Dimethyl ester of terephthalic acid

Because of the difficulty encountered in removing the water that is produced when an acid reacts with an alcohol, PET is produced commercially by the reaction of dimethyl terephthalate, the dimethyl ester of terephthalic acid, with ethylene glycol in an ester interchange reaction. The methanol that is formed in this reaction is readily removed by distillation. 

The only practical means for ensuring the desired polymer quality is to use scrupulously pure monomers. Purification of a polymer after it is synthesized would be prohibitively expensive, because these materials are sparingly soluble and are often difficult or impossible to crystallize or free of solvent. The overall least expensive route to good quality polyfethylene terephthalate) was therefore through the dimethyl ester of terephthalic acid as shown in reaction (b). The byproduct methanol was recovered to generate more diester from the acid. In more recent years, methods have been developed to produce the diacid with satisfactory purity, and reaction (a) is now the preferred route to this polymer because the esterification step with methanol can be eliminated. Reactions (d), (e), and others, which the reader may be able to write, will be more expensive in the final analysis for the various reasons mentioned above. 

Dimethyl ester of terephthalic acid /a = 2-2 X Diethyl ester of terephthalic acid /x = 2-3 X... 

DMT dimethyl ester of terephthalic acid DS dust suppressed... 

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-... 

Although the reaction shown above works satisfactorily in the laboratory, it is not the process by which PET is made commercially. Instead, the methyl ester of terephthalic acid, dimethyl terephthal-ate (H3COOCC6H4COOCH3), is used in place of terephthalic acid. In this reaction, methyl alcohol, rather than water, is eliminated dur-... 

A,A -Dimethyl-A, A -dinitrosoterephthalamide DTA 90-105 126 N2 Esters of terephthalic acid Nitrosan (Du Pont)... 

The polyether diols derived from polyesters seem to represent a compromise between cost and their contribution to superior elongation and tensile properties as compared to plain polyether diols polyether diols from polyester account for about 10% of the flexible PUR production. Examples of useful products formed from hydroxy-terminated esters of terephthalic acid (TPA)— formed, in turn, by the reaction of an excess of glycols with dimethyl terephthalate (DMT) or TPA—and TDI or MDI-PMDI are flexible ski clothing, gaskets, rollers for printing presses, etc. [85],... 

TEREPHTHALIC ACID, DIMETHYL ESTER or TEREPHTHALIC ACID, METHYL ESTER (120-61-6) Combustible solid (286°F/141°C). The dust or powder forms an explosive mixture with air. Incompatible with strong acids, nitrates, strong oxidizers. Flow or agitation of substance may generate electrostatic charges due to low conductivity, and may cause ignition of flammable vapors or dust. 

Several chemical recycling processes for postconsumer PET have been scaled up [1, 116]. For example, reacting PET with ethylene glycol forms bis-hydroxyethyl terephthalate, a starting monomer for the synthesis of PET. Hydrolysis of PET yields terephthalic acid, another monomer. A third process uses methanol to depolymerize PET to the dimethyl ester of terephthalic, which can also serve as a monomer for the mannfactnre of PET. 

The first polyester, developed in the 1940s, involved the polymerization of benzene 1,4-dicarboxylic acid (terephthalic acid) with 1,2-ethanediol (ethylene glycol) to give poly-(ethylene terephthalate), abbreviated PET. Virtually aU PET is now made from the dimethyl ester of terephthahc acid by the following transesterification reaction (Section 14.4C) ... 

Derivatives. In general, the esters of terephthaHc acid derived from saturated alcohols undergo the same reactions as dimethyl terephthalate. Some physical properties of six of these esters are Hsted in Table 23. The di- -butyl and di-2-ethyIhexyl esters find use as plasticizers (qv). Terephthaloyl chloride, which is prepared by reaction of terephthaHc acid and thionyl chloride, is used to prepare derivatives of terephthaHc acid. 

We note, however, that even if methane comes from the photolysis of the methyl ester, this does not necessarily mean that all of it arises as a result of first breaking down the PET itself by photolysis. Both the PET of early reports and also the PECT were undoubtedly produced using dimethyl terephthalate (DMT) instead of terephthalic acid and so have methyl ester end groups owing to the well-known incomplete reaction of the DMT. There may be only a small level of these ester groups, but the amount of methane produced was small as well. This, at the very least, causes some potential confusion about the source of all the methane should some of it come from methyl ester photolysis. No such confusion would exist for the ethane should that be coming from photolysis of an ethyl ester. 

On the basis of bulk production, polytethylenc lerephthalale) manufacture is the most important ester producing process. This polymer is produced by either the direct esterification of terephthalic acid and ethylene glycol, or hy the transesterilication of dimethyl terephthalutc with ethylene glycol. Dimethyl lerephthalale is produced by the direct esterification of terephthalic acid and methanol. 

Preparation 211.—Dimethyl Terephthalate (Dimethyl ester of 1 4-benzenedicarboxylic acid). 

Polymerization is a two-stage process (Fig. 1) in which the monomer is first prepared either by an ester interchange between dimethyl terephthalate and ethylene glycol, or by direct esterification of terephthalic acid. 

In the Dynamit Nobel/Hercules process no solvent is used. A mixture of cobalt and manganese ethyl hexanoate is used as the catalyst under relatively mild conditions, about 160°C and 7 atm pressure. The product under these conditions is toluic acid, which is isolated and then converted into the methyl ester. The important point to note is that under the operating conditions toluic acid does not undergo any further oxidation. This means that toluic acid is more difficult to oxidize than p-xylene. The methyl ester of toluic acid is then co-oxidized with p-xylene. The product obtained is monomethyl terephthalate, which by reaction with methanol is then converted to dimethyl terephthalate. 

Other procedures to obtain the polymer include the use of terephthalic acid esterified to its dimethyl ester, which by a transesterification reaction with ethylene glycol generates the polymer. In addition to ethyleneglycol, other diols can be used in the esterification readion, such as 1,4-butanediol, 1,4-cyclohexanedimethanol, 1,6-hexanediol, etc. 

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