Catalysts manganese acetate bromide

Small amounts of cobalt on the manganese acetate bromide catalyst [Mn"(OAc)2/HBr] promote the oxidation of Mn to Mn by peracids. The synergistic effect of a little manganese upon [Co"(OAc)2/HBr] can be assigned to the acceleration of the reduction of CoBr by bromide with formation of bromine radicals Br2. ... 

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). 

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. 

The TPA process. The technology involves the oxidation of p-xylene, as shown already in Figure 18—2. The reaction takes place in the liquid phase in an acetic acid solvent at 400°F and 200 psi, with a cobalt acetate/ manganese acetate catalyst and sodium bromide promoter. Excess air is present to ensure the p-xylene is fully oxidized and to minimize by-products. The reaction time is about one hour. Yields are 90—95% based on the amount of p-xylene that ends up as TPA. Solid TPA has only limited solubility in acetic acid, so happily the TPA crystals drop out of solution as they form. They are continuously removed by filtration of a slipstream from the bottom of the reactor. The crude TPA is purified by aqueous methanol extraction that gives 99 % pure flakes. 

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. 

In the Amoco process, p-xylene is oxidized at 200 °C under 15-20 atm in acetic acid and in the presence of a catalyst consisting of a mixture of cobalt acetate (5% weight of the solution), manganese acetate (1%) and ammonium bromide. Owing to the highly corrosive nature of the reaction mixture, special titanium reactor vessels are required. One of the main difficulties of this process is to remove the intermediate oxidation products such as p-toluic acid or p-carboxybenzal-dehyde which contaminate TPA obtained by precipitation from the reaction medium. A series of recrystallization and solvent extraction apparatus is required to obtain fiber grade TPA with 99.95% purity. The overall yield in TPA is ca. 90% for a 95% conversion of p-xylene. 

Soluble cobalt salts (acetate or naphthenate) are used as catalysts, most often together with manganese and bromide ions. Particularly in the presence of bromide source (as HBr, sodium bromide, or even organic bromides), the rate of the oxidation of methylbenzenes increases by up to 400 x. None of the other halogens approaches bromide in its promoting activity. The maximum effect is achieved with a 1 1 cobaltrbromine atomic ratio. 

The purification of terephthalic acid is complicated because it does not melt and, as it was not soluble in either water or other solvents, it could not be crystallized. On the other hand, the dimethyl ester of terephthalic acid could be easily crystallized from methanol or xylene. When the Mid Century Process was introduced by Scientific Design and Amoco in 1956, it became possible to produce and purify terephthalic acid directly. This process used air oxidation conditions similar to those for previous processes, with a ttuxed trivalent cobalt and manganese acetate catalyst in glacial acetic acid, but introduced an ammonium bromide cocatalyst in conjunction with tetrabromomethane. Cobalt or molyb-demun bromides or hydrobromic acid have also been used, and following reaction with the trivalent cobalt, provided a source of brottune free radicals. The free radicals activated the methyl groups of the /7-xylene and led to the for-... 

Allylic acetates can be added to ketones employing an iron(II) catalyst, zinc(II) bromide as additive, and manganese metal as reductant (Scheme 4—320). The procedure provides homoallylic alcohols in good yields. Introducing either 1- or 3-substituted allylic acetates leads to the formation of the linear homoallylic product. This implies the intermediacy of an allyliron complex. 

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. 

The liquid-phase oxidation of hydrocarbons with transition metal/bromide catalysts, mainly containing cobalt(ll) and manganese(Il) acetates and, depending on the application, additionally salts of Ce , Mo , Ni , Pd Ti V and... 

A SF value >1.00 indicates a synergistic interaction and a value < l.(X) indicates an antagonistic interaction while a value of 1.00 would indicate the absence of synergy. Cobalt(II) acetate itself is an autoxidation catalyst [11], as is manganese(II) acetate [11], and as are bromide compounds [12]. Under the mild conditions employed in these... 

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.)... 

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