Vol. 28, No. 6 (2016)
Synthesis of Liquid Crystalline Organosiloxanes Containing 4-Methoxyphenyl 4-(2-alkenyloxy)benzoate 1271
with a liquid nitrogen cooling accessory. Heating and cooling
rates were 10 °C/min. Thermal transition reports were collected
during the second heating and cooling scans.A Nikon Microphot-
FX polarized optical microscope (POM) equipped with a Mettler
FP 82 hot stage and a FP 80 central processor was used to
observe the thermal transitions and analyze the anisotropic
textures. Polymerization reactions were traced using a Nicolet
520 FT-IR spectrometer.
The general synthetic routes of intermediates and target
molecule were shown in Scheme-I. The purity and chemical
structures of the intermediates and target compounds could
be easily verified by TLC and 1H NMR spectroscopy.
All the four compounds viz., ethyl-4-(2-propenyloxy)-
benzoate (1), ethyl-4-(3-butenyloxy)benzoate (2), ethyl-4-(4-
pentenyloxy)benzoate (3) and ethyl-4-(5-hexenyloxy)benzoate
(4) were prepared by the similar method.
The synthesis of ethyl-4-(5-hexenyloxy)benzoate (4) is
described as follows: Ethyl-4-hydroxybenzoate (2.0 g, 0.012
mol), 6-bromo-1-hexene (1.96 g, 0.012 mol) and potassium
carbonate (8.0 g, 0.058 mol) were dissolveted in 100 mL of
anhydrous ethyl-methyl ketone in a 250 mL two-neck flask.
The solution was heated to reflux for 48 h. The solution was
cooled and filtrated. Following the solvent being evaporated,
the residue was purified by column chromatography (silica gel,
using n-hexane/ethyl acetate as an eluent) to yield 2.53 g (85 %)
of oil liquid. 1H NMR (300 MHz, CDCl3, δ, ppm): 1.27-2.10
(m, 11H, –(CH2)4– and –CH2–CH3), 3.96 (t, 2H, –CH2O–),
4.03 (t, 2H, –COO–CH2–), 5.02 (m, 2H, CH2=CH–), 5.84 (m,
1H, CH2=CH–), 6.86 (m, 2H, aromatic protons), 7.83 (m, 2H,
aromatic protons).
4-(N,N-dimethylamino)pyridine (DMAP, 0.2 g) were added
to react under nitrogen. The reaction mixture was stirred for
24 h at room temperature. The solution was filtered. After
removal of the solvent by evaporation under reduced pressure,
the residue was purified by recrystallization from ethanol to
yield 1.74 g (66 %) of white crystal. m.p.: 71.7 °C. 1H NMR
(300 MHz, CDCl3, δ, ppm): 1.50-2.20 (m, 6H, -(CH2)3-, 3.80
(s, 3H, -OCH3) 4.03 (t, 2H, -CH2O-), 5.02 (m, 2H, CH2=CH-),
5.84 (m, 1H, CH2=CH-), 6.92 (m, 4H, aromatic protons), 7.10
(m, 2H, aromatic protons), 8.11 (m, 2H, aromatic protons).
Compound 3M was obtained as white solid (56 %). m.p.: 94.2 °C.
1H NMR (300 MHz, CDCl3, δ, ppm): 1.50-2.20 (m, 4H,
-(CH2)2-,3.80 (s, 3H, -OCH3) 4.03 (t, 2H, -CH2O-), 5.02 (m,
2H, CH2=CH-), 5.84 (m, 1H, CH2=CH-), 6.92 (m, 4H, aromatic
protons), 7.10 (m, 2H, aromatic protons), 8.11 (m, 2H, aromatic
protons). Compound 2M was obtained as white solid (69 %).
m.p.: 87.4 °C. 1H NMR (300 MHz, CDCl3, δ, ppm): 1.83 (m,
2H, -CH2-),3.80 (s, 3H, -OCH3) 4.03 (t, 2H, -CH2O-), 5.02
(m, 2H, CH2=CH-), 5.84 (m, 1H, CH2=CH-), 6.92 (m, 4H,
aromatic protons), 7.10 (m, 2H, aromatic protons), 8.11 (m,
2H, aromatic protons). Compound 1M was obtained as white
solid (72 %). m.p.: 101 °C. 1H NMR (300 MHz, CDCl3, δ, ppm):
3.80 (s, 3H, -OCH3) 4.49 (t, 2H, -CH2O-), 5.31 (m, 2H, CH2=CH-),
6.03 (m, 1H, CH2=CH-), 6.92 (m, 4H, aromatic protons), 7.10
(m, 2H, aromatic protons), 8.11 (m, 2H, aromatic protons).
Liquid crystal siloxane compounds 1A-4A and 1B-4B:
Siloxane dimer synthesized from 1M-4M are marked as 1A-
4A and siloxane trimer from 1M-4M are marked as 1B-4B.
Compounds 1A-4A and 1B-4B were prepared using the same
method. The synthesis of compound 4A is described below.
To a degassed solution of compound 4M (0.26 g, 0.0008
mol) and pentamethyl-hydrodisiloxane (0.14 g, 0.0009 mol)
in 10 mL of dry and freshly distilled toluene was added divinyl-
tetramethyldimethylsiloxyl (2.5 mg) as catalyst. The reaction
mixture was stirred at 75 °C under nitrogen for 48 h. After the
solvent being evaporated, the residue was purified by column
chromatography (silica gel, using n-hexane/ethyl acetate as
an eluent) to yield 0.33 g (76 %) of white crystals. 1H NMR
(CDCl3, δ, ppm): 0.0 (m, 15H, -Si-CH3), 0.53 (m, 2H, -Si-
CH2-CH2-), 1.50-2.20 (m, 8H, -CH2-), 3.80 (s, 3H, -O-CH3),
4.03 (t, 2H, -O-CH2-), 6.92 (m, 4H, aromatic protons), 7.10
(m, 2H, aromatic protons), 8.11 (m, 2H, aromatic protons).
Compound 3A was obtained as white solid (78 %).1H NMR
(CDCl3, δ, ppm): 0.0 (m, 15H, -Si-CH3), 0.53 (m, 2H, -Si-
CH2-CH2-), 1.50-2.20 (m, 6H, -CH2-), 3.80 (s, 3H, -O-CH3),
4.03 (t, 2H, -O-CH2-), 6.92 (m,4H, aromatic protons), 7.10
(m, 2H, aromatic protons), 8.11 (m, 2H, aromatic protons).
Compound 2A was obtained as white solid (76 %).1H NMR
(CDCl3, δ, ppm): 0.0 (m, 15H, -Si-CH3), 0.53 (m, 2H, -Si-
CH2-CH2-), 1.50-2.30 (m, 4H, -CH2-), 3.80 (s, 3H, -O-CH3),
4.03 (t, 2H, -O-CH2-), 6.92 (m,4H, aromatic protons), 7.10
(m, 2H, aromatic protons), 8.11 (m, 2H, aromatic protons).
Compound 1A was obtained as white solid (67 %). 1H NMR
(CDCl3, δ, ppm): 0.0 (m, 15H, -Si-CH3), 0.53 (m, 2H, -Si-
CH2-CH2-), 1.87 (m, 2H, -CH2-), 3.80 (s, 3H, -O-CH3), 4.49
(t, 2H, -O-CH2-), 6.92 (m,4H, aromatic protons), 7.10 (m, 2H,
aromatic protons), 8.11 (m, 2H, aromatic protons). Compound
4B was obtained as white solid (81 %).1H NMR (CDCl3, δ,
Compounds 5-8 viz., 4-(2-propenyloxy)benzoic acid (5),
4-(3-butenyloxy)benzoic acid (6), 4-(4-pentenyloxy)benzoic
acid (7) and 4-(5-hexenyloxy) benzoic acid (8) were prepared
by the similar method.
The synthesis of 4-(5-hexenyloxy)benzoic acid (8) is
described as follows: Ethyl-4-(5-hexenyloxy)benzoate (1.2 g,
0.0048 mol) was added to a solution of sodium hydroxide
(1.2 g, 0.030 mol) in 90 % methanol (30 mL). The solution
was heated to reflux for 3 h.The solution was cooled and poured
into 10 mL of 6 N HCl and the solution was then extracted
with 30 mL of dichloromethane. The extraction solution was
dried over anhydrous magnesium sulfate. Following removal
of the solvent by evaporation under reduced pressure, the
residue was purified by recrystallization from ethanol to yield
1.00 g (95 %) of white crystal. 1H NMR (300 MHz, CDCl3, δ,
ppm): 1.50-2.20 (m, 4H, –(CH2)3–), 3.96 (t, 2H, –CH2O–),
5.02 (m, 2H, CH2=CH–), 5.84 (m, 1H, CH2=CH–), 6.86 (m,
2H, aromatic protons), 7.96 (m, 2H, aromatic protons).
Compounds 1M-4M viz., 4-methoxyphenyl 4-(2-propeny-
loxy)benzoate (1M), 4-methoxyphenyl 4-(3-butenyloxy)-
benzoate (2M), 4-methoxyphenyl 4-(4-pentenyloxy)benzoate
(3M) and 4-methoxyphenyl 4-(5-hexenyloxy)benzoate (4M)
were prepared by the similar method.
The synthesis of 4-methoxyphenyl 4-(5-hexenyloxy)-
benzoate (4M) is described as follows: 4-(5-Hexenyloxy)
benzoic acid (8) (1.6 g, 0.0081 mol) and 4-methoxyphenol
(1 g, 0.0081 mol) dissolved in dry dichloromethane (100 mL),
N,N-dicyclohexylcarbodiimide (DCC, 2.0 g, 0.0097 mol) and