Co-Mn-Br catalyst

The complete mechanism of the autoxidation of methylaromatics mediated by the Amoco, Co/Mn/Br catalyst cocktail is depicted in Figure 18. The development of such a complex, elegant system must surely be considered a work of art. 

Nature of the Co—Mn—Br Catalyst in the Methylaromatic Compounds Process Kinetic and Thermodynamic Studies... 

The peroxides and peracids formed in autocatalytic systems are highly energetic molecules. We now see that the Co/Mn/Br catalyst serves to rapidly relax this energy in increasingly lower steps winding up with a highly selective bromide(O) radical (probably as a complex with the metal). The bromide(O) transient species quickly reacts with methylaromatic compounds to form PhCHj radicals and hence continues to propagate the chain sequence. 

An improvement of catalyst activity, especially for the oxidation of electron-poor, deactivated systems like p-toluic acid, can be reached by addition of other transition metal compounds to the Co/Mn/Br catalyst. The most prominent additive is zirconium(IV) acetate, which by itself is totally inactive. An addition of zirconi-um(IV) acetate (ca. 15 % of the amount of cobalt) can yield reaction rates which are higher than those observed using a tenfold amount of cobalt acetate. This amazing co-catalytic effect can be attributed to the common ability of zirconium to attain greater than sixfold coordination in solution, to the high stability of Zr toward reduction, and to the ability of zirconium or Hf to redistribute the dimer/ monomer equilibrium of dimerized cobalt acetates (Co 7Co, Co VCo " systems) by forming a weak complex with the catalytically more active monomeric Co species [17]. 

There have been many efforts to commercialize 2,6-dicarboxynaphthalene for the preparation of poly(ethylene-2,6-naphthalate) due to its favorable thermoplastic properties compared with PET. Therefore, there are numerous patents in which 2,6-alkyl-substituted (alkyl = methyl, ethyl, isopropyl) naphthalenes are oxidized to the corresponding aromatic di-acids, applying mostly Co/Mn/Br catalysts with various co-catalysts such as Zr or Pd in acetic acid as the solvent. The major byproduct is formed by the oxidation of the naphthalene ring to give trimellitic acid (TMA) [5a, 8]. Sumikin Chemical has developed a method to prepare 2,6-naphtha-lenedicarboxylic acid by oxidation of 2,6-diisopropylnaphthalene (2,6-DIPN) in the liquid phase with air in a 500 tpy plant. Sumikin uses a newly developed catalyst based on Co/Mn with an addition of a few ppm of Pd giving advantages such as yields higher than 90 %, suppression of TMA production to around 1 %, and thus better catalyst recovery, and reduced consumption of acetic acid. 

Catalysts by Rational Design Prediction and Confirmation of the Properties of the Co/Ce/Br liquid -phase autoxidation Catalyst Based on the Kinetic Similarity to the Co/Mn/Br Catalyst... 

The synergistic interaction for the Co/Mn/Br catalyst has been previously reported Ravens [9] based on the replacement of some of the cobalt by manganese in a Co/Br catalyst and by us [10] based on the fact that the sum of the activities of Mn/Br and Co/Br catalysts is less than the Co/Mn/Br catalyst. 

The amount of catalytically active bromide is different for each due to the variation of the concentration of a-bromotoluene during the experiments. a-Bromotoluene is an inactive form of bromine in these reactions [14]. The appropriate manner to express the yield of benzylic bromides is on the initial sodium bromide added rather than on the initial toluene basis since sodium bromide is the limiting reagent. The benzylic bromide yields, on a sodium bromide basis, range from 22% for the Mn/Br catalyst to 93 for the Co/Mn/Br catalyst, see figure 5. Thus the effective bromide concentration varies from 7 to 78%... 

From a mechanistic point of view, the MC catalyst, that is, Co-Mn-Br, is essentially a cobalt-bromide catalyst (Co-Br) promoted by Mn ions. The reason for this definition is that the Co-Br catalyst exhibits all properties of the Co-Mn-Br catalyst, while the Mn-Br catalyst is much less active and has significant mechanistic differences from the Co-Br catalyst. For this reason, we first discuss the nature of the Co-Br catalysis mechanism and then the mechanism of the Co-Mn-Br system. 

This chapter provides an industrial perspective on several oxidation routes to new bio-based molecules. In particular, it focuses on the use of Co/Mn/Br catalyst systems in air oxidations, based on the Amoco Mid-Century catalyst system used for / r -xylene oxidation (also see Chapter 4), as an efficient methodology for the conversion of 5-(hydroxymethyl)furfural (HMF) and 5-(methoxymethyl)furfural (MMF) to 2,5-furandicarboxylic acid (FDCA) in Avantium s YXY process. In addition, other less-studied conversions, such as methyl levulinate (ML) to succinic acid (SA), lignin to a variety of aromatic and phenolic carboxylic acids, are discussed as well. 

In analogy with the oxidation of para-xy ene to TA in the so-called Amoco Mid-Century process, the Co/Mn/Br homogeneous catalyst system has also been used for producing FDCA. In March 2000, Dupont filed a provisional patent application, which was granted in 2013 on the stepwise air oxidation of HMF in acetic acid using a Co/Mn/Br catalyst system [27]. In this stepwise oxidation, 2,5-diformylfuran (DFF), formylfuroic acid, and FDCA were obtained respectively, depending on the conditions. In May 2009, ADM filed a provisional patent application, which was granted in 2013, on the air oxidation of 5-(butoxymethyl)furfural (BMF) with a Co/Mn/Br catalyst in acetic acid to predominantly the monobutyl ester of FDCA [28]. 

Avantium showed in their patent application filed in October 2009 and granted in 2013 that the air oxidation of MMF using a Co/Mn/Br catalyst in acetic acid predominantly leads to FDCA in a single step [29]. In 2013, a subsequent patent was filed that described the continuous oxidation of MMF to FDCA [30]. These processes have been scaled to multiton scale in Avantium s pilot plant in Geleen, the Netherlands. At this moment, Avantium seems to be the only company that can produce purified FDCA on multiton scale. 

Table 19.2 FDCA obtained with Co/Mn/Br catalyst systems. 

Both ADM [31] and Avantium [29,30] have reported on the oxidation of MMF, the more stable methyl ether of HMF. Avantium is currently scaling up its process based on an optimized process in its pilot plant, yielding greater than 96 mol% FDCA -I- FDCAMe from MMF. Though this compound could not be oxidized over heterogeneous catalyst systems (discussed earlier), facile oxidation using the Co/Mn/Br catalyst system has been reported (see Table 19.3). Since ethers are hydrolytically very stable, it clearly indicates that the activation of MMF must proceed via a direct oxidation of the methylene carbon of the methoxymethyl moiety. 

The safe industrial oxidation of furanics using the Co/Mn/Br catalyst system needs a similar heat removal system as FDCA, like TA, is a very insoluble diacid, preventingthe use of jacketed cooling. In contrast to para-xylene, HMF, MMF, and AcMF are already partially oxidized on the benzylic positions, and consequently less heat is formed in their oxidation to FDCA, and reactor temperature may be... 

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