Dimethyl ester of terephthalic

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... 

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 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-... 

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

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],... 

The direct polyesterification reaction of diacids with glycols is the most important industrial synthetic route to polyester polyols. The second most important synthetic route is the transesterification reaction between dimethyl esters of dicarboxylic or dibasic acids (dimethyl adipate, dimethyl terephthalate, dimethyl carbonate or even polyethylene terephthalate) and glycols (reaction 8.2) [1, 3-8]. 

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. 

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) ... 

A number of copolyesters have also been described in the literature, combining such mixtures as the dimethyl ester of 2 and dimethyl terephthal-ate with ethylene glycol or 1,4-butanediol. The process of melt-transester-ification was employed in the reported synthesis of copolyesters from dimethyl 2,5-furan dicarboxylate, dimethyl terephthalate, ethylene glycol, and glycerol. Similarly, melt-polycondensation has produced thermally-stable... 

The first oxidation step proceeds under conditions that lead only to the reaction of one methyl group and the monoacid is formed. To convert the second methyl group as well, it is necessary to form the monoadd methyl ester in the next step. After the second oxidation step the terephthalic dimethyl ester is formed under the same esterification conditions by reaction with methanol. Terephthahc dimethyl ester is later reacted directly with ethylene glycol to form the PET polymer with liberation of methanol. The total process provides a yield in terephthalic acid dimethyl ester of 85% with respect to p-xylene. 

The multi-stage processes include those in the synthesis of adipinic acid, which is required for nylon manufacture, the production of synthetic detergents—alkylaryl sulphonate, and the synthesis of the dimethyl ester of tere-phthalic acid (terephthalate), that is required for the processing of terylene fibre. The last example will include a description of the system (2.3) according to components by means of system (2.7). 

Ester interchange reactions are valuable, since, say, methyl esters of di-carboxylic acids are often more soluble and easier to purify than the diacid itself. The methanol by-product is easily removed by evaporation. Poly (ethylene terephthalate) is an example of a polymer prepared by double application of reaction 4 in Table 5.3. The first stage of the reaction is conducted at temperatures below 200°C and involves the interchange of dimethyl terephthalate with ethylene glycol... 

Ak2o has been iastmmental ia developiag a new process for the stereospecific synthesis of 1,4-cyclohexane diisocyanate [7517-76-2] (21). This process, based on the conversion of poly(ethylene terephthalate) [25038-59-9] circumvents the elaborate fractional crystallisation procedures required for the existing -phenylenediamine [108-45-2] approaches. The synthesis starts with poly(ethylene terephthalate) (PET) (32) or phthaUc acid, which is converted to the dimethyl ester and hydrogenated to yield the cyclohexane-based diester (33). Subsequent reaction of the ester with ammonia provides the desired bisamide (34). The synthesis of the amide is the key... 

Phthahc anhydride (1) is the commercial form of phthaUc acid (2). The worldwide production capacity for the anhydride was ca 3.5 x 10 metric tons ia 1993, and it was used ia the manufacture of plasticizers (qv), unsaturated polyesters, and alkyd resins (qv) (see Polyesters, unsaturated). Sales of terephthahc acid (3) and its dimethyl ester are by far the largest of any of the benzenepolycarboxyhc acids 14.3 x 10 t were produced in 1993. This is 80% of the total toimage of ah. commercial forms of the benzenepolycarboxyhc acids. Terephthahc acid is used almost exclusively for the manufacture of poly(ethylene terephthalate), which then is formed into textiles, films, containers, and molded articles. Isophthahc acid (4) and trimehitic anhydride (5) are commercial products, but their worldwide production capacities are an order of magnitude smaller than for terephthahc acid and its dimethyl ester. Isophthahc acid is used primarily in the production of unsaturated polyesters and as a comonomer in saturated polyesters. Trimehitic anhydride is used mainly to make esters for high performance poly(vinyl chloride) plasticizers. Trimesic acid (6), pyromehitic dianhydride (7), and hernimehitic acid (8) have specialized commercial apphcations. The rest of the benzenepolycarboxyhc acids are not available commercially. 

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. 

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