Mater. Res. Soc. Symp. Proc. Vol. 1279 © 2010 Materials Research Society
New Route for the Tetraphenylfuran Synthesis Using a Superacid Sulfonic Clay (SASC) as Catalyst Carlos Damián Cea1, Eloy Vázquez Labastida2, Manuel Salmon S 1, Sergio O. Flores Valle
3
1
Instituto de Química, Universidad Nacional Autónoma de México. Circuito Exterior, Ciudad Universitaria, Coyoacán, México. D.F. 04510 2 Departamento de Química Orgánica y Polímeros, ESIQIE-IPN, Zacatenco, México, D. F. 07738 3 Laboratorio de Catálisis y Materiales, ESIQIE-IPN, Zacatenco, México, D. F. 07738 Corresponding author:Email:
[email protected]
ABSTRACT The transformation of benzoin to tetraphenylfuran catalyzed with a superacid sulfonic clay under different reaction conditions was investigated. Three products with different yields were produced under a nitrogen stream and four products were obtained under an air atmosphere. Keywords: Catalyst, superacid sulfonic clay, tetraphenylfuran
INTRODUCTION Montmorillonites are a special group of clays characterized by their layered structure and their Brönsted and Lewis acid sites. They have been essentially employed as solid acids in a variety of methodologies [-6]. Big neutralization laundries are avoided when such superacids are used to replace H2SO4 and p-toluensulfonic acid. It has been reported that tetraphenylfuran could be obtained by using concentrated sulfuric acid in an aqueous solution of benzoin [7], which is an electron-rich compound widely used as test compound in (photo) oxidation experiments [8]. This procedure was modified by replacing the sulfuric acid with p-toluensulfonic acid in dry toluene [9]. Other procedures involving in the use of trialkyl phosphites on 2-ene-1,4-diones were also reported [10], their disadvantage is that it requires 1,2-dibenzoylstilbene which is not of easy acquisition. However, the goal product yield is low (10-42%) and by-products are obtained with moderate yields (150%, approximately). Tetraphenylfuran was synthesized by Dams [11] et al. leaving of benzoyl chloride in a procedure consisting of three steps, using species of low valence titanium; the tetraphenylfuran yield is as high as 80 %; however, one has to generate those compounds for using LiAlH4 on TiCl3. In 1999, Vazquez [6] et al. reported the preparation, characterization and evaluation of a superacid sulfonic clay (SASC). In the present work, we employed this kind of super acid solid as catalyst in the study of benzoin transformation. We report herein the synthesis of tetraphenylfuran with a single step procedure and the variation in the product yields under
various reaction conditions. Figure 1 describes the reaction pathways in the tetraphenylfuran synthesis.
O
O
O SASC
+
C6H6
O
OH
III
I II
O
O
+ (E)
O
+ O
O H
IV V
Figure 1. Transformation route of benzoin using a superacid sulfonic clay
EXPERIMENTAL Reaction 1 Benzoin (I) (2.0015 g, 0.0094 mol) and SASC (250 mg) were refluxed in dry benzene (20 mL) for 24 hours. The reaction advance was determined by Thin Layer Chromatography (TLC): Catalyst was removed by filtration in vacuum. The reaction mixture was concentrated by evaporation, and the solvent and the residues were chromatographed in silica gel. Elution with hexane (100 %), gradients of polarity with the system n-C6H14:AcOEt and finally ethyl acetate (100%) gave 0.2404 g of II (12%) mp 175 oC (lit. 173-175 oC), 1.2741 g of III (63.61%) mp 90 o C (lit. 94-95 oC) and 0.0443 g of IV (2.21%) mp 212 oC (lit. 212-213 oC) as well as 0.1803 g of V (9.00%) mp 118 oC. Reaction 2 To a stirred solution of benzoin (2.00 g, 0.0094 mol), SASC (250 mg) in dry benzene (20 mL) under a current of N2 was refluxed for 24 hours. After the removal of solvents, the products (II-IV) were obtained whose melting points are identical with those products obtained in reaction 1 and the yields are given in Table 1. DISCUSSION
Because the reaction I presents high selectivity for the oxidation products, it was carried out under inert atmosphere (N2), in order to displace the occluded oxygen from the breast of the reaction. 2,3-epoxi-1,2,3,4-tetraphenyl-4-hydroxy-1-butanone, not previously described, may be obtained as given in the experimental section. The compound forms white needles with MW 406 g/mol (C28H22O3) mp 118 oC, IR 3467.9 (OH); 3066.7 (aromatics); 1681.8 (carbonyl of ketone) cm-1. NMR 1H δ 7.92-7.24; 5.95; 4.55. NMR 13C δ 197.08; 128.37-140.76; 84.06; 77.00; 76.90. The benzoin reaction in atmosphere of N2, in presence of the clay (SASC) produced only three products: II, III and IV with various yields. Table 1. Influences of the reaction atmosphere in the products formation. Yield (%)
Yield (%)
Atm O2
Atm. N2
II
12.00
69.06
III
63.31
20.56
IV
2.21
5.37
V
9.00
------
Product
As it can be observed in the Table 1, the 2,3-epoxi-1,2,3,4-tetraphenyl-4-hydroxy-1butanone was not formed in reaction II. This reaction is more selective to products of acid catalyzed reaction like the tetraphenylfuran. In addition, 1,2-diketone was also produced. It is inferred that this oxidation product might be obtained by other routes using a different oxidizing agent from oxygen like hydrogen peroxide. Their formation mechanism is under study. For both reactions, condensation products are obtained and their differences in yields and distribution products could be explained taking into account a further oxidative mechanism, where oxygen from air plays an important role. It is well known, in the oxidation of inorganic substrates, that oxygen is activated by superacids [12].
CONCLUSIONS In comparison with other methods, superacid sulfonic clay shows in general a good catalytic activity, being able to catalyze different kind of organic synthesis and leading to good product yields and high selectivity. Acid catalyzed reactions and oxidations can be carried out in a one-pot synthesis procedure, to obtain more complexes products; where atmospheric oxygen is activated by superacid sulfonic clays. ACKNOWLEDGMENTS Thanks to COFAA-IPN and projects SIP-20100083 and SIP-20090999 for the financial support.
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