Title : Metal-free photocatalysis at charged aqueous interfaces: boosting the photocatalytic oxidative coupling of arylamines to azoaromatics under ambient conditions
Abstract:
Controlling the reaction mechanism, dynamics, selectivity, and yield of chemical reactions at the nanoscale or sub-nanoscale resolution are the ultimate goals of a chemist. In the present study, we have developed a highly efficient metal-free aqueous photocatalytic approach for the synthesis of functional azoaromatics via utilizing a micellar assembly with excellent yields (up to 100%) and selectivity (100%) under ambient atmosphere.1 Nanoscale aqueous micelles act as an efficient reaction crucible to host both Eosin Y as the photocatalyst and arylamines as substrates for a non-diffusive photoinduced electron transfer with a time constant of 0.3 ps. Notably, the charged aqueous interface of micelles also modulates the redox potential of the catalyst as well as the organic substrates in favourable manner to carry out the reaction. Our present synthetic strategy exhibits fast kinetics and a broad substrate scope with only 0.6 mol% of photocatalyst. Our present approach outperforms all the previously reported catalytic methodologies for the synthesis of azoaromatics. Most of the methods suffer from slow kinetics, poor selectivity, high temperature, and/or an inert atmosphere. On the other hand, photocatalytic reductive coupling of nitrobenzenes in the presence of various photocatalysts suffers from poor product selectivity due to the simultaneous generation of azoxyaromatics or nitrosobenzene and the requirement of an inert atmosphere, which limits their large-scale practical applicability. To the best of our knowledge, this is the first report for the selective synthesis of azo compounds in an aqueous medium under an ambient atmosphere without any unwanted toxic byproducts via utilizing a metal-free low-cost organic photocatalyst, Eosin Y and tripotassium phosphate as the base (Figure 1). This remarkable boosting of the catalytic efficacy arises mainly due to the non-diffusive photoinduced electron transfer and modulation of redox potentials at the charged aqueous interfaces of micellar assemblies.
Audience Take Away
- The present synthetic approach is the most efficient, sustainable, and first report on the aqueous phase synthesis of azo compounds. Therefore, we strongly believe that our developed strategy will be a benchmark for the synthesis of a wide variety of azo compounds.
- This work is a perfect blend of physical and organic chemistry which will help the researchers of these fields to employ the understanding of this work in their future studies.
