Reaction kinetics and reaction techniques for mediated oxidation of methylarenes to aromatic ketones

Abstract

The Mn³⁺-mediated anodic oxidation of toluene and some substituted toluenes (p-chloro-,p-xylene-,p-nitro-) in 60 wt % H₂SO₄ has been investigated with respect to reaction kinetics and process techniques. The mediators Co³⁺ in 3.5 N HNO₃ and Ce⁴⁺ in 60 wt % H₂SO₄ are compared with Mn³⁺ in 60 wt % H₂SO₄ for unsubstituted toluene. The mediated oxidation of the toluenes proceeds in three well-distinguished steps: benzyl alcohol, benzaldehyde, benzoic acid. The last step, which destroys the desired product, the aldehyde, is crucial. Therefore, for continuous resaturation of the electrolyte with toluene and for extraction of benzaldehyde, the benzaldehyde content in the emulgated organic phase has to be kept below a critical value. For toluene,p-chlorotoluene and xylene Mn³⁺-mediated oxidation only becomes attractive with process temperatures above 60°C. The conversion ofp-nitrotoluene top-nitrobenzaldehyde can only be carried out by Co³⁺. The reactivities of the oxidants declines in the order: Co³⁺>Mn³⁺>Ce⁴⁺. Current efficiencies for the recuperation of all oxidants approaches 100%.