensation reaction was performed according to Scheme 1. The compound
1
-(phenyl)-2-(a-pyridyl)ethanol was obtained from reactants 2-methylpyridine
50 mmol) (Aldrich) and benzaldehyde (50 mmol), (Productos Qu ´ı micos Monter-
(
rey) at the molar relationship 1:1, which were freshly distilled and then refluxed in
the absence of a condensing agent at 120 °C for 41 h in constant stirring. Changes
in the coloration of the mixture were observed through the reaction. Initially, the
mixture was colorless, then it was yellow, then orange, and finally a red-brown
mixture was obtained. The oily and red-brown reaction mixture was distilled at
9
2 °C to evaporate the chemical reagents that did not react. The mixture was treated
with a solution of NaOH, 2 N (643 mL) to precipitate a pale brown powder after
constant stirring during 24 h, which was filtered and dried at vacuum. The product
was obtained as a mixture of 1-phenyl-2-(2-pyridyl)ethanol with the corresponding
trans compound. To obtain the intermediate, the mixture was treated with hot
hexane to dissolve 1-phenyl-2-(2-pyridyl)ethanol and by solvent evaporation at
ambient temperature, then the final product was obtained as a yellow powder.
Finally, by the evaporation standard method, the compound was obtained in single
crystal form.
123

3566
M. J. Percino et al.
Characterization of 1-phenyl-2-(2-pyridyl)ethanol
The compound was obtained with 4 % yield. Its melting point was of 110 °C, which
was measured using with a SEV apparatus (0–300 °C) (Sistemas y Equipos de
Vidrio, SEV Mexico) and reported as the uncorrected value. It was characterized by
1
IR and H-NMR spectroscopy. The IR spectrum of the compound was recorded on a
750 FT-IR Vertex spectrophotometer (model 70; Bruker Optics, Germany) by
1
attenuated total reflectance ATR. H-NMR spectra were obtained using the
compound dissolved in CDCl on a Varian 300-MHz NMR spectrometer (Varian
3
NMR, Walnut Creek, CA, USA). The structure of the intermediary was confirmed
by single crystal X-ray crystallography. All reflection intensities were measured at
1
10(2) K using a KM4/Xcalibur (detector: Sapphire3) with enhanced graphite-
˚
monochromated Mo Ka radiation (k = 0.71073 A) using the CrysAlisPro program
v.1.171.35.11; Oxford Diffraction, 2011).
(
X-ray crystallography
All reflection intensities were measured using a KM4/Xcalibur (detector: Sap-
˚
phire3) with enhanced graphite-monochromated Mo Ka radiation (k = 0.71073 A)
under the program CrysAlisPro (v.1.171.34.36; Oxford Diffraction, 2010). The
program CrysAlisPro was used to refine the cell dimensions and for data reduction.
The structure was solved with the program SHELXS-97 (Sheldrick, 2008) and was
2
refined on F with SHELXL-97 (Sheldrick, 2008) [17]. Analytical numeric
absorption corrections based on a multifaceted crystal model were applied using
CrysAlisPro (v.1.171.34.36; Oxford Diffraction, 2010). The temperature of the data
collection was controlled using the system Cryojet (manufactured by Oxford
Instruments). The H atoms were placed at calculated positions using the instructions
AFIX 13, AFIX 23, AFIX 43, or AFIX 147 with isotropic displacement parameters
having values 1.2 or 1.5 times U(eq) of the attached C or O atoms.
Results and discussion
The IR spectrum (Fig. 1) showed the characteristic bands that confirmed that the
compound obtained was the intermediate. These bands include a broad band at
-
1
3
of a stronger H-bonded –OH [16, 18], a strong band at 1,056 cm assigned to the
,189 cm which is typically for the mO–H due to the –OH group in the presence
-1
-
1
mC–O of the alcohol moiety, as well as a strong band at 1,301 cm , corresponding
to a bending vibration of the –OH group. When the trans compound was formed,
1
these bands disappeared [9]. From the H-NMR spectrum (Fig. 2), the main
evidence of the structure of the isolated compound 1-phenyl-2-(2-pyridyl)ethanol
was the dd at 5.20–5.12 ppm for 1H with a J = 11.7, 7.5 and 4.2 Hz assigned to the
H of the chiral carbon; the multiplet at 3.21–3.07 ppm with an integration of 2H
with J = 11.4, 7.2, and 4.2 Hz assigned to –CH –, and the singlet at 5.78 ppm
2
1
assigned to the proton of the OH group. The principal difference between the H-
NMR spectra of the title compound and the reported 2-styrylpyridine compound
1
23

1-Phenyl-2-(2-pyridyl)ethanol intermediary
3567
Fig. 1 IR spectrum of the 1-phenyl-2-(2-pyridyl)ethanol
1
Fig. 2 H-NMR of the 1-phenyl-2-(2-pyridyl)ethanol in CDCl
3
were the two doublets at 7.65–7.60 and 7.35–7.30 ppm with an integrated intensity
of one and with a J = 15.0 and J = 15.0 Hz, characteristic of vinylic protons
[
9, 18]. The structure of the intermediate rac-1-phenyl-2-(2-pyridyl)ethanol was
123

3568
M. J. Percino et al.
Table 1 Summary of the crystal data and structure refinement for compound 1-phenyl-2-(2-
pyridyl)ethanol
Compound
1-(Phenyl)-2-(a-pyridyl)ethanol
Color/habit
Colorless/lath
Chemical formula
Crystal system
Temperature
13
C H13NO
Monoclinic
110(2) K
Space group
1
P2 /c
˚
a = 5.2481(3) A
Unit cell dimensions
˚
b = 8.2862(4) A
˚
c = 23.8498(14) A
a = 90.00°
b = 96.761(5)°
c = 90.00°
3
˚
1,029.94(10) A
Volume
Z
4
Formula weight
Density (calc.)
Absorption coefficient (l)
F(000)
199.24
-
3
1.285 g cm
-1
0.081 mm
424
Diffractometer/scan
KM4/Scalibur (detector: Sapphire3) Oxford Diffraction Ltd., 2010
2
h range for data collection (°)
1.72°–25.138
11,111
Reflections collected
Independent reflections
Absorption correction range
Goodness-of-fit
1,884 (Rint = 4.09 %)
0.980–0.994
1.078
Final R indices (I [ 2r(I))
Final R indices (all data)
Radiation
R
1
1
= 5.48 %, wR
= 6.09 %, wR
2
2
= 13.86 %
R
= 14.18 %
˚
Mo-K
0
a
(k = 0.71073 A)
0
Crystal dimensions (mm)
hkl range
0.41 9 0.19 9 0.07
-6 B h B 6, -9 B k B 6, -28 B l B 28
SHELXS-97 and SHELXL-97
1,697/138
Solution and refinement
Data-to-parameters ratio
confirmed by X-ray crystallography (Tables 1, 2, 3). Data were collected at
10(2) K after the crystal had been flash-cooled from room temperature. The
structure was solved and refined in the centrosymmetric space group P2 /c with
1
1
0
Z = 1 showing that it was a racemic mixture as was expected. The structure of
1
-phenyl-2-(2-pyridyl)ethanol was ordered. The crystal was pseudo-merohedrally
twinned. The twin relationship (-1 0 0/0 -1 0/1 0 1) was found via TwinRotMat
from the Platon program [19] and the batch scale factor refined to 0.140(2).
The X-ray structure refinement produced data to support the following
observations: bond lengths and angles were in good agreement with values
retrieved from [20]. The –CH –CHOH moiety of the molecule showed the typical
2
1
23

1-Phenyl-2-(2-pyridyl)ethanol intermediary
3569
2
Table 2 Atomic coordinates and equivalent isotropic displacement coefficients (A ) for 1-phenyl-2-(2-
˚
pyridyl)ethanol
Atom
x
y
z
U(eq)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
C(9)
C(10)
C(11)
C(12)
C(13)
N(1)
O(1)
0.9892(5)
0.7939(5)
0.7536(5)
0.9047(5)
1.0954(5)
1.1367(5)
0.8637(5)
0.6092(5)
0.5805(5)
0.3860(5)
0.3717(5)
0.5496(5)
0.7350(5)
0.7518(4)
0.8637(4)
0.2765(3)
0.3786(3)
0.4009(3)
0.3215(3)
0.2186(3)
0.1970(3)
0.3471(3)
0.2766(3)
0.2837(3)
0.3724(3)
0.3770(3)
0.2914(3)
0.2039(3)
0.1993(2)
0.5124(2)
0.46263(10)
0.43927(11)
0.38160(11)
0.34603(10)
0.36991(10)
0.42751(11)
0.28289(10)
0.25628(10)
0.19306(10)
0.16214(10)
0.10430(11)
0.07779(10)
0.11115(10)
0.16736(8)
0.26793(7)
0.0297(6)
0.0311(6)
0.0280(6)
0.0231(5)
0.0265(6)
0.0302(6)
0.0262(6)
0.0263(6)
0.0229(5)
0.0266(6)
0.0292(6)
0.0290(6)
0.0267(6)
0.0246(5)
0.0336(5)
U(eq) is defined as one-third of the trace of the orthogonalized Uij tensor
˚
Table 3 Bond lengths (A) and angles (°) for 1-phenyl-2-(2-pyridyl)ethanol
˚
Length (A)
Bond
Bond angle (°)
Angle (°)
C(1)–C(6)
C(1)–C(2)
C(2)–C(3)
C(3)–C(4)
C(4)–C(5)
C(4)–C(7)
C(5)–C(6)
C(7)–O(1)
C(7)–C(8)
C(8)–C(9)
C(9)–N(1)
C(9)–C(10)
C(9)–C(11)
C(11)–C(12)
C(12)–C(13)
C(13)–N(1)
1.374(4)
1.393(4)
1.379(4)
1.392(4)
1.386(3)
1.511(3)
1.377(3)
1.415(3)
1.526(3)
1.499(3)
1.342(3)
1.396(3)
1.373(4)
1.383(4)
1.387(3)
1.334(3)
C(6)–C(1)–C(2)
C(3)–C(2)–C(1)
C(2)–C(3)–C(4)
C(5)–C(4)–C(3)
C(5)–C(4)–C(7)
C(3)–C(4)–C(7)
C(6)–C(5)–C(4)
C(1)–C(6)–C(5)
O(1)–C(7)–C(4)
O(1)–C(7)–C(8)
C(4)–C(7)–C(8)
C(9)–C(8)–C(7)
N(1)–C(9)–C(10)
N(1)–C(9)–C(8)
C(10)–C(9)–C(8)
C(11)–C(10)–C(9)
C(10)–C(11)–C(12)
C(11)–C(12)–C(13)
N(1)–C(13)–C(12)
C(13)–N(1)–C(9)
119.2(2)
119.9(2)
120.9(2)
118.4(2)
120.5(2)
121.1(2)
120.7(2)
120.8(2)
112.5(2)
107.0(2)
112.1(2)
112.5(2)
121.3(2)
116.4(2)
122.2(2)
119.7(2)
119.0(2)
118.1(2)
123.4(2)
118.4(2)
123

3570
M. J. Percino et al.
3
Csp –Csp distance for C(8)–C(7) = 1.526(3) A, which is similar to 1.509(3),
3
˚
˚
1
pyridyl)ethanol, 1-phenyl-2-(4-pyridyl)ethanol, and 5-ethyl-2-(4-nitro-7-ol-styryl)-
.508(8), and 1.517(9) A obtained for the intermediates 1-(p-fluorophenyl)-2-(a-
3
pyridine, respectively, as reported in the literature [8, 11, 13], whereas for a Csp –O
˚
distance, C(7)–O(1) = 1.415(3) A is a typical value for alcohols [20] (Table 3).
Meanwhile, the carbon–carbon distances were representative of pyridyl and phenyl
groups. Also, the bond angles between 120° and 116° for the two rings are typical of
aromatic compounds, and the bond angles in the CH –CHOH moiety are typical of
2
3
an sp hybridization for the two carbons (Fig. 3).
The molecular crystal packing of 1-phenyl-2-(2-pyridyl)ethanol (Fig. 4) shows
intermolecular H-bonding between the OH group of one molecule and nitrogen
˚
atom of pyridine ring of the next one [O1–H1AÁÁÁN1 = 2.014 A, O1ÁÁÁN1 =
˚
.849 A], forming two independent parallel molecular chains along the b-axis, one
2
chain is formed by (R)-isomer and the adjacent chain by (S)-isomers of the alcohol
molecules, which can stabilize the crystalline structure (Fig. 4). The intermolecular
hydrogen bonds are similar than other systems presenting NÁÁÁH–O interactions
between the stacked molecules [21]. It has been demonstrated these hydrogen bonds
Fig. 3 The molecular structure
of the title compound with atom
labeling. Thermal ellipsoids are
drawn at the 50 % probability
level
Fig. 4 Molecular crystal packing of the title compound showing the H-bonding scheme with two parallel
molecular chains viewed along the b-axis
1
23

1-Phenyl-2-(2-pyridyl)ethanol intermediary
3571
play an important role in the symmetry of the unit cell and the packing modes in
conjugated compounds [21, 22].
The identification of the intermediate compound supported the condensation
mechanism proposed in 1969 [2], which states that an alcohol of the form (–CH2–
CHOH–), defined as an alkine in Ref. [7], could be dehydrated during the reaction
process to produce a double bond in the final compound [1, 2]. To obtain
2
-styrylpyridine as the unique product in a higher yield, it is sufficient to increase
the temperature or to include a catalyst such as acetic anhydride, zinc chloride,
hydrogen chloride, iodine, or analogous catalysts.
Conclusion
The 1-phenyl-2-(2-pyridyl)ethanol was isolated and obtained in adequate crystal
form to be characterized by X-ray analysis. The crystallography data gave evidence
that it is the intermediate, which had been detected, but according to our knowledge
its molecular structure has not been reported, because its condensation yielded the
2
-styrylpyridine.
The isolation of the intermediary appears as a step in the formation of
-styrylpyridine from the interaction of equimolecular proportions of 2-methylpyr-
2
idine and benzaldehyde. This synthesis is reported to be novel because it is carried
out in the absence of a condensing agent, allowing us to control what is obtained
between the intermediary or trans product, which is different from procedures
reported before. The intermediate step of this reaction gives the formation of the
group (–CH –CHOH–), named alkine for its origins. Similar intermediate alcohols
2
were obtained in the presence of zinc chloride and acetic anhydride in higher yields.
In our case, the intermediate alcohol was obtained in 4 % yield in green chemistry
conditions. This result could be attributed to the absence of an electron-withdrawing
substituent on benzaldehyde reactivity, as well as the absence of a condensing agent
in the reaction. We consider the results obtained on the synthesis and mechanism of
condensation reaction of styrylpyridine-like compounds by green chemistry using
different electron donor and acceptor substituents to be important.
The results showed that it is actually the alcohol just before the dehydration
process that yields the trans double bond in 2-styrylpyridine. The 1-phenyl-2-(2-
pyridyl)ethanol crystal structure shows the formation of an intermolecular hydrogen
bond O–HÁÁÁN between the oxygen atom of the O–H and the nitrogen atom of a
pyridine group of the adjacent molecule.
Supplementary material
Crystallographic data (excluding structure factors) reported in this paper have been
deposited with the Cambridge Crystallographic Data Centre as supplementary
publication no. CCDC# 960695. Copies of available material can be obtained, free
of charge, on application to the CCDC, 12 Union Road., Cambridge CB2 IEZ, UK
(
fax: ?44-(0)1223-336033 or e-mail: deposit@ccdc.cam.ac.uk).
123

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M. J. Percino et al.
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