Catalysis is a process of increasing the rate of a chemical reaction by adding a substance known as a catalyst [1]. Catalyst may be classified as homogenous or heterogenous catalyst. Homogenous catalyst shows the same phase as the reaction mixture (gas or liquid) as the reactant, while heterogenous catalyst possess different phase in reactant (gas or solid) [2, 3]. Homogenous catalyst shows many disadvantages of the reaction but heterogenous catalyst possess many advantages such as non-toxic, simple work-up procedure, catalyst can be easily removed form the reaction and catalyst can be reused for several time of the reaction. Heterogeneous catalysis is widely used in various industrial processes, such as petroleum refining, chemical synthesis, environmental remediation, and energy production. It offers versatility in terms of the types of reactions that can be catalyzed, ranging from oxidation, reduction, hydrogenation, dehydrogenation, and many others. One advantage of heterogeneous catalysis is that the catalyst can be easily separated from the reaction mixture and reused. This makes it a cost-effective and sustainable approach for many industrial applications [4–12].
Metal silicates can indeed be used as catalysts in various catalytic processes. Silicates are compounds containing silicon and oxygen, and when combined with metal ions, they can exhibit catalytic activity due to the presence of active sites on their surfaces. Silicate-supported metal catalysts show greater importance in various fields, where the metal silicates can also be used as supports for metal catalysts. The metal ions can be incorporated into a silicate matrix to create bimetallic catalysts. These catalysts can exhibit enhanced catalytic activity and selectivity due to the synergistic effects between the metal ions and the silicate support. One of the silicates containing tin (SnO2/SiO2) have important catalytic activity such as aminolysis of styrene oxide with aniline for the Meerwein–Ponndorf–Verley reduction of 4-tert-butylcyclohexanone [13], hydroxylation of phenols [14], Baeyer–Villiger oxidations [15], Meerwein–Ponndorf–Verley reductions [16], sugar isomerization [17], epimerization [18], oxidative dehydrogenation of cyclohexane [19] and Cannizzaro-type reactions [20]. Here, we focus synthesis of new heterogenous SnO2/SiO2 nanocomposite catalytic materials for the synthesis of Bis(indoyl)methane derivatives.
The importance of indole and its derivatives are well recognized by synthetic as well as biological chemists. Indoles and their derivatives are used as antibiotics in the field of pharmaceuticals [21]. Bisindolylalkanes and their derivatives constitute an important group of bioactive metabolites of terrestrial and marine origin [22–25]. Bis(indolyl)methanes are most active cruciferous substances for promoting beneficial estrogen metabolism and inducing apoptosis in human cancer cells [26].
Synthesis of bis(indolyl)methanes derivatives such as montmorillonite K10 clay [27], I2 in acetonitrile [28], HY-Zeolites [29], trichloro-1,3,5-triazine (10 mol%) [30], AlPW12O40 [31], I2 in solvent free [32], CuBr2 [33], SSA [34], metal hydrogen sulfate [35], H3PW12O40 [36], H2NSO3H [37], ZrOCl2 [38], Polyaniline salt or complex [39] and ionic liquid [40]. However, some of these methods are plagued by one or many drawbacks such as long reaction time, use of volatile solvents, low yields and harsh reaction conditions. Therefore, it is necessary to develop an improved route for the synthesis of bis(indolyl)methanes.
In continuous, of our research work we developed new heterogenous nanocomposite catalytic materials for the synthesis of heterocyclic organic compounds [41–47]. Here, we focused on the synthesis of new heterogenous SnO2/SiO2 nanocomposite catalytic materials. Present paper shows SnO2/SiO2 nanocomposite catalyzed one-pot synthesis of Bis(indoyl)methane derivatives.