A new route to 2,3,5,6-tetrafluoroterephthal aldehyde and its chemical transformation

Article abstract of DOI:10.1016/j.jfluchem.2003.11.017

The title compound was prepared from commercial available and cheaper starting material terephthalolyl chloride by six-step reaction sequence in total 40% yield. Its chemical transformations were also studied.

Full text of DOI:10.1016/j.jfluchem.2003.11.017

Journal of Fluorine Chemistry 125 (2004) 451–454
A new route to 2,3,5,6-tetrafluoroterephthal aldehyde
and its chemical transformation
*
Shizheng Zhu , Jingwei Zhao, Xian Cai
Key Laboratory of Organofluorine Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences,
3
54 Fenglin Lu, Shanghai 200032, China
Received 22 September 2003; received in revised form 19 November 2003; accepted 28 November 2003
Abstract
The title compound was prepared from commercial available and cheaper starting material terephthalolyl chloride by six-step reaction
sequence in total 40% yield. Its chemical transformations were also studied.
#
2003 Elsevier B.V. All rights reserved.
Keywords: Terephthaloyl chloride; 2,3,5,6-Tetra-fluoroterephthalaldehyde; Synthesis; Chemical transformation
1
. Introduction
In this paper, we describe a new synthetic route to this
versatile compound using terephthaloyl chloride as starting
material and some its chemical transformations.
Within the past two decades the literature on the subject of
fluorinated aromatic polymer has expanded dramatically [1].
Due to the strong inductive effect, small atomic radius of the
fluorine atom and high bond energy of C–F bond, the
fluorine-containing aromatic polymers have some excellent
properties such as high thermal and chemical stability, low
dielectric constant, and excellent electron- or photolumines-
2. Results and discussion
The title product was prepared through six-step reaction
sequence from the commercially available and cheaper
terephthaloyl chloride 1 in total 40% yield, as outlined in
Scheme 2.
0
0
cence. For example, poly(a,a,a ,a -tetrafluoro)-p-xylene
parylene AF4) is an interesting and commercially valuable
(
material [2], while polytetrafluoropheylenevinylene (FPPV)
is a good photoluminescence material, and application in a
light emitting diode with low turn-on voltage has been
reported recently [3].
Many of the synthetic procedures, however, require read-
ily accessible fluorinated materials and detailed reports on
versatile synthetic procedures leading to fluorine-containing
materials are not as preponderant as for the hydrogen
containing analogues.
Chlorination of 1 was carried out at 180 8C in the presence
of catalytic amount iron powder using chlorine gas. Try to
use cheaper starting material terephthaldehyde failed to
obtain the chlorinated product 2, because the formation of
high melting point product terephthalic acid which solidified
in the reaction flask at 180 8C and could not be further
chlorinated.
In the second step the ammonia gas was bubbled into a
petroleum ether solution of the chlorinated product 2 at 0 8C.
During our study on the fluorinated aromatic materials,
we have synthesized the precursor of parylene AF4, octa-
fluoro [2,2] paracyclophene and dodecafluoro [2,2] para-
cyclophane [4]. We also reported the preparation of 6-FDA
and its oligemers with diamines [5] (Scheme 1).
Recently Krebs et al. reported the preparation of 2,3,5,6-
tetrafluoro terephthalaldehyde from 1,2,4,5-tetrafluoroben-
zene by four reaction steps [6].
The formed diamide 3 was treated with excess POCl giving
3
the dehydrated product 1,4-dicyno-2,3,5,6-tetrachloroben-
zene 4 in 89% yield. Using other dehydrants such as SOCl2
and P O could also obtain the product 4, but the yield is
2
5
little low (70–75%).
The fluorination of 4 is the key step for the preparation of
the title compound. It was accomplished by treatment of 4
with dry KF in polar non-protonic solvents (such as DMSO,
DMF) and in the presence of catalyst. In order to establish
the optimal conditions for this reaction, we screened various
reaction conditions. Some typical reaction conditions and
*
Corresponding author. Fax: þ86-21-64166128.
E-mail address: zhusz@mail.sioc.ac.cn (S. Zhu).
0022-1139/$ – see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2003.11.017

452
S. Zhu et al. / Journal of Fluorine Chemistry 125 (2004) 451–454
CF2X
Al/PbBr2
DMF
(
F2C
CF2
)
CF2
n
CF2
CF2X
X= Br, Cl
n = 1, 2
O
O
O
O
O
CF3
C
CF3
C
CH3
CH3
2
NH -Y-NH2
)
n
O
H2N (Y
N
N
CF3
CF3
O
O
O
O
Scheme 1.
COCl
COCl
Cl
CONH2
CN
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl /Fe
NH3
ether
2
POCl
0
3
1
80 C
0
1
35 C
Cl
Cl
Cl
Cl
COCl
1
COCl
2
CONH2
3
CN
4
CN
CH(OMe)2
CHO
F
F
F
F
KF/DMF
Ni/H2
F
F
F
H SO
0
2
r.t.
4
130 C
H SO /CH OH
2
4
3
F
F
F
F
F
CN
CH(OMe)2
6
CHO
7
5
Scheme 2.
the results obtained are summarized in Table 1. We found
that the best condition is to use five equal mole KF and
reaction was carried in a mixture solution of methanol and
sulfuric acid (98%) at room temperature. After stirring for
48 h, the reaction mixture was filtrated and distilled to
remove the methanol. The rest oil was washed by distilled
water and then extracted using methylene dichloride, after
evaporation the solvent, the white solid 2,3,5,6-tetrafluoro-
terephthalaldehyde dimethylacetal 6 was obtained in 80%
yield. The product 6 was easily de-protected in aqueous
5
mole% catalyst (t-Bu) NCl, the fluorination was carried
4
out in DMF at 140 8C (Entry 5) which gave the fluorinated
product 1,4-dicyno-2,3,5,6-tetrafluorobenzene 5 in 92%
yield. It is a white solid with mp 106 8C.
The 1,4-dicyno-2,3,5,6-tetrafluorobenzene 5 was then
reduced by hydrogen gas in presence of Raney Ni. This
Table 1
Fluorination of 1,4-dicyno-2,3,5,6-tetrachlorobenzene 4 under different reaction conditions
a
KF
b
c
Yield (%)
Entry
Temperature (8C)
Time (h)
Solvent
Catalyst (%)
1
2
3
4
5
6
7
8
9
140
140
140
140
140
140
140
180
180
160
4
4
4
6
8
8
6
6
8
8
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMSO
DMSO
NMP
4
6
6
5
5
5
5
5
5
5
–
–
44
46
70
75
90
92
92
85
90
85
(t-Bu)
(t-Bu)
(t-Bu)
(t-Bu)
4
4
4
4
NCl, (3)
NCl, (3)
NCl, (5)
NCl, (5)
18-Crown-6, (2)
(t-Bu)
(t-Bu)
(t-Bu)
4
4
4
NCl, (5)
NCl, (5)
NCl, (5)
1
0
a
b
c
Mole ratio of KF/compound 4.
Mole ratio of the catalyst/compound 4.
Isolated yield based on compound 4.

S. Zhu et al. / Journal of Fluorine Chemistry 125 (2004) 451–454
CH OH
453
was added. Chlorine gas was introduced into the flask
through a inlet tube. The reaction temperature was kept at
180 8C using a oil bath. The reaction was continued for 24 h.
The product was slowly poured into 2 l petroleum ether,
stirred intensively to make sure that all 2,3,5,6-tetra-chloro-
terephthalolyl chloride solved in the petroleum ether. After
the iron dregs were filtrated, the petroleum ether was evapo-
rated, and 60 g crude 2 was obtained. 56 g (yield 65%) white
pure solid was obtained by recrystallation from petroleum
ether and methylene dichloride. Mp 145–146 8C [7].
2
F
F
LiAlH4
THF
CHO
F
F
F
F
F
F
CH OH
2
F
F
F
F
8
PhNH
30 c
2
CHO
PhN=CH
CH=NPh
0
1
7
9
Scheme 3.
4.2. The preparation of 2,3,5,6-tetra-chloro-terephthalolyl
amide (3)
sulfuric acid solution giving desired fluorinated terephtha-
laldehyde 7 in total 40% yield from the starting terephtha-
loyl chloride 1.
2,3,5,6-Tetrafluoro terephthalaldehyde 7 could be trans-
formed into other compounds. For example, it was reduced
Under stirring, NH gas (in a cylinder) was bubbled in to a
3
500 ml flask contenting a solution of 2,3,5,6-tetra-chloro-
terephthalolyl chloride (10.3 g, 30 mmol) and 300 ml ether
at 0 8C. After 30 min, about 2 l NH gas was introduced, the
3
to 2,3,5,6-tetrafluoro xylene-diol 8 by LiAlH or hydrogen
4
valve of the NH gas cylinder was stopped. The mixture was
3
gas in the presence of Raney Ni, while Krebs et al. prepared
diol 8 by reducing terephthalaldehyde 7 with (CH ) S*BH
3
stirred for another 8 h and the reaction temperature raised
from 0 8C to room temperature. TLC analysis showed the
starting chloride 2 were all consumed, then the solvent was
evaporated and the remained solid was washed by the water
and baked, the white solid product diamide 3 8.2 g (yield
91%) was obtained [8].
3
2
[
1
6]. The terephthalaldehyde 7 with aniline was heated at
20 8C for 16 h to give 2,3,5,6-tetrafluoro xylene-diimide 9
in 75% yield. (Scheme 3) The physical and chemical proper-
ties of the diimides now are under investigation and the
results will be published elsewhere.
þ
MS m/z (ion, %): 304, 302, 300 (M , 4), 288, 286, 284
þ þ
M –NH , 7), 220, 218, 216 (M –2Cl–NH , 2), 142
2 2
(
(
þ
C Cl , 15).
6
2
3
. Conclusion
4.3. Preparation of 1,4-dicyno-2,3,5,6-tetrachlorobenzene
(4)
In summary, we have developed a new and cost-effective
method for the preparation of 2,3,5,6-tetrafluoro terephtha-
laldehyde 7 which is versatile reagent and can participate in
numerous reactions. Its derivatives 2,3,5,6-tetrafluoro
xylene-diol 8 and 2,3,5,6-tetrafluoro xylene-diimide 9 have
been prepared. Their physical properties and chemical
transformations are now under investigation.
A mixture of 2,3,5,6-tetra-chloro-terephthalolyl amide
(6.04 g, 0.02 mol) and 25 ml POCl in a 50 ml flask was
3
stirred at 135 8C for 6 h. The reaction mixture was poured
into a beaker with 150 ml ice–water and stirred for 15 min.
The precipitation was filtrated, and 4.6 g white solid was
obtained. The yield was 89% [9].
þ
þ
MS m/z (ion, %): 268, 266 (M , 100), 264, 229 (M –Cl,
þ
4
. Experimental
12), 124 (M –4Cl, 23).
1H NMR and 19F NMR spectra were recorded in CDCl3
on a Bruker DRX-300 spectrometer operating at 282 MHz
4.4. Preparation of 1,4-dicyno-2,3,5,6-tetrafluorobenzene
(5)
for 19F (internal standard CFCl ) and 300 MHz for 1H
3
(
CCl F are negative. IR spectra were obtained with a Perkin-
internal standard TMS). Highfield shifts from TMS and
1,4-Dicyno-2,3,5,6-tetrachlorobenzene (8 g, 0.03 mol),
KF (7.54 g, 0.13 mol) and 0.3 g t-Bu NBr were put into a
3
4
Elmer 983G spectrophotometer using KBr disks. Lower
resolution mass spectra were obtained on a Finnigan GC-
MS 4021. Elemental analyses were undertaken by the ana-
lysis department of Shanghai Institute of Organic Chemistry.
100 ml flask content 60 ml DMF and the mixture was stirred
at 130 8C for 6 h. 19F NMR analysis showed all the 1,4-
dicyno-2,3,5,6-tetrachlorobenzene (4) consumed. Then the
reaction mixture was poured into a beaker with 100 ml ice–
water, and filtrated. The precipitate was washed by water and
baked, then 5.4 g (yield 90.1%) yellow solid was obtained
which is identified with literature reference [10].
4.1. Preparation of 2,3,5,6-tetra-chloro-terephthalolyl
chloride (2)
1
9
F NMR d (ppm): À131.7 (s, 4F, CF); MS m/z (ion, %):
þ þ þ
200 (M , 100), 181 (M –F, 1), 155 (M –F–CN, 4), 124
Terephthalolyl chloride (51 g, 0.25 mol) was charged into
a 100 ml flask and heated to120 8C, then iron powder 1 g
þ þ
(M –4F, 6), 100 (C F N ,10).
4 2

454
S. Zhu et al. / Journal of Fluorine Chemistry 125 (2004) 451–454
4.5. Preparation of 2,3,5,6-tetrafluoro terephthalaldehyde
dimethylacetal (6)
aqueous and filtrated. The filtrate was dried and evaporated,
and 0.52 g white solid was obtained. The yield was 52%. Mp
1
06 8C which is identified with literature reference [6].
1
1,4-Dicyno-2,3,5,6-tetrafluorobenzene (5 g, 0.025 mol)
H NMR d (ppm): 3.39 (s, 4H, 2CH ), 4.85 (s, 2H, 2OH);
2
1
9
and sulfuric acid (3.2 ml, 98%) were added into 50 ml
methanol in a 100 ml flask. Then 2 g Ni was put in the
reaction mixture at 0 8C. After addition, the hydrogen gas
was filled in at 30 8C. After 48 h, the reaction mixture was
filtrated and distilled the methanol, and then the remained
mixture was extracted by methylene chloride. After the
methylene chloride was evaporated, there were 6 g (yield
F NMR d (ppm): À145.2 (s, 4F, 4CF); MS m/z (ion, %):
þ
þ
þ
210 (M , 100), 192 (M –CHO, 16), 189 (M –H O–H , 33),
2
3
163, 145, 133.
4.8. Preparation of 2,3,5,6-tetrafluoro xylene-diimide (9)
A mixture of terephthalaldehyde 7 (103 mg, 0.5 mmol)
and aniline (102 mg, 1.1 mmol) was stirred at 120 8C for
16 h. Then extracted by dichloro methane, the crude product
was obtained. It was purified by column chromatogram to
give diimide 9 (147 mg, yield 75%). Mp 178–179 8C.
8
8
0%) tetrafluoro-terephthalaldehyde dimethylacetal 6. Mp
5–86 8C [11].
1
H NMR d (ppm): 3.47 (s, 12H, 4CH ), 5.60 (s, 2H, 2CH,);
3
1
9
F NMR d (ppm): À145.0 (s, 4F, 4CF); MS m/z (ion, %): 268
þ
þ
þ
À1
(
M , 100), 221 (M –H–OMe, 7), 193 (C F OMe , 89), 177
6
FT-IR (nmax, cm ): 2966 (s, C–H), 1627 (s, C¼N), 1360,
4
þ
1
(
C F CHO , 8).
6
1110 (s, C–F); H NMR d (ppm): 7.19–7.27 (t, 6H, 6CH),
4
1
9
7
.35–7.40 (t, 4H, 4H), 8.61 (s, 2H, 2CH¼N); F NMR d
þ
4
.6. Preparation of 2,3,5,6-tetrafluoroterephthalaldehyde
(ppm): À142.9 (s, 4F, 4CF); MS m/z (ion, %): 356 (M , 55),
þ
þ
þ
(
7)
337 (M –F, 1), 252 (M –CH¼NPh, 11), 233 (M –
þ þ
6 5
CH¼NPh–F, 4), 124 (CH¼N Ph, 34), 77 (C H , 100).
2,3,5,6-Tetrafluoro terephthalaldehyde dimethylacetal
1.5 g, 0.05 mol) and 20 ml 63% sulfuric acid were added
Anal. Calcd. For C H F N C 67.42, H 3.37 and N 7.86%,
20 12 4 2
(
found C 67.63, H 3.62 and N 7.57%.
into a 50 ml flask, and stirred at room temperature for 2 h.
Then the product was extracted by dichloromethane. After
the solvent was evaporated, the white solid 2,3,5,6-tetra-
fluoro-terephthalaldehyde 7 0.9 g was obtained. The yield
was 87%. Mp 130–132 8C which is identified with literature
reference [6].
References
[
[
1] R.E. Banks, E. Horwood, Preparation, properties and industrial
applications of organofluorine compounds, New York, 1982.
2] W.R. Dolbier, X.X. Rong, Y.L. Xu, J. Org. Chem. 62 (1997) 7500–
1
19
H NMR d (ppm): 10.37 (S, 2H, 2CH); F NMR d (ppm):
7
502.
[3] L.H. Gan, Y.M. Wang, Y. Xu, N.K. Goh, Y.Y. Gan, Macromolecules
4 (2001) 7409–7413.
þ
À143.6 (S, 4F, 4CF); MS m/z (ion, %): 206 (M , 100), 177
þ þ
M –CHO, 35), 149 (M H–2CHO, 39), 130 (C F H , 8).
4
þ
3
(
3
[
4] S.Z. Zhu, Y.Y. Mao, G.F. Jin, C.Y. Qin, Q.L. Chu, C.M. Hu,
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4
.7. Preparation of 2,3,5,6-tetrafluoro xylene-diol (8)
[
2
25.
LiAlH (0.78 g, 0.023 mol) was added in 20 ml anhydrous
4
[6] K.F. Krebs, T. Jensen, J. Fluorine Chem. 120 (2003) 77–84.
[
[
[
7] K. Ramirez, J. Org. Chem. 40 (1975) 1101–1105.
8] J. Rabjohn, J. Am. Chem. Soc., 70 (1948) 3518.
9] US Rubber Co. NL.6408879, 1965.
ether at 0 8C, and a solution of 2,3,5,6-tetrafluoroterephtha-
laldehyde 7 (1.05 g, 0.05 mol) in 10 ml anhydrous ether
dropped into the reaction mixture. Then the reaction mixture
was heated and the solvent refluxed for 2 h. After cooling to
room temperature, the mixture was washed by 10% HCl
[
10] L.J. Belf, M.W. Buxton, G. Fuller, J. Chem. Soc. (1965) 3372–
379.
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3