General Papers ARKIVOC 2006 (xiii) 8-15
expensive reactants and reagents by safer and economical ones. In achieving many of these goals, catalysts help the synthetic chemist in a big way. They are capable of making impracticable reactions to occur under the mildest possible conditions.
Montmorillonite clays have been used as catalysts for number of organic reactions and offer several advantages over classical acids. For example the strong acidity, non-corrosive properties, cheapness, mild reaction conditions, high yields and selectivity and the ease of setting and working-up.17
In the last few years a growing interest has been shown in the use of microwave irradiation in organic synthesis, also.18, 19 In addition, microwave solvent-free synthesis offers advantages for reducing hazardous explosions and removal of the high boiling solvents from the reaction mixtures.20
In continuation of our studies on microwave-assisted reactions on solid surfaces,21 herein we wish to describe a convenient and simple method for the synthesis of different bismaleimides and bisphthalimides from the condensation reaction between an appropriate mixture of maleic or phthalic anhydrides with different diamines on montmorillonite KSF and montmorillonite K-10 clays as solid acidic catalysts and microwave irradiations under the solvent-free conditions in good yields and short reaction times (scheme 1). A comparative data between our applied procedure and the conventional method has been shown in the general procedure section.
O OO
O OO
O H2N R NH2 N R+ KSF or K-10 Clay Microwaves N 1) Maleic anhydride 2) Phthalic anhydride 1a-h, 2a, 3a, 4a 3) 4-Chlorophthalic anhydride 4) 3,6-Dichlorophthalic anhydride
Scheme 1
Results and Discussion
Several examples (22 entries) illustrating this simple and convenient method for the synthesis of bismaleimides and bisphthalimides were summarized in table 1. According to this table, the percentage of the products obtained by the KSF clay is more than those prepared by the K-10 clay, while the reaction times with the montmorillonite K-10 clay are less. This observation can be attributed to the more surface area in K-10 and the more acidic character of the KSF clay,
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