Tunable acid-base bifunctional catalytic activity of FeOOH in an orthogonal tandem reaction

In this report, we have explored the acid-base bifunctional catalytic activity of iron oxohydroxides (FeOOH) by catalyzing deacetalization and Henry condensation reactions successively in a single pot. The crystalline polymorphs of FeOOH, namely goethite (alpha FeOOH), akaganeite (beta FeOOH), lepidocrocite (gamma FeOOH) and delta FeOOH, were chemically prepared and tested for the catalytic activity. All the polymorphs of FeOOH exhibited acid-base bifunctional catalytic activity. The relative selectivity for products varied with the polymorphs of FeOOH. Whereas alpha FeOOH produced benzaldehyde in high yield, the polymorphs beta FeOOH, gamma FeOOH and delta FeOOH showed high selectivity for trans-beta-nitrostyrene. In addition, beta FeOOH also exhibited a unique activity towards the formation of 1,3-dinitro-2-phenylpropane. The difference in the catalytic activity of FeOOH polymorphs was explained based on the strength and density of acidic and basic active sites on the surface. Selectivity for the products was tuned by changing the synthesis parameters of the catalysts and reaction conditions.