Pseudocumene oxidation

Of the three benzenetricarboxyhc acids, only trimellitic acid as the anhydride is commercially produced in large volume, by Hquid-phase air oxidation of either pseudocumene or dimethyl benzaldehyde. The pseudocumene oxidation is another variant of the cobalt—manganese—bromine catalyst in acetic acid solvent as described in the terephthaUc acid section. The acid is available as a laboratory chemical (99). The lUPAC name of trimellitic anhydride is 5-isobenzofurancarboxyhc acid (l,3-dihydro-l,3-dioxo). 

Figure 8.1 Flow diagram of pseudocumene oxidation with dilute nitric acid...

SCHEME 14.9 Proposed mechanism of pseudocumene oxidation with CH ReOj/H O (Reproduced with permission from Ref. [48]. Copyright (2011) Elsevier). 

In 1991, Alusuisse Italia announced the constmction of a 20 x 10 t/yi" trimellitic anhydride unit at Bergamo, Italy (109) and commenced production in late 1994. A European patent appHcation (110) assigned to Alusuisse suggests that the process used is very similar to that of Amoco, that is, pseudocumene is air oxidized in the Hquid phase using heavy-metal catalysts and bromine. A number of other companies have shown interest in the production of trimellitic anhydride (111—113). 

Mitsubishi Gas Chemical Co. in Japan produces pyromellitic dianhydtide in the same unit used for trimellitic anhydtide production (105). This process starts with pseudocumene, which is first carbonylated with carbon monoxide in the presence of boron trifluotide and hydrogen fluotide to form 2,4,5-trimethylbenzaldehyde. The Hquid-phase oxidation of the trimethylbenzaldehyde to pyromellitic acid and subsequent processing steps ate much the same as described for the Mitsubishi Gas Chemical process in the trimellitic acid section. The production of pyromellitic anhydtide is in conjunction with a joint venture agreement with Du Pont. 

Pseudocumene. The Hquid-phase air oxidation of pseudocumene yields trimeUitic acid [528-44-9] (15) which is dehydrated to trimeUitic anhydride [552-30-7] (TMA) (16). Amoco Chemical is the sole U.S. producer with a plant at JoHet, Illinois, having a capacity of ca 47,000 t/yr. Lonza ia Italy is the sole European TMA producer. 

Pseudocumene is used as a component in liquid scintillation cocktails for clinical analyses. Pseudocumene and durene are oxidized to trimel-litic anhydride and pyromellitic dianhydride, respectively. Mesitylene is a key building block for important antioxidants and agricultural chemicals. Prehnitene, isodurene, pentamethylbenzene, and hexamethylbenzene... 

Law and Mollwo Perkin 4 report on the electrolytic oxidation of toluene, the three xylenes, mesilylene, and pseudocumene. In a sulphuric-acid-acetqne solution of toluene they obtained a little benzaldehyde and perhaps benzyl alcohol. The electrolysis of an emulsion of toluene and dilute sulphuric acid leads to a complete combustion of the toluene to carbonic acid and water. 

Pseudocumene, in the presence of acetone and sulphuric acid, gives apparently a mixture of the three isomeric dimethyl-benzaldehydes. Analogously, mesitylene is oxidized to mesity-lenic aldehyde. 

Properties Colorless crystals. Mp 220C. Partially soluble in DMF and alcohol insoluble in benzene and carbon disulfide slightly soluble in water. Derivation Oxidation of pseudocumene. 

Pseudocumene is an item of commerce, and comprises approximately 15% of the heavy gasoline fraction. Its major use is for oxidation to trimellitic acid or its anhydride. These compounds have a number of uses, but the major ones are to form temperature resistant plasticizers for pvc (e.g. as the trioctyl ester), to form high performance plastics (e.g. the polyamide-imides),... 

Although little experimental data is available, numerous patents have been issued for the vapor phase catalytic oxidation of various other derivatives containing the benzene nucleus, as well as heterocyclic compounds Thus, fluorene (diphenyl methane) is oxidized to fluorenone with air in the presence of a catalyst containing iron vanadate or other suitable metal salt of the fifth or sixth group of the periodic system at a temperature of 360° to 400°.1,2 Maleic acid and anhydride are formed by the catalytic oxidation of compounds of the furan series, such as furan, furfural alcohol, furfural, methyl furfural, hydroxymethylfurfural, pyromucic acid or mixtures, with air over catalysts of molybdenum, vanadium, or other metals.133 Dimethyl benzaldehyde is formed by oxidizing pseudocumene with air at 550° C. in the presence of a tungsten oxide catalyst. Molybdenum, vanadium, or tantalum oxide catalysts may also be used to form aromatic aldehydes from o-, m-, or p-xylenes, mesitylene, p-cymene, or o-chlorotoluene by air oxidation. Times of contact of 0.3 to 0.4 seconds... 

PSEUDOCUMENE or PSEUDOCUMOL (95-63-6) Forms explosive mixture with air (flash point 112°F/44°C). Violent reaction with oxidizers, nitric acid. May accumulate static electrical charges, and may cause ignition of its vapors. 

Syntheses of 2,3,5-trimethylquinone, a key product in the fabrication of tocopherol, as well as of vitamin K3 (2-methyl-1,4-naphthoquinone) using this method are of practical importance. Peroxo-acid oxidation models xenobiotic oxidation by means of monooxygenase. Peroxo-acid oxidation of 1,2,4-trimethylbenzene (pseudocumene) to trimethylquinone using peracetic acid also yields acetic acid, which reduces the price of the products obtained (Eq. (12-26)). 

The only diacid anhydride of practical importance is trimellitic acid anhydride. Trimellitic acid is produced by the oxidation of pseudocumene [23]. 4-(a-Methylnadimido)-benzoic acid is prepared from 4-aminobenzoic acid and a-methylnadic anhydride [5]. 

The oxidation of pseudocumene to trimellitic anhydride can be carried out in the liquid-phase using cobalt/manganese salts and bromine compounds as catalysts in acetic acid Amoco process). 

Arene oxide intermediates were postulated for the acid-catalyzed oxidation of arenes by dimeth-yldioxirane [46] and aromatic hydroxylations with hydrogen peroxide activated by methylrhenium trioxide (MTO, CH ReOj) [47,48]. Scheme 14.9 shows a proposed mechanism for pseudocumene (PC) oxidation with the MTO/H O system. 

The authors exploited this three-step oxidation system to transform pseudocumenes (0.46 mM substrate concentration) into the corresponding carboxylic acids. 

Aromatic Oxidation. Oxidation of pseudocumene with MTO-based catalysis has been reported. The use of Lewis basic ligands has a beneficial effect on both, yield and selectivity, especially with (A-salicylidene)aniline-derived Schiff bases bearing electron-withdrawing substituents. Selectivity can be improved up to 80% when amphiphiles are used as additives (eq 55). ... 

Precaution Wear protective gloves, chemical safety goggles incompat. with strong oxidizers keep away from all ignition sources Hazardous Ingredients Petroleum sov. (CAS 64742-95-6) 4-6% pseudocumene... 

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