Optimization of the time and temperature of the microwave-assisted amination of phenylene-PMO

Abstract

In this paper we report a study on the optimization of the amination of periodic mesoporous phenylene–silica (PMO) using microwave heating. The optimization was carried out for two key steps in the reaction, namely, (1) nitration of the bissilylated phenylene bridge, and (2) reduction of the nitro group to a primary amine. The temperatures of both reaction steps were varied between 37, 60, 75 and 90 °C. The reaction times studied were between 15 to 360 minutes. Microwave heating lead to significant reduction in the reaction times needed to achieve the maximum degree of nitration and amination compared to conventional means. After 15 minutes of reaction at 60 °C, a nitrogen density similar to that obtained for the same material synthesized conventionally was observed, and after 240 minutes of reaction time at 60 °C the nitrogen density was exceeded. A complete reduction of the nitro to the amine groups was observed after 15 minutes of reaction at 60 °C, which demonstrates the great potential of microwave irradiation in enhancing the kinetics of the post-synthesis functionalization of PMO materials, while preserving the molecular and mesoporous orders.