Oxidation p-xylene to terephthalic acid

Mid-Century Also called M-C. A process for oxidizing p-xylene to terephthalic acid, using oxygen in acetic acid and catalyzed by a mixture of cobalt and manganese bromides. Developed in the 1950s by Halcon International and commercialized by Standard Oil Company (Indiana). The first plant was built at Jolet, IA, in 1938. The Amoco and Maruzen processes are improved versions. 

Teijin A process for oxidizing p-xylene to terephthalic acid. The catalyst used is a soluble cobalt compound, used at a high concentration. Developed by Teijin, Tokyo. 

The carboxylic acid produced in the greatest fflnounts is 1,4-benzenedicarboxylic acid (terephthalic acid). About 5 X 10 Ib/year- is produced in the United States as a starting material for the preparation of polyester fibers. One important process converts p-xylene to terephthalic acid by oxidation with nitric acid ... 

You will recognize the side-chain oxidation of p-xylene to terephthalic acid as a reaction type discussed previously (Section 11.13). Examples of other reactions encountered earlier that can be applied to the synthesis of carboxylic acids are collected in Table 19.4. 

In the oxidation of p-xylene the first methyl group undergoes rapid autoxidation to afford p-toluic acid (Fig. 8). The second methyl group is, however, deactivated by the electron-withdrawing carboxyl group, and further oxidation of p-toluic to terephthalic acid is much slower, i.e. the relative reactivities of toluene and p-toluic acid are 26 1 (Fig. 8). It is not surprising, therefore, that the autoxidation of p-xylene to terephthalic acid proved to be a difficult proposition. 

Meanwhile attempts to find an air oxidation route directly from p-xylene to terephthalic acid (TA) continued to founder on the relatively high resistance to oxidation of the /Moluic acid which was first formed. This hurdle was overcome by the discovery of bromide-controlled air oxidation in 1955 by the Mid-Century Corporation [42, 43] and ICI, with the same patent application date. The Mid-Century process was bought and developed by Standard Oil of Indiana (Amoco), with some input from ICI. The process adopted used acetic acid as solvent, oxygen as oxidant, a temperature of about 200 °C, and a combination of cobalt, manganese and bromide ions as catalyst. Amoco also incorporated a purification of the TA by recrystallisation, with simultaneous catalytic hydrogenation of impurities, from water at about 250 °C [44], This process allowed development of a route to polyester from purified terephthalic acid (PTA) by direct esterification, which has since become more widely used than the process using DMT. 

Fire and explosion hazards of processes involving the oxidation of hydrocarbons are reviewed, including oxidation of cyclohexane to cyclohexanone/cyclohexanol, ethylene to ethylene oxide, of cumene to its hydroperoxide, and of p-xylene to terephthalic acid. 

Terephthalic Acid. The oxidation of p-xylene to terephthalic acid is a more difficult reaction.866 Once one of the methyl groups is oxidized, the second methyl group in p-toluic acid formed is deactivated by the electron-withdrawing effect of the carboxylic group. Bromine-promoted catalytic processes and cooxidation in the presence of suitable additives are usually practiced.970,978,990... 

A new reagent, AMiydroxyphthalimide combined with Co(acac)n (n = 2,3), transforms alkylbenzenes to ketones, whereas methylbenzenes give the corresponding carboxylic acids.1121 Phthalimide N-oxyl was found to be the key intermediate. Novel oxoperoxo Mo(VI) complexes mediate the cost-effective and environmentally benign oxidation of methylbenzenes to carboxylic acids.1384 Similar green oxidation of p-xylene to terephthalic acid was reported by using a Ru-substituted heteropolyanion.1385... 

The heavy metal-catalyzed oxidation of p-xylene to terephthalic acid in stirred autoclaves was greatly accelerated by adding catalytic quantities of nitric acid to the acetic acid solvent (9). Reactions carried out for 2 hours at 200°C. afforded 60-80% yields of terephthalic and p-toluic acids in varying ratios the highest yield of terephthalic acid was 70%. In the absence of either the heavy metal catalyst or nitric acid under otherwise identical conditions p-toluic acid was produced in 20-40% yields, but no terephthalic acid was formed. 

A major problem associated with such autoxidations is that they are largely indiscriminate, i.e. they exhibit poor chemo- and regio- selectivities. They are synthetically useful only with relatively simple substrates containing one reactive position, e.g. the oxidation of toluene to benzoic acid or p-xylene to terephthalic acid. Any catalytic oxidation has to complete with this non-catalytic pathway. Moreover, the situation is further complicated by the fact that transition metal ions also catalyze autoxidations by mediating the decomposition of trace amounts of hydroperoxides into chain-initiating radicals, via the so-called Haber-Weiss mechanism ... 

Peracetic acid can also be formed directly by liquid-phase oxidation at 5 to 50°C with a cobalt salt catalyst. Nitric acid oxidation of acetaldehyde yields glyoxal and the oxidation of p-xylene to terephthalic acid and of ethanol to acetic acid is activated by acetaldehyde. 

The oxidation of p-xylene to terephthalic acid (Table 4, entry 33) would only result in the formation of p-toluic acid. To convert the second group in high yield and selectivity, the oxidation must be influenced in one of three ways ... 

Acetic acid is used in the manufacture of a wide variety of products including adhesives, polyester fibres, plastics, paints, resins and solvents. About 40% of the acetic acid made industrially is used in the manufacture of vinyl acetate monomer for the plastics industry other large uses are to make cellulose acetate, a variety of acetate esters that are used as solvents, as well as monochloracetic acid, a pesticide. Acetic acid is also used as a solvent for the oxidation of p-xylene to terephthalic acid, a precursor to the important polyester, polyethylene terephthalate (PET). A minor, but important use is as non-brewed condiment, a vinegar substitute widely used in British fish and chip shops this is made using food-grade industrial acetic acid and is less expensive than fermentation vinegar. 

One of the largest industrial-scale applications of homogeneous catalysis is represented by the oxidation of hydrocarbons, especially the transition metal-catalyzed autoxidation of p-xylene to terephthalic acid or its esters (cf. Section 2.8.1.2, [1], (eq. (1)). 

NHPI has been introduced as an effective system for C—H activation by hydrogen abstraction on several different substrates [30i,j,s,31a-e]. In 2001, Daicel commercialized the process used to synthesize dihydroxyadamantane, and has carried out pilot trials not only for the oxidation of cyclohexane but also for the oxidation of p-xylene to terephthalic acid. In the latter case, the advantage lies in being able to avoid using special anticorrosive metals currently required in the production of terephthalic acid because of the use of bromine. NHPI can also be used as a catalyst for the in situ production of hydroperoxides, reactants for epoxidation and for the oxidation and ammoxidation of cyclohexanone to caprolactone and caprolactam, respectively. 

Terephthalic Acid. Acetic acid is a solvent for the air-based oxidation of p-xylene to terephthalic acid. This accounts for more than 10% of acetic acid output. Over oxidation of p-xylene destroys about 6-7% of acetic acid solvent and another 1-2% is lost in the recycle vent stream. Terephthalic acid is a large volume commodity and thus 7-9% solvent make up amounts to a substantial quantity of acetic acid. 

Wang, Q., Cheng, Y., Wang, L. and Li, X. (2007) Semicontinuous studies on the reaction mechanism and kinetics for the liquid-phase oxidation of p-xylene to terephthalic acid. Industrial and Engineering Chemistry Research, 46 (26), 8980-8992. 

Direct attack on the substrate by the metal complex is exemplified by the oxidation of p-xylene to terephthalic acid, which is very important industrially, or in general by the oxidation of alkylbenzenes [3]. 

The oxidation of p-xylene to terephthalic acid occurs by the same general mechanism as described above for alkylaromatics. Bromide ions and nitrogen-containing ligands provide synergetic mixtures with metal salts [56-58,61]. Pyridine is one of the most efficient additives [59,60j. Oxo-centered cobalt(III) clusters have been isolated from the reaction mixtures, which can be regarded as active intermediates [34,62,63]. The optimum catalytic activity was found to be associated with the composition corresponding to Co Br py = 1 2 (1-2) [64]. 

Various metal ions and complexes have been used to promote the catalytic air oxidation of hydrocarbons. There are some classical reactions that have developed into commercial processes, like the oxidation of n-butane to acetic acid, the oxidation of cyclohexane to adipic acid, or of p-xylene to terephthalic acid, all of which utilize cobalt salts as catalysts. 

These reactors (Fig. 3.2a) have been suggested for the oxidation of p-xylene to terephthalic acid (Carra and Santacesaria 1980 Arpentinier 2006 Wang et al. 2007). 

The foregoing discussion shows the superiority of the spray tower for oxidation of p-xylene to terephthalic acid. Li et al. (2013) suggest that this concept can be extended to replace existing stirred reactors for other similar gas-liquid mass transfer limited reactions. 

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