Facile sulfur-assisted carbonylation of diaminoresorcinol with carbon monoxide

Article abstract of DOI:10.1002/hc.20746

4,6-Diaminoresorcinol, which is a raw material of ZYLON (PBO fiber), has an instability in air atmosphere. Therefore, very stable benzo[1,2-d:5,4-d']bis- 2(3H)-oxazolone recognized a useful equivalent of 4,6-diaminoresorcinol during the stages of production, storage, and transportation. By combining the sulfur-assisted carbonylation of 4,6-diaminoresorcinol dihydrochloride with carbon monoxide and triethylamine under 0.1 MPa at 20°C for 4 h in DMF with the oxidation of resulting hydrogen sulfide salt with molecular oxygen for 2 h, benzo-[1,2-d:5,4-d']bis-2(3H)-oxazolone was obtained in a quantitative yield. Also, carbonylation of 2,5-diaminohydroquinone dihydrochloride and 2,5-diamino-1,4-benzenedithiol dihydrochloride was smoothly performed to give benzo[1,2-d:4,5-d']bis-2(3H)-oxazolone and benzo[1,2-d:4,5-d']bis-2(3H)- thiazolone, respectively, in good to excellent yields under similar reaction conditions. Furthermore, 2,6-dimercaptobenzo[1,2-d:5,4-d']bisoxazole, which is another equivalent of 4,6-diaminoresorcinol, was obtained in excellent yield by the thiocarbonylation of 4,6-diaminoresorcinol dihydro-chloride with carbon disulfide in the presence of 1-methylpyrrolidine at 20°C for 24 h in DMF.

Full text of DOI:10.1002/hc.20746

Heteroatom Chemistry
Volume 23, Number 1, 2012
Facile Sulfur-Assisted Carbonylation of
Diaminoresorcinol with Carbon Monoxide
Takumi Mizuno, Takeo Nakai, Masatoshi Mihara, and Takatoshi Ito
Osaka Municipal Technical Research Institute, 1-6-50, Morinomiya, Joto-ku,
Osaka 536-8553, Japan
Received 6 May 2011; revised 16 June 2011
Heteroatom Chem 23:111–116, 2012; View this article
online at wileyonlinelibrary.com. DOI 10.1002/hc.20746
ABSTRACT:
4,6-Diaminoresorcinol,
is raw material of ZYLON (PBO fiber),
which
a
has an instability in air atmosphere. There-
fore, very stable benzo[1,2-d:5,4-d’]bis-2(3H)-
oxazolone recognized
a
useful equivalent of
INTRODUCTION
4,6-diaminoresorcinol during the stages of pro-
duction, storage, and transportation. By com-
bining the sulfur-assisted carbonylation of 4,6-
diaminoresorcinol dihydrochloride with carbon
monoxide and triethylamine under 0.1 MPa at 20◦C
for 4 h in DMF with the oxidation of resulting
hydrogen sulfide salt with molecular oxygen for 2 h,
benzo-[1,2-d:5,4-d’]bis-2(3H)-oxazolone was ob-
tained in a quantitative yield. Also, carbonylation
of 2,5-diaminohydroquinone dihydrochloride and
2,5-diamino-1,4-benzenedithiol dihydrochloride was
smoothly performed to give benzo[1,2-d:4,5-d’]bis-
2(3H)-oxazolone and benzo[1,2-d:4,5-d’]bis-2(3H)-
thiazolone, respectively, in good to excellent yields
under similar reaction conditions. Furthermore,
2,6-dimercaptobenzo[1,2-d:5,4-d’]bisoxazole, which
is another equivalent of 4,6-diaminoresorcinol, was
obtained in excellent yield by the thiocarbonylation of
4,6-diaminoresorcinol dihydro-chloride with carbon
disulfide in the presence of 1-methylpyrrolidine at
Poly(p-phenylene-2,6-benzobisoxazole)
(ZYLON,
PBO fiber), which is a thermoset liquid crystalline
polyoxazole, was invented and developed by SRI
International (California, USA) in the 1980s. ZYLON
is the super fiber that shows almost double strength
and modulus, and 100◦C higher decomposition
temperature compared with p-Aramid fiber. This
fiber is now manufactured by Toyobo Co., Ltd. for
applications such as body armor, which requires
very high strength with excellent thermal stability
[1–3].
This fiber is produced by the polymerization
of 4,6-diaminoresorcinol dihydrochloride (2a) with
paraphthalic acid (Scheme 1). However, for the sup-
ply of 2a as a pure monomer in large scale, it has
a serious problem because 2a is unstable for oxi-
dation in the air atmosphere during the stages of
production, storage, and transportation. Therefore,
benzo[1,2-d:5,4-d’]bis-2(3H)-oxazolone (1a), which
has great stability for oxidation with air, was found
as a useful equivalent of 2a. Also, 1a is easily con-
verted quantitatively into 2a by the hydrolysis with
concentrated hydrochloric acid [4–6].
20◦C for 24 h in DMF.
2011 Wiley Periodicals, Inc.
ꢀ
C
Correspondence to: Takumi Mizuno; e-mail: tmizuno@omtri
.or.jp.
Contract grant sponsor: Grant-in-Aid for Scientific Research,
Ministry of Education, Culture, Sports, Science and Technology,
Japan.
Among the few synthetic methods for benzo[1,2-
d:5,4-d’]bis-2(3H)-xazolone (1a), the direct synthe-
sis of 1a by the carbonylation of 2a with 1,1’-
carbonyldiimidazole or phosgene dimer has been
studied to afford 1a in good yields [4]. Also, 1a was
Contract grant number: 22550144.
2011 Wiley Periodicals, Inc.
c
ꢀ
111

112 Mizuno et al.
SCHEME 1 Polymerization of PBO fiber.
TABLE 1 Effect of Base and Solvent on Synthesis of 1a
prepared from 4,6-dinitroresorcinol by multistep
reactions, including carbonylation with ethyl chlo-
roformate, hydrogenation with hydrogen over Pd/C,
and cyclization [5]. Furthermore, synthesis of 1a
from 4,6-dinitroresorcinol by the reductive carbony-
lation with pressured carbon monoxide in the pres-
ence of sulfur or selenium was reported [6], based
upon our research group’s results [7]. However, 4,6-
dinitroresorcinol is considerably explosive under dry
conditions.
Entry
Base
Solvent
Yielda(%)
1
2
3
4
5
6
7
8
K2CO3
NaoH
Triethylamine
1-Methylpyrrolidine
DBUb
DMF
DMF
DMF
DMF
DMF
DMSO
THF
Tolune
72
48
99
100
44
27
0
Triethylamine
Triethylamine
Triethylamine
0
In 1994, we reported a useful synthetic method
for benzoxazolone by the sulfur-assisted carbonyla-
tion from 2-aminophenol with carbon monoxide and
the oxidation with molecular oxygen under mild con-
ditions (0.1 MPa, 20◦C) [8].
Reaction conditions:4,6-diaminoresorcinol dihydrochloride (2a)
(1.065g, 5 mmol),sulfur (641 mg, 20 mmol), base (40 mmol), sol-
vent (20 mL), CO (0.1 MPa), 20◦C, 4 h for carbonylation and O2 (0.1
MPa), 20◦C, 2 h for oxidation.
aIsolated yields.
b1,8-Diazabicyclo [5.4.0]undec-7-ene.
Therefore, our objectives have been to develop a
straightforward protocol for benzo[1,2-d:5,4-d’]bis-
2(3H)-oxazolone (1a), which is a promising equiva-
lent of raw material of ZYLON, by the carbonylation
of 4,6-diamino- resorcinol dihydrochloride (2a) with
carbon monoxide and sulfur followed by oxidation
with molecular oxygen under mild conditions.
Furthermore, 2-mercaptobenzoxazole synthesis
from 2-aminophenol is well known using carbon
disulfide [9–14] or potassium O-ethyl dithiocarbon-
ate [15–17]. Then, we also performed research to
find another equivalent of 4,6-diamino-resorcinol
by the thiocarbonylation of 2a with carbon
disulfide.
ing to the previous results [8], reaction of 2a (5
mmol) with carbon monoxide (0.1 MPa) and sulfur
(20 mmol) in the presence of potassium carbonate
(40 mmol) at 20◦C for 4 h in DMF solvent was per-
formed. The generated salt in DMF was oxidized
under an ambient pressure of molecular oxygen
at 20◦C for 2 h to obtain 1a in good yield (72%)
(Table 1, entry 1). However, because of low solu-
bility of potassium carbonate in DMF, yield of 1a
was slightly diminished. Using sodium hydroxide
in DMF, the yield of 1a was reduced for a sim-
ilar reason (entry 2). Then, for the improvement
of yields of 1a, the reactions using a variety of
liquid bases were tried (Entries 3-5). Surprisingly,
the use of triethylamine or 1-methylpyrrolidine af-
forded benzo[1,2-d:5,4-d’]bis-2(3H)-oxazolone (1a)
in quantitative yields (entries 3 and 4). The strong
base, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), is
not effective to give 1a in low yield, because of the
formation of colored tar (entry 5).
RESULTS AND DISCUSSION
For the synthesis of benzo[1,2-d:5,4-d’]bis-2(3H)-
oxazolone (1a) from 4,6-diaminoresorcinol dihy-
drochloride (2a), the carbonylation of 2a with car-
bon monoxide, sulfur and base, and the follow-
ing oxidation with molecular oxygen under mild
conditions were examined (Scheme 2). Accord-
Recently, we found that sulfur-assisted carbony-
lation of amines and alcohols with carbon monoxide
SCHEME 2 Synthesis of benzo[1,2-d:5,4-d’]bis-2(3H)-oxazolone (1a).
Heteroatom Chemistry DOI 10.1002/hc

Carbonylation of Diaminoresorcinol 113
was strongly accelerated by DMF or DMSO [18];
therefore, the effect of several solvents was tested
in the presence of triethylamine (entries 3 and 6–8).
Solvent DMF gave 1a in excellent yield; however,
other solvents (DMSO, THF, toluene) were unsuit-
able for the synthesis of 1a.
The preparation of benzo[1,2-d:4,5-d’]bis-
2(3H)-oxazolone (1b) and benzo- [1,2-d:4,5-d’]bis-
2(3H)-thiazolone (1c) was also tried in a similar
manner. The sulfur-assisted carbonylation of
2,5-diaminohydroquinone dihydrochloride (2b) and
Scheme 4 shows possible paths for the forma-
tion of benzo[1,2-d:5,4-d’]bis- 2(3H)-oxazolone (1a)
by the sulfur-assisted carbonylation of 4,6-diamino-
resorcinol dihydrochloride (2a) with carbon monox-
ide followed by oxidation with molecular oxygen.
First, 2a reacted with carbon monoxide and sulfur
via the formation of carbonyl sulfide (3) to form
thiocarbamate salt (4a). The formed 4a converts
into isocyanate (5a), which is accompanied by the
elimination of hydrogen sulfide salt (6a). Benzo[1,2-
d:5,4-d’]bis-2(3H)-oxazolone (1a) is formed from
isocyanate (5a), and hydrogen sulfide salt (6a) is
oxidized by molecular oxygen to recover elemental
sulfur.
2,5-diamino-1,4-benzenedithiol
dihydrochloride
(2c) with carbon monoxide readily proceeded
to afford 1b and 1c, respectively, in good to
excellent yields under mild reaction conditions
(Scheme 3).
Next, the synthesis of 2,6-dimercaptobenzo[1,2-
d:5,4-d’]bisoxazole (1d), which is a candidate of
SCHEME 3 Synthesis of benzo[1,2-d:5,4-d’]bis-2(3H)-oxazolone (1b) and benzo[1,2-d:5,4-d’]bis-2(3H)-thiazolone (1c).
SCHEME 4 A possible path for the formation of benzo[1,2-d:5,4-d’]bis-2(3H)-oxazolone (1a).
Heteroatom Chemistry DOI 10.1002/hc

114 Mizuno et al.
SCHEME 5 Synthesis of 2,6-dimercaptobenzo[1,2-d:5,4-d’]bisoxazole (1d).
SCHEME 6 A plausible path for 2,6-dimercaptobenzo[1,2-d:5,4-d’]bisoxazole (1d).
the raw material of ZYLON, was examined by
the thiocarbonylation of 4,6-diaminoresorcinol di-
hydrochloride (2a) with carbon disulfide and several
bases at 20◦C for 24 h in DMF (Scheme 5). Using 1-
methylpyrrolidine, 1d was given in excellent yield.
DBU which is a strong base is unsuitable to bring to
only mixture.
In Scheme 6, a credible route for the prepara-
tion of 2,6-di-mercaptobenzo[1,2-d:5,4-d’]bisoxazole
(1d) was shown by the thiocarbony-lation with
carbon disulfide and 1-methylpyrrolidine at 20◦C.
4,6-Diamino-resorcinol dihydrochloride (2a) is sub-
ject to thiocarbonylation with carbon disulfide in
the presence of base to give dithiocarbamate salt
(7a). Then, the isothiocyanate derivative (8a) is
formed by the elimination of hydrogen sulfide
salt (9a) from 7a. Finally, 2,6-dimercaptobenzo[1,2-
d:5,4-d’]bisoxazole (1d) is generated from 8a, and 9a
is oxidized by molecular oxygen to recover elemental
sulfur.
CONCLUSION
In summary, a facile synthesis of benzo[1,2-d:5,4-
d’]bis-2(3H)-oxazolone (1a), which is an equiva-
lent of raw material of ZYLON, has been de-
veloped by the sulfur-assisted carbonylation of
4,6-diaminoresorcinol dihydrochloride (2a) with
carbon monoxide and triethylamine and the ox-
idation of resulting hydrogen sulfide salt with
molecular oxygen under mild conditions. Prod-
uct (1a) was obtained in quantitative yields. Also,
the preparation of 2,6-dimercaptobenzo- [1,2-d:5,4-
d’]bisoxazole (1d) was performed in excellent yield
by the thiocarbonylation of 4,6-diaminoresorcinol
Heteroatom Chemistry DOI 10.1002/hc

Carbonylation of Diaminoresorcinol 115
dihydrochloride (2a) with carbon disulfide and 1-
methylpyrrolidine. From the viewpoint of an insta-
bility of 4,6-diaminoresorcinol dihydrochloride (2a),
which is a raw material of ZYLON, in air atmo-
sphere the development of a stable equivalent of 2a
is very important. Therefore, the present easy proto-
col for benzo[1,2-d:5,4-d’]bis-2(3H)-oxazolone (1a)
might give an additional possibility for the produc-
tion of PBO fiber.
Benzo[1,2-d:4,5-d’]bis-2(3H)-oxazolone
(1b).
Yield: 940 mg (98%) yield; mp >300◦C; IR (KBr,
cm−1): ν 3222, 1737 (C O), 1475, 1321, 962, 691;
1H NMR (d6-DMSO): δ(ppm) 7.10 (s, 2H, CH), 11.59
(s, 2H, NH); 13C NMR (d6-DMSO): δ(ppm) 93.4,
124.6, 139.3, 154.4; MS (EI) m/z (%): 192 (M+,
12), 138 (100), 111 (16), 110 (14), 70 (15), 68 (14);
Exact MS: calcd for C8H4O4N2: 192.0171; found:
192.0169.
Benzo[1,2-d:4,5-d’]bis-2(3H)-thiazolone
(1c).
Yield: 750 mg (67%) yield; mp >300◦C; IR (KBr,
cm−1): ν 3101, 1649 (C O), 1460, 1189, 639; 1H
NMR (d6-DMSO): δ(ppm) 7.33 (s, 2H, CH), 11.86
(s, 2H, NH); 13C NMR (d6-DMSO): δ(ppm) 105.7,
121.9, 131.8, 169.5; MS (EI) m/z (%): 224 (M+, 42),
192 (100), 166 (26), 136 (22); Exact MS: calcd for
C8H4O2N2S2: 223.9714; found: 223.9703.
Procedure for the Preparation of 2,6-
Mercaptobenzo[1,2-d:5,4-d’]Bisoxazole (1d). Into
the DMF (20 mL) solution containing 4,6-
diaminoresorcinol dihydro-chloride (2a) (1.065
g, 5 mmol) and carbon disulfide (6.0 mL, 100
mmol), 1-methylpyrrolidine (4.3 mL, 40 mmol) was
added. The reaction mixture was stirred at 20◦C
for 24 h. The resulting red solution was stirred for
an additional 2 h at 20◦C under molecular oxygen
(0.1 MPa). Then, the resulting mixture was poured
into 1 M HCl (100 mL), filtered, and washed with
AcOEt (100 mL × 2) and toluene (50 mL × 2). After
dried under vacuum, 2,6-mercaptobenzo[1,2-d:5,4-
d’]bisoxazole (1d) was obtained.
EXPERIMENTAL
Melting points were determined on a Mettler FP 5 in-
strument and were uncorrected. FT-IR spectra were
recorded on a JASCO FT/IR-4100 instrument. 1H
and 13C NMR spectra were obtained on a JEOL
JNM-AL300 (300 MHz, 75 MHz) instrument. Chem-
ical shifts were reported in ppm relative to tetra-
methylsilane (δ-units). Mass spectra were measured
on a JEOL JMS-600 spectrometer. Elemental anal-
ysis was performed on a CE instruments EA1110.
4,6-Diaminoresorcinol dihydrochloride (2a), 2,5-
diaminohydroquinone dihydro-chloride (2b), 2,5-
diamino-1,4-benzenedithiol dihydrochloride (2c),
potassium carbonate, sodium hydroxide, triethy-
lamine, 1-methylpyrrolidine, DBU, DMF, DMSO,
THF, toluene, sulfur (99.5%), carbon disulfide, car-
bon monoxide (99.9%), and oxygen (99.9%) were
used as purchased.
Typical Procedure for the Synthesis of Benzo[1,2-
d:5,4-d’]bis-2(3H)-oxazolone (1a).
A dark red
mixture containing 4,6-diaminoresorcinol di-
hydrochloride (2a) (1.065 g, 5 mmol), sulfur
(641 mg, 20 mmol) and triethylamine (5.5 mL,
40 mmol) with DMF (20 mL) was vigorously
stirred under carbon monoxide (0.1 MPa) at 20◦C
for 4 h. After the reaction, molecular oxygen
(0.1 MPa) was charged at 20◦C into the resulting
white emulsion. The reaction mixture was stirred
for additional 2 h at 20◦C. Then, the resulting
mixture was poured into 1 M HCl (100 mL), fil-
tered, and washed with AcOEt (100 mL X 2) and
toluene (50 mL × 2). After dried under vacuum,
benzo[1,2-d:5,4-d’]bis-2(3H)-oxazolone (1a) was
given.
2,6-Mercaptobenzo[1,2-d:5,4-d’]bisoxazole (1d).
◦
Yield: 1.045 g (93%) yield; mp >300 C; IR (KBr,
1
cm−1): ν 3358, 1493, 1442, 1380, 1136, 924, 506; H
NMR (d6-DMSO): δ(ppm) 6.91 (s, 1H, CH), 7.85 (s,
1H, CH), 13.96 (brs, 2H, SH); 13C NMR (d6-DMSO):
δ(ppm) 91.8, 94.2, 128.7, 144.8, 180.1; MS (FD) m/z
(%): 224 (M+); Anal. Calcd. for C8H4O2N2S2: C, 42.85,
H, 1.80, N, 12.49, S, 28.60. Found: C, 42.64, H, 1.75,
N, 12.14, S, 28.20.
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