National Journal of Chemistry,2010, Volume 40, 664-673
‫ المجلد األربعين‬0202-‫المجلة القطرية للكيمياء‬
Synthesis and Characterization of Liquid Crystalline Behaviour of New
Materials Incorporating Two Heterocyclic 1,3,4-Oxadiazole and 1,3,4Thiadiazole Rings
Maha T. Sultan, Jumbad H. Tomma, Isam A. Latif, and Ammar H. Al-Dujaili*
Department of Chemistry, College of Education Ibn Al- Haitham, University of Baghdad
Baghdad, Iraq
(NJC)
(Recevied on 23/5/2010)
(Accepted for publication 29/11/2010)
Abstract
The synthesis and mesomorphic properties of 5-(4-methoxyphenyl)-2-[2-(4'-nalkoxy)-1,3,4-thiadiazole-5-methylenethio]-1,3,4-oxadiazole (series [VI]n), were described
for the number of the carbon atoms in alkoxy chains varying from 1-8. In addition, four
compounds containing 4'-chloro [VI]a, 4'-nitro [VI]b, 4'-methoxate [VIII]1 and 4'-heptoxate
[VIII]7 instead of 4'-alkoxy group were also synthesized to study the effect of terminal
substituent. All compounds have been characterized by elemental analysis, and FTIR, mass
1
HNMR spectrometry. The liquid crystalline properties were investigated by differential
scanning calorimetry (DSC) and optical polarized microscopy (OPM). The homologous with
n=2-4 show enantiotropicnematicmesophase. The higher homologous (n = 5-8) and
compound with 4'-heptaloxate [VIII]7 substituent show enantiotropicnematic and smectic
phases. Finally, the three compounds 4'-chloro [VI]a, 4'-nitro [VI]b, and 4'-metoxate [VIII]1
did not show any mesomorphic properties.
‫الخالصة‬
5-(4-methoxyphenyl)-2-)[2-(4'-n-alkoxy)-‫لقد ددد حد ددد حسةد ددير اد ارود ددة الل د دااس ال لاريد ددة الود ددا لة للولود ددلة‬
‫ ابمعاةدداا الكايوددية يرددا راا‬1,3,4-thiadiazole-5-methylenethio]-1,3,4-oxadiazole (series [VI]n
‫[ ااالود ددحر‬VI]b ‫ند ددايحرا‬-4 ‫[ ا‬VI]a ‫يلد ددارا‬-4 ‫ اةد ددا ة ل د د ل حد ددد حسةد ددير ارب د د مريبد دداا ا د د‬.) 8-1 ‫الكد دداربان مد ددن‬
‫ حدددد ح ددليس بعد ددا د د د المريب دداا باود ددحلداد الحسليد د الد ددد ي‬.[VIII]7 ‫[ ااالو ددحر الر حايود ددايا‬VIII]1 ‫الميثايو ددايا‬
‫) ابراحددان الدرنين الندداان الميناطيود‬MS ‫للعناصددر امطيدداك الكحلددة‬
‫) يمددا احددد ح ليصددرا جميعددا باوددحلداد‬1H-NMR
‫) االمجردر ن الةداء المودحقطل المد اد‬DSC
.)FTIR ‫مطيا ية اال عة اق السمراء عالية االداء‬
‫لصا اللااس ال لارية الوا لة بأوحلداد موعر الموح الحفاةل‬
‫) لدااس لاريددة ودا لة نيماحيدة ينمدا ظهرددرا‬n=2-4
‫) مد‬VI n ‫ لقدد ظهردرا مريبدداا الولودلة‬.)OPM ‫بمنصدة حودلين‬
.‫ حالايود لدااس لاريددة ودا لة محعدددد االطداار النيماحيددة االوددميحية‬-4 ‫) اةدا ة الددل المريدل‬n=5-8 ‫مريبداا الولوددلة‬
‫[ ظن لدااس لاريدة ودا لة اانمدا انحقلدا مدن الطدار ال لدارن الدل الطدار‬VIII]7 [VIII]1 [VI]1 ‫ينمدا لدد حهردر المريبداا‬
. ‫االي احراب مبا ر‬
*To whom all corresponding should be addressed
E.Mail:ahdujaili@yahoo.com
664
‫ المجلد األربعين‬0202-‫المجلة القطرية للكيمياء‬
National Journal of Chemistry,2010, Volume 40
Introduction
are one of the most widely investigated
During the last decades a large number of
classes
liquid crystalline compounds containing
synthesis and studied symmetrical bi-
heterocyclic units have been synthesized (1-
1,3,4-oxadiazole derivatives [1] and [2]
7)
respectively,
. 1,3,4-Oxadiazole and 1,3,4-thiadiazole
derivatives , a
whichwere
phase
18)
exhibited
liquid
crystalline
behaviour.
consisting of
oxygen or sulfur atoms,
O
R2
R2
OC
O
O
O
CO
OR
[1]
O
N N
O
CO
R1
O
R2
O
OC
N N
RO
N N
N N
nitrogen and
. Recently Zhang et al.(17,
smecticC
type of five membered
heterocyclic compounds
(8-16)
R2
R1
[2]
The goal of this work was the synthesis
Instruments: Uncorrected melting points
and study liquid crystallinebehaviour of
were determined by using an Electro
new design of novel thermotropic liquid
thermal melting point apparatus. FTIR
crystalline compounds containing two
spectra
types of heterocyclicring in the same
Shimadzu Spectrophotometer by using
molecule namely, 1,3,4-oxadiazole and
potassium bromide disc. 1H-NMR spectra
1,3,4-thiadiazol rings with SCH2bridge.
were obtained with a Varian Mercury plus
Experimental
spectrometer 400 MHz instrument using
MATERIALS : Most of chemicals used
suitable duterated solvent and TMS as
were supplied from Flukaand Aldrich
internal standard.The optical behavior
Chemicals, and were used without further
observations were made using Olympus
purification .
BX40
were
recorded
microscope
on
equipped
a
8400S
with
a
LeitzLaborlux 12 Pols hot stage and
665
National Journal of Chemistry,2010, Volume 40
‫ المجلد األربعين‬0202-‫المجلة القطرية للكيمياء‬
PR600 controller. The textures shown by
solution of sodium hydroxide (10 mL)
the compounds were observed using
was added, the mixture was refluxed for
polarized light with crossed polarizers with
3hrs. After cooling, the solution was
the sample in a thin film sandwiched
acidified with concentrated hydrochloric
between a glass slide and cover slip.
acid(22). The precipitate was filtered and
Differential scanning calorimetry (DSC)
recrystallized from ethanol to yield pale
measurements were conducted with TA
yellow solid 82%, m.p=160-163oC.
instruments Q1000 DSC, Ramp rate: 10
FTIR (KBr disc , cm-1 ) ν : 2750-3298 (OH
degree
under
of CO2H) ; 2960 (CH aliph.) ; 1685 (C=O
nitrogen atmosphere. Temperature and
of carboxylic moeity) ; 1616 (C=N in
heat flow calibrated with standard indium
oxadiazole ring) ; 1595 (C=C benzene
of purity <99.99%.
ring) ; 1255 (CO , ether) ; 840 of bending
Synthesis of Compounds
para substituted benzene ring .MS: m/z=
centigrade
Preparation
carboxylic
minute
of
acid
methoxy
per
n-alkylbromide,
266.
chlorides,methyl-4-
benzoate[I]
5-(4-Methoxyphenyl)-2-(2-amino-1,3,4-
and4-n-
alkoxybenzaldehyde
thiadiazole-5-methylenethio)-1,3,4-
were
preparedaccording to references
(19,20)
oxadiazole[V]
.4-
A mixture of compound [IV] (0.01mol),
Methoxyphenylhydrazide [II] and 5-(4-
thiosemicarbazide
methoxyphenyl)-1,3,4-oxadiazole-2-
phosphorusoxychloride(10
thiol[III] were
prepared according to
refluxed gently for 48 hs. After cooling,
procedure previously described in our
ice water (50 mL) was added in portions
previous work(21) .
with stirring. The yellow precipitate was
The new compounds were synthesized
filtered,
according
recrystallized from ethanol, yield 60%
to
Scheme
1
by
the
washed
(0.01mol),
with
mL)was
hot
water(23),
following general procedure.
,m.p196-198oC.
5-(4-Methoxyphenyl)-2-thioaceticacid
FTIR (KBrdisc , cm-1 ) ν : two peaks at
1,3,4-oxadiazole[IV]
3213 and 3100 (NH2 , asym.and sym.);
To a stirring of -chloro acetic acid
(0.01mol)
in
hydroxide
(10
10%
mL),
aqueous
a
2839-2935 (CH aliph.) ;two peaks around
1615 and 1606 (C=N in oxadiazole and
sodium
solution
thiadiazole rings) and 835 of bending para
of
substituted benzene ring.
oxadiazole [III] (0.01mol) in 10% aqueous
666
‫ المجلد األربعين‬0202-‫المجلة القطرية للكيمياء‬
National Journal of Chemistry,2010, Volume 40
1
HNMR (DMSO ,ppm) δ : 7.9-9.9(d-d ,
FTIR of compounds [VII] (KBr disc , cm) ν : 3414 (OH group) ; 3093-(CH
4H , aromatic proton);6.4(broad s, 2H ,
1
NH2); 6.0 (s, 2H , SCH2);4.6 (s , 3H ,
aromatic) ; 2928 (CH aliph.) ; 1650 (C=N ,
OCH3).
imin group) ; 1255-1265 (CO , ether) ;
5-(4-Methoxyphenyl)-2-[2-(4'-
833 of bending para substituted benzene
substituted
ring .MS: m/z = 425.
or
hydroxybenzelidene-
amino)-1,3,4-thiadiazole-5-
5-(4-Methoxyphenyl)-2-[2-(4'-n-
methylenethio]1,3,4-oxadiazole [VI]a,b,n
acyloxybenzelideneamino)-1,3,4-
and [VII]
thiadiazole-5-methylenethio]1,
A mixture of compound[III] (0.001mol) ,
oxadiazole [VIII]m
4-substitutedbenzaldehyde (0.012 mol),
To a stirred solution of compound[VII]
ethanol absolute (10mL)
and 3drops of
(0.01mol), Et3N (0.02) in dried mixture of
glacial acetic acid was refluxed for 5 hs.
(4mL DMF : 6 mL THF), was added
After cooling the precipitate solid was
dropwise
filtered
0.014mol) at (0-4)oC . After the addition
and
recrystallized
using
chloroform.
Calc.
carboxylic
acid
3,
chloride
4-
(
had been completed the mixture was
[VI]1,
stirred for 3hs at the same temperature .
C20H17O2N5S2, C%, 54.67; H%, 3.87; N%,
The reaction mixture was poured into
15.95; Found: C%, 54.65; H%, 4.01; N%,
(50mL) ice-water then the mixture was
15.75. MS:m/z+1 = 440.
extracted by adding (50mL)
FTIR (KBr disc, cm-1 ) ν : 3003-3076(CH
The ether solution was evaporated to give
aromatic) ; 2837-2958 (CH aliph.); 1640
a residue which was dried in air . FTIR of
(C=N , imin group); 1259 (CO , ether);
compounds [VIII]1 (KBr disc , cm-1 ) ν :
831 of bending para substituted benzene
2852-2955 (CH aliph.) ; 1730(C=O , ester
ring
group) ; 1645 (C=N , imin group) ; 1257
1
for
compounds
HNMR (DMSO , ppm) δ : 9.8 (s , 1H ,
(CO , ether)
CH=N ) ; 7.7-7.9 (d-d , 4H , aromatic
; 835 of
of ether .
bending para
substituted benzene ring.MS: m/z=467.
proton) ; 6.9-7.1(m, 4H aromatic ,
N=CHPh ) ; 3.6 (s, 2H , SCH2) ; 2.6 (s ,
3H , OCH3 near from oxadiazole ring) ;
2.2 (s , 3H , OCH3 near from shiff base).
667
‫ المجلد األربعين‬0202-‫المجلة القطرية للكيمياء‬
National Journal of Chemistry,2010, Volume 40
Results and Discussion
these compounds and FTIR spectroscopy
Synthesis and Characterization
for all synthesized compounds confirmed
Scheme 1 outline the synthesis of the
the structural formula and indicating
eight compounds of series [VI]n and four
structure of respective compounds.The
compounds [VI]a,
physical
[VI]b,
[VIII]1 and
1
for
all
synthesized
compounds are listed in Table 1.
[VIII]7. The elemental analysis and mass
and
data
HNMR spectroscopy of some of
Table 1: Physical data of series [VI]n and compounds [VI]a, [VI]b, [VIII]1 and[VIII]7.
Comp.
Yield
X-
R_
Formula
[VI]a
NO2
-
C19H14N6O4S2
75
Orange
[VI]b
Cl
-
C19H14N5O2S2Cl
80
Green
[VI]1
OCH3
-
C20H17N5O3S2
65
Yellow
[VI]2
OC2H5
-
C21H19N5O3S2
40
Brown
[VI]3
OC3H7
-
C22H21N5O3S2
64
Yallow
[VI]4
OC4H9
-
C23H23N5O3S2
60
Yallow
[VI]5
OC5H11
-
C24H25N5O3S2
40
Brown
[VI]6
OC6H13
-
C25H27N5O3S2
44
Brown -Yallow
[VI]7
OC7H15
-
C26H29N5O3S2
42
Brown -Yallow
[VI]8
OC8H17
-
C27H31N5O3S2
76
yellow
[VIII]1
-
CH3
C21H17N5O4S2
40
Green-Brown
[VIII]7
-
C7H15
C28H31N5O4S2
52
Brown -Yallow
No.
All
Color
compounds
temperatures obtained by (DSC) and
scanning
verified by (POM) for all eight compounds
calorimeter (DSC) and verified by hot-
of series [V]nand four compounds [VI]a,
stage
[VI]b,
examined
synthesized
%
by
optical
differential
polarizing
microscopy
(OPM). Table 2 collects the transition
[VIII]1
and
[VIII]7.
The
ethercompounds [VI]nwith n=2-8 and ester
668
National Journal of Chemistry,2010, Volume 40
compound
[VIII]7
exhibited
showed anisotropic fluid after melting.
The
The compounds [VI]n with n=5-8 and
[VI]1and
[VI]8displayed enantiotropicnematic and
mesomorphicbehaviour.
compounds[VI]a,
[VI]b,
‫ المجلد األربعين‬0202-‫المجلة القطرية للكيمياء‬
[VIII]1did not show any liquid crystalline
smecticSm
properties but simply change from solid
typicalfocal conicsmectic A texture of
crystal to isotropic liquid .
[VI]8
The ether compounds [VI]n with n= 2-4
characteristic of the nematic phase was
showed pure enantiotropicnematic phase
observed as shown in Figure 2.
and
phases.Figure1
theSchlieren
shows
texture
(nematogene), All three compounds of
series were they examined under POM
Table 2: Liquid crystalline transition temperatures ( oC) of series [VI]n and compounds
[VI]a, [VI]b, [VIII]1 and [VIII]7.
Comp.
No.
Cr SmN
I
[VI]a
•
150 -
[VI]b
•
168-
[VI]1
•162.5
- -•
[VI]2
•170
- •252
[VI]3
•181
- • 269
[VI]4
•138
-
[VI]5
•145
• 187
[VI]6
•132
•
[VI]7
•147
•
[VI]8
•131
•194
[VII]1
•>300•
[VII]7
• 117
-•
•
-
•177
•
•
• 192
• 223
•
182
•
•215
185
•
• 238
• 221
• 220•
669
•
•
‫ المجلد األربعين‬0202-‫المجلة القطرية للكيمياء‬
National Journal of Chemistry,2010, Volume 40
CH3O
COOH
MeOH
H2SO4
CH3O
COOMe
[I]
NH2NH2
CH3O
CONHNH 2
[II]
CS2
KOH
N N
CH3O
SH
O
[III]
ClCH2COOH
NaOH
N N
CH3O
O
[IV]
SCH2COOH
POCl3
N N
CH3O
N N
SCH2
O
[V]
XPhCHO
CH3O
N N
O
NH 2
S
HOPhCHO
N N
SCH2
S
[VI] a,b,n
N=CH
X
X= OR ; R = CnH2n+1 ; n=1-8 ; [VI]n
or X= NO2 , Cl ;
[VI]a,b
N N
N N
CH3O
O
SCH2
[VII]
N=CH
S
OH
RCOCl
ET3N
N N
N N
CH3O
R = methyl ; [VIII]1
or heptyl ; [VIII]7
O
Scheme 1
670
SCH2
[VIII]m
N=CH
S
OCOR
National Journal of Chemistry,2010, Volume 40
‫ المجلد األربعين‬0202-‫المجلة القطرية للكيمياء‬
Figure 1 : Polarizing micrograph ofSmectic phaseSA(x200 magnification) of compound
[VI]8 at 150 oC on heating.
Figure 2 : Polarizing micrograph of schlieren texture of the nematicphase(x200
magnification) of compound [VI]8 at 210 oC on heating.
high
Liquid Crystalline Behaviour
may
be
cause
disappear
This behaviour of above could be
mesomorphicbehaviour
explain in term of terminal /lateral (t/l)
[VI]a,b,1and [VIII]1(23) .
interaction forces ratio . When this ratio is
The phase transition temperatures versus
high, compounds tend to give less ordered
the number of carbon atoms of alkyl chain
mesophases
(n) of compounds [VI]n are plotted in
(nematicmesophase)as
as
the
compounds
Figure 3, from this Figure one can see:
compounds [VI]2-4. While this ratio is low
that mean the alkyl group is now
1) The usual odd-even effect of the
sufficiently long and thus more polarizable
nematic –isotropic transitions andcrystal-
to overcome residual terminal cohesive
smectic transitions can be clearly seen
forces
from this Figure3. The liquid crystalline
and
smectic
phaseappear,
as
compounds [VI]5-8 and ester compounds
thermal
[VIII]7 . Finally, when this ratio is very
(temperature difference temperature) is
671
stability
of
nematic
phase
‫ المجلد األربعين‬0202-‫المجلة القطرية للكيمياء‬
National Journal of Chemistry,2010, Volume 40
some what wider for the odd member than
3) All compounds [VI] with n=2-8
for the even members. While the thermal
except n=4 shows good phase range and
stability of smectic phase is wider for even
thermal
member thanfor the odd member .
exhibited low transition temperatures of
2) The increase of (n) of alkyl group
of
CnH2n+1O-
stability,
compound
[VI]4
the nematic to isotropic and a narrow
in the series [VI]n were
phase range.
found to play an important role in
mesophase type and formation
280
N to I
Temperature ( oC )
260
Sm to N
240
220
200
180
160
0
1
2
3
4
5
6
7
8
9
10
No. of carbon atoms (n)
Figure 3: Plot of transition temperature against alkyl chain length (n) of series [VI]n.
Acomparison
of
the
mesomorphic
liquid crystalline behaviourwith a narrow
properties and transition temperatures of
range of transition temperatures and lower
these compounds [VI]n n=1-8 with a
thermal stability . probably, the high
homologous series (24) of structural
thermal stability of our ether compounds
formula [3]n one can found that the later
[VI]nis due to that the 1,3,4-oxadiazole
compound [3] with n=2,4 and 5 did not
core give rise to
show any liquid crystalline properties only
polariazble ring than the 1,2,4-triazole
compounds [3] with n= 1 and 3 exhibited
ring.
N
N
H3CO
N
N
S-CH2
N
H
N=CH
S
[3]n
R= CnH2n+1 , n=1-5
672
more planar and
OR
National Journal of Chemistry,2010, Volume 40
‫ المجلد األربعين‬0202-‫المجلة القطرية للكيمياء‬
15)A. H. Al- Dujaili , N. R. Jaber , and A.
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