The Study of Photosensitized Reactions of Nitrobenzene and m-Dinitro Benzene Using Benzophenone As a Sensitizer under Visible Light Irradiation

Abstract

The photosensitized reaction of nitrobenzene and its derivatives, including dinitrobenzene, has been extensively investigated in an aqueous alkaline medium using Benzophenone as a sensitizer under visible light irradiation. A 100 W tungsten lamp was employed for the purpose of irradiation. The presence of the strongly electron-withdrawing NO₂ group leads to polarization of the C–H bond. In this process, the triplet excited state of benzophenone initiates H⁺ abstraction from the polarized C–H bond of nitrobenzene (NB) and meta-dinitrobenzene (m-DNB) through exciplex formation. Proton abstraction results in the formation of free radicals for both NB and m-DNB, followed by dimerization of the free radicals. The observed rate of the reaction follows the order m-DNB > NB. However, no photochemical reaction was observed for p-dinitrobenzene (p-DNB). Various parameters such as pH, substrate concentration, sensitizer concentration, light intensity, solvent effect, and the rate of the photochemical reaction were investigated. The quantum efficiency of the product was determined using a potassium ferrioxalate actinometer. The formation of the product occurs through exciplex formation from the triplet excited state. The possible products, namely 2,2'-dinitro biphenyl and 2,2'-4,4'-tetranitro biphenyl, were confirmed using UV–visible spectrophotometry and mass spectrometry. Finally, a proposed reaction mechanism was suggested based on the experimental findings.