http://www.chemistrymag.org/cji/2000/02c054ne.htm |
Dec. 1, 2000 Vol.2 No.12 P.54 Copyright |
Hu Wenxiang, Peng Qingtao
(Institute of Military Medicine, Headquarters of General Equipment, Beijing 100101)
Received July 23, 2000; Supported by National Natural Science Foundation of China
Abstract Rapid reaction of pyrrole and
benzaldehyde in xylene with microwave irradiation affords the tetraphenylporphyrin in good
yield, and purification of the product is very simple. Combination of physical-chemical
catalysis is a very useful tool to catalyze chemical reaction.
Keywords Rapid synthesis, Tetraphenylporphyrin, Microwave irradiation.
During recent years, many different types of
organic reactions have been reported to be efficiently carried out under microwave
irradiation conditions. By using microwave irradiation, many reactions proceed fast with
high chemical yields[1]. This rapid new synthetic method could be used to
synthesize a wide range of organic compounds, such as tetraphenylporphyrin(TPPH2)
which plays an important role in bionics, host-guest chemistry and bioinorganic chemistry.
The synthesis of tetraphenylporphyrin has been very well documented in
the literature[2-5]. The classical methods involve the refluxing of
benzaldehyde with pyrrole in the presence of acid as catalyst. These reactions have some
limitations such as relatively poor yields, severe reaction conditions and intractable
purification problems.Loupy and co-workers reported the preparation of
tetraphenylporphyrins under microwave irradiation in dry media in 1992[6], but
the reaction suffered from small scale and low yield. In this work a procedure to perform
rapid and efficient synthesis of tetraphenylporphyrin in microwave oven (scheme 1) is
described.
Scheme 1
This reaction is modified by changing media and catalyst. We have found that in the presence of p-nitro-benzoic acid as catalyst, the product (TPPH2) was easily obtained by microwave irradiation of the mixture of benzaldehyde and pyrrole in xylene for a few minutes. Recrystallization of crude product from ethanol yields about 30% yield of pure TPPH2 and at least twofold higher than that of dry reactions[6]. The other advantage is the ease of product purification when compared to the conventional methods. The product was identified on the basis of elemental analysis, NMR, FT-IR and FAB-MS. With decreasing activation energy and increasing reaction rate, the microwave techniques may be called “high-energy techniques” in organic synthesis[1]. With other examples reported by us, we have shown that microwave irradiation, coupled with other techniques are very useful tools in chemical synthesis[7-10].
EXPERIMENTAL
The microwave oven used for this study is a domestic National model NN-K652. The NMR
spectra was recorded with a JNM-GX400 NMR spectrometer (using TMS as an internal standard)
and the FT-IR spectra with a Nicolet Magna-LR spectrometer, FAB-MS datas were obtained
using a Labspec instrument.
A solution of pyrrole (1.4mL) and benzaldenyde (2.1mL) was added in
xylene (45mL), and catalyzed by 4-nitro-benzoic acid. The mixture was introduced into a
microwave oven, and heated for 3 minutes in 850 watts setting. After cooling to room
temperature, the crude product was recrystallized with ethanol 2-3 times to yield pure
tetraphenylporphyrin with violet color, m. p.= 370°C.
Anal. Found (%) (Calcd.%) C 85.16(85.91), H 4.87(4.89), N 8.92(9.12). FT-IR (KBr, cm-1):3436.6,
3315.1 (uNH);
3052.8, 3030.6 (uNH,
ArH); 1594.9, 1473.4, 1442.5 (In-plane skeletal vibrations); 798.4, 698.1 (d CH, out-of-plane bending
deformation, monosubstitute benzene). 1HNMR (d ppm, CDCl3): 7.78 (3H x 4, o, p-position of benzyl),
8.24 (2H x 4, pyrrole), 8.86 (2H x 4, m-position of benzyl). 13C NMR (d ppm, CDCl3): 142.2, 134.5,
130.8, 128.0, 127.7, 126.7, 120.1. FAB-MS [propanetriol (M=92) was used as substrate in
FAB-MS]: 613 (M+-1), 370 (1/2M+64-1), 462 (370+92), 554(462+92), 644 (554+90),
276 (370-94), 167, 259 (167+92), 351 (167+92´ 2), 443 (167+92´ 3), 535 (167+92´ 4), 184
(92´ 2), 94 (92+2).
REFERENCES
[1] Lu M W, Hu W X, Yun L H. Chin. J. Org. Chem., 1995, 15, 561-566; 1997, 17, 289-294.
[2] Rothemund P. J. Am. Chem. Soc., 1935, 57, 2010-2020.
[3] Adler A D. J. Org. Chem., 1967, 32, 476-479.
[4] Treibs A, Haberle N. Liebigs Ann. Chem., 1968, 718, 183-191.
[5] Lindsey J S. Tetrahedron Lett., 1986, 27, 4969-4973.
[6] Petit A, Loupy A. Synth. Commun., 1992, 22 (8), 1137-1140.
[7] Hu W X, Yun L H. Sci. Techno. Bull., 1996, 12, 320-321.
[8] Hu W X, Yun L H. Bull. Acad. Mili. Med. Sci., 1995, 19, 253-254.
[9] Hu W X. Chemistry (Huaxue Tongbao), 1995, (8), 35-39; 1999, (10), 34-38.
[10] Hu W X. Chin. Chem. Lett., 1992, 3 (3), 167-170; Acta Chemica Sinica, 1996, 54, 77-83.