Elsevier

Journal of Catalysis

Volume 213, Issue 1, 1 January 2003, Pages 1-6
Journal of Catalysis

Application of natural phosphate modified with sodium nitrate in the synthesis of chalcones: a soft and clean method

https://doi.org/10.1016/S0021-9517(02)00017-9Get rights and content

Abstract

The solid obtained by impregnation of natural phosphate (NP) with a solution of sodium nitrate, followed by calcination at 900 °C, is a strongly basic catalyst that is easily prepared from cheap precursors. The catalytic activity of this solid in the Claisen–Schmidt condensation was studied and high yields were obtained with small amounts of catalyst. The reaction rate depends on the substitution in both benzaldehyde and acetophenone derivatives. The effect of the solvent, as well as the addition of water and ammonium salt, was investigated as well. The catalyst can be easily recovered and efficiently reused.

Introduction

Heterogeneous catalysts are clearly advantageous over homogeneous ones in large-scale preparations. In this regard, catalysis of organic reactions by inorganic solids is an important new dimension in preparative organic chemistry. Among the different inorganic solids, natural phosphate (NP) has advantages in that it is cheap, readily available, nontoxic, and not a pollutant. During the past seven years we have studied the use of natural phosphate to promote organic transformations [1] and have shown that its mild basic and acidic properties can be exploited in many synthetic applications [2].

Chalcones represent one of the most abundant and ubiquitous groups of natural products [3]. In the last few years they have been shown to possess interesting biological properties, including anti-invasive [4], anticancer [5], inhibitory activation [6], antimalarial [7], antimicrobial [8], antimutagenic [9], radioprotective [10], and anti-inflammatory [11] effects. Furthermore, chalcones have attracted much attention as synthetic intermediates in the preparation of other compounds [12].

The Claisen–Schmidt condensation is the most useful reaction in the synthesis of chalcones and, for this reason, several excellent methods have been developed to carry out the reaction in the homogeneous phase. The use of heterogeneous basic catalysts, such as alumina [13], barium hydroxide [14], hydrotalcite and zeolite [15], facilitates the separation of the catalyst from the reaction medium. Furthermore, in many cases the catalyst may be reused. We previously reported that natural phosphate is capable of catalyzing the Claisen–Schmidt condensation, but that a large amount of catalyst is required [16]. We have also shown that doping with sodium nitrate increases the activity of natural phosphate [17].

In this paper we report a mild and convenient method for the heterogeneous catalysis of the Claisen–Schmidt condensation using NP modified by sodium nitrate.

Section snippets

Methods

All commercial reagents and solvents were used without further purification. NP was purchased from CERPHOS (OCP). X-ray diffraction (XRD) patterns of the catalysts were obtained on a Philips 1710 diffractometer using Cu-Kα radiation. Surface areas were determined at 77 K using a Coulter SA 31000 instrument with an automated gas volumetric method employing nitrogen as the adsorbate. NMR spectra were recorded on a Bruker ARX 300 spectrometer. Mass spectra were recorded on a VG Autospec

Effect of catalyst preparation and reaction conditions

Natural phosphate exists under several mineralogical classes [18] which generally belong to the family of phosphocalcic apatites (Ca10(PO4)6F2 for fluoroapatite in its pure state). In sedimentary rocks, phosphates are formed from compounds derived from apatite by partial isomorphic substitution: Ca2+ ions by Na+, Mg2+, Co2+, Fe3+, or Al3+, PO43− ions by VO43−, SO42−, CO32− or MnO4, and F by OH or Cl. These different substitutions cause distortions of the structure which depend on the nature

Conclusions

Natural phosphate modified by impregnation with sodium nitrate and calcination at 900 °C is an efficient basic catalyst for the Claisen–Schmidt condensation. Several chalcones can be synthesized with high yields using catalytic amounts of NaNO3/NP. The results depend on several factors, with the nature and amount of solvent playing a decisive role. The advantages of this solid over other basic heterogeneous catalysts are the high activity, the simplicity of the preparation method, the ready

Acknowledgements

Financial assistance from the Ministry of Education, Government of Morocco (PROTAS, P2T3/59), Office Chérifien des Phosphates (OCP), CICYT, Spain (Project MAT99-1176), and AECI (Project 2001 MA0005) is gratefully acknowledged.

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