Mesomorphic 1,2,4-triazine-4-oxides in the synthesis of new heterocyclic liquid crystals

Article abstract of DOI:10.1039/b718432h

New liquid-crystalline materials are described, which are obtained using a versatile synthetic methodology that employs the intermediacy of 1,2,4-triazines. Triazines, triazine-N-oxides, pyridine and laterally cyanated pyridines are among the compounds reported and the mesomorphism of the different structures shows how function affects mesomorphism. In particular, systems based on laterally cyanated pyridines turn out to be materials with low melting points and wide phase ranges. Lateral dipole moments, calculated at the Hartree-Fock level for the triazine-N-oxides and the cyanopyridines, showed a significant dependence on conformation and confirmed that the dipole moment was great for the latter materials. Appreciable spontaneous polarisation was measured for chiral derivatives of the triazine-N-oxides. The Royal Society of Chemistry 2008.

Full text of DOI:10.1039/b718432h

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www.rsc.org/materials | Journal of Materials Chemistry
Mesomorphic 1,2,4-triazine-4-oxides in the synthesis of new heterocyclic
liquid crystals
*
Valery N. Kozhevnikov, Stephen J. Cowling, Peter B. Karadakov and Duncan W. Bruce
Received 29th November 2007, Accepted 23rd January 2008
First published as an Advance Article on the web 19th February 2008
DOI: 10.1039/b718432h
New liquid-crystalline materials are described, which are obtained using a versatile synthetic
methodology that employs the intermediacy of 1,2,4-triazines. Triazines, triazine-N-oxides, pyridine
and laterally cyanated pyridines are among the compounds reported and the mesomorphism of the
different structures shows how function affects mesomorphism. In particular, systems based on
laterally cyanated pyridines turn out to be materials with low melting points and wide phase ranges.
Lateral dipole moments, calculated at the Hartree–Fock level for the triazine-N-oxides and the
cyanopyridines, showed a significant dependence on conformation and confirmed that the dipole
moment was great for the latter materials. Appreciable spontaneous polarisation was measured for
chiral derivatives of the triazine-N-oxides.
liquid crystals containing the 1,2,4-triazine unit, and show how
they can be used in the synthesis of new mesomorphic pyridines.
Introduction
The incorporation of a heterocyclic moiety into a mesogenic
molecule is one of the common ways to influence liquid crystal
properties, and among aza heterocycles, pyridines,1 pyrimi-
dines,2 pyrazines3 and pyridazines4 have been used most
commonly. Reports of 1,2,4-triazine-containing liquid crystals
are, however, relatively rare, which might be the direct result
of their high reactivity and, therefore, low stability. On the other
hand, this high reactivity makes them interesting as building
blocks for further modification. For instance they can be trans-
formed into pyridines by reverse Diels–Alder reactions. In the
present paper, we describe the synthesis and properties of new
Synthesis
If 1,2,4-triazines are to be incorporated into rod-like mesogens,
then a 3,6-substitution pattern is essential. The method commonly
employed for the synthesis of mesomorphic 3,6-disubstituted-
1,2,4-triazines is the condensation of bromoacetophenones with
two equivalents of acid hydrazides in the presence of sodium
acetate. Yields of around 30–60% are obtained where benzoic
acid hydrazides are used and 15–30% in the case of aliphatic
hydrazides.5 However, 3,6-disubstituted 1,2,4-triazine-4-oxides
are ready available through a recently reported methodology,6
and we now describe its adaptation to liquid crystal synthesis
(Scheme 1).
Department of Chemistry, University of York, Heslington, York, UK,
YO10 5DD. E-mail: db519@york.ac.uk; Fax: (+44) 1904 432516
Scheme 1 Synthesis of mesogenic 1,2,4-triazine-4-oxides. i) anhydrous K2CO3, CnH2n+1Br, DMF, 80–90%; ii) EtONa, isopropyl nitrite, EtOH, RT, 12
h, followed by neutralization with AcOH, 45–55%; iii) 2 eq. hydrazine hydrate, EtOH, RT, 50–60%; iv) AcOH, P3O4, RT, 45–60%.
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Thus, a standard alkylation of 4-hydroxyacetophenone with
a 1-bromoalkane yielded 4-alkoxyacetophenones, 1, which were
further transformed into ketooximes, 2, by nitrosation with
isopropyl nitrite. Treatment of the ketooxime with hydrazine
provided the first building block, hydrozone oximes, 3. The reac-
tion of 3 with carboxaldehydes (the second building block) results
in an open-chain Schiff base (triazahexatrienes A), which are
known7 to exist in equilibrium with their cyclic form of dihydro-
1,2,4-triazines B (Scheme 1). This interesting feature of such
(reduction) has been used previously in the synthesis of 1,2,4-
triazine liquid crystals.1 In this study however, we explored the
ability of 1,2,4-triazine-4-oxides to undergo nucleophilic
aromatic substitution of hydrogen.
Thus, lateral cyanation was achieved readily by direct substi-
tution of the hydrogen in the 5-position of the triazine ring by
a cyanide group to give 5-cyano-1,2,4-triazines (6; Scheme 2).
The N-oxide function plays a key role here in providing condi-
tions for water elimination from intermediate s-adducts. It
should be noted that the cyano group could easily be substituted
further by nucleophiles such as water, alcohols or amines,
providing further possibilities to modify the structure. One
such example is shown in Scheme 2, where a 1,2,4-triazin-
5(2H)-one (7) is synthesised; this compound is not liquid crystal-
systems allows
a one-pot oxidative aromatisation to be
performed, which proceeds without being affected by the ratio
of the ring-chain isomers, giving the target 1,2,4-triazine-4-oxides.
Obviously the use of aliphatic aldehydes yields 6-(alkoxy-
phenyl)-3-alkyl-1,2,4-triazine-4-oxides, 4, having a central core
unit consisting of two aromatic rings, while the use of 4-alkoxy-
benzaldehydes yields 3,6-di(40-alkoxyphenyl)-1,2,4-triazine-
4-oxides, 5, with the core having three aromatic rings (Fig. 1).
1,2,4-Triazine-4-oxides are well known to be useful building
blocks in heterocyclic synthesis8 and can be functionalised to
give a wide range of new products. For example, deoxygenation
ꢀ
line and simply melts to the isotropic state at 254 C.
We have also explored the interesting and important ability of
1,2,4-triazines to participate as reagents for inverse Diels–Alder
reactions. Thus, the reaction of cyanotriazines with norborna-
diene in dichlorobenzene under reflux provided 2-cyanopyridines
(8) in excellent yields (Scheme 3).
Fig. 1 Mesomorphic 1,2,4-triazine-4-oxides.
Scheme 2 Preparation of mesomorphic cyanotriazines and a 1,2,4-triazin-5(2H)-one: i) acetone cyanohydrin, TEA, DCM, RT, 80–90%; ii) AcOH,
HCl (conc.), reflux.
Scheme 3 Preparation of 2-cyanopyridine derivatives.
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All of the new compounds were characterised chemically using
1H NMR spectroscopy and elemental analysis. Full details are
reported in the Experimental section.
Table 1 Thermal behaviour of the new compounds
DH/kJ
molꢁ1
DS/J Kꢁ1
molꢁ1
Compound
n
m
Transition
T/ꢀC
Mesomorphic properties
4a
8
3
Crys–Crys
Crys–SmA
SmA–I
Crys–Crys
Crys–SmA
SmA–I
Crys–Crys
Crys–SmC
SmC–SmA
SmA–I
Crys–Crys
Crys–SmC
SmC–SmA
SmA–I
Crys–SmC
SmC–SmA
SmA–I
Crys–SmC
SmC–N
N–I
Crys–SmC
SmC–N
N–I
Crys–SmC
SmC–I
Crys–SmC
SmC–I
Crys–SmC
SmC–I
Crys–SmC
SmC–I
Crys–SmC
SmC–N
N–I
Crys–SmC
SmC–N
N–I
Crys–SmC
SmC–I
Crys–I
(I–N)
Crys–I
(I–N)
Crys–I
85
95
120
89
104
121
77
100
110
121
72
13.7
16.5
7.6
13.4
14.7
7.6
10.6
15.4
0.4
7.8
9.9
13.3
0.4
7.6
18.8
0.6
8.0
27.6
1.0
2.2
33.1
2.4
2.2
24.3
10.3
19.6
10.4
27.8
11.1
28.1
11.0
15.4
1.3
38
45
19
37
39
19
30
41
1
20
28
36
1
19
51
2
20
69
2
Thermal data for the new compounds are collected in Table 1;
representative textures are given in Fig. 2. Compounds 4 are
all mesomorphic and show a SmA phase, characterised by its
focal conic texture. At the shortest chain lengths this is the
only phase seen, but as the chain attached to the triazine ring
is extended, a SmC phase appears in addition. The compounds
melt at around 100 ꢀC and clear close to 120 ꢀC; the SmC phase
gradually increases in stability with increasing m. Compounds 5
are also all mesomorphic, but this time the mesomorphism is
dominated by the formation of a SmC phase with an extremely
wide temperature range. Thus, most of the melting points are
below 100 ꢀC while clearing points are generally in excess of
210 ꢀC. A nematic phase is seen for two shortest chain length
homologues examined. The phase behaviour of 4 and 5 is
represented graphically in Fig. 3.
4b
4c
8
8
5
6
4d
8
7
95
116
124
97
4e
5a
5b
8
8
8
8
2
4
117
123
129
204
230
101
215
222
94
219
89
213
93
4
88
5
Liquid crystal properties of some 3-alkyl-6-(alkoxyphenyl)-
1,2,4-triazine-4-oxides have been reported previously and show
a narrow smectic range.1
5
5c
5d
5e
5f
8
8
8
8
4
6
8
65
21
54
21
76
23
77
23
38
2
It is interesting to compare the mesomorphic properties of
1,2,4-triazines with those of 1,2,4-triazine-4-oxides (Fig. 4). In
the case of aliphatic substitution in the 3-position, the transition
10
12
4
214
93
208
131
186
233
100
206
225
86
215
115
(113)
102
(102)
99
5g
2.1
20.0
0.9
2.2
45.4
4.9
4
54
2
5h
4
8
5
5i
4
8
8
8
8
8
12
2
126
10
119
(–2)
83.4
(–3)
108
(– 3)
112
(– 4)
107
(– 5)
(– 1)
25
27
88
2
6a
6b
6c
6d
6e
46.2
(– 0.9)
31.3
(– 1.0)
40.1
(– 1.1)
41.7
(– 1.3)
40.4
(– 1.9)
(– 0.5)
12.6
14.3
30.5
0.6
4
8
(I–N)
Crys–I
(I–N)
Crys–I
(I–N)
(N–SmA)
Crys–Crys
Crys–I
Crys–N
N–I
Crys–N
N–I
Crys–SmC
SmC–N
N–I
(100)
99
10
12
(97)
103
(97)
(78)
239
254
75
98
35
95
36
7
8
8
8
8
8
2
4
6
8a
8b
8c
27.8
0.5
39.3
0.7
90.2
1
127
2
51
95
1.7
5
8d
8e
8f
8
8
8
8
10
12
Crys–SmC
SmC–N
N–I
Crys–SmC
SmC–N
N–I
26
88
101
27
101
104
43
33.2
0.3
1.7
30.6
0.6
2.1
111
1
5
102
2
6
Crys–SmC
SmC–I
27.6
2.0
87
5
106
Fig. 2 (a) Nematic phase and (b) SmC phase of 8d at 100.3 and 84 ꢀC,
respectively, taken on cooling.
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Fig. 3 Phase diagram for the 1,2,4-triazine-4-oxide mesogens 4 and 5.
Fig. 4 Comparison of the transition temperatures of some two- and three-ring 1,2,4-triazines and the related 1,2,4-triazine-4-oxides.
temperatures of the N-oxides are higher and the liquid crystal
ranges narrower than those of 1,2,4-triazine analogues.5 In the
case of aromatic substitution in the 3-position, the situation
changes drastically and the transitions temperatures are almost
the same with or without the N-oxide function. It should be
noted that the N-oxide group is not very often applied as lateral
substitution, despite the fact that it is known that the influence of
the N-oxide function on dielectric anisotropy is even greater than
that of two fluorine atoms in common ortho-difluorobenzenes.9
With lateral cyano substitution, a different story is found.
Thus, the three-ring 5-cyano-1,2,4-triazꢀines 6 melt directly to
the isotropic phase between 99 and 115 C and then, just a few
degrees below the melting point, a monotropic nematic phase
is seen on cooling. Although not reported in detail here, it is
interesting to note that 5-cyano derivatives derived from the
two-ring triazine oxides 4 are not mesomorphic (e.g. 5-cyano-
3-hexyl-6-(40-octyloxyphenyl)-1,2,4-triazine: Cr ꢂ 28 ꢂ I).
and melting points ranged from 26 to 75 ꢀC, with clearing points
ꢀ
between 95 and 106 C. The shortest chain homologues (n ¼ 2
and 4) showed only a nematic phase, but for the latter of these,
its range was 60 K. Beyond this chain length, a SmC phase
appeared on melting and quickly increased in stability with chain
length so that by n ¼ 12, the nematic phase had disappeared and
a pure mesomorphic range of 63 K was observed.
The lateral cyano group has a number of possible effects in
these molecules. First, it is a large, lateral substituent and as
such is expected to destabilise both the melting and clearing
points of the analogous, unsubstituted compound. This it
certainly does as revealed when considering the mesomorphism
of compound 9, which shows a SmC, SmI and crystal J phase
(Cr ꢂ 107 ꢂ J ꢂ 137 ꢂ SmI ꢂ 187 ꢂ SmC ꢂ 221 ꢂ I).10 Thus, clearing
ꢀ
is destabilised by more than 100 C. Another common effect of
lateral substituents is often to destabilise smectic phases in
favour of the nematic phase, which is a steric effect connected
with the ability of the molecule to pack into layers. However,
this effect depends upon the position of the lateral substituent,
Considering next the three-ring cyanopyridine mesogens 8,
enantiotropic phases were seen for all homologues prepared
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its size and its polar nature, and the strong stabilisation of the
SmC phase as the terminal chain length increase clearly indicates
a strong dipolar effect. This effect is much bigger in 8 when
compared to 6 (cyanopyridine versus cyanotriazine) due to the
elimination of two nitrogen atoms from the opposite side of
the molecule.
Results of calculations
To study this further, we calculated the dipole moment of 8 in
which both terminal chains were reduced to methoxy. The
molecule incorporates a significant degree of conformational
flexibility, so the first task was to carry out a molecular
mechanics-based conformational search allowing rotations about
the two C–C bonds connecting the rings and the two C–O
bonds. This search was performed using the GMMX approach
implemented in PCModel,11 and it identified nine low-energy
conformers. The geometries of the three lowest-energy conformers
were thenre-optimised at the HF/6-31G* level of theory (Hartree–
Fock wavefunction utilising a 6-31G* basis). Two of these optimi-
sations converged to the same final geometry, and the two
different geometries that were obtained are shown in Fig. 5.
The mutual orientations of the three rings stay very much the
same in the two conformers, while the main differences are in the
placements of the methoxy groups, which have a dramatic effect
on the dipole moment. The energy gap between the two
conformers is quite small, about 2.1 kJ molꢁ1 (0.5 kcal molꢁ1).
In both cases, the direction of the dipole moment is very much
the same, but its magnitude is much lower in the lower-energy
conformer. The calculations, however, are carried out on an
isolated molecule at 0 K and, with such a small difference in
energy, it would be expected that at some finite temperature an
Fig. 6 Lowest-energy conformers of 6 with both terminal chains
reduced to methoxy (HF/6-31G* geometries) and corresponding dipole
moments. HF/6-31G* energy and dipole moment of 6a (upper):
ꢁ1057.2385 Hartree and 4.3038 D; HF/6-31G* energy and dipole
moment of 6b (lower): ꢁ1057.2386 Hartree and 1.7349 D. The dipole
moment vectors are drawn in atomic units (1 a.u. ¼ 2.5418 D).
averaging of these structures (and in all probability several
others) would occur. This was tested by optimising a structure
in which the methoxy groups were substituted by hydrogens as
the barriers associated with rotations about the ring-connecting
bonds are much larger in comparison to those about C–O bonds.
This showed that the direction of the dipole moment remained
much the same, and that its magnitude is 5.6470 D, almost
halfway between the previous two values. This is a substantial
lateral dipole moment that clearly markedly influences the
mesogenic properties of this system.
We also carried out calculations on a three-ring 5-cyano-1,2,4-
triazine 6 with methoxy terminal chains. In this case, the GMMX
conformational search produced thirteen low-energy structures.
Upon further optimisation of the three lowest-energy structures
at the HF/6-31G* level of theory, two of these turned out to be
enantiomers, and we were left with the two distinct structures
shown in Fig. 6.
The energy gap between the conformers 6a and 6b is very small,
under 0.3 kJ molꢁ1 (0.07 kcal molꢁ1). This is due to the fact that, in
comparison to 8a and 8b (see Fig. 5), the absence of the hydrogens
from the central ring decreases significantly the energy barriers
associated with rotations about the ring-connecting bonds. The
difference in the dipole moments of 6a and 6b can be attributed,
just as in the case of 8a and 8b, to the different orientations of
the methoxy groups. In fact, the shape of 6b suggests that the
effects of the two methoxy groups on the dipole moment should
nearly cancel one another. This was confirmed by calculating
the dipole moment of a HF/6-31G* optimised structure with
the methoxy groups substituted by hydrogens which turned out
to be 1.7139 D, very close to that of 6b.
Fig. 5 Lowest-energy conformers of 8 with both terminal chains
reduced to methoxy (HF/6-31G* geometries) and corresponding dipole
moments. HF/6-31G* energy and dipole moment of 8a (upper):
ꢁ1025.2900 Hartree and 7.5847 D; HF/6-31G* energy and dipole
moment of 8b (lower): ꢁ1025.2908 Hartree and 3.5920 D. The dipole
moment vectors are drawn in atomic units (1 a.u. ¼ 2.5418 D).
Electro-optic investigation
Compounds incorporating a 1,2,4-triazine ring have been
prepared previously and shown to have rather moderate values
of their spontaneous polarisation (0.1 nC cmꢁ2 at a reduced
temperature of 10 ꢀC).1 We were curious to see what
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electro-optic properties 1,2,4-triazine-4-oxides might have and so
we undertook the synthesis of the chiral material (5*; DH in
brackets in kJ molꢁ1) using (S)-2-methylheptyl as one terminal
chain as the parent system showed wide SmC ranges.
polarisation are typical of a material with a SmA–SmC transition.
The polarisation reached a maximum of 61 nC cmꢁ2 at a reduced
temperature of 40 ꢀC and then remained constant whereas the tilt
angle continued to rise steadily until crystallisation.
Although in principle also attractive to study, chiral analogues
of 8 (e.g. having an octyl chain at one end and a 2-methylheptyl
chain at the other) did not show a SmC* phase, rather the
mesomorphism was suppressed completely.
Conclusions
In this paper we have demonstrated the utility of the rich
chemistry of 1,2,4-triazine-4-oxides for the design of new liquid
crystals incorporating either heterocyclic 1,2,4-triazine or
pyridine units in the central core. It also allows control to be
exerted over the peripheral structure of the molecule and to
access symmetrical, unsymmetrical and chiral derivatives and
those with different lateral substituents. Further, the N-oxide
function in chiral 1,2,4-triazine-4-oxides has been found to
play a critical role in achieving relatively high values of the
spontaneous polarisation.
The temperature dependence of the spontaneous polarization
and tilt angle of a chiral 1,2,4-triazine-4-oxide are shown in
Fig. 7; the behaviour of both the tilt angle and spontaneous
Calculations showed that the lateral dipole moment generated
by a lateral cyano group was significantly greater than that of
a triazine N-oxide and, given the limiting PS value of 60 nC
cmꢁ2 for the N-oxides, this suggests that the cyano materials
could be very attractive targets, particularly as the compounds
have low melting points and wide phase ranges. However, this
could not be tested in the present system as the use of chiral
2-methylheptyl terminal chains destabilised the mesophases of
the materials.
Experimental
Nuclear magnetic resonance spectra were recorded on a Jeol
1
JNM-EX 270 FT NMR system at 270 MHz for H NMR and
68 MHz for 13C NMR. Microanalyses were performed at
Department of Chemistry, University of Newcastle upon Tyne
using a Carlo Erba 1108 Elemental Analyser controlled with
CE Eager 200 software. UV-Vis and infrared spectra were
obtained by using a Shimadzu UV-2401 PC and a Shimadzu
IR Prestige-21 spectrometers respectively. The phase transition
temperatures were determined using a Mettler Toledo DSC-
822e differential scanning calorimeter with a heating and cooling
rate of 10 C minꢁ1 (the apparatus was calibrated with indium,
ꢀ
156.6 ꢀC). Texture observations were made using an Olympus
BX 50 polarizing microscope in conjunction with a Linkam
LTS 350 hot stage and a Linkam TMS 92 control unit. Literature
procedures were followed for the preparation of hydrazono-(4-
alkoxyphenyl)acetaldehyde oximes and alkoxybenzaldehydes.
Analytical data for the new compounds are presented in Table 2.
All Hartree–Fock calculations were carried out using the
GAUSSIAN03 package.12
Electro-optic measurements
The chiral 1,2,4-triazine-4-oxide (5*) was flow-filled by capillary
action into a 4 mm antiparallel-buffed, polyimide cell (Linkam).
The material was aligned in its smectic A phase at 145 ꢀC by
applying a square waveform of 10 V mmꢁ1 at 200 Hz until homo-
geneous alignment was attained. Spontaneous polarisation was
Fig. 7 Plots of spontaneous polarisation (a) and tilt angle (b) as a func-
tion of reduced temperature (T) for chiral material 5*.
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Table 2 Analytical data for the new compounds
triethylamine (0.32 g, 3.2 mmol) were added to a stirring solution
of 1,2,4-triazine-4-oxide 5d (800 mg, 1.6 mmol) in dichlorome-
thane (20 cm3). The reaction mixture was stirred at room temper-
ature for 30 min and subsequently at 40 ꢀC (reflux) for 1 h. The
solvent and other volatile reaction components were removed in
vacuum; the residue was redissolved in dichloromethane (5 cm3)
and applied to a column (silica gel 60, dichloromethane as
eluent). The first bright yellow fraction was collected giving after
evaporation of the solvent and drying in high vacuum the title
compound as a yellow powder.
Calculated (Found) (%)
Compound
Yield (%)
C
H
N
5a
5b
5c
5d
5e
5*
6a
6b
6c
6d
6e
6f
6g
6h
6i
7a
7b
7c
7d
7e
8
54
48
60
61
55
28
62
57
54
52
59
54
60
51
48
83
78
86
80
85
68
78
76
80
82
77
72
69.94 (70.89)
71.12 (71.91)
71.65 (71.90)
72.14 (72.41)
72.60 (73.36)
72.13 (71.74)
71.23 (71.76)
72.13 (72.07)
72.92 (72.98)
73.63 (73.71)
74.62 (74.54)
74.83 (74.90)
70.21 (70.22)
72.13 (72.11)
73.63 (73.09)
72.32 (72.53)
73.11 (73.33)
74.50 (74.67)
75.02 (75.24)
75.71 (75.75)
73.22 (73.63)
78.47 (78.48)
78.91 (79.00)
79.30 (79.39)
79.65 (79.66)
79.96 (79.90)
80.24 (80.18)
8.51 (8.68)
8.95 (9.13)
9.15 (9.43)
9.33 (9.49)
9.50 (9.57)
7.85 (7.87)
7.41 (7.50)
7.85 (7.84)
8.23 (8.13)
8.57 (9.09)
8.88 (8.89)
9.15 (9.51)
6.92 (6.95)
7.85 (7.91)
8.57 (8.56)
7.12 (7.02)
7.43 (7.47)
8.25 (8.22)
8.18 (8.54)
8.72 (8.83)
8.44 (8.57)
7.53 (7.60)
7.95 (8.09)
8.32 (8.42)
8.65 (8.79)
8.95 (8.94)
9.21 (9.45)
12.23 (12.20)
11.31 (11.35)
10.90 (10.89)
10.52 (10.51)
10.16 (10.24)
9.35 (9.28)
9.97 (10.03)
9.35 (9.30)
8.80 (8.80)
8.31 (8.32)
7.87 (7.96)
7.48 (7.50)
10.68 (10.67)
9.35 (9.36)
8.31 (8.56)
13.10 (13.01)
12.54 (12.22)
10.77 (10.89)
10.17 (10.32)
9.79 (9.82)
8.50 (8.31)
6.54 (6.55)
6.13 (6.23)
5.78 (5.77)
5.46 (5.46)
5.18 (5.20)
4.92 (5.05)
dH (CDCl3): 0.88 (t, 6 H, J ¼ 7.3 Hz, 2CH3), 1.2–1.5 (m, 20 H,
10CH2), 1.82 (br. q, 4 H, J ¼ 8.1 Hz, 2CH2), 4.03 (t, 2 H, J ¼ 6.8
Hz CH2), 4.05 (t, 2 H, J ¼ 6.8 Hz CH2), 7.02 (AA0XX0, J ¼ 8.9
Hz, 2 H, aromatic), 7.09 (AA0XX0, J ¼ 8.9 Hz, 2 H, aromatic),
8.08 (AA0XX0, J ¼ 8.9 Hz, 2 H, aromatic), 8.48 (AA0XX0,
J ¼ 8.9 Hz, 2 H, aromatic).
3,6-Di(4-octyloxyphenyl)-1,2,4-triazine-5(2H)-one 7. Cyano-
triazine 6c (100 mg, 0.2 mmol) was dissolved in hot acetic acid,
two drops of concentrated hydrochloric acid were added and
the reaction mixture was reflux for 15 min. After cooling the
precipitated solid was filtered off and crystallised from acetic
acid to give 7 as colourless crystals.
9a
9b
9c
9d
9e
9f
dH (DMSO-D6): 0.86 (br. t, 6 H, J ¼ 7.4 Hz, 2CH3), 1.2–1.5
(m, 20 H, 10CH2), 1.81 (br. q, 4 H, J ¼ 8.1 Hz, 2CH2), 3.92
(t, 2 H, J ¼ 6.8 Hz CH2), 4.01 (t, 2 H, J ¼ 6.8 Hz CH2), 6.87
(AA0XX0, J ¼ 8.9 Hz, 2 H, aromatic), 6.92 (AA0XX0, J ¼ 8.9
Hz, 2 H, aromatic), 8.18 (AA0XX0, J ¼ 8.9 Hz, 2 H, aromatic),
8.32 (AA0XX0, J ¼ 8.9 Hz, 2 H, aromatic).
determined using a current reversal technique and tilt angle was
determined with the aid of a photodiode. The measurements
were carried out using an applied voltage of 10 V mmꢁ1 at 30 Hz.
General procedure for the synthesis of 2-cyanopyridines
2-Cyano-3,6-di(4-octyloxyphenyl)pyridine.
A
mixture of
5-cyano-3,6-di(4-octyloxyphenyl)-1,2,4-triazine (515 mg,
1
mmol), 2,5-norbornadiene (460 mg, 0.54 cm3, 5 mmol) and
1,2-dichlorobenzene (25 cm3) was heated under reflux for 12 h.
The solvent and other volatile reaction components were
removed under reduced pressure and the residue was recrystal-
lised from methanol to give the title compound.
Synthesis
General procedure for the synthesis of 1,2,4-triazine-4-oxides 4
and 5
3,6-Di(4-octyloxyphenyl)-1,2,4-triazine-4-oxide 5d. 4-Octy-
loxybenzaldehyde (2.34 g, 10 mmol) was added to a solution of
hydrazone oxime (2.91 g, 10 mmol) in acetic acid (40 cm3) and
the reaction mixture was stirred at room temperature for 3
hours. Pb3O4 (6.85 g, 10 mmol) was added in approximately 1
g portions over 4 h, theꢀtemperature of the reaction mixture
was maintained at 17–20 C during the addition. After comple-
tion of the addition the reaction mixture was stirred for 1 hour
at room temperature and then diluted with cold water (40
cm3). A precipitated solid was collected by suction filtration,
washed with water (3 ꢃ 30 cm3), ethanol (2 ꢃ 10 cm3) and
recrystallised from ethanol to give the title compound.
dH (CDCl3): 0.88 (t, 6 H, J ¼ 7.2 Hz, 2CH3), 1.2–1.5 (m, 20 H,
10CH2), 1.80 (q, 4 H, J ¼ 8.1 Hz, 2CH2), 4.00 (t, 2 H, J ¼ 6.8 Hz
CH2), 4.01 (t, 2 H, J ¼ 6.8 Hz CH2), 6.97 (AA0XX0, J ¼ 8.9 Hz, 2
H, aromatic), 7.02 (AA0XX0, J ¼ 8.9 Hz, 2 H, aromatic), 7.52
(AA0XX0, J ¼ 8.9 Hz, 2 H, aromatic), 7.80 (d, 1 H, J ¼ 8.2
Hz, pyr H4), 7.88 (d, 1 H, J ¼ 8.2 Hz, pyr H5), 7.99 (AA0XX0,
J ¼ 8.9 Hz, 2 H, aromatic).
References
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20 H, 10CH2), 1.80 (br. q, 4 H, J ¼ 8.1 Hz, 2CH2), 4.01 (t, 2
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8.48 (AA0XX0, J ¼ 8.9 Hz, 2 H, aromatic), 8.51 (s, 1 H, trzH5).
General procedure for the synthesis of 5-cyano-1,2,4-triazines
5-Cyano-3,6-di(4-octyloxyphenyl)-1,2,4-triazine 6c. Molec-
ular sieves (1 g), acetone cyanohydrin (0.4 g, 4.8 mmol) and
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