Convenient preparation of hydroxymethyl-substituted diaminodiphenyloxybenzenes

Article abstract of DOI:10.1080/00397910802419714

Two hydroxymethyl-substituted monomers of diaminodiphenyloxybenzene were synthesized in three or four steps in 95% and 74% overall yields, respectively. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910802419714

Synthetic Communications1, 39: 654–663, 2009
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910802419714
Convenient Preparation of Hydroxymethyl-
Substituted Diaminodiphenyloxybenzenes
Matthew C. Davis
Chemistry and Materials Division, Michelson Laboratory, Naval Air
Warfare Center, China Lake, California, USA
Abstract: Two hydroxymethyl-substituted monomers of diaminodiphenyloxy-
benzene were synthesized in three or four steps in 95% and 74% overall yields,
respectively.
Keywords: Borane, diamine, polyimide, SNAr
The hydroxymethyl-diaminodiphenyloxybenzene 1 was first reported by
Shigemitsu and coworkers[1] (Fig. 1). Later, Takeuchi et al.[2] and Tajima
et al.[3] used the 2-furanoic acid ester of 1 to prepare a polyimide that was
heat resistant and photosensitive. Interest in this monomer has been
renewed by Wright and coworkers,[4] who prepared polyimide from 1
to which they tethered hydroxy-substituted dyes through diacid dichlor-
ide or diisocyanate. This report will describe an alternate method for the
preparation of 1 and its bis-(hydroxymethyl) analog 2.
The route of Shigemitsu et al.[1,2] to synthesize 1 started with the
reaction of 3 and 1-fluoro-4-nitrobenzene.[5,6] It was found that heating
a mixture of 3 with a slight excess of 1-fluoro-4-nitrobenzene in N,N-
dimethylformamide in the presence of anhydrous potassium carbonate
consistently gave only ꢀ40% of the dinitro 4. The crude product was
typically contaminated with 10–15% impurity 5 resulting from further
reaction of 4 with 1-fluoro-4-nitrobenzene (Fig. 2). However, 4 was easily
purified by extraction into ethanol, due to the highly insoluble nature of 5.
Received June 28, 2008.
Address correspondence to Matthew C. Davis, Code 4L4200D, 1900 N. Knox
Road, China Lake, CA 93555. E-mail: matthew.davis@navy.mil
654

Convenient Preparation of Hydroxymethyl
655
Figure 1. Chemical structures.
Repeated attempts to improve the yield of this reaction were unsuccess-
ful, and it was abandoned.
Another method for the preparation of 4 was sought. The benzoic
acid 7 has been previously reported[7–9] (Scheme 1). Several small-scale
reactions showed that heating 6 with a slight excess of 1-fluoro-4-nitro-
benzene in polar aprotic solvent in the presence of anhydrous potassium
carbonate gave 7 in good yield. It was found that N,N-dimethylacetamide
was a convenient solvent in which to conduct this reaction. Because it has
1
no H resonances in the aromatic region, reaction progress was easily
monitored by dissolving an aliquot in dimethylsulfoxide-d6. Interestingly,
the intermediate 8 was not observed at any time in the 1H spectral analysis
of the reaction (Fig. 2). This suggests that the first arylation is the slow
step and the second is fast. This is reasonable because the phenol of 8 is
inductively coupled to a nitro group, making it more acidic and reactive.
Upon completion, the reaction mixture was poured into water, and an
unexpected crystalline precipitate formed. Isolation and analysis of the
precipitate identified it as the potassium salt of 7, which is only partially
soluble in water. Acidification of the workup mixture caused precipitation
of 7, which was filtered and typically did not require further purification.
Figure 2. Impurities.

656
M. C. Davis
Scheme 1. Reagents and conditions: (a) 1-fluoro-4-nitrobenzene, K2CO3, DMF,
60 ꢁC; (b) H2, Pd=C, EtOH; (c) BH3, BF3 ꢂ Et2O, THF, rt; (d) 1-fluoro-4-
nitrobenzene, K2CO3, DMAc, 120 ꢁC.
However, when increasing the scale of this reaction (6–7), an
impurity was found, typically occurring at 15%. Basic extraction of this
contaminated material enabled its isolation, and it was identified as
4,40-dinitrodiphenylether 9 (Fig. 2). This was curious because diphenyl
ethers are typically synthesized by the copper-catalyzed Ullmann reaction
between phenols and aryl halides.[10–14] A literature survey found that
Gale et al.[15,16] had also encountered this impurity in SNAr reactions
using 1-fluoro-4-nitrobenzene. They showed that simply heating the lat-
ter in dimethylsulfoxide in the presence of anhydrous potassium carbo-
nate gave 9 in 50% yield. Furthermore, patent literature[17,18] taught
that this reaction is catalyzed (ꢀ95% yields) by the salts of carboxylic
acids at temperatures of 200 ꢁC, making an excellent preparation of
dinitrodiphenylethers. Apparently, at 120 ꢁC, the reaction of 1-fluoro-4-
nitrobenzene at the phenolic groups of 6 and 8 is more facile than the
hydrolysis/diphenylether pathway. The small amount of 9 generated
may be the result of the slight excess 1-fluoro-4-nitrobenzene charged.
The impurity was conveniently removed by reslurrying the product in
diethyl ether because of the low solubility of 7 in nonpolar solvents.
Borane reagents readily reduce carboxylic acids to the corresponding
alcohols.[19,20] Because aromatic acids are slightly more resistant to bor-
ane reduction than alkyl acids, reduction of 7 was carried out using the
conditions of Chen et al.[21] The acid 7 was stirred in tetrahydrofuran
in the presence of boron trifluoride etherate and reduced with two
molar equivalents of borane–tetrahydrofuran complex. After carefully

Convenient Preparation of Hydroxymethyl
657
Scheme 2. Reagents and conditions: (a) 1-fluoro-4-nitrobenzene, K2CO3, DMAc,
120 ꢁC; (b) LiOH, H2O, THF, 50 ꢁC; (c) BH3, BF3 ꢂ Et2O, THF, rt; (d) H2, Pd=C,
EtOH.
quenching the reaction, 4 was readily isolated simply by pouring the
reaction mixture into water. The yield of the reduction was quantitative.
Catalytic hydrogenation was employed for the reduction of 4 to dia-
mine 1. For expediency, the reaction was run with 40torr hydrogen pres-
sure. After filtration of the palladium catalyst, evaporation of the ethanol
solvent gave the solid diamine 1 in quantitative yield. Recrystallization gave
the monomer in analytically pure form ready for polymerization studies.
The bis-(hydroxymethyl) analog 2 was also prepared by this route,
starting from the diethyl diester 10[22] (Scheme 2). Apart from the addi-
tional step necessary to hydrolyze the ester groups of 11, the chemistry
followed a similar course as described previously. In conclusion, the dia-
minodiphenyloxybenzene monomers 1 and 2 were synthesized in overall
yields of 95% and 74%, respectively.
EXPERIMENTAL
The melting points were collected on an electrothermal capillary melting-
point apparatus and are not corrected. All NMR data were collected
on a Bruker Avance II 300 MHz spectrometer (1H at 300 MHz, 13C at

658
M. C. Davis
75MHz). NMR data (free induction delays) were processed using NUTS
1
software from Acorn NMR (Livermore, CA). All H and 13C spectra are
referenced to tetramethylsilane. Potassium carbonate (K2CO3, anhydrous)
was purchased from Polarchem Corp. (Garden Grove, CA). N,N-
Dimethylformamide 99% (DMF) was purchased from Acros Organics
and used as received. Diethyl 2,5-dihydroxyterephthalate 98% was
purchased from Riedel-de Hae¨n AG (Seelze, DE). Palladium 5% on carbon
(Pd/C) was purchased from Lancaster Synthesis (Windham, NH).
Tetrahydrofuran anhydrous (containing 0.025% 2,6-di-tert-butyl-4-methyl-
phenol), 1-fluoro-4-nitrobenzene 99%, methyl 3,5-dihydroxybenzoate 97%,
3,5-dihydroxybenzyl alcohol (3) 99%, 3,5-dihydroxybenzoic acid (6) 97%,
1 M borane-tetrahydrofuran (BH3/THF) complex in tetrahydrofuran,
boron trifluoride diethyl etherate (BF3 ꢀ Et2O), N,N-dimethylacetamide
99% (DMAc), and all other reagents were purchased from Sigma-Aldrich
(Milwaukee) and used as received. Element alanalyses were made by
Atlantic Microlab, Inc. (Norcross, GA).
3,5-Bis(4-nitrophenyloxy)benzyl Alcohol (4)
Method A, from 3
A 500-mL, round-bottomed flask equipped with magnetic stirbar was
charged with 23.6 g 3 (0.17 mol), 47.54 g 1-fluoro-4-nitrobenzene (0.34 mol,
2 equiv), 70.5 g pulverized anhydrous K2CO3 (0.5 mol, 3 equiv), 100 mL
DMF, and 250 mL acetone. The mixture was heated to 65 ꢁC for 5.5 h.
The mixture was cooled to rt and filtered through a medium glass frit to
remove solids. The filtrate was poured into 1.5 L H2O, and a yellow solid
precipitated. After air drying on the frit, the solid was transferred to a bea-
ker and boiled in 600 mL EtOH. The mixture was cooled and filtered
through a medium glass frit to remove an insoluble solid that was shown
to be 1-(4-nitrophenyloxymethyl)-3,5-bis(4-nitrophenyloxy)benzene (5).
Mp 164–166 ꢁC. dH (DMSO): 8.26 (d, J ¼ 9.3 Hz, 2H), 8.21 (d, J ¼ 9.3 Hz,
2H), 7.22 (m, 8H), 7.05 (t, J ¼ 1.9 Hz, 1H), 5.31 (s, 2H); dC (DMSO):
163.16, 161.93, 156.05, 142.77, 141.15, 140.81, 125.84, 125.57, 118.08,
115.69, 115.41, 111.84, 68.90. Elemental analysis calculated for
C25H17N3O9: C, 59.65; H, 3.40; N, 8.35. Found: C, 59.69; H, 3.40; N, 8.33.
The filtrate was poured into 3 L of vigorously stirred H2O, and a pale
yellow solid precipitated. The solid was collected on a coarse-porosity
glass frit (30.7 g, 48%). The title compound was obtained in analytically
pure form by recrystallization from toluene. Mp 132–134 ꢁC. dH (DMSO):
8.26 (d, J ¼ 8.7 Hz, 4H), 7.22 (d, J ¼ 9.2 Hz, 4H), 7.02 (d, J ¼ 1.9 Hz, 2H),
6.92 (t, J ¼ 2.0 Hz, 1H), 5.43 (t, J ¼ 5.8 Hz, OH), 4.55 (d, J ¼ 5.8 Hz, 2H);

Convenient Preparation of Hydroxymethyl
659
dC (DMSO): 162.27, 155.77, 147.87, 142.60, 126.18, 117.91, 114.33,
110.62, 61.95. Elemental analysis calculated for C19H14N2O7: C, 59.69;
H, 3.69; N, 7.33. Found: C, 59.82; H, 3.74; N, 7.25.
Method B, from 7
A 3-L, round-bottomed flask equipped with magnetic stirbar was
charged with 116 g 7 (0.293 mol) and 300 mL THF. After all the solids
dissolved, 37.8 mL BF3 ꢀ Et2O (0.293 mol, 1 equiv) was added in one por-
tion. An addition funnel was attached, and the reaction was protected
with an N2 bubbler. The reaction mixture was stirred at ice-bath tempera-
ture, and the addition funnel was charged with 586 mL 1 M BH3 ꢀ THF
(0.586 mol, 2 equiv). The borane solution was added over 30 min, and
an H2 by-product was generated early in the addition, then tapered off.
The cooling bath was removed, and the mixture was stirred for 12 h at
rt. The cooling bath was replaced, and the addition funnel was charged
with 50 mL H2O. The water was added over a period of 30 min, and an
H2 by-product was generated early in the addition, then tapered off.
The reaction mixture was poured into a beaker containing H2O under
vigorous stirring. An off-white solid precipitated, and after stirring for
2 h it was filtered on a coarse-porosity glass frit. The solid was washed
with copious H2O and then air dried on the frit for 3 h. The crude product
weighed 112 g (theory 111.93 g), and further purification was not neces-
sary for the subsequent step. Recrystallization from toluene gave the title
compound, which was analytically pure and spectroscopically identical to
the product from method A.
3,5-Bis(4-nitrophenyloxy)benzoic Acid (7)
A 1-L, two-necked, round-bottomed flask equipped with magnetic stirbar
was charged with 30.82 g 6 (0.2 mol) and 400 mL DMAc. Into one neck
was inserted a thermometer to measure internal temperature and to the
other was equipped a reflux condenser with N2 purge. The mixture was
stirred until all the solids dissolved, and then 100 g powdered,
anhydrous K2CO3 (0.725 mol, 3.6 equiv) was added, followed by 60 g
1-fluoro-4-nitrobenzene (0.43 mol, 2.15 equiv). The mixture was heated
to 120 ꢁC and became orange in color shortly after reaching temperature.
1
After 18 h, H NMR of an aliquot dissolved in DMSO-d6 showed the
reaction was complete. The mixture was poured into 2 L H2O, and a solid
precipitated as colorless plates. This precipitate was shown to be potas-
sium 3,5-bis(4-nitrophenyloxy)benzoate. dH (DMSO): 8.22 (d, J ¼ 9.2 Hz,

660
M. C. Davis
4H), 7.49 (d, J ¼ 2.3 Hz, 2H), 7.18 (d, J ¼ 9.2 Hz, 4H), 6.98 (t, J ¼ 2.3 Hz,
1H); dC (DMSO): 167.37, 162.68, 155.24, 142.63, 126.32, 117.97, 117.43,
1
113.04. Elemental analysis calculated for C19H12KN2O8 ꢂ 2 H2O: C, 51.47;
H, 2.71; N, 6.32. Found: C, 51.40; H, 2.53; N, 6.24.
The mixture was acidified to pH 4 with 120 mL conc. HCl, and the
precipitate transformed into a pale yellow solid. The crude solid was fil-
tered on a coarse-porosity glass frit and air dried several hours. The solid
was slurried with 250 mL Et2O and refiltered. The product at this stage
was >97% by 1H NMR (36.3 g, 95%). Recrystallization from MeCN gave
the title compound as off-white needles. Mp 227–229 ꢁC (lit.). dH
(DMSO): 13.59 (bs, CO2H), 8.27 (d, J ¼ 8.9 Hz, 4H), 7.48 (d, J ¼ 2.4 Hz,
2H), 7.38 (t, J ¼ 2.4 Hz, 1H), 7.29 (d, J ¼ 9.2 Hz, 4H); dc (DMSO):
165.63, 161.72, 156.28, 143.03, 134.83, 126.23, 118.43, 116.86, 116.58.
Elemental analysis calculated for C19H12N2O8: C, 57.58; H, 3.05; N,
7.07. Found: C, 57.41; H, 2.99; N, 6.96.
3,5-Bis(4-aminophenyloxy)benzyl Alcohol (1)
A suspension of 39.9 g 4 (0.1 mol) and 1.8 g 5% Pd=C in 600 mL EtOH
was hydrogenated in a Parr1 apparatus at 2068 torr for 4 h. The mixture
was filtered through diatomaceous earth, and the colorless filtrate was
rotary evaporated. The crude off-white solid (33.6 g, 100%) was recrystal-
lized from 10% MeCN in toluene to give the title compound as colorless
needles. Mp 93–95 ꢁC (lit. 100.2–101.9 ꢁC). dH (CDCl3): 6.79 (d,
J ¼ 8.9 Hz, 4H), 6.59 (d, J ¼ 9.1 Hz, 4H), 6.48 (d, J ¼ 2.2 Hz, 2H), 6.42
(t, J ¼ 2.2 Hz, 1H), 3.46 (bs, 4H, NH2), 1.9 (bs, OH); a¨C (CDCl3):
160.61, 148.31, 143.88, 143.13, 121.53, 116.47, 108.98, 105.79, 65.14.
Elemental analysis calculated for C19H18N2O3: C, 70.79; H, 5.63; N,
8.69. Found: C, 70.66; H, 5.54; N, 8.69.
Diethyl 2,5-Bis(4-nitrophenyloxy)terephthalate (11)
A similar procedure to that used for 7, starting with 2.54 g 10 (0.01 mol),
2.96 g 1-fluoro-4-nitrobenzene (0.02 mol,
2 equiv), 4.14 g K2CO3
(0.03 mol, 3 equiv), and 25 mL DMAc. The crude product was weighed
4.2 g (85%). The title compound was obtained as colorless needles by
recrystallization from MeCN. Mp 180–183 ꢁC. dH (CDCl3): 8.17 (d,
J¼ 9.2 Hz, 4H), 7.71 (s, 2H), 6.93 (d, J ¼ 9.2 Hz, 4H), 4.15 (q, J ¼ 7.4 Hz,
4H), 1.08 (t, J ¼ 6.9 Hz, 6H); dC (CDCl3): 163.24, 163.22, 150.37,
143.14, 129.79, 127.04, 126.23, 116.54, 62.34, 14.07. Elemental analysis
calculated for C24H20N2O10: C, 58.07; H, 4.06; N, 5.64. Found: C,
57.97; H, 4.01; N, 5.50.

Convenient Preparation of Hydroxymethyl
661
2,5-Bis(4-nitrophenyloxy)terephthalic Acid (12)
A 250-mL round-bottomed flask equipped with magnetic stirbar was
charged with 3.37 g 11 (6.8 mmol) and 50 mL THF. The mixture was
heated briefly to dissolve all the solids. Then in one portion a solution
of 1.13 g LiOH ꢂ H2O (27 mmol, 4 equiv) dissolved in 10 mL H2O was
added. The biphasic mixture was vigorously stirred and heated to 50 ꢁC
for 1 h. The mixture was poured into 400 mL H2O, generating a clear
yellow solution. The mixture was acidified to pH 5 with conc. HCl, caus-
ing a white solid to precipitate. The solid was collected on a coarse-
porosity glass frit, washed with H2O, and then air dried on the frit
(11.1 g, 87%). Further purification was not necessary for the subsequent
step. The title compound was obtained as colorless needles by recrystalli-
zation from 1,4-dioxane. Mp > 300 ꢁC. dH (DMSO, 370 K): 8.24 (d,
J ¼ 8.9 Hz, 4H), 7.70 (s, 2H), 7.19 (d, J ¼ 9.5 Hz, 4H). Elemental analysis
calculated for C20H12N2O10: C, 54.55; H, 2.75; N, 6.36. Found: C, 54.38;
H, 2.74; N, 6.28.
2,5-Bis(4-nitrophenyloxy)-1,4-bis(hydroxymethyl)benzene (13)
An analogous procedure to that used for 4 started with 13.8 g 12
(0.31 mol), 50 mL THF, 8.1 mL BF3 ꢂ Et2O (8.92 g, 0.62 mol, 2 equiv),
and 124 mL 1 M BH3 ꢂ THF (0.124 mol, 4 equiv). Reaction was quenched
with 15 mL H2O. A crude mass of 12.9 g (100%) was obtained after air
drying on the frit. Recrystallization from MeCN gave the title compound
as pale yellow needles. Mp 238–240 ꢁC. dH (DMSO): 8.26 (d, J ¼ 9.2 Hz,
4H), 7.24 (s, 2H), 7.14 (d, J ¼ 9.2 Hz, 4H), 5.37 (t, J ¼ 5.4 Hz, 2 OH), 4.42
(d, J ¼ 5.1 Hz, 4H); dC (DMSO): 162.98, 148.19, 142.42, 135.15, 126.36,
120.62, 117.00, 57.39. Elemental analysis calculated for C20H16N2O8:
C, 58.25; H, 3.91; N, 6.79. Found: C, 58.22; H, 3.84; N, 6.83.
2,5-Bis(4-aminophenyloxy)-1,4-bis(hydroxymethyl)benzene (2)
A procedure similar to that used for 1 was used for 2, except THF was
used as solvent. Reaction of 9.82 g 13 (0.024 mol), 500 mg 5% Pd=C,
and 250 mL THF gave 8.3 g crude product (100%). The title compound
was obtained as small, colorless needles from MeOH. Mp 208–210 ꢁC.
dH (DMSO): 6.84 (s, 2H), 6.69 (d, J ¼ 8.8 Hz, 4H), 6.56 (d, J ¼ 8.8 Hz,
4H), 5.07 (t, J ¼ 5.3 Hz, 2 OH), 4.89 (s, 2 NH2), 4.47 (d, J ¼ 5.3 Hz,
4H); dC (DMSO): 149.70, 147.25, 144.68, 131.57, 119.58, 115.71,
114.90, 57.54. Elemental analysis calculated for C20H20N2O4: C, 68.17;
H, 5.72; N, 7.95. Found: C, 67.92; H, 5.81; N, 7.83.

662
M. C. Davis
ACKNOWLEDGMENT
The generous financial support from the Army Research Laboratory is
gratefully acknowledged. Thanks to Mses. Ann M. Moorehead, Cynthia
M. Kitchens, and the staff of the NAWC Technical Library (China Lake)
for obtaining references 1, 7, and 22. Special thanks to Dr. Yusuke
Tajima (RIKEN, Wako Japan) for translating a portion of his patent.
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