Facile and inexpensive synthesis of α,β,β'-deuterated liquid crystalline and classical acrylate monomers

Article abstract of DOI:10.1021/ma010838m

An inexpensive synthesis of ²H₃-labeled acrylate monomers was presented. Multistep routes to prepare deuterated side-end and side-on liquid crystalline acrylate monomers were presented. The level of deuterium incorporation in the syn

Full text of DOI:10.1021/ma010838m

Macromolecules 2002, 35, 581-584
581
monomers are presented in Schemes 1-3, and the
synthesis of benzyl 2H3-acrylate is outlined in
Scheme 4.
F a cile a n d In exp en sive Syn th esis of
r,â,â′-Deu ter a ted Liqu id Cr ysta llin e a n d
Cla ssica l Acr yla te Mon om er s
The first step in the synthesis of deuterated side-on
and side-end liquid crystalline acrylate monomers in-
volved the transformation of a terminal carbon-carbon
double bond to a terminal hydroxyethyl group using
borane chemistry.12 The hydroboration reaction, using
9-borabicyclo[3.3.1]nonane (9-BBN), was followed by an
oxidation step to obtain the hydroxy function using
m-chloroperbenzoic acid as oxidant as proposed by
Pelter.13 The gentle reaction conditions used are well
adapted to the presence of ester groups in the starting
material, thus avoiding most of the side reactions
produced when using the classical H2O2/NaOH oxida-
tion route and base-sensitive compounds.
The hydroxy-functionalized liquid crystalline com-
pounds were then esterified14 with bromoacetic acid in
the presence of dicyclohexylcarbodiimide and pyrroli-
dinopyridine to give the bromoesters.
These bromoesters were reacted with triphenylphos-
phine at room temperature to give, by a Arbuzov
reaction, the phosphonium salts which were used in the
next step without further purification.
P . Keller ,*,†,‡ D. L. Th om sen III,§ a n d M-H. Li†
Laboratoire Physicochimie Curie (UMR 168 CNRS-IC),
Institut Curie-Section de Recherche, 11 rue P et M Curie,
75231 Paris, Cedex 05, France; Ferroelectric Liquid Crystals
Material Research Center, Department of Chemistry and
Biochemistry, University of Colorado, Boulder, Colorado
80309-0215; and NASA, Langley Research Center,
Hampton, Virginia 23681-0001
Received May 14, 2001
Revised Manuscript Received October 16, 2001
Neutron scattering, associated with selective deute-
rium labeling, has long been recognized as a very
powerful tool for studying the backbone conformation
of both “classical”1,2 and liquid crystalline polymers.3-6
Over the years, the systems being investigated have
become more and more chemically and structurally
complex (elastomers, polyelectrolytes, block copolymers,
brushes of polymers, etc.), so new methods of deuterium
incorporation at well-defined positions in more “sophis-
ticated” or functionalized monomers are needed. In the
course of our work on liquid crystalline polymers, we
developed the synthesis of backbone-deuterated meso-
morphic polymethacrylates and polyacrylates. Although
it is relatively easy and inexpensive to prepare perdeu-
Treating these phosphonium salts dissolved in dry
THF with the 2H-labeled formaldehyde (as a commercial
20% solution in D2O) in the presence of solid potassium
carbonate at room temperature produced the expected
2H3-labeled acrylates.
2
Similarly, reacting the triphenylphosphonium salt of
terated H5-methacrylic acid derivatives from perdeu-
2
terated acetone using classic textbook chemistry,7,8 there
is no well-established simple route for the synthesis of
2H3-acrylic derivatives.9 To push further our recent
studies on nematic acrylate elastomers10 as model
systems for artificial muscle actuators, we became
interested in gaining specific structural information,
such as the order parameters of the backbone and the
mesogenic group using FTIR and the backbone confor-
mation using SANS. Most of the studies we were
planning were based on easy access to selectively
deuterated acrylate elastomers.
benzyl bromoacetate with H2-formaldehyde in dry THF
in the presence of K2CO3 produced the benzyl 2H3-
acrylate in good yield and high level of deuteration.
For all the monomers synthesized, the level of deu-
terium incorporation was determined by proton NMR
to be better than 95% and slightly different for the R
and â positions. Deuteration at the â and â′ positions
was better than 98%, while it was around 96% for the
R position. This difference originates from the chemistry,
the â and â′ deuterium atoms coming from the deuter-
ated formaldehyde via the Wittig reaction and the R
deuterium atom by fast exchange between the hydrogen
in R of the phosphonium group and D2O prior to the
Wittig reaction. (1H NMR spectra for all the deuterated
monomers synthesized are presented in the Supporting
Information.)
In our quest for a simple and inexpensive route for
the synthesis of 2H3-acrylic acid derivatives, we became
aware of a recent paper by Pitlik and Townsend11 which
described the synthesis of multiply labeled (i.e., 13C and
2H) carbohydrates. In their synthesis, the preparation
as intermediates of selectively deuterated acrylic acid
derivatives was described, the key step being a Wittig
reaction between a phosphonium salt and commercially
available deuterated formaldehyde (as a 20% solution
in D2O). Making use of this key reaction, we have
developed a very simple, efficient, and inexpensive route
for the preparation of 2H3-labeled liquid crystalline
acrylate monomers and explored the possibility of
synthesizing “classical” or simple acrylate monomers
such as benzyl 1,2,2-2H3 acrylate, which could find
application in the synthesis of backbone-deuterated
poly(acrylic acid) after deprotection.
In conclusion, we have described a very simple,
inexpensive, but efficient synthesis of 2H3-labeled acryl-
ate monomers. The deuterated side-on liquid crystalline
monomers will be used in the synthesis of new macro-
scopically oriented nematic elastomers. Making use of
the specific labeling, FTIR and SANS experiments will
be performed in order to obtain structural information
about these new materials which are promising models
of “artificial muscles”.10
Exp er im en ta l Section
Ma t er ia ls a n d Tech n iq u es. 2,5-Dihydroxybenzoic acid,
4-bromo-1-butene, 3-bromo-1-propene, 4-butyloxybenzoic acid,
4-pentylcyclohexylcarboxylic acid, bromoacetic acid, benzyl
bromoacetate, triphenylphosphine, N,N-dicyclohexylcarbodi-
imide, and pyrrolidinopyridine were used as received from
Aldrich. 3-Chloroperbenzoic acid (pract.,70%) and 9-BBN (as
a 0.5 M solution in THF) were from Fluka. Formaldehyde-2H2
Multistep routes designed to prepare typical deuter-
ated side-on and side-end liquid crystalline acrylate
† Institut Curie-Section de Recherche.
‡ University of Colorado.
§ NASA.
10.1021/ma010838m CCC: $22.00 © 2002 American Chemical Society
Published on Web 12/13/2001

582 Notes
Macromolecules, Vol. 35, No. 2, 2002
Sch em e 1. Sid e-On Liqu id Cr ysta llin e Mon om er Syn th esis
Sch em e 2. Str u ctu r e of Oth er Syn th esized Sid e-On
Mon om er s
at 70 °C for 1 h. 4-Bromo-1-butene (2.7 g, 20 mmol) was then
added, and the reaction was maintained at 70 °C for 7 h. The
reaction mixture was cooled, diluted with water (100 mL), and
extracted twice with 60 mL of a 50:50 hexane/ethyl acetate
mixture. The organic phases were washed twice with water
(100 mL) and dried over Na2SO4. After evaporation of the
solvents, the solid residue was purified by column chromatog-
raphy on a short column of silica gel with diethyl ether as
eluting solvent; yield 3.75 g (18 mmol, 90%) of white solid (K
53 °C I).1H NMR: 2.52 (m, 2H, -CH2-CH)), 4.37 (m, 2H,
-CO2-CH2-), 5.19 (m, 2H, dCH2), 5.84 (m, 1H, -CHdCH2),
6.8 (d, 1H, arom), 7 (m, 1H, arom), 7.2 (m, 1H, arom), 10.4 (s,
-OH). Anal. Calcd (C11H12O4):
Found: C (63.47%), H (5.79%).
C (63.45%), H (5.80%).
was from Isotech Inc. or Aldrich (as a 20% solution in 2H2O).
All other reagents and solvents were commercially available
and used as received.
(But-3′′-enyl) 2,5-di(4′-butyloxybenzoyloxy)benzoate (2): A
solution of 1 (3.75 g, 18 mmol), 4-butyloxybenzoic acid (7.7 g,
39.6 mmol), N,N-dicyclohexylcarbodiimide (8.77 g, 42.5 mmol),
and pyrrolidinopyridine (0.6 g, 4 mmol) in 180 mL of dichlo-
romethane was stirred at room temperature for 24 h. The N,N′-
dicyclohexylurea was removed by filtration, and the filtrate
was washed with water (200 mL), a 5% acetic acid solution
(150 mL), water (200 mL), and dried over Na2SO4. After
evaporation of the solvent, the crude product was recrystallized
twice from ethanol and dryied under vaccuum to give 7.5 g
(13.3 mmol, 74%) of white solid (K 101 °C N 114 °C I). 1H NMR:
1 (t, 6H, -CH3), 1.53 (m, 4H, -CH2-CH3), 1.83 (m, 4H, -CH2-
CH2-CH3), 2.26 (m, 2H, -CH2-CHd), 4.05 (t, 4H, O-CH2-),
4.21 (t, 2H, -CO2-CH2-), 5 (m, 2H, H2CdCH-), 5.68 (m, 1H,
-CHdCH2), 6.98 (d, 4H, arom), 7.25 (m, 1H, arom), 7.45 (m,
1H, arom), 7.88 (d, 4H, arom), 8.1 (m, 4H, arom). Anal.
Textures and transition temperatures for the synthesized
compounds were observed by polarizing optical microscopy
using a Leitz Ortholux polarizing microscope in conjunction
with a Mettler FP 82 heating stage (K ) crystal; N ) nematic
phase; I ) isotropic phase).
1H NMR spectra (δ, ppm) were recorded on either a Bruker
300 MHz or 400 MHz spectrometer. All spectra were recorded
in CDCl3. Elemental microanalyses were performed at Service
de Microanalyse (I.C.S.N.-CNRS, Gif, France).
Syn th esis of (4′′-((r,â,â′-2H3)-a cr yloyloxy)bu tyl) 2,5-Di-
(4′-bu tyloxyben zoyloxy)ben zoa te (6). (But-3′-enyl) 2,5-
dihydroxybenzoate (1): To a stirred solution of 2,5-dihydrox-
ybenzoic acid (3.08 g, 20 mmol) in DMF (30 mL) was added
solid NaHCO3 (4.95 g, 58.5 mmol). The mixture was stirred

Macromolecules, Vol. 35, No. 2, 2002
Sch em e 3. Sid e-En d Liqu id Cr ysta llin e Mon om er Syn th esis
Notes 583
Sch em e 4. Deu ter a ted Ben zyl Acr yla te Syn th esis
Calcd (C33H36O8): C (70.69%), H (6.47%). Found: C (70.75%),
H (6.25%).
CH2-, 3.79 (s, 2H, Br-CH2-), 4.05 (m, 6H, CH2-CO2-CH2,
-O-CH2-), 4.2 (m, 2H, -CO2-CH2-), 6.99 (m, 4H arom), 7.26
(m, 2H, arom), 7.46 (m, 1H, arom), 7.88 (d, 1H, arom), 8.15
(m, 4H, arom). Anal. Calcd (C35H39BrO10): C (60.09%), H
(5.61%). Found: C (60.14%), H (5.55%).
((4′′-(Bromoacetyloxy)butyl) 2,5-di(4′-butyloxybenzoyloxy)
benzoate) triphenylphosphonium bromide (5): To a solution
of 4 (3 g, 4.29 mmol) in toluene (15 mL) was added in one
portion triphenylphosphine (1.2 g, 4.58 mmol), and the reaction
mixture was stirred at room temperature for 48 h. The white
solid which has precipitated was removed by filtration and
washed with hexane. Drying under vacuum provided 5 (4.02
g, 4.18 mmol) (97%), which was used for the Wittig reaction
without further purification or characterization.
(4′′-Hydroxybutyl) 2,5-di(4′-butyloxybenzoyloxy)benzoate (3).
To a stirred solution of 2 (7 g, 12.5 mmol) in 100 mL of dry
THF kept under argon was added via syringe 9-BBN as a 0.5
M solution in THF (27.5 mL, 13.75 mmol). The mixture was
stirred overnight at room temperature under argon.
The solution was then cooled in an ice/water bath, and solid
m-chloroperbenzoic acid (m-CPBA) (12.4 g, of commercial
(70%) acid) was added slowly in small portions. After stirring
at room temperature overnight, the reaction mixture was
diluted with water (200 mL) and extracted twice with dichlo-
romethane. The organic phases were washed thoroughly with
a saturated sodium bicarbonate solution (4 × 250 mL) and
water (250 mL) and then dried over Na2SO4. After evaporation
of the solvent, the solid residue was purified by recrystalliza-
tion from ethanol to give 6.4 g (11 mmol, 88%) of white solid
(K 79 °C N 104 °C I). (Alternatively, the compound might be
purified by column chromatography on silica gel using a 50/
(4′′-((R,â,â′-2H3)-Acryloyloxy)butyl) 2,5-di(4′-butyloxybenzoy-
loxy)benzoate (6). Phosphonium salt 5 (2 g, 2.08 mmol) was
dissolved in dry THF (50 mL). Anhydrous potassium carbonate
(0.29 g, 2.1 mmol) and 2H2-formaldehyde (as a 20% solution
in 2H2O) (2 mL) were added, and the reaction mixture was
stirred at room temperature overnight. The THF was evapo-
rated under reduced pressure, and the residue was dissolved
in dichloromethane (60 mL). The organic phase was washed
with water (100 mL) and brine (2 × 100 mL) and dried over
Na2SO4. After evaporation of the solvent, the crude product
was purified by column chromatography on silica gel with a
80/20 hexane/ethyl acetate mixture as eluting solvent followed
by two recrystallizations from ethanol to give 0.81 g (1.27
mmol, 61%) of white solid (K 77 °C N 86.5 °C I). 1H NMR: 1 (t,
6H, -CH3), 1.55 (m, 8H), 1.81 (m, 4H, -O-CH2-CH2-), 4.06
(m, 6H, -O-CH2, dCD-CO2-CH2-), 4.2 (m, 2H, -CO2-
CH2-), 5.78 (s, O.O1H, HCdCH), 6.07 (s, 0.04H, dCH-CO2),
6.34 (s, 0.01H, HCdCH), 6.98 (m, 4H, arom), 7.25 (m, 1H,
arom), 7.46 (m, 1H, arom), 7.88 (d, 1H, arom), 8.15 (m, 4H,
arom). Anal. Calcd (C36H372H3O10): C (68.01%), H (5.86%).
Found: C (68.18%), H (5.88%).
1
50 hexane/ethyl acetate mixture.) H NMR: 1 (t, 6H, -CH3),
1.53 (m, 8H), 1.81 (m, 4H, -O-CH2-CH2-), 3.52 (t, 2H, HO-
CH2-), 4.05 (m, 4H, -O-CH2-), 4.2 (m, 2H, -CO2-CH2-),
6.98 (d, 4H, arom), 7.26 (m, 1H, arom), 7.45 (m, 1H, arom),
7.88 (d, 1H, arom), 8.15 (m, 4H, arom). Anal. Calcd (C33H38O9):
C (68.49%), H (6.61%). Found: C (68.30), H (6.64).
(4′′-(Bromoacetyloxy)butyl) 2,5-di(4′-butyloxybenzoyloxy) ben-
zoate (4): A solution of 3 (2.89 g, 5 mmol), bromoacetic acid
(0.76 g, 5.5 mmol), N,N-dicyclohexylcarbodiimide (1.13 g, 5.5
mmol), and pyrrolidinopyridine (0.08 g, 0.55 mmol) in 50 mL
of dichloromethane was stirred at room temperature for 12 h.
The N,N-dicyclohexylurea was removed by filtration, and the
filtrate was washed with water (100 mL), a 5% acetic acid
solution (100 mL), and water (100 mL) and dried over Na2-
SO4. After evaporation of the solvent, the crude product was
recrystallized twice from ethanol to give 2.6 g (3.7 mmol, 75%)
1
of white solid (K 101 °C I (79 °C monotropic N)). H NMR: 1
Using the same synthetic scheme, (4′′-((R,â,â′-2H3)-acryloyl-
oxy)propyl) 2,5-di(4′-butyloxybenzoyloxy)benzoate (7) and (4′′-
(t, 6H, -CH3), 1.56 (broad m, 8H), 1.81 (m, 4H, -O-CH2-

584 Notes
Macromolecules, Vol. 35, No. 2, 2002
((R,â,â′-2H3)-acryloyloxy)butyl) 2,5-di(5′-pentylcyclohexylcar-
boxyloxy)benzoate (8) were prepared.
7 (K 75 °C N 100 °C I). H NMR: 1 (t, 6H, -CH3), 1.52 (m,
4H, -CH2-CH3), 1.85 (m, 6H, -O-CH2-CH2-, -CO2-CH2-
CH2-), 4 (m, 6H, -O-CH2-, -CH2-O2C-CDd), 4.26 (m, 2H,
-CO2-CH2-), 6.98 (m, 4H, arom), 7.26 (m, 1H, arom), 7.47
(m, 1H, arom), 7.88 (d, 1H, arom), 8.15 (m, 4H, arom). Anal.
Calcd (C35H35O102H3): C (67.61%), H (5.67%). Found: C (67.42%),
H (5.74%).
layer was washed with brine (2 × 50 mL) and water (50 mL)
and dried over Na2SO4.
1
After evaporation of the solvent, the residue was purified
by column chromatography on silica gel with a 70/30 hexane/
ethyl acetate mixture as eluting solvent to yield, after recrys-
tallization from ethanol, 0.24 g (0.62 mmol, 50%) of white solid
1
(K 69 °C I (45 °C monotropic N)). H NMR: 1.6 (m, 2H, -O-
CH2-CH2-CH2-), 1.84 (m, 4H, -O-CH2-CH2-CH2-CH2-),
3.81 (s, 3H, -OCH3), 4.05 (m, 2H, -O-CH2-), 4.2 (m, 2H,
-CO2-CH2-), 6.94 (m, 4H, arom), 7.12 (m, 2H, arom), 8.12
(m, 2H, arom).Anal. Calcd (C22H212H3O6): C (68.19%), H
(5.46%). Found: C (68.69%), H (5.38%).
8 (K 81 °C I (45 °C monotropic N)). 1H NMR: 0.88 (t, 6H,
-CH3), 0.98 (m, 4H), 1.27 (m, 18H), 1.54 (m, 4H), 1.84 (m, 8H),
2.15 (m, 4H), 250 (m, 2H), 4.20 (m, 2H, -CH2-O2C-CDd),
4.29 (m, 2H, -CO2-CH2-), 7.04 (d, 1H, arom), 7.25 (m, 1H,
arom), 7.64 (d, 1H, arom). Anal. Calcd (C38H53O82H3): C
(70.88%), H (8.29%). Found: C (70.63%), H (8.29%).
Syn th esis of Ben zyl (r,â,r′)2H3-Acr yla te (14). Benzyl
bromoacetate triphenylphosphonium bromide (13) (0.92 g, 2
mmol) was dissolved in dry THF (48 mL). Anhydrous potas-
Syn t h esis of (4′-Met h oxyp h en yl) 4-(5′′-((r,â,â′-2H 3)-
Acr yloyloxy)p en tyloxy)ben zoa te (12). (4′-Methoxyphenyl)
4-(5′′-hydroxypentyloxy)benzoate (10): To a stirred solution
of 4′-methoxyphenyl 4-(pentenyloxy)benzoate (9) (1 g, 3.2
mmol) in 25 mL of dry THF kept under argon was added via
syringe 9-BBN as a 0.5 M solution in THF (7 mL, 3.5 mmol).
The mixture was stirred overnight at room temperature under
argon. The solution was cooled in an ice/water bath, and solid
m-chloroperbenzoic acid (3.2 g of commercial (70%) acid) was
added slowly in small portions. After stirring at room tem-
perature overnight, the reaction mixture was diluted with 100
mL of water and extracted twice with dichloromethane. The
organic phase was washed thoroughly with a saturated sodium
bicarbonate solution (4 × 100 mL) and water and then dried
over Na2SO4. After evaporation of the solvent, the residue was
purified by column chromatography on silica gel using a 50/
50 hexane/ethyl acetate mixture as eluting solvent to give 0.96
2
sium carbonate (0.28 g, 2 mmol) and H2CO (as a 20% solution
in 2H2O) (2.4 mL) were added, and the reaction mixture was
stirred at room temperature overnight.
The THF was evaporated under reduced pressure, and the
residue was dissolved in dichloromethane (60 mL). The organic
layer was washed with brine (2 × 100 mL) and water (100
mL) and dried over Na2SO4. After evaporation of the solvent,
the crude product was purified by column chromatography on
silica gel with a 80/20 hexane/ethyl acetate mixture as eluting
solvent to yield 0.25 g (1.51 mmol, 75%) of liquid. 1H NMR:
5.2 (s, 2H, -CO2-CH2-), 7.35 (m, 5H, arom). Anal. Calcd
(C10H72H3O2): C (72.69%), H (4.27%). Found: C (72.73%), H
(4.06%).
Ack n ow led gm en t. Part of this work was performed
at the University of Colorado during a visit of P. Keller
to Professor D. M. Walba’s group. Work performed there
was supported by NSF Materials Research Science and
Engineering Centers (Grant DMR 98-09555).
1
g (2.9 mmol, 90%) of white solid (K 102 °C I). H NMR: 1.64
(m, 4H, HO-CH2-CH2-CH2-), 1.88 (m, 2H, -O-CH2-CH2-),
2.15 (broad m, 1H, HO-), 3.7 (m, 2H, HO-CH2-), 3.81 (s, 3H,
CH3-O-), 4.05 (m, 2H, -O-CH2-), 6.95 (m, 4H, arom), 7.1
(m, 2H, arom), 8.12 (m, 2H, arom). Anal. Calcd (C19H22O5): C
(69.07%), H (6.71%). Found: C (68.66%), H (6.65%).
(4′-Methoxyphenyl) 4-(5′′-(bromoacetyloxy)pentyloxy)ben-
zoate (11): A solution of 10 (0.86 g, 2.6 mmol), bromoacetic
acid (0.4 g, 2.86 mmol), N,N-dicyclohexylcarbodiimide (0.59 g,
2.86 mmol), and pyrrolidinopyridine (0.042 g, 0.28 mmol) in a
mixture of dichloromethane (50 mL) and THF (20 mL) was
stirred at room temperature for 12 h. The N,N-dicyclohexy-
lurea was removed by filtration, and the filtrate was washed
with water (100 mL), a 5% acetic solution (100 mL), water (100
mL), and dried over Na2SO4.
After evaporation of the solvent, the residue was recrystal-
lized from ethanol to give 0.62 g (1.37 mmol, 53%) of white
solid (K 53 °C I). 1H NMR: 1.6 (m, 2H, -O-CH2-CH2-CH2-),
1.81 (m, 4H, -O-CH2-CH2-CH2-CH2-), 3.81 (s, 3H, -O-
CH3), 4.06 (m, 2H, -O-CH2-), 4.22 (m, 2H, -CO2-CH2-),
6.94 (m, 4H, arom), 7.1 (m, 2H, arom), 8.12 (d, 2H, arom). Anal.
Calcd (C21H23BrO6): C (55.88%), H (5.13%). Found: C (56.84%),
H (5.35%).
Su p p or tin g In for m a tion Ava ila ble: 1H NMR spectra for
all the deuterated monomers synthesized. This material is
available free of charge via the Internet at http://pubs.acs.org.
Refer en ces a n d Notes
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Academic Press: London, 1988.
(4′-Methoxyphenyl) 4-(5′′-((R,â,â′-2H3)acryloyloxy)pentyloxy)-
benzoate (12): 11 (0.55 g, 1.21 mmol) was dissolved in toluene
(5 mL). Triphenylphosphine (0.35 g, 1.31 mmol) was added,
and the reaction mixture was stirred for 2 days. Toluene was
evaporated under reduced pressure, and the solid residue was
dissolved in 30 mL of dry THF.
2
Anhydrous potassium carbonate (0.18 g, 1.3 mmol) and H2-
(13) Pelter, A.; Hughes, L.; Madhusudhana Rao, J . J . Chem. Soc.,
Perkin Trans. 1 1982, 719.
(14) Hassner, A.; Alexanian, V. Tetrahedron Lett. 1978, 4475.
CO (as a 20% solution in 2H2O) (1.5 mL) were added, and the
reaction mixture was stirred at room temperature overnight.
The THF was evaporated under reduced pressure, and the
residue was dissolved in dichloromethane (50 mL). The organic
MA010838M