Paradoxes in thermal stability of the liquid-crystal phase of phenylpropargyl phenyl ethers: I. Synthesis and mesogenic properties of phenylpropargyl phenyl ethers

Article abstract of DOI:10.1023/A:1013182427261

The ethers PhC≡CCH₂OC₆H₃RR′ were prepared in 51-83% yields by reactions of phenylpropargyl tosylate in alkaline solution with appropriate p- and o-substituted phenols. Below are given R, R′, and the ranges of existence of

Full text of DOI:10.1023/A:1013182427261

Russian Journal of General Chemistry, Vol. 71, No. 7, 2001, pp. 1130 1132. Translated from Zhurnal Obshchei Khimii, Vol. 71, No. 7, 2001,
pp. 1197 1199.
Original Russian Text Copyright
2001 by Shchelkunov, Abulyaisova, Mataeva, Sivolobova, Muldakhmetov.
Paradoxes in Thermal Stability of the Liquid-Crystal Phase
of Phenylpropargyl Phenyl Ethers: I. Synthesis and Mesogenic
Properties of Phenylpropargyl Phenyl Ethers
S. A. Shchelkunov, L. K. Abulyaisova, S. O. Mataeva,
O. A. Sivolobova, and Z. M. Muldakhmetov
Institute of Organic Synthesis and Coal Chemistry, Ministry of Science and Higher Education
of the Kazakhstan Republic, Karaganda, Kazakhstan
Received January 27, 2000
Abstract The ethers PhC CCH2OC6H3RR were prepared in 51 83% yields by reactions of phenylpropar-
gyl tosylate in alkaline solution with appropriate p- and o-substituted phenols. Below are given R, R , and the
ranges of existence of the nematic mesophase ( C): p-I, H, 104 137; p-Cl, H, 65 117; p-F, H, 33 53; p-OMe,
H, 79 120; H, H, 44 115; p-(Me)3C, H, 74 82; p-COOH, H; p-NO2, H, 77 96; o-NO2, H, 83 139; o-CHO,
H, 75 115; p-Br, o-NO2, 95 132; p-Cl, o-NO2, 71 123; p-F, o-NO2, 79 120; o-Cl, H, none; p-COOPr, H,
none; and p-COOPh, H, 116 134. In contrast to the traditional views, the presence of the o-nitro group
enhances, rather than distorts, the thermal stability of the mesophase. The stability increases in parallel with
the R effect of the o-substituent.
It was shown previously [1] that in hydroquinone
bis(phenylpropargyl) diether the nematic phase exists
in a relatively broad range (C 128 N 183 I). In going
to shorter-chain analogs based on p-cresol (C 60 N 78 I)
and p-bromophenol (C 84 N 120 I) the melting
point, as expected, decreased, but the thermal stability
of the mesophase decreased also [2].
The ranges of thermal stability of the mesophase
of I VI and VIII XVI are listed in Table 1.
The results (compounds I VI) follow the trends
observed with other classes of liquid crystals: The
thermal stability of the mesophase increases when the
molecule contains polar substituents at the para posi-
tions; the ordering decreases with increasing branch-
ing of the radical and with replacement of heavier
halogens by fluorine [3].
In this work we continued a study of the thermal
stability of the mesophase of phenylpropargyl phenyl
ethers in relation to their structure. The ethers were
prepared by the following scheme:
The results obtained with VIII and IX appeared to
be rather unexpected: In contrast to common views,
introduction of the nitro group into the ortho position
enhanced, rather than distorted, the thermal stability
of the mesophase as compared to the p-substituted
analog.
PhC CCH2OTs + HOC6H3RR
K2CO3
PhC CCH2OC6H3RR ,
R = H; R = p-I (I), p-Cl (II), p-F (III), p-OMe (IV), H
(V), p-(Me)3C (VI), p-COOH (VII), p-NO2 (VIII), o-NO2
(IX), o-CHO (X). R = o-NO2; R = p-Br (XI), p-Cl (XII),
p-F (XIII). R = o-Cl, R = H (XIV).
Study of the liquid-crystal properties of XI XIII
showed that the effect of the o-nitro group tends to
grow as the size of the p-substituent decreases. For
example, the thermal stability of the mesophase of
XIII sharply increases as compared to III.
With 2,4-dinitrophenol, there was no conversion
even when the reaction was performed in high-boiling
cyclohexanone, which is due to extremely low nucleo-
philicity of the corresponding phenolate.
We think that the observed paradoxes are due to
the following factors.
(1) Possible formation of quasi-rings in phenyl-
propargyl o-nitrophenyl ethers through Coulombic
interaction of the oxymethylene protons with the lone
electron pairs of the oxygen atoms of the nitro group,
favoring closer packing of molecules. Similar phe-
Compound VII was subsequently treated with
thionyl chloride, and the resulting acid chloride
without isolation was converted to n-propyl (XV) and
phenyl (XVI) esters.
1070-3632/01/7107-1130$25.00 2001 MAIK Nauka/Interperiodica

PARADOXES IN THERMAL STABILITY OF THE LIQUID-CRYSTAL PHASE ... : I.
1131
nomena were observed to some extent previously [3]
but formation of a quasi-ring was detected only in the
case of a strong hydrogen bond (with the Schiff base
derived from salicylaldehyde). Naturally, the strength
of this Coulombic interaction should vary in parallel
with the negative resonance effect of the substituent
in the phenol ring, increasing the positive charge of
the hydrogen atoms in the methylene bridge.
Table 1. Rangesa of thermal stability of the mesophase of
the synthesized phenylpropargyl phenyl ethers
Comp.
no.
Comp.
no.
Range,
C
Range,
C
I
II
104 137
65 117
33 53
79 120
44 115
74 82
X
XI
75 115
95 132
71 123
79 120
III
IV
V
VI
VIII
IX
XII
XIII
XIV
XV
XVI
(2) Terminal interactions between the nitro group
and the positively charged hydrogen atoms of the
o-nitrophenol ring.
77 96
83 139
116 134
(3) Intermolecular interactions between the oxy-
methylene and nitro groups.
a
The lower boundary corresponds to the C
the upper boundary, to the N
N transition, and
I transition.
To check these assumptions, we prepared com-
pounds X and XIV. We expected that the effects of
substituents would decrease the thermal stability of
the mesophase, with its total disappearance in the
case of XIV. The relative contributions of hypotheti-
cally possible interactions to the thermal stability of
the mesophase are refined by quantum-chemical cal-
culations which are in progress.
was complete (monitored by TLC, Silufol plates,
development with aqueous KMnO4, eluent benzene).
The mixture was decomposed with water, alkalized
to pH 10, extracted with benzene, and dried with
CaCl2, after which low-boiling fractions were dis-
tilled off. The residue was recrystallized from ethanol;
2.54 g (76%) of phenylpropargyl p-iodophenyl ether
was obtained. Compounds II XIV were prepared sim-
ilarly; their physicochemical constants and yields are
given in Table 2.
1
The H NMR spectra of II, IV, V, and IX contain
a benzene multiplet in the range 6.9 7.7 ppm; the
methylene protons give a singlet at 4.2 4.8 ppm. In
the case of IV, the methoxyl protons give a singlet at
2.7 ppm. The IR spectra of all the compounds contain
p-(Phenylpropargyloxy)benzoic acid (VII). To a
suspension prepared from 70 ml of absolute ethanol,
0.46 g of sodium metal, and 1.38 g of p-hydroxyben-
zoic acid was added 2.86 g of phenylpropargyl tosy-
late. Then 20 ml of DMSO was added, and the mix-
ture was allowed to stand at room temperarture for
48 h and then heated for 3 h at 80 C. The alcohol was
distilled off, and the residue was acidified with 10%
HCl. The precipitate was filtered off on a Schott filter
and then recrystallized from ethanol. The yield and
physicochemical constants are given in Table 2.
1
C C absorption bands at 2220 2230 cm ,
stretching absorption bands of the benzene rings at
1
1580 1600 cm , and stretching absorption bands
1
of the ether moiety at 1240 1250 cm . In the IR
spectra of VIII, IX, and XI XIII are also observed
1
bands at 1500 1530 and 1320 1350 cm belonging
to stretching vibrations of the nitro group. The car-
1
bonyl group gives rise to a band at 1720 1750 cm
1
in the case of VII, XV, and XVI and at 1690 cm in
the case of X.
EXPERIMENTAL
n-Propyl p-(phenylpropargyloxy)benzoate (XVI).
To 0.45 g of VII in 20 ml of benzene was added
0.43 g of SOCl2, and the mixture was refluxed for
7 h. The solvent and unchanged thionyl chloride were
distilled off in a vacuum. To the resulting solution,
at cooling with ice-cold water, was added a solution
of 0.17 g of phenol and 0.2 ml of triethylamine in
15 ml of benzene. The mixture was heated for 5 h at
80 C and broken down with water; the organic layer
was separated and dried over CaCl2. Low-boiling
fractions were distilled off, and the residue was re-
crystallized from ethanol. Compound XV was pre-
pared similarly. The yields and physicochemical con-
stants are listed in Table 2.
The IR spectra were taken on a UR-20 spectro-
photometer (thin films or KBr pellets). The H NMR
spectra were taken on a Tesla BS-587 spectrometer
(80 MHz, C6D6, internal reference TMS). The phase
transition points were determined using a polarization
microscope with a heating stage equipped with a
VRT-3 temperature-control unit.
1
p-Iodophenyl phenylpropargyl ether (I). A mix-
ture of 2.86 g of phenylpropargyl tosylate, 2.20 g of
p-iodophenol, and 1.38 g of potassium carbonate in
20 ml of acetone was refluxed until the conversion
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 7 2001

1132
SHCHELKUNOV et al.
Table 2. Physicochemical constants and elemental analyses of I XIV
Found, %
Calculated, %
Comp.
no.
Yield, %
mp,
C
Formula
C
H
C
H
I
II
III
IV
V
VI
VII
VIII
IX
76
68
62
72
83
68
60
79
73
69
73
70
60
63
52
55
104
64 65
33
78 79
44
74
208 210
76 77
83
75
95
71
78 79
54.01
74.19
79.59
81.94
85.98
86.25
77.58
71.14
71.12
81.28
54.15
62.59
66.54
74.22
77.48
80.34
3.37
4.59
4.81
5.91
5.66
7.76
4.83
4.25
4.29
5.10
3.12
3.51
3.67
4.58
6.10
4.82
C15H11IO
54.05
74.23
79.65
82.35
86.54
86.36
77.77
71.15
71.15
81.36
54.22
62.61
66.42
74.23
77.55
80.49
3.30
4.54
4.87
5.88
5.77
7.58
4.76
4.35
4.35
5.08
3.01
3.48
3.69
4.54
6.12
4.88
C15H11ClO
C15H11FO
C16H14O2
C15H12O
C19H20O
C16H12O3
C15H11NO3
C15H11NO3
C16H12O2
C15H10BrNO3
C15H10ClNO3
C15H10FNO3
C15H11ClO
C19H18O3
C22H16O3
X
XI
XII
XIII
XIVa
XV
XVI
37 38
116
a
20
20
n
1.6120, d 1.1617.
D
4
ACKNOWLEDGMENTS
The authors are grateful to M.E. Agel’menev for
1991, vol. 56, nos. 5 6, pp. 729 733.
2. Muldakhmetov, Z.M., Shchelkunov, S.A., Agel’me-
nev, M.E., Bazhikov, K.T., and Bobkina, S.M., Izv.
Nats. Akad. Nauk Resp. Kaz., Ser. Khim., 1993, no. 2,
pp. 20 23.
thorough determination of the phase transition points.
REFERENCES
3. Grebenkin, M.F. and Ivashchenko, A.V., Zhidkokristal-
licheskie materialy (Liquid-Crystal Materials), Moscow:
Khimiya, 1989, pp. 14 45.
1. Muldakhmetov, Z.M., Agel’menev, M.E., Bazhi-
kov, K.T., and Shchelkunov, S.A., Zh. Prikl. Spektrosk.,
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 7 2001