A convenient synthetic route to 2,5-dialkoxyterephthalaldehyde

Article abstract of DOI:10.1081/SCC-200046485

A convenient method for synthesizing 2,5-dialkoxyterephthalaldehyde by oxidation of 1,4-dialkoxy-2,5-bis(halogenomethyl)benzene with dimethyl sulfoxide in one step is described.

Full text of DOI:10.1081/SCC-200046485

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A Convenient
Synthetic Route to
2,5‐Dialkoxyterephthalaldehyde
Pin Shao a , Zhen Li a , Jianlin Luo a , Hongli Wang a
& Jingui Qin a
a Department of Chemistry , Wuhan University ,
Wuhan, P. R. China
Published online: 05 Aug 2006.
To cite this article: Pin Shao , Zhen Li , Jianlin Luo , Hongli Wang & Jingui Qin
(2005) A Convenient Synthetic Route to 2,5‐Dialkoxyterephthalaldehyde, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 35:1, 49-53, DOI: 10.1081/SCC-200046485
To link to this article: http://dx.doi.org/10.1081/SCC-200046485
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Synthetic Communicationsw, 35: 49–53, 2005
Copyright # Taylor & Francis, Inc.
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1081/SCC-200046485
A Convenient Synthetic Route to
2,5-Dialkoxyterephthalaldehyde
Pin Shao, Zhen Li, Jianlin Luo, Hongli Wang, and Jingui Qin
Department of Chemistry, Wuhan University, Wuhan, P. R. China
Abstract: A convenient method for synthesizing 2,5-dialkoxyterephthalaldehyde by
oxidation of 1,4-dialkoxy-2,5-bis(halogenomethyl)benzene with dimethyl sulfoxide
in one step is described.
Keywords: Dimethyl sulfoxide, 2,5-dialkoxyterephthalaldehyde, 1,4-dialkoxy-2,5-
bis(halogenomethyl)benzene
2,5-Dialkoxyterephthalaldehydes (2) are very important intermediates for
organic synthesis and polymer preparation.[1–13] Their two aldehyde groups
can react with some other molecules of functional groups like amine or
ylide reagent to form an extended conjugated structure (symmetrical or
unsymmetrical), and the two alkoxyl pendants will help to improve the
solubility of the compounds with rigid moiety, which make them very attrac-
tive in the preparation of organic opto-electronic materials such as poly-para-
phenylenevinylene[7,8,13] and polyazomethine[6] among the others.
Usually, three traditional synthetic methods[1–3,7,8,10–12] were used to
prepare aldehydes 2. The first method started from 1,4-dialkoxy-2,5-bis(halo-
genomethyl) benzene (1)[10] and gave aldehyde 2 after three steps. This
method was somewhat complicated and time-consuming (the reaction lasted
over 2 days). The second one included only one-step reaction of the
Received in Japan August 19, 2004
Address correspondence to Jingui Qin, Department of Chemistry, Wuhan Univer-
sity, Wuhan, P. R. China. E-mail: jgqin@whu.edu.cn

50
P. Shao et al.
treatment of 2,5-dialkoxy-1,4-dihalogenobenzene with n-butyllithium and
dimethylformamide,[9] but the synthesis involved the air-sensitive material.
In the third synthetic route, 2 could be obtained from 1 directly by Sommlet
reaction. This procedure is simple, and can give moderate yields (62%)[3]
for short chain length 2,5-dimethoxyterephthalaldehyde, but poor yields
(6.8 ꢀ 15%)[9] for long chain length dialkoxyhalides. So another convenient
and efficient synthetic method should be developed, especially for long
chain length dialkoxyhalides.
Recently, we have developed a convenient and efficient synthetic route to
aldehydes 2 from halides 1 directly (Scheme 1). In our new method, halides 1
were oxidized by dimethyl sulfoxide (DMSO) with excessive sodium bicar-
bonate as auxiliary agent. Parallel experiments indicated that this reaction
could be carried out in either nitrogen or air, and the yields were almost the
same (Table 1). DMSO is a common solvent, and sometimes it can behave
as a kind of oxidant.[14] In this paper DMSO was used in the preparation of
2 from 1 for the first time. Here we shall describe the synthesis of six 2,5-dia-
lkoxyterephthalaldehydes 2, in which the longest chain length of the alkoxyl is
OC16H33.
This reaction can be easily monitored by the color change of the reaction
mixture. If the reaction takes place at the room temperature, there is not color
change after 24 h stirring. When the reactants were heated, the mixture turned
from colorless to pale yellow. Thin-layer chromatography showed that the
halides 1 were completely consumed after more than 90 min at 1008C and
only half an hour at 1158C. But even higher temperature was not necessary.
When the reaction was kept at 1508C, the halides 1 could be consumed
within 25 min and the color of the mixture turned to dark orange, which
means more by-product was formed. So the reaction was preferred to be
kept at 1158C in the air, and aldehydes 2 were obtained with moderate
yields (Table 2). The reactions could be scaled-up with the same proportion
of the starting materials, and the reaction mixture should be stirred vigorously
due to the poor solubility of sodium bicarbonate in DMSO.
In conclusion, we have successfully converted halides 1 to aldehydes 2
employing DMSO as oxidant. The whole synthetic procedure was fairly con-
venient and efficient, the reaction time was short, and the yields were also
satisfying.
Scheme 1.

Convenient Synthetic Route to 2,5-Dialkoxyterephthalaldehyde
51
Table 1. The yields of 2ea in nitrogen and air
Entry
Atmosphere
Yieldb/%
1
2
Nitrogen
Air
79
75
aBoth reactions were performed at 1158C and accom-
plished within 30 min.
bValues of isolated yields after purification by column
chromatography.
EXPERIMENTAL
1H NMR spectra were recorded in CDCl3 on Varian Mercury VX300 FT-
NMR spectrometer (Varian, USA) operating at 298 K. Chemical shifts were
recorded in parts per million (ppm) relative to tetramethylsilane (TMS).
The 1,4-dialkoxy-2,5-bis(halogenomethyl)benzene 1a–1f were prepared
as the literature reported.[8] All the compounds and solvents were purchased
from Chemical Reagents Company, China National Medicines Group, and
used without further purification.
General Procedure for the Synthesis of
2,5-dialkoxyterephthalaldehydes 2
Halides 1a–1f (0.5 mmol) and sodium bicarbonate (0.63 g, 7.5 mmol) were
stirred in 8 mL DMSO at 1158C for 0.5 h. And then the reaction mixture
was poured into 200 mL of water. The precipitate was filtered and dried.
Table 2. Synthesis of 2,5-dialkoxyterephthalaldehydes (2a–2f)
Yielda
(%)
m.p.b (Lit.)
Entry
R
R0
X
(8C)
a
b
b0
c
Me
Me
Br
Br
Cl
Br
Br
Br
Br
69
77
60
66
74
75
78
207–209 [206[15]
102–103
102–103
]
(CH3)2CH(CH2)2 (CH3)2CH(CH2)2
(CH3)2CH(CH2)2 (CH3)2CH(CH2)2
n-C6H13
n-C10H21
n-C12H25
n-C16H33
n-C6H13
n-C10H21
n-C12H25
Me
74–75 [73–74[12]
]
d
e
85–86 [84–85[6]
]
90–91 [90–90.5[8]
93
]
f
aValues of isolated yields after purification by column chromatography.
bUncorrected.

52
P. Shao et al.
The crude aldehydes were purified by silica gel column chromatography using
petroleum ether/CHCl3 (1/2, V/V) as the eluent.
2,5-Bis(30-methylbutyloxy)terephthalaldehyde (2b & 2b0): 1HNMR
(300 MHz, CDCl3): d ¼ 0.99 (d, J ¼ 5.7 Hz, 12H), 1.77 (m, 4H), 1.88
(m, 2H), 4.11 (t, J ¼ 8.7 Hz, 4H), 7.42 (s, 2H), 10.48 (s, 2H).
2-Hexadecyloxy-5-methoxy-1,4-terephthalaldehyde
(2f):
1HNMR
(300 MHz, CDCl3): d ¼ 0.81 (t, J ¼ 6.3 Hz, 3H), 1.18–1.40 (m, 26H),
1.73–1.79 (m, 2H), 3.86 (s, 3H), 4.00 (t, J ¼ 6.3 Hz, 2H), 7.34 (s, 2H),
10.40 (s, 1H), 10.43 (s,1H).
ACKNOWLEDGMENT
This work was supported by the National Natural Science Foundation of
China (No. 90201002).
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