Pyrimidine compounds and their use as liquid crystals

The present invention discloses an optically active pyrimidine compound represented by the following general formula: ##STR1## wherein, n is 3 to 5; X is hydrogen atom or chlorine atom; when X is hydrogen atom, R.sub.1 is normal alkyl having from 1 to 12 carbon atoms and when X is chlorine atom, R.sub.1 is hydrogen atom or normal alkyl having from 1 to 12 carbon atoms; R.sub.2 is normal alkyl having from 1 to 18 carbon atoms; and C* represents an asymmetric carbon atom.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an optically active pyrimidine compound which is 
a liquid crystal compound useful as an electrooptic element which has 
excellent properties at high temperature. 
2. Description of the Prior Art 
Liquid crystals have been employed as various electrooptic elements such as 
a display device of a watch or an electronic calculator. Most of liquid 
crystal display devices which have been put into practical use hitherto 
are those wherein the dielectric orientation effect of a nematicor 
cholesteric liquid crystal is utilized. However, the application of these 
liquid crystals to a display device involving a large number of pixels is 
accompanied by some troubles such as a low response, poor contrast caused 
by the lack of drive margin and unsatisfactory visual angles. Therefore, 
there has been frequently attempted to develop a MOS or TFT panel 
involving formation of a switching device for each pixel. 
U.S. Pat. No. 4,367,924 has disclosed a liquid crystal device wherein a 
smectic phase based on a novel displaying principle is used to thereby 
overcome the disadvantages as described above. 
Further it has been known that a liquid crystal compound exhibiting a C* or 
H phase consisting of opticallyactive molecules generally has an 
electrical dipole density P and is ferroelectric. Such a chiral smectic 
liquid crys-tal having electrical dipoles is more strongly affected by an 
electric field than dielectric anisotropic ones. As a result, the polarity 
of P is made parallel to the direction of the electric field. Thus the 
direction of the moleculescan be controlled by reversing the direction of 
the applied electric field. Then the average change in the direction of 
the major axes of these molecules is detected with the use of two 
polarizing plates. Thus the liquid crystal can be used as an 
electroopticelement. 
The effect of the spontaneous polarization of this electrooptic element, 
wherein the response of the smectic C* or H phase to an electric field is 
utilized, and the electric field exert an action 10.sup.3 to 10.sup.4 
times as high as thoseof dielectric anisotropic ones. Thus the former 
shows a high-speed response compared with a TN liquid crystal device. 
Further it is possible to impart thereto a memory function by 
appropriately controlling the orientation. Therefore itis expected to 
apply the same to a high-speed optical shutter or to a display of a large 
capacity. 
There have been synthesized various chiral smectic liquid crystal compounds 
having a ferroelectricity and the properties therefof have been studied. 
For example, an optically active 2-(4-alkoxyphenyl)-5-alkylpyrimidine 
compound has been proposed as a compound which is stable to water and 
shows a chiral smectic phase within a wide range of temperature in 
Japanese Patent Laid-Open Nos. 93170/1986 and 129169/1986. 
However, each compound as described above is available only within a 
restricted range of temperature. Namely, itsinsufficient properties, in 
particular, at a high temperature make it unsatisfactory from the 
practical viewpoint. 
SUMMARY OF THE INVENTION 
It is the main object of the present invention to provide a compound useful 
as a liquid crystal which is suitablefor preparing a composition available 
over an unlimited temperature range and, in particular, having a liquid 
crystal temperature at higher temperature. 
We have attempted to develop a pyrimidine liquid crystal compound which 
shows a chiral nematic phase (N*) and/or chiral smectic phase (SmC*) over 
a wide temperature range. As a result, we have found that an optically 
activepyrimidine compound of the following general formula, wherein an 
alkyl group has an asymmetrical carbon atom shows a chiral nematic phase 
and/or a chiral smectic phase over a wide range of temperature involving, 
in particular, a high temperature region, thus completing the present 
invention. 
##STR2## 
wherein, n is 3 to 5; X is hydrogen atom or chlorine atom; when X is 
hydrogen atom, R.sub.1 is normal alkyl having from 1 to 12 carbon atoms 
and when X is chlorine atom, R.sub.1 is hydrogen atom or normal alkyl 
having from 1 to 12 carbon atoms; R.sub.2 is normal alkyl having from 1 to 
18 carbon atoms; and C* represents an asymmetric carbon atom.

DETAILED DESCRIPTION OF THE INVENTION 
The compound of the present invention as represented by the above general 
formula can be prepared by a common methodused in synthesizing 
phenylpyrimidine compounds. 
For example, it may be prepared by esterifying 
5-alkyl-2-(4-hydroxyphenyl)pyrimidine with corresponding 4-opticallyactive 
alkoxy benzoic acid; or by esterifying 4-cyanophenol with corresponding 
4-optically active alkoxy benzoic acid and converting the resulting 
product into pyrimidine in a conventional manner. 
A 5-alkyl-2-(4-hydroxyphenyl)pyrimidine compound may be prepared by a 
conventional method comprising, for example, converting 4-cyanophenol into 
a benzyl ether in a conventional manner, converting the resulting ether 
into 4-benzyloxy-benzamidine hydrochloride, reacting the obtained product 
with an n-alkylmalonic acid diester to give a 
2-(4-benzyloxyphenyl)-4,6-dihydroxy-5-n-alkylpyrimidine and then 
thenchlorinating and reducing the product. 
The obtained compound of the present invention as represented by the above 
general formula can be used alone as a liquid crystal material. 
Alternately it can be mixed with other liquid crystal compound(s). 
To further illustrate the present invention, the following Examples will be 
given. 
EXAMPLE 1 
Synthesis of (R)-4-(6'-chloro-4'-methylhexyloxy) benzoic acid 
4-(5'-n-octyl-2'-pyrimidinyl)phenyl ester 
##STR3## 
1.08 g of (R)-4-(6'-chloro-4'-methylhexyloxy)benzoic acid ([.alpha.].sub.D 
=+5.00.degree., C=1, at 25.degree. C., CHCl.sub.3 solution), 1.14 g of 
4-(5'-n-octyl-2'-pyrimidinyl)phenol, 0.83 g of 
N,N'-dicyclohexylcarbodiimide, 0.08 g of 4-pyrrolidinopyridine and 20 ml 
of dichloromethane were stirred for three hours at room temperature. 
The precipitated dicyclohexylurea were filtered and 2.59 g of crude product 
was obtained by removal of solvent. 
The product was purified on a silica gel column with the use of 
hexane/ethylacetate (85/15) as a developing solvent. Thus 1.79 g of 
(R)-4-(6'-chloro-4'-methylhexyloxy) benzoic acid 
4-(5'-n-octyl-2'-pyrimidinyl)phenyl ester was obtained. 
Infrared spectroscopy (cm.sup.-1) 2900(s), 2850(s), 1725(s), 1600(s), 
1580(m), 1540(vw), 1510(m), 1460(m), 1430(s), 1385(vw), 1310(m), 1250(vs), 
1200(s), 1160(s), 1075(m), 1055(m), 1010(m), 885(m), 845(m), 790(m), 
760(m), 720(w), 685(w), 650(m), 550(vw), 505(vw) and 475(vw). 
Optical rotation [.alpha.].sub.D =+3.64.degree. (C=1, CHCl.sub.3 solution, 
26.degree. C.). 
This compound was poured into a transparent glass cell and the following 
phase transition was observed under a polarization microscope. 
##STR4## 
It has been confirmed that the above compound of the present invention 
shows an N* phase over a wide temperature range involving a temperature 
higher than 120.degree. C., which obviously suggests that it is suitable 
for the preparation of a composition showing a high liquid crystal 
temperature. 
EXAMPLE 2 
Synthesis of (R)-4-(6'-chloro-4'-methylnonyloxy) benzoic acid 
4-(5'-n-decyl-2'-pyrimidinyl)phenyl ester 
##STR5## 
The procedure of Example 1 was followed using 1.25 g of 
(R)-4-(6'-chloro-4'-methylnonyloxy)benzoic acid ([.alpha.].sub.D 
=+3.37.degree., C=1, at 23.degree. C., CHCl.sub.3 solution) and 1.26 g of 
4-(5'-n-decyl-2'-pyrimidinyl)phenol and 2.70 g of crude product was 
obtained. 
The product was purified on a silica gel column with the use of 
hexane/ethylacetate (90/10) as a developing solvent. Thus 2.08 g of 
(R)-4-(6'-chloro-4'-methylnonyloxy) benzoic acid 
4-(5'-n-decyl-2'-pyrimidinyl)phenyl ester was obtained. 
Infrared spectroscopy (cm.sup.-1) 2900(s), 2850(s), 1720(s), 1600(s), 
1585(m), 1545(w), 1510(w), 1460(m), 1425(s), 1380(vw), 1310(vw), 1250(vs), 
1200(s), 1165(s), 1075(m), 1055(m), 1010(m), 930(vw), 885(w), 845(m), 
790(m), 760(m), 720(vw), 690(vw), 650(w), 610(vw), 550(vw) and 510(vw). 
Optical rotation [.alpha.].sub.D =+2.64.degree. (C=1, CHCl.sub.3 solution, 
26.degree. C.). 
This compound was poured into a transparent glass electrode cell of 2 .mu.m 
in thickness, which had been subjected to orientation by rubbing, and 
heated to 140.degree. C. to thereby give an isotropic liquid. 
The liquid crystal cell thus obtained was cooled under a crossed Nicol 
prism while applying rectangular pulses (15 V. 1 Hz) thereto. As a result, 
definite switching behaviors were observed from 66.1 to -3.degree. C. 
The following phase transition was observed under a polarization 
microscope. 
##STR6## 
It has been confirmed that the above compound of the present invention 
shows an N* phase over 100.degree. C. and SmC* phase at 66.degree. C., 
which obviously suggests that it is suitable for the preparation of a 
composition showing a high liquid crystal temperature. 
EXAMPLE 3 
Synthesis of (S)-4-(4'-methyloctoxy)benzoic acid 
4-(5'-n-decyl-2'-pyrimidinyl)phenyl ester 
##STR7## 
The procedure of Example 1 was followed using 1.06 g of 
(S)-4-(4'-methyloctoxy)benzoic acid ([.alpha.].sub.D =+3.53.degree., C=1, 
at 26.degree. C., CHCl.sub.3 solution) and 1.25 g of 
4-(5'-n-decyl-2'-pyrimidinyl)phenol, and 2.25 g of crude product was 
obtained. 
The product was purified on a silica gel column with the use of 
hexane/ethylacetate (90/10) as a developing solvent. Thus 1.82 g of 
(S)-4-(4'-methyloctoxy)benzoic acid 4-(5'-n-decyl-2'-pyrimidinyl)phenyl 
ester was obtained. 
Infrared spectroscopy (cm.sup.-1) 2900(s), 2850(s), 1720(s), 1600(s), 
1580(m), 1540(vw), 1510(m), 1460(m), 1425(s), 1375(vw), 1310(m), 1250(vs), 
1200(s), 1165(s), 1075(m), 1055(m), 1010(m), 930(vw), 880(w), 840(m), 
790(m), 760(m), 720(vw), 690(w), 650(w), 550(vw) and 505(vw). 
Optical rotation [.alpha.].sub.D =+2.64.degree. (C=1, CHCl.sub.3 solution, 
26.degree. C.) 
This compound was poured into a transparent glass electrode cell of 2 .mu.m 
in thickness, which had been subjected to orientation by rubbing, and 
heated to 140.degree. C. to thereby give an isotropic liquid. 
The liquid crystal cell thus obtained was cooled under a crossed Nicol 
prism while applying rectangular pulses (15 V. 1 Hz) thereto. As a result, 
definite switching behaviors were observed from 85.1.degree. to 2.degree. 
C. 
The following phase transition was observed under a polarization 
microscope. 
##STR8## 
It has been confirmed that the above compound of the present invention 
shows an N* phase over 100.degree. C. and SmC* phase at 66.degree. C., 
which obviously suggests that it is suitable for the preparation of a 
composition showing a high liquid crystal temperature. 
EXAMPLE 4 
Synthesis of (S)-4-(6'-methyldecyloxy)benzoic acid 
4-(5'-n-decyl-2'-pyrimidinyl)phenyl ester 
##STR9## 
The procedure of Example 1 was followed using 1.17 g of 
(S)-4-(6'-methyldecyloxy)benzoic acid ([.alpha.].sub.D =+1.70.degree., 
C=1, at 26.degree. C., CHCl.sub.3 solution) and 1.25 g of 
4-(5'-n-decyl-2'-pyrimidinyl)phenol and 2.13 g of crude product was 
obtained. The product was purified on a silica gel column with the use of 
hexane/ethylacetate (85/15) as a developing solvent followed by 
recrystalization from ethanol/acetone (80/20). Thus 1.48 g of 
(S)-4-(6'-methyldecyloxy)benzoic acid 4-(5'-n-decyl-2'-pyrimidinyl)phenyl 
ester was obtained. 
Infrared spectroscopy (cm.sup.-1) 2900(s), 2850(s), 1725(s), 1605(s), 
1590(s), 1545(w), 1510(m), 1460(m), 1430(s), 1390(vw), 1375(vw), 1310(w), 
1250(vs), 1200(s), 1170(s), 1110(vw), 1075(m), 1060(m), 1010(m), 960(vw), 
880(vw), 845(m), 790(m), 760(m), 720(vw), 690(w), 655(m) and 505(vw). 
Optical rotation [.alpha.].sub.D =+3.71.degree. (C=1, CHCl.sub.3 solution, 
26.degree. C.). 
This compound was poured into a transparent glass electrode cell of 2 .mu.m 
in thickness, which had been subjected to orientation by rubbing, and 
heated to 140.degree. C. to thereby give an isotropic liquid. 
The liquid crystal cell thus obtained was cooled under a crossed Nicol 
prism while applying rectangular pulses (15 V. 1 Hz) thereto. As a result, 
definite switching behaviorswere observed from 102.7.degree. to 
20.9.degree. C. 
The following phase transition was observed under a polarization 
microscope. 
##STR10## 
It has been confirmed that the above compound of the present invention 
shows an N* phase over 100.degree. C. and SmC* phase at 66.degree. C., 
which obviously suggests that it is suitable for the preparation of a 
composition showing a high liquid crystal temperature.