Abstract
The photocatalytic reduction of nitrobenzene to aniline in alcoholic solutions appears as an interesting alternative to the classical hydration. However, little is known about the influence of reaction parameters on the kinetics of the reaction which were therefore studied herein. The effects of light intensity, catalyst concentration, initial concentration, and temperature were systematically investigated under more than 50 different conditions and accurately described with an appropriate kinetic model. The results show that the efficiency of the reaction is extremely high and apparent quantum yields of up to 142 % were observed under optimized conditions. Particularly interesting is the fact high efficiencies were also obtained at high reaction rates of up to 74.3 mM h−1. Overall these results demonstrate that heterogeneous photocatalytic reactions can be very efficient and productive at the same time and may therefore present a powerful tool in synthetic organic chemistry.
Highlights
With an annual world production of about 4 Mt, Aniline is one of the 100 most important building blocks in the chemical industry (Kahl et al, 2011)
In order to better understand the kinetics and the influence of reaction parameters, the photocatalytic reduction of nitrobenzene in ethanol using TiO2 as a photocatalyst was studied under a variety of different conditions, with the light intensity (4 μmol L−1s−1 to 100 μmol L−1s−1) and catalyst concentration (0.25 g L−1 to 12.5 g L−1) each spanning about 2 orders of magnitude
Since the complete reduction of nitrobenzene to aniline requires six electrons, these results indicate that given sufficiently fast kinetics, apparent quantum yields (AQY) of up to 184 % (6 × φ) should be possible for this reaction
Summary
With an annual world production of about 4 Mt, Aniline is one of the 100 most important building blocks in the chemical industry (Kahl et al, 2011). The studied reaction is the nitrobenzene reduction in ethanol that yields the abovementioned condensated products such as quinolines (Hakki et al, 2013a,b; Hirakawa et al, 2015).
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