hydrogen bonding, which has been shown to efficiently
promote molecular ordering and stability in a liquid crystal-
line phase by allowing it to assume the shape of a large
disk.10,11
expected from their disklike structures, all of the hydrazone
compounds showed liquid crystalline properties.
4-Alkyloxyphenylamines (2) and 3,4,5-trishexyloxyphen-
ylamine (5) were prepared according to Scheme 1.
Hydrazones are generally prepared by the condensation
reaction between a hydrazine and a carbonyl compound.19
They can also be obtained from an azo compound which
has a labile proton at the position conjugated with an azo
group because a hydrazone is a tautomer of an azo
compound. Azo and hydrazone tautomerization has been
extensively studied because the two tautomers show different
optical properties such that certain hydrazone forms absorb
light at longer wavelengths and have higher photoconductiv-
ity than their azo counterparts. Hydrazones have been
investigated as potential charge-transport materials for
organic photoconductors20-23 and nonlinear optical poly-
mers.24-26 Hydrazone dendrimers have reportedly been used
as hole-transport materials for electroluminescence devices.27
Scheme 1. Preparation of Aromatic Amines
In this paper, we report on the synthesis of discotic liquid
crystalline hydrazone compounds by the azo coupling
reaction of 1,3,5-trisacetoacetamidobenzene and diazonium
salts of 4-alkyloxyphenylamines. 1,3,5-Trisacetoacetamido-
benzene having three 1,3-diketo groups was easily obtained
by the reaction of 1,3,5-triaminobenzene with diketene.28,29
The stable disklike hydrazone structures were derived from
the formation of six intramolecular hydrogen bonds around
a benzene ring. Spectroscopic analysis showed that all of
the N-H groups of the hydrazone units participated in
hydrogen bondings so as to render the compounds more
hydrophobic. Indeed, the compounds showed good solubility
in low polar solvents such as toluene and chloroform. As
A flexible alkyl group was introduced into the benzene
ring by the reaction of 4-nitrophenol with 1-bromoalkane in
DMF in the presence of potassium carbonate. The nitro group
was reduced to the amino group by catalytic hydrogenation
to give 2. 3,4,5-Trishexyloxyphenylamine (5) was prepared
from 1,2,3-trihydroxybenzene in three steps. 1,2,3-Trishexyl-
oxybenzene (3), obtained by the reaction of 1,2,3-trihydroxy-
benzene with 1-bromohexane under basic conditions, was
nitrated using HNO3 supported on SiO2 and subsequently
reduced by catalytic hydrogenation to produce 3,4,5-
trishexyloxyphenylamine (5).
1,3,5-Triaminobenzene (6) was prepared by the catalytic
hydrogenation of 3,5-dinitroaniline. The amine was reacted
with diketene in DMF, resulting in the formation of 1,3,5-
trisacetoacetamidobenzene (7) having three 1,3-diketo moi-
eties around the benzene ring (Scheme 2).
30
(12) Percec, V.; Dulcey, A. E.; Balagurusamy, V. S. K.; Miura, Y.;
Smidrkal, J.; Peterca, M.; Nummelin, S.; Edlund, U.; Hudson, S. D.; Heiney,
P. A.; Duan, H.; Magonov, S. N.; Vinogradov, S. A. Nature 2004, 430,
764.
(13) Percec, V.; Dulcey, A. E.; Peterca, M.; Ilies, M.; Nummelin, S.;
Sienkowska, M. J.; Heiney, P. A. PNAS 2006, 103, 2518.
(14) Demus, D.; Goodby, J.; Grat, G. W.; Spiess, H. W. Handbook of
Liquid Crystals; Wiley-VCH: New York, 1998; Vol. 2B.
(15) Bengs, H.; Renkel, R.; Ringsdorf, H.; Baehr, C.; Ebert, M.;
Wendorff, J. H. Makromol. Chem., Rapid Commun. 1991, 12, 439.
(16) Percec, V.; Glodde, M.; Bera, T. K.; Miura, Y.; Shiyanovskaya, I.;
Singer, K. D.; Balagurusamy, V. S. K.; Heiney, P. A.; Schell, I.; Rapp, A.;
Spiess, H.-W.; Hudson, S. D.; Duan, H. Nature 2002, 419, 384.
(17) Ujiie, S.; Iimura, K. Macromolecules 1992, 25, 3174.
(18) Percec, V.; Cho, W.-D.; Ungar, G.; Yeardley, D. J. P. Chem.-Eur.
J. 2002, 8, 2011.
Scheme 2. Synthesis of 1,3,5-Trisacetoacetamidobenzene
(19) Norman, R. O. C.; Coxon, J. M. Principles of Organic Synthesis,
3rd ed.; Blackie Academy & Professional: New York, 1993.
(20) Gordon, P. F.; Gregory, P. Organic chemistry in colour; Springer:
New York, 1987.
(21) Peters, A. T.; Freeman, H. S. Colour chemistry; Elsevier: New York,
1991.
(22) Waring, D. R.; Hallas, G. The chemistry and application of dyes;
Plenum Press: New York, 1990.
(23) Peters, A. T.; Freeman, H. S. Modern colorants; Blackie Academic
& Professional: London, U.K., 1995.
(24) Hayden, L. M.; Kim, W. K.; Chafin, A. P.; Lindsay, G. A.
Macromolecules 2001, 34, 1493.
(25) Hayden, L. M.; Kim, W. K.; Chafin, A. P.; Lindsay, G. A.
Macromolecules 2001, 34, 6152.
(26) Hayden, L. M.; Kim, W. K.; Chafin, A. P.; Lindsay, G. A. J. Polym.
Sci., Part B: Polym. Phys. 2001, 39, 895.
(27) Nam, H.; Kang, D. H.; Kim, J. K.; Park, S. Y. Chem. Lett. 2000,
11, 1298.
The protons on the carbon between two carbonyl groups
of 7 are easily removed under mild basic conditions,
(28) Kim, B. J.; Chang, J. Y.; Kim, C. H. Polym. Bull. 2001, 46, 285.
(29) Boese, A. B. Ind. Eng. Chem. 1940, 32, 16.
(30) Percec, V.; Ahn, C. H.; Bera, T. K.; Ungar, G.; Yeardly, D. J. P.
Chem.-Eur. J. 1999, 5, 1070.
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