Nitric acid oxidation, / -xylene

Oxidation. Acetaldehyde is readily oxidised with oxygen or air to acetic acid, acetic anhydride, and peracetic acid (see Acetic acid and derivatives). The principal product depends on the reaction conditions. Acetic acid [64-19-7] may be produced commercially by the Hquid-phase oxidation of acetaldehyde at 65°C using cobalt or manganese acetate dissolved in acetic acid as a catalyst (34). Liquid-phase oxidation in the presence of mixed acetates of copper and cobalt yields acetic anhydride [108-24-7] (35). Peroxyacetic acid or a perester is beheved to be the precursor in both syntheses. There are two commercial processes for the production of peracetic acid [79-21 -0]. Low temperature oxidation of acetaldehyde in the presence of metal salts, ultraviolet irradiation, or osone yields acetaldehyde monoperacetate, which can be decomposed to peracetic acid and acetaldehyde (36). Peracetic acid can also be formed directiy by Hquid-phase oxidation at 5—50°C with a cobalt salt catalyst (37) (see Peroxides and peroxy compounds). Nitric acid oxidation of acetaldehyde yields glyoxal [107-22-2] (38,39). Oxidations of /)-xylene to terephthaHc acid [100-21-0] and of ethanol to acetic acid are activated by acetaldehyde (40,41). 

Initial production of the dimethyl terephthalate started with the oxidation of -xylene to terephthaUc acid using nitric acid both companies reportedly used similar technology (43—45). Versions of the nitric acid oxidation process, which has been abandoned commercially, involved the use of air in the initial oxidation step to reduce the consumption of nitric acid (44,46,47). The terephthaUc acid was then esterified with methanol to produce dimethyl terephthalate, which could be purified by distillation to the necessary degree (48). 

An alternative route to DMT was introduced in 1953. This was based on air oxidation of y -xylene to /Moluic acid, which was esterified by methanol to form methyl /Moluate, which was oxidised by air to monomethyl terephthalate [40], which in turn was esterified by methanol to make DMT. The two oxidations could be combined so that p-xylene and methyl p-toluate were oxidised in the same vessel, and so could the two esterifications [41], The process was due to Katzschmann of Imhausen, a firm based at Witten and later known as Chemische Werke Witten. This process, known variously by its inventor s name and by various combinations of the names of the companies involved in its development, i.e. Hercules, Imhausen, Witten, and Dynamit Nobel, rapidly replaced the rather unsatisfactory and sometimes hazardous nitric acid oxidation route to DMT. 

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 first commercial processes for the production of DMT made use of nitric acid oxidation of p-xylene to crude terephthalic acid, followed by esterification with methanol and purification by distillation [3]. Air oxidation of p-xylene displaced the use of nitric acid with the development of the Witten process [5]. In the Witten process, p-xylene is air-oxidized at 140-180 °C and 0.5-2 MPa over a homogeneous cobalt or cobalt/manganese catalyst system to give p-toluic acid, which is then esterified to methyl p-toluate, oxidized again over the cobalt/manganese catalyst, and finally esterified to DMT (see Scheme 1). The four process steps are accomplished in two reactors (see Figure 1). The Witten process uses no solvent. 

Nitric acid and nitrogen oxides are assuming new significance as oxidizing agents. Toluic acids may be made by the nitric acid oxidation of xylenes p-toluic acid is obtained from oxidation of p-cymene through the oxidation of the isopropyl group. Nitric acid in the presence of sulfuric acid and a... 

An ab initio MO study of the mechanism of chlorination of benzene by chlorine in the presence of aluminium chloride has appeared. The rate-limiting stage leads to the formation of the ion-pair complex CeHeCl AlCU" without the explicit formation of Cl, the formation of C-Cl and Al-Cl bonds occurring synchronously with the breaking of the Cl-Cl bond. The introduction of a 3-chloro substituent into benzoyl chloride deactivates the system to further chlorination at the 5-position by a factor of about 6. ° Benzene, toluene, the xylenes, durene, mesitylene, nitrobenzene, and p-nitrotoluene are selectively brominated at 50-65 °C in an HBr-HN03-H2S04-H20 mixture with the participation of oxygen. The small catalytic amount of nitric acid oxidizes HBr to Br+, which reacts with the aromatic compound, and the nitrous acid formed reacts... 

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

Consequently, as a result of increasing environmental pressure many chlorine and nitric acid based processes for the manufacture of substituted aromatic acids are currently being replaced by cleaner, catalytic autoxidation processes. Benzoic acid is traditionally manufactured (ref. 14) via cobalt-catalyzed autoxidation of toluene in the absence of solvent (Fig. 2). The selectivity is ca. 90% at 30% toluene conversion. As noted earlier, oxidation of p-xylene under these conditions gives p-toluic acid in high yield. For further oxidation to terephthalic acid the stronger bromide/cobalt/manganese cocktail is needed. 

Anthraquinone itself is traditionally available from the anthracene of coal tar by oxidation, often with chromic acid or nitric acid a more modern alternative method is that of air oxidation using vanadium(V) oxide as catalyst. Anthraquinone is also produced in the reaction of benzene with benzene-1,2-dicarboxylic anhydride (6.4 phthalic anhydride) using a Lewis acid catalyst, typically aluminium chloride. This Friedel-Crafts acylation gives o-benzoylbenzoic acid (6.5) which undergoes cyclodehydration when heated in concentrated sulphuric acid (Scheme 6.2). Phthalic anhydride is readily available from naphthalene or from 1,2-dimethylbenzene (o-xylene) by catalytic air oxidation. 

The original route from p-xylene was oxidation in the presence of nitric acid. But the use of nitric acid is always problematical. There are corrosion and potential explosion problems, problems of nitrogen contamination of the product, and problems due to the requirement to run the reactions at high temperatures. Just a lot of problems that all led to the development of the liquid air phase oxidation of p-xylene. Ironically the nitrogen contamination problem was the reason that the intermediate DMT route to polyester was developed, since that was easy to purify by distillation. Subsequently, DMT has secured a firm place in the processing scheme. 

Irradiation of ///-xylene isomerizes to p-xylene (Calvert and Pitts, 1966). Glyoxal, methylglyoxal, and biacetyl were produced from the photooxidation of ///-xylene by OH radicals in air at 25 °C (Tuazon et al, 1986a). The photooxidation of ///-xylene in the presence of nitrogen oxides (NO and NO2) yielded small amounts of formaldehyde and a trace of acetaldehyde (Altshuller et al, 1970). ///-Tolualdehyde and nitric acid also were identified as photooxidation products of ///-xylene with nitrogen oxides (Altshuller, 1983). The rate constant for the reaction of ///-xylene and OH radicals at room temperature was 2.36 x 10 " cmVmolecule-sec (Hansen et al., 1975). A rate constant of 1.41 x 10" L/molecule-sec was reported for the reaction of ///-xylene with OH radicals in the gas phase (Darnall et ah, 1976). Similarly, a room temperature rate constant of 2.35 x 10"" cmVmolecule-sec was reported for the vapor-phase reaction of ///-xylene with OH radicals (Atkinson, 1985). At 25 °C, a rate constant of 2.22 x 10"" cm /molecule-sec was reported for the same reaction (Ohta and Ohyama, 1985). Phousongphouang and Arey (2002)... 

Since nitric acid, especially red fuming nitric acid RFNA which contains a small amount of nitrogen oxides, reacts vigorously with aromatic amines, during World War II the Germans employed solutions of these amines (e.g. aniline or phenylenediamine) in benzene or xylene as the combustible component. They added a small amount of ferric chloride as a reaction catalyst to the nitric acid. It was also shown that the addition of vinyl ethers to amine solutions reduces the induction period. 

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. 

Recently Milczak et al.[57] have reported the nitration of o-xylene using 100% nitric acid over silica supported metal oxide solid acid catalysts with high yields (up to 90 %) but low selectivity to 4-o-NX (40-57 %). Choudary et a/. 5X 591 performed the nitration of o-xylene and other aromatic hydrocarbons by azeotropic removal of water over modified clay catalysts achieving low yields of 4-o-NX and a selectivity of 52%. Better results were obtained when HBeta zeolite was used as catalyst, performing the reaction in dichloromethane at reflux temperature.[60] Conversions of 40 % and maximum selectivity 68 % of 4-o-NX were obtained. Similar conversions and higher selectivities for 4-o-NX (65-75 %) were reported by Rao et al M 1 using a nanocrystaUine HBeta sample and working at 90 °C in the absence of solvent. 

Toluic acid has been prepared by the oxidation of cymene, -xylene,4 or dihydro-/>-tolualdehyde 6 with nitric acid by the... 

On the other hand, although o-phthalic acid, or rather its anhydride, had long been produced in enormous amounts for use in the manufacture of alkyd resins, the para derivative was less well known and not available on a large scale. The synthesis is a straightforward one, however, from p-xylene, which is oxidized to terephthalic acid, either by means of nitric acid in the older process or by air (catalyzed) in the newer one. In the early years this compound then was converted to the easily purified dimethyl ester in order to obtain a colorless polymer adequate for the manufacture of commercially acceptable fibers. 

The oxidation of cyclohexanone by nitric acid leads to the generation of nitrogen dioxide, nitric oxide, and nitrous oxide. The first two gases can be recycled for the synthesis of nitric acid. Nitrous oxide, however, is an ozone depleter and cannot be recycled. Indiscriminate nitrous oxide emission from this process is therefore the cause of considerable concern. As shown by 8.9, part of the cyclohexanone can also be converted to the corresponding oxime and then to caprolactam—the monomer for nylon 6. Phthalic acids are one of the monomers for the manufacture of polyesters. As shown by Eq. 8.10, it is made by the oxidation of p-xylene. A general description of polyamides (nylons) and polyesters are given in Section 8.4. 

Escherichia coli (see Draths and Frost, 1994). Hydroquinone is a very practical intermediate in the manufacture of polymeric materials—almost 2 billion kg of adipic acid are produced from it and used annually in the manufacture of nylon 66. Most commercial syntheses of adipic acid utilize benzene as the starting material, derived from the benzene/toluene/xylene (BTX) fraction of petroleum refining. Benzene is hydrogenated over a metal catalyst to form cyclohexane, which is then oxidized over another catalyst that produces both cyclohexanone and cyclohexanol. See Figure 12.6. These molecules are catalytically oxidized in the presence of nitric acid to form adipic acid. 

The partial oxidation of polyalkylated aromatic compounds is also observed. o-Xylene is oxidized to o-toluic acid by heating with ozone and oxygen at 115-120 °C in the presence of cobalt acetate in acetic acid (yield 77%) [68] or by refluxing with dilute nitric acid (1 2) (yield 53-55%) [463]. In p-cymene (p-isopropylbenzene), the isopropyl group is oxidized in preference to the methyl group to give a 51% yield of p-toluic acid on refluxing with dilute nitric acid (1 36) [464]. On the contrary, biochemical oxidation with Nocardia strain 107-332 converts p-cymene into p-isopropylbenzoic acid [1071]. 

H3C)2C6H(N02)2.COOH mw 240.17, N 11.67%. Only three isomers are known 3,5 Dinitro-2,4 dimethylbenzoic Acid, firysts (acetic acid), mp 197-203° mod sol in ale, eth chlf si sol in hot w can be prepd by nitrating 2,4-dimethylbenzoic acid with mixed acid, or by oxidizing 3,5-dimtro-2,4-dimethyl-acetophenone with KMnO (Refs 1 4). Its expl props are not reported 2,4 i iiTO 3,3 dimethylhenzoic Acid, ndls (from w or xylene), mp 210.5—211° mod sol in ale hot xylene v si sol in w petr eth was ohtd with the 2,6-dinttro deriv when 3,5 dimethylbenzoic acid was treated with nitric acid Cd 1.525) at 40-50°(Refs 2 3). Us expl props are not reported... 

Commercially available Cyanex 923, or TRPO (see Table 19), has been used for the successful extraction of ions from nitric acid solutions into xylene. Extractant dependency gives a slope of two for hexavalent uranium, similar to the behavior observed for trioctylphosphine oxide... 

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