New derivatives of thiazole with mesomorphous properties

Article abstract of DOI:10.1023/B:COHC.0000033545.34829.2a

Azomethines containing a thiazole ring have been synthesized and their liquid crystal properties have been investigated. The influence of the central group and substituents in the azomethine component on the type and temperature range of the mesomorphous

Full text of DOI:10.1023/B:COHC.0000033545.34829.2a

Chemistry of Heterocyclic Compounds, Vol. 40, No. 4, 2004
NEW DERIVATIVES OF THIAZOLE
WITH MESOMORPHOUS PROPERTIES
Z. Kh. Kuvatov, M. G. Safarov, and M. M. Murza
Azomethines containing a thiazole ring have been synthesized and their liquid crystal properties have
been investigated. The influence of the central group and substituents in the azomethine component on
the type and temperature range of the mesomorphous properties of the compounds synthesized has been
elucidated.
Keywords: azomethines, thiazole ring, liquid crystal properties.
We have previously investigated the effect of the structure of azomethines with thiazole rings on the type
of mesomorphism and its temperature range, with introduction of alkoxy groups with varying length of the
aliphatic chain into the benzylidene component [1, 2].
In continuation of the study of the liquid crystal properties of azomethine derivatives of 2-aminothiazole,
we have obtained compounds 1-14, which contain substituents of various types (halogens, nitro, dimethylamino,
and methoxy groups) in the benzylidene unit using the following scheme:
O2N
O2N
H2N
NH2
S
X
CH2Cl
X
N
NH2
O
S
15, 16
17, 18
O2N
R
X
N
CHO
N
C
H
S
R
1–14
1–7, 15, 17 X = O; 8–14, 16, 18 X = NH; 1, 8 R = 2-F, 2, 9 R = 3-Br; 3,10 R = 4-Cl;
4, 11 R = 2-NO2; 5,12 R = 4-NO2; 6, 13 R = 4-NMe2; 7, 14 R = 2,4-(OMe)2
__________________________________________________________________________________________
Bashkir State University, Ufa 450074, Russia; e-mail: KuvatovZK@ic.bashedu.ru. Translated from
Khimiya Geterotsiklicheskikh Soedinenii, No. 4, 596-598, April 2004. Original article submitted March 30,
2001.
500
0009-3122/04/4004-0500©2004 Plenum Publishing Corporation

Sodium p-nitrophenoxide, which was quantitatively acylated with chloroacetyl chloride in alkaline
medium, was used as the starting material for the preparation of compounds 1-7. Chloroacetyl derivative 15
reacted with thiourea in absolute ethanol to give the corresponding 2-aminothiazole 17, which condensed with
aromatic aldehydes in absolute ethanol in the presence of a catalytic amount of piperidine to give compounds 1-7.
The Schiff's bases 8-14 were obtained analogously. In this case p-nitroaniline was used as the starting
material: chloroacetylation was carried out in ether, but condensation with aldehydes – in dry THF.
Investigation of the mesophase properties of azomethines prepared showed that all of the compounds
1-14 possess nematic liquid crystal properties. It should be noted that with X = O the mesophase existed over
about twice the range as with X = NH (Table 1), however when nitro group was introduced into the ortho
position in the benzylidene component (compound 11) the mesophase interval was 81° for X = NH too, i.e., it
was comparable with the temperature ranges for compounds 1-7 (X =O).
Evidently there are intramolecular hydrogen bonds between the proton of the N=CH group and the NO2
group in the ortho-position of the benzylidene component of compounds 4 and 11, thanks to which the
intermolecular interactions in these crystals are not very strong and therefore the temperature range of the
mesophase is increased and for the compound with X=O it is maximal (Table 1). Compounds 8-14 are more
stable and show enantiotropic mesomorphism (the liquid crystal state is retained on super-cooling the crystalline
modification), whereas compounds 1-7 decompose above 200°C and possess monotropic mesomorphism.
TABLE 1. Characteristics of Compounds 1-13, 17, and 18
Found, %
——————
Calculated, %
Т, °С*
n.m.
Com-
pound
Empirical
formula
Yield, %
С
H
N
i.m.
116
112
152
146
158
148
132
133
152
150
124
129
137
161
1
С16H10FN3O3S
С16H10BrN3O3S
С16H10ClN3O3S
С16H10N4O5S
С16H10N4O5S
С18H16N4O3S
С18H16N3O5S
С16H11FN4O2S
С16H11BrN4O2S
С16H11ClN4O2S
С16H11N5O4S
С16H11N5O4S
С18H17N5O2S
С18H16N4O4S
С9H7N3O3S
55.82
55.97
47.12
47.54
53.06
53.40
51.64
51.89
51.48
51.89
58.30
58.69
55.58
55.96
56.02
56.14
43.88
44.15
53.22
53.56
51.84
52.03
51.76
52.03
58.50
58.86
55.92
56.25
45.32
45.57
45.40
45.76
2.55
2.92
2.24
2.49
2.45
2.80
2.36
2.72
2.48
2.72
4.10
4.35
3.92
4.15
3.04
3.22
2.35
2.53
2.84
3.07
2.70
2.98
2.64
2.98
4.42
4.63
3.96
4.17
2.64
2.95
3.24
3.40
12.04
12.24
10.10
10.39
11.52
11.70
14.88
15.13
15.04
15.13
14.96
15.22
10.72
10.88
16.14
16.37
12.62
12.87
15.44
15.62
18.80
18.97
18.64
18.97
18.86
19.07
14.32
14.58
17.48
17.72
23.45
23.73
47
80
56
62
58
55
61
68
65
52
64
68
56
57
63
57
2
3
62
4
49
5
70
6
77
7
85
8
100
125
120
43
9
10
11
12
13
14
17
18
64
76
114
С9H8N4O2S
_______
* Temperatures at which the nematic (n.m.) and isotropic (i.m.)
modifications exist.
501

EXPERIMENTAL
Phase transition temperatures were measured on MIN-10 polarizing microscope with a thermal adapter in a
heating regime. The individuality and purity of all the compounds described were monitored by TLC on aluminum
oxide with toluene–chloroform (1:3) as eluent.
o-Chloroaceto-4-nitroaniline (15) and N-chloroaceto-4-nitroaniline (16) were synthesized by a known
method [3].
N-(2-Aminothiazol-4-yl)-4-nitroaniline (18). Solution of compound 16 (14.2 g, 0.06 mol) and thiourea
(4.6 g, 0.06 mol) in absolute ethanol (100 ml) was boiled for 8 h. At the end of the reaction the solvent was
evaporated and the residue was neutralized with 20% sodium carbonate solution. The precipitate was filtered off
and crystallized from water.
Compound 17 was prepared analogously.
4-[Amino-p-(4-nitrophenyl)]-2-benzylidenaminothiazoles (8-14). Mixture of compound 18 (1 g, 0.042
mol) and aromatic aldehyde (0.0042 mol) in dry THF (40 ml) was boiled for 4 h in the presence of a catalytic
quantity of piperidine. The solvent was evaporated and the residue was crystallized from ethanol.
The Benzylidene Derivatives 1-7 were prepared analogously from compound 17.
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1.
2.
3.
M. M. Murza, A. S Golovanov, and M. G. Safarov, Khim. Geterotsikl. Soed., 546 (1996).
M. M. Murza, A. S Golovanov, and M. G. Safarov, Zh. Org. Khim., 31, 1701 (1995).
I. A. Khrizman (Ed.), Advances in Organic Synthesis in the Chemization of the Agricultural Industry
[in Russian], Ufa, 113 (1970).
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