Synthesis and Liquid Crystalline Properties of Novel Imides and Thioimides with Chiral Aliphatic Tails

Article abstract of DOI:10.1515/znb-2003-1013

Three chiral compounds (R)-octan-2-ol, (S)-citronellol and (S)-citronellyl bromide were used for the synthesis of novel ester imides with biphenyl moieties as mesogenic units. Observations by means of polarising microscopy as well as DSC measurements revealed the presence of SmC* and/or SmA phases for all the compounds examined. It was found that the biphenyl units with long chiral alkoxy substituents induce smectic C phases.

Full text of DOI:10.1515/znb-2003-1013

Synthesis and Liquid Crystalline Properties of Novel Imides
and Thioimides with Chiral Aliphatic Tails
Andrzej Orzeszkoa,b, Dorota Melon-Ksytaa, Ewa Kowalczyka, and Krzysztof Czupryn´skib
a Agriculture University, Institute of Chemistry, ul. Nowoursynowska 159c, 02-787 Warsaw, Poland
b Military University of Technology, 00-908 Warsaw, Poland
Reprint requests to Prof. A. Orzeszko. E-mail: Orzeszkoa@delta.sggw.waw.pl
Z. Naturforsch. 58b, 1015 – 1020 (2003); received May 2, 2003
Three chiral compounds (R)-octan-2-ol, (S)-citronellol and (S)-citronellyl bromide were used for
the synthesis of novel ester imides with biphenyl moieties as mesogenic units. Observations by means
of polarising microscopy as well as DSC measurements revealed the presence of SmC∗ and/or SmA
phases for all the compounds examined. It was found that the biphenyl units with long chiral alkoxy
substituents induce smectic C phases.
Key words: Imides, Thioimides, Liquid Crystals
Introduction
SmC∗, SmC∗F [6 – 10]. A wide variety of liquid crys-
talline derivatives of (S)-citronellol were prepared and
for these compounds ferroelectric (SmC∗F) and anti-
ferroelectric (SmC∗A) phases were found [11]. This
opens the possibility to apply these compounds in
optoelectronic and display technology. It is difficult
to foresee exactly liquid crystalline properties refer-
ring only to chemical structures of a molecule. So,
in this paper we would like to present the synthesis
and examine the thermotropic behaviour of new 4’-
alkoxybiphenyl esters of trimellitimides (the IUPAC
name for trimellitimide is 5-carboxy-2,3-dihydro-1H-
isoindole-1,3-dione) with chiral tails attached to the
rigid ester imide core. It should be interesting to find
how the liquid crystalline properties are influenced
by a structure and a position of a chiral centre in
molecules. We have obtained two types of such com-
pounds. The first group are imides with chiral sub-
stituents on the nitrogen atom. The other group are es-
ter imides possessing the same substituents but con-
nected to biphenyl moieties.
Systematic studies by Kricheldorf’s group have
proved that aromatic imide moieties are relatively poor
mesogens despite their planarity, rigidity and polar-
ity [1 – 4]. Surprisingly, the symmetrical imide units
which were expected to be rather good mesogens
proved to be almost non-mesogenic. Another tendency
is observed for ester groups. They highly favour the
formation of liquid crystalline phases. It should be no-
ticed that these findings were made for high molecular
compounds such as polyimides and poly(ester imides).
However, low molecular liquid crystalline ester imides
were studied mainly by our team [5 – 10]. In our previ-
ous publication we described the synthesis of a series
of imides and thioimides with chiral N-substituents
derived from (S)-2-methylbutan-1-ol as well as (S)-2-
aminobutane [6]. Liquid crystalline smectic phases oc-
curred in all the compounds studied. The general for-
mula is recalled in Fig. 1.
Imides can be easily converted into thioimides with
Lawesson’s reagent. The comprehensive studies of
the thionation reaction mechanism have been reported
many times, also in this journal [12, 13]. Now, we have
applied our experience in this field to the preparation
of liquid crystalline monothio- and dithioimides. We
would like to compare their thermotropic properties
with those of parent trimellitimides.
Fig. 1. General structure of liquid crystalline imides and
thioimides
The presence of chiral centres in molecules may in-
The synthetic pathways to the compounds studied
duce various smectic phases, for example N∗, SmA∗, are presented in Schemes 1 and 2.
c
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1016
A. Orzeszko et al. · Novel Imides and Thioimides with Chiral Aliphatic Tails
O
O
O
O
CnH2n+l
O
OH +
CnH2n+l
O
OOC
Cl
C
O
O
n=4,11
O
1,2
3,4
O
N
H
H2NCONH2
CnH2n+l
O
OOC
3 or 4
O
5,6
O
N
CnH2n+l
O
OOC
Mitsunobu
reaction
O
5 or 6 + (R)-2-octanol
7,8
O
N
C4H9O
OOC
S
7a
S
N
7 + Lawesson's reagent
C4H9O
OOC
O
7b
S
N
C4H9O
OOC
S
7c
Scheme 1
Results and Discussion
4’-carboxylate makes it possible to identify them cor-
rectly [15]. The compounds studied have SmA or both
SmA and SmC∗ phases. The compounds 7b and 8 ex-
hibit monotropic transitions meaning that mesophases
appear on cooling only. The temperature ranges of the
mesophase are listed in Table 1.
Ester imide 7 and its sulphur analogues 7a – c de-
rived from 4’-butoxy-4-hydroxybiphenyl (1) possess-
ing an (S)-N-2-octylimide group show only the SmA
The introduction of chiral tails into rod-like struc-
tures of ester imides as well as thioimides was achieved
in two ways [14]. The compounds 7 - 9 having N-
substituents with chiral centres at α- or γ-positions
were derived from (R)-2-octanol and (S)-citronellol,
while chirality of the imides 14-16 rests in the alkenyl-
oxy chains attached to the biphenyl ring.
The DSC measurements revealed the presence of phase. The similar imide 8 with a longer aliphatic
two or three phase transitions for all compounds occur- tail attached to the biphenyl moiety (C11H23O-) also
ring on heating and/or cooling courses. Also the obser- exhibits a monotropic SmA phase. For the monoth-
vation by means of a polarising microscope proved that ioimides 7a,b and the dithioimide 7c an introduction of
all of the imides examined exhibit liquid crystalline sulphur atoms into carbonyl groups results in a reduc-
properties. They showed focal conic microscopic tex- tion of phase transition temperatures. The compounds
tures very typical for smectic mesophases. The mis- form only SmA phase, too. This is a consequence of
cibility with smectic C∗ and A phases of the well- a considerable change of the compound polarity and
known (S)-4-(2-methylbutyl)phenyl-4-octylbiphenyl- of the increase of the molecular dimensions. It should

A. Orzeszko et al. · Novel Imides and Thioimides with Chiral Aliphatic Tails
1017
O
N
Mitsunobu
C4H9O
OOC
HO
5 +
reaction
O
9
KOH
HO
OH
+
O
OH
Br
DMSO
10
O
O
10
DMF
O
+
H2N CnH2n+l
N
CnH2n+l
DCC/CH2Cl2
HOOC
HOOC
O
O
n = 4,6,9
11-13
O
N
CnH2n+l
OOC
O
O
14-16
Scheme 2
Table 1. Temperatures (◦C) and enthalpies (KJ mol−1) (italic
characters) of phase transitions of compounds studied with
DSC.
are in agreement with our previous findings [6, 10].
Also, the imide 9 with its short butoxy chain and N-
citronellyl substituent has only a SmA mesophase. It is
worth noting that its isomer, the N-butyltrimellitimide
14 carrying a citronellyl group on the opposite site of
the molecule, shows both SmA and SmC∗ phases. This
appears from comparing the DSC curves as well as
the microscopic images of liquid crystalline textures
of imides 9 and 14. The miscibility with SmC∗ and
SmA of the phase standard confirmed the above con-
clusion. The DSC curves for these isomers are◦shown
in Fig. 2. The small thermal effect at 121– 122 C cor-
responding to a SmA-SmC∗ transition exists also for
14. Fig. 3 presents the microphotographs of smectic
phases of both isomers. These pictures show quite dif-
ferent textures of the smectic phases for the two simi-
lar compounds. So-called skew smectic phases (SmC∗)
occur for 15 as well as for 16.
Com- Cr1
pound
Cr2
SmC∗
SmA
Iso
7
–
–
–
–
–
–
–
•
–
•
143.5
30.2
129.0
30.7
136.2
38.6
104.8
28.8
119.1
46.1
113.1
16.9
103.9
24.7
105.2
3.0
–
–
–
–
–
–
•
•
•
•
154.8
10.0
139.2
8.4
115.5
−8.8)a
123.2
7.9
119.0
−5.7)
180.2
8.3
•
7a
7b
7c
8
•
•
•
•
(•
•
•
•
•
•
(•
•
•
9
•
•
14
15
16
a
•
122.9
0.10
135.9
•
•
•
155.6
5.7
152.1
•
101.5
23.6
•
•
0.23 5.8
•
•
133.2
38.2
144.1
0.31
•
149.8
6.3
•
The results show that the presence of long chiral N-
substituents does not warrant the appearance of a skew
smectic phase (7 – 9). On the other hand, such aliphatic
chains connected directly to the biphenyl moiety can
involve SmC∗ phases (14– 16).
In parentheses: monotropic transitions; • presence of mesophase.
be noticed that thioimides, in contrast to other types of
thiocarbonyl compounds, are thermochemically stable.
Heating them for several hours over the clearing tem-
It should be admitted that in our previous paper we
perature does not cause their decomposition, and tem- found that for short chiral N-groups (2-methylbutyl-
peratures of phase transitions do not alter. These results and 1-methylpropyl-), smectic C∗ phases were formed,

1018
A. Orzeszko et al. · Novel Imides and Thioimides with Chiral Aliphatic Tails
OLAR equipped with a LINKAM heating stage THMs 600.
Temperatures and enthalpies were measured by means of a
DSC 141 SETARAM microcalorimeter. The measurements
were made in both heating and cooling cycles at the rate of
1 K min−1. The sample quantity was about 30 mg and spe-
cial aluminium crucibles, with good thermal contact, were
used. The hermetically sealed crucible with a sample was
heated to the sample clearing temperature and then cooled
to the crystallisation temperature. After this procedure, the
DSC measurement was started. The values of temperature
and enthalpy were read directly from the calorimeter inte-
gration curves after preliminary calibration using standards
(gallium of 99.99% purity; 6CHBT of 99.95% purity; in-
dium of 99.999% purity; tin of 99.999% purity). The ac-
curacy of phase transition temperature measurements was
about 0.1 K.
Synthesis: All the chemicals used were analytical grade
commercial products and were applied without further pu-
rification.
4’-Butyloxy-biphenyl-4-ol (1) and 4’-undecyloxybiphen-
yl-4-ol (2): These compounds were obtained as described
previously in dry DMSO on solid KOH, in room tempera-
ture; for 1: m.p. 172 ◦C [16]; for 2: m.p. 153 ◦C [16].
4-[(4’-Butyloxybiphenyl-4-yl)oxycarbonyl]phthalic anhy-
dride (3) and 4-[(4’-undecyloxybiphenyl-4-yl)oxycarbonyl]-
phthalic anhydride (4): These compounds were obtained as
described previously from trimellitanhydride chloride and
proper 4-alkoxybiphenols [6]. For 3: yield 63%; m.p. 191 ◦C
for 4 yield 58%; m.p. 174 ◦C. Analytical data of compound
4 were identical as described in a prior publication [6].
[(4-Butyloxybiphenyl-4’-yl)oxycarbonyl]phthalimide (5)
and [(4-undecyloxybiphenyl-4’-yl)oxycarbonyl]phthalimide
(6): The mixture of 2 mmol of 3 or 4 and 1 mmol of urea was
carefully melted for 5 min. Next, the alloys were powdered
and recrystallised from dry THF. For 5: yield 77%; m. p.
239 ◦C; FT-IR (CH2Cl2): ν = 3688 (N-H), 1744 (C=Oimide),
1741 (C=Oester), 1704 (C=Oimide) cm−1. Compound 6 was
identical to the one described previously; m. p. 245 ◦C [6].
N-[(S)-1-methylheptyl]-4-[(4’-butyloxybiphenyl-4’-yl)-
oxycarbonyl]phthal-imides (7) and N-[(S)-1-methylheptyl]-
4-[(4-undecyloxybiphenyl-4’-yl)oxycarbonyl]-phthalimides
(8): The general procedure of obtaining compounds 7 and
8 according to the Mitsunobu method [6, 17] is multiply
published frequently in the literature. The syntheses were
carried out from equimolar amounts of (R)-2-octanol and
imides 5 or 6, respectively. The crude products of interest
were washed with methanol, then the deposits were crys-
tallised from heptane and next purified by means of flash-
column chromatography (SiO2) using chloroform/methanol
(20:1) as an eluent.
Fig. 2. Phase transitions for 9 and 14 as measured by DSC.
too. In this case, biphenyl moieties with the long unde-
cyloxy substituent were always present [6]. The pre-
sented results as well as our former findings suggest
that SmC∗ phases may occur on the condition that the
biphenyl units contain long alkoxy tails. On the other
hand, the position of a chiral centre most likely does
not play the main role in the molecular ordering and
for the appearance of SmA or SmC∗ phases.
Experimental Section
Instrumentation: All product structures were confirmed in
the same way as described in the previous papers by FT-IR,
1H NMR and 13C NMR spectroscopy [1, 5]. The infrared
spectra (in CH2Cl2) were recorded on a Perkin-Elmer 2000
apparatus equipped with Pegrams 2000 software, and the
NMR spectra (in CDCl3) were recorded using a Varian Gem-
ini 200 MHz spectrometer. The structures were confirmed
also by elemental analysis and the data indicated by sym-
7: Yield 20%; FT-IR (CH2Cl2): ν = 1777 (C=Oimide),
bols were within 0.4% of the theoretical values. The phase 1741 (C=Oester), 1716 (C=Oimide
) ;
cm−1 1H NMR
transitions were observed using a polarising microscope BI- (200 MHz, CDCl3): δ = 0.85 (t, 3 H, CH3), 0.97 (t, 3 H,

A. Orzeszko et al. · Novel Imides and Thioimides with Chiral Aliphatic Tails
1019
Fig. 3. Smectic textures of isomers 9 and 14.
CH3), 1.25 – 2.05 (m, 16 H, CH2), 4.02 (t, 2 H, OCH2), 4.38 CDCl3): δ = 0.87 (t, 3 H, CH3), 0.96 (t, 3 H, CH3), 1.21 –
(m, 1 H, NCH), 6.96 – 7.00 (m, 2 H), 7.30 (m, 2 H), 7.50 – 2.07 (m, 30 H, CH2), 4.02 (t, 2 H, OCH2), 5.04 (m, 1 H,
7.66 (m, 4 H), 7.99 (m, 1 Himide), 8.55 – 8.65 (m, 2 Himide); NCH), 6.96 – 7.00 (m, 2 H), 7.30 (m, 2 H), 7.50 – 7.66 (m,
calcd. C 75.63, H 7.93, N 2.45; found C 75.69, H 7.94, 4 H), 7.91 (m, 1 Himide), 8.52 – 8.74 (m, 2 Himide); calcd.
N 2.50.
8: Yield 27%; FT-IR (CH2Cl2): ν = 1777 (C=Oimide),
1740 (C=Oester), 1715 (C=Oimide) cm−1 1H NMR
C 73.56, H 7.72, N 2.38, S 5.45; found C 73.44, H 7.67,
N 2.35, S 5.4.
;
7c: Yield 29%; FT-IR (CH2Cl2): ν = 1742 (C=Oester),
(200 MHz, CDCl3): δ = 0.85 (t, 3 H, CH3), 0.95 (t, 3 H, 1287 (C=S) cm−1; 1H NMR (200 MHz, CDCl3): δ = 0.82 –
CH3), 1.22,– 2.06 (m, 30 H, CH2), 4.00 (t, 2 H, OCH2), 4.33 2.56 (m, 36 H), 4.02 (t, 2 H, OCH2), 5.60 (m, 1 H, NCH),
(m, 1 H, NCH), 6.96 – 7.00 (m, 2 H), 7.30 (m, 2 H), 7.50 – 6.96 – 7.00 (m, 2 H), 7.30 (m, 2 H), 7.50 – 7.66 (m, 4 H),
7.66 (m, 4 H), 7.99 (m, 1 Himide), 8.55 – 8.65 (m, 2 Himide); 8.04 (m, 1 Himide), 8.60 – 8.65 (m, 2 Himide); calcd. C 71.60,
calcd. C 77.09; H 8.88; N 2.09; found C 77.15; H 8.92; H 7.52, N 2.32, S 10.62; found C 71.45, H 7.57, N 2.35,
N 2.01.
S 10.99.
Synthesis of monothioimides (7a,b) and dithioimide (7c):
(S)-N-2-(3,7-Dimethyl-oct-6-enyl)-4-[(4-butyloxybiphen-
The thionation procedure by means of Lawesson’s reagent yl-4’-yl)oxy-carbonyl]phthalimide (9): The synthesis was
was the same as described previously [6, 10, 13]. Also, the the same as for the ester imides 7,8. Compound 5 and
separation and identification of monothioimides, as well as (S)-citronellol were used as substrates.
of the dithioimide were performed according to the method
described in detail.
Yield 29%; FT-IR (CH2Cl2): ν = 1776 (C=Oimide),
1742 (C=Oester), 1736 (C=Oimide
) ;
cm−1 1H NMR
7a: Yield 18%; FT-IR (CH2Cl2): ν = 1741 (C=Oester0), (200 MHz, CDCl3): δ = 0.96 – 1.03 (m, 12 H, CH3), 1.58 –
1736 (C=Oimide), 1277 (C=S) cm−1 1H NMR (200 MHz, 2.06 (m, 11 H, CH2), 3.75 (t, 2 H, OCH2), 4.01 (t, 2 H,
;
CDCl3): δ = 0.85 (t, 3 H, CH3), 0.97 (t, 3 H, CH3), 1.24 – NCH2), 6.96 – 7.00 (m, 2 H), 7.30 (m, 2 H), 7.50 – 7.64
2.07 (m, 30 H, CH2), 4.01 (t, 2H, OCH2), 5.03 (m, 1H, (m, 4 H), 7.99 (m, 1Himide), 8.55 – 8.67 (m, 2 Himide);
NCH), 6.96 – 7.00 (m, 2H), 7.30 (m, 2H), 7.50 – 7.66 (m, calcd. C 76.13, H 7.77, N 2.40; found C 76.17, H 7.77,
4 H), 8.02 (m, 1 Himide), 8.59 – 8.62 (m, 2 Himide); calcd. N 2.34.
C 73.56, H 7.72, N 2.38, S 5.45; found C 73.44, H 7.68,
N 2.25, S 5.40.
4’-[(S)-3,7-Dimethyl-oct-6-enyloxy]biphenyl-4-ol (10):
This compound was obtained as described previously from
7b: Yield 20%; FT-IR (CH2Cl2): ν = 1742 (C=Oester), 4,4-dihydroxybiphenyl and (S)-citronellyl bromide [16].
1736 (C=Oimide), 1257 (C=S) cm−1 1H NMR (200 MHz, M. p. 118 ◦C; yield 33%.
;

1020
A. Orzeszko et al. · Novel Imides and Thioimides with Chiral Aliphatic Tails
N-Alkyltrimellitimides (11-13): Trimellitimides with N- 2.06 (m, 11 H, CH2), 3.78 (t, 2 H, OCH2), 4.00 (t, 2 H,
butyl, N-hexyl and N-nonyl substituents were synthesized NCH2), 6.96 – 7.00 (m, 2 H), 7.30 (m, 2 H), 7.50 – 7.66 (m,
according to the well known and patented method from 4 H), 7.99 (m, 1 Himide), 8.55 – 8.67 (m, 2 Himide); calcd.
trimellitic anhydride and proper amines in dry boiling C 76.13, H 7.77, N 2.40; found C 76.19, H 7.76, N 2.36.
DMF [18].
N-Alkyl-4-[(S)-4’-citronellylbiphenyl-4’-yl)oxycarbonyl]-
15: Yield 32%; FT-IR (CH2Cl2): ν = 1777 (C=Oimide),
1741 (C=Oester), 1736 (C=Oimide); 1H NMR (200 MHz,
CDCl3): δ = 0.96 – 1.03 (m, 12 H, CH3), 1.58 – 2.06 (m,
15 H, CH2), 3.75 (t, 2 H, OCH2), 4.01 (t, 2 H, NCH2), 6.96 –
7.00 (m, 2 H), 7.30 (m, 2 H), 7.50 – 7.64 (m, 4 H), 7.99 (m,
1 Himide), 8.55 – 8.67 (m, 2 Himide); calcd. C 77.07, H 7.46,
N 2.40; found C 77.17, H 7.49, N 2.32.
phthalimide (14-16): The general procedure of obtaining
compounds 14-16 were frequently published in the literature
[6 – 10]. The synthesis was carried out from mesogenic units
10 and proper N-alkyltrimellitimides 11-13 in methylene
chloride using dicyclohexylcarbodiimide (DCC) and DMAP
as catalyst. The crude products of interest were crystallised
from a benzene/methanol mixture and then the crystals were
purified by means of flash-column chromatography (SiO2)
using chloroform/methanol (20:1) as an eluent.
16: Yield 34%; (CH2Cl2): ν = 1776 (C=Oimide), 1741
(C=Oester), 1735 (C=Oimide) cm−1 1H NMR (200 MHz,
;
CDCl3): δ = 0.96 – 1.03 (m, 12 H, CH3), 1.56 – 2.09 (m,
21 H, CH2), 3.75 (t, 2 H, OCH2), 4.01 (t, 2 H, NCH2), 6.96 –
7.00 (m, 2 H), 7.30 (m, 2 H), 7.50 – 7.64 (m, 4 H), 7.99 (m,
1 Himide), 8.55 – 8.67 (m, 2 Himide); calcd. C 77.15, H 8.48,
N 2.14; found C 77.17, H 8.49, N 2.10.
14: Yield 28%; FT-IR (CH2Cl2): ν = 1776 (C=Oimide),
1742 (C=Oester), 1736 (C=Oimide
) ;
cm−1 1H NMR
(200 MHz, CDCl3): δ = 0.96 – 1.08 (m, 12 H, CH3), 1.59 –
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