Catalytic Liquid Phase Oxidation of Toluene to Benzoic Acid

The production of benzoic acid from toluene in the liquid phase with pure oxygen was studied. Investigations have been carried out with a view to determining the most suitable reaction conditions with respect to operating variables including oxygen flow rate, reaction temperature, batch time and catalyst loading. In a series of batch experiments carried out at 4 atm, the optimum values of mole ratio of oxygen to toluene, temperature, reaction time, and catalyst loading were found to be 2, 157 °C, 2 h and 0.57 g/L, respectively. In addition, a kinetic study was carried out by taking into consideration the optimum reaction conditions. The model dependent on the formation of benzyl radical was found to be feasible for describing the catalytic oxidation of toluene to benzoic acid in the liquid phase. The activation energy was determined as 40 kJ/mol.     

The Complex Synergy of Water in Metal/Bromide Autoxidations. Part II. Effect of Water and Catalyst on the Aerobic Oxidation of Benzaldehydes and the Effect of Water on the Elementary Catalytic Pathways

All of the rates of the elementary steps in the Co/Br and Co/Mn/Br homogeneous, liquid‐phase catalyzed reactions decrease with increasing water concentration in acetic acid. The step‐wise replacement of the acetic acid ligands by water ligands in the coordination sphere of the catalyst metals may be responsible for this behavior. The non‐catalyzed and metal‐catalyzed (Co, Co/Mn/Br and Co/Mn) aerobic oxidations of benzaldehyde and 4‐methylbenzaldehyde are reported. The non‐catalyzed autoxidations are quite vigorous reactions in acetic acid/water mixtures but by‐products from the Baeyer–Villiger reaction, the thermal decomposition of the peroxy acid, and over‐oxidation to carbon dioxide limit the yield to the aromatic carboxylic acids. As the concentration of a Co or Co/Mn/Br catalyst increases these by‐products are first reduced and then eliminated probably due to the very fast, selective reaction of [Co(II)]₂ with the peroxy acid. A Co/Mn catalyst completely inhibits the autoxidation of the benzaldehydes. There is a gradual change in the yield of terephthaldicarboxaldehyde from 4‐methylbenzaldehyde with increasing Co/Mn/Br concentration suggesting that the non‐catalyzed steps are being replaced by catalyzed ones. The autoxidation of heptaldehyde generates about 500 times more carbon monoxide than does benzaldehyde using a Co/Mn/Br catalyst and gives only a 50% yield to heptanoic acid consistent with excessive amounts of decarbonylation with aliphatic aldehydes.     

Synthesis of 2,5‐Diformylfuran and Furan‐2,5‐Dicarboxylic Acid by Catalytic Air‐Oxidation of 5‐Hydroxymethylfurfural. Unexpectedly Selective Aerobic Oxidation of Benzyl Alcohol to Benzaldehyde with Metal=Bromide Catalysts

The alcohol group of hydroxymethylfurfural (compound 1, HMF) is preferentially oxidized by dioxygen and metal/bromide catalysts [Co/Mn/Br, Co/Mn/Zr/Br; Co/Mn=Br/(Co+Mn) = 1.0 mol/mol] to form the dialdehyde, 2,5‐diformylfuran (compound 2, DFF) in 57% isolated yield. HMF can be also oxidized, via a network of identified intermediates, to the highly insoluble 2,5‐furandicarboxylic acid (compound 5, FDA) in 60% yield. For comparison, benzyl alcohol gives benzaldehyde in 80% using the same catalyst system. Over‐oxidation (to CO₂) of HMF is much higher than that of the benzyl alcohol but can be greatly reduced by increasing catalyst concentration.