Cobalt acetates terephthalic acid

Technical-Grade Terephthalic Acid. All technical-grade terephthahc acid is produced by catalytic, hquid-phase air oxidation of xylene. Several processes have been developed, but they all use acetic acid as a solvent and a multivalent heavy metal or metals as catalysts. Cobalt is always used. In the most popular process, cobalt and manganese are the multivalent heavy-metal catalysts and bromine is the renewable source for free radicals (51,52). 

Terephthalic acid is made by air oxidation of /i-xylene in acetic acid with cobalt and manganese salts of metal bromide at 200 °C and 400 tit. 

The catalyzed oxidation of p-xylene produces terephthalic acid (TPA). Cobalt acetate promoted with either NaBr or HBr is used as a catalyst in an acetic acid medium. Reaction conditions are approximately 200°C and 15 atmospheres. The yield is about 95% ... 

In the late 1950 s two groups - one at ICI (ref. 1) and the other at the Mid-Century Corporation (ref. 2) - independently discovered that p-xylene is oxidized to terephthalic acid in almost quantitative yield when soluble bromides are used together with cobalt and manganese catalysts in acetic acid solvent at temperatures > 130 °C (ref. 3). This discovery formed the basis for what became known as the Mid-Century process and later, when the Mid-Century Corporation was acquired by Amoco, as the Amoco MC process for the commercial production of terephthalic acid. A large part of the ca. 6 million tons of the latter that are manufactured annually, on a worldwide basis, are produced via this method. This makes it the most important catalytic oxidation process (ref. 4). 

Amoco Amoco Chemicals Company, a subsidiary of Amoco Corporation, formerly Standard Oil Company (IN), is best known in the chemicals industry for its modification of the Mid-Century process for making pure terephthalic acid. /7-Xylene in acetic acid solution is oxidized with air at high temperature and pressure. Small amounts of manganese, cobalt, and bromide are used as catalysts. The modification allows the use of terephthalic acid, rather than dimethyl terephthalate, for making fiber. The process can also be used for oxidizing other methylbenzenes and methylnaphthalenes to aromatic carboxylic acids. See also Maruzen. 

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. 

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. 

Terephthalic acid is commonly abbreviated TA or TPA. The abbreviation PTA (P = pure) is reserved for the product of 99% purity for polyester manufacture. For many years polyesters had to be made from dimethyl terephthalate (DMT) because the acid could not be made pure enough economically. Now either can be used. TA is made by air oxidation of /7-xylene in acetic acid as a solvent in the presence of cobalt, manganese, and bromide ions as catalysts at 200°C and 400 psi. TA of 99.6% purity is formed in 90% yield. This is called the Amoco process. 

Homolytic liquid-phase processes are generally well suited to the synthesis of carboxylic acids, viz. acetic, benzoic or terephthalic acids which are resistant to further oxidation. These processes operate at high temperature (150-250°C) and generally use soluble cobalt or manganese salts as the main catalyst components. High conversions and selectivities are usually obtained with methyl-substituted aromatic hydrocarbons such as toluene and xylenes.95,96 The cobalt-catalyzed oxidation of cyclohexane by air to a cyclohexanol-cyclohexanone mixture is a very important industrial process since these products are intermediates in the manufacture of adipic acid (for nylon 6,6) and caprolactam (nylon 6). However, the conversion is limited to ca. 10% in order to prevent consecutive oxidations, with roughly 70% selectivity.97... 

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. 

Two important commercial diacids are adipic acid (hexanedioic acid) and tere-phthalic acid (benzene-1,4-dicarboxylic acid). Adipic acid is used in making nylon 66, and terephthalic acid is used to make polyesters. The industrial synthesis of adipic acid uses benzene as the starting material. Benzene is hydrogenated to cyclohexane, whose oxidation (using a cobalt/acetic acid catalyst) gives adipic acid. Terephthalic acid is produced by the direct oxidation of para-xylene in acetic acid using a cobalt-molybdenum catalyst. 

Commercially two main processes, that of Mid-century/Amoco and Dynamit Nobel/Hercules, are operated. In the former acetic acid is used as a solvent. Mixtures of cobalt and manganese bromide and acetate salts are used to catalyze the initiation step. The reaction conditions, a temperature of about 220°C and a pressure of 15 atm, are relatively severe. Under these conditions bromine and CH2C02H radicals are formed. These radicals can effect new initiation steps. In the overall process, though toluic acid is an intermediate, it is never isolated. The final isolated product is terephthalic acid (see reaction 8.10). 

The cobalt(II) acetate/acetic acid/sodium bromide (CAB) combination is well known for the autoxidation of alkyl benzenes.287 It is normally employed for the production of terephthalic acid from 1,4-dimethylbenzene.281 However, the use of hydrogen peroxide, as mentioned earlier, means the systems are generally more selective, and can be operated at ambient pressure and relatively low temperatures. 

Oxidation. Acetaldehyde is readily oxidized 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 liquid-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 believed 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 ozone yields acetaldehyde monoperacetate, which can be decomposed to peracetic acid and acetaldehyde (36). Peracetic acid can also be formed directly by liquid-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 terephthalic acid [100-21-0] and of ethanol to acetic acid are activated by acetaldehyde (40,41). 

Catalytic oxidation of p-xylene with air is the chief commercial method used to produce terephthalic acid. A solution of p-xylene in acetic acid, together with manganese or cobalt derivative and heavy metal bromides, which serve as cocatalysts, is fed to a continuous reactor, vigorously stirred, and heated to 200°C while under about 25 atm pressure. Air is continuously fed into the reactor at the same time as a small stream of partially reacted solution is removed (Eq. 19.66). 

Industrially, terephthalic acid is produced by the cobalt(III) acetate, manganese(III) acetate, or ammonium molybdate-catalyzed air oxidation of />-xylene in acetic acid. Sodium bromide reduces the induction period and increases the rate of conversion to terephthalic acid. p-Xylene is initially oxidized to p-methylbenzyl hydroperoxide, and further oxidation gives p-methylbenzaldehyde and p-methylbenzoic acid ... 

This method has been licensed world-wide to prepare terephthalic acid from p-xylene. We have used the reaction of m-chloroperbenzoic acid (MCPBA) with mixtures of Co(II) acetate/ Mn(II) acetate/bromide in acetic acid/water solutions to understand the functions of each catalyst component. The sequence of redox reactions that occurs is first the reaction of MCPBA with Co(n) to give Co(III) Co(III) then oxidizes Mn(II) to Mn(III) and finally, Mn(III) oxidizes bromide to bromine. Some of the functions of each component are 1) the cobalt rapidly reacts (very selectively) with the MCPBA (Mn and Br react slowly), 2) Mn lowers the steady state of Co(III) which significantly reduces solvent decomposition and also avoids Co(III) re-arranging into a less reactive form, and 3) bromine reacts rapidly with the methylaromatic compound to generate methylaromatic radicals (Co(III) and Mn(III) react slowly). The dimeric structure of Co(II) in acetic acid is partly responsible for the highly selective nature of the MCPBA oxidation of Co(II). The order of the redox reactions is the opposit to that expected from thermodynamics. 

Ethylene glycol, 2,6-NDA, terephthalic acid (TPA), and IPA are condensed using 10% aqueous tetramethylammonium hydroxide solution. Antimony trioxide and cobalt acetate are used as catalysts. The reaction is conducted in an inert atmosphere initially under pressure, up to 260°C, then the pressure is reduced in steps and the temperature is increased up to 274-288°C. 

In the U.S.A., the Far East and the U.K. (ICI), most terephthalic acid (1,4-benzenedicarboxylic acid) is produced by the liquid-phase oxidation of p-xylene in acetic acid with a cobalt/manganese romide catalyst system, originated by Amoco. Several non-bromide variants, requiring the addition of readily oxidizable precursors of acetic acid, were commercialized, but most, if not all, have been shut down. Increasingly, the final product is the high-purity diacid, whereas most older plants converted the crude acid to the dimethyl ester for purification and sale. (Small quantities of isophthalic acid are manufactured in a similar manner.)... 

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. 

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