Esterification of terephthalic acid

Kemkes256 assumes that the overall order relative to the esterification of terephthalic acid by 1,2-ethanediol in oligo(l,2-ethanediyl terephthalate) is two no mechanism has however been suggested. Mares257 considers that during the esterification of terephthalic acid with 1,2-ethanediol, two parallel kinetic paths take place, one corresponding to a reaction catalyzed by non-dissociated add and the other to a non-catalyzed process. In fact, Mares257 is reserved about the existence of protonic catalysis. Some other orders were found for the system terephthalic atid/l,2-ethanediol 0 (overall)318 2 (add) andO (alcohol)203 1 (add) and 1 (alcohol)181 1 (add)194 . These contradictory results could be partly due to the low solubility of terephthalic acid in 1,2-ethanediol. 

In the case of the esterification of terephthalic acid with an excess of 1,2-ethanediol a zero overall order is obtained this is due to the control of the reaction rate by the dissolution of terephthalic add. 

Here the polymer grows by successive esterification with elimination of water and no termination step. Polymers formed by linking monomers with carboxylic acid groups and those that have alcohol groups are known as polyesters. Polymers of this type are widely used for the manufacture of artificial fibers. For example, the esterification of terephthalic acid with ethylene glycol produces polyethylene terephthalate. 

Bishydroxyethyl terephthalate (BHET) is the monomer used to make the PET polymer. BHET can be made either by the esterification of terephthalic acid (TPA) with ethylene glycol (EG) ... 

The largest commercial use of ethylene glycol is its reaction with dicarboxylic acids to form linear polyesters. Polyethylene terephthalate) [25038-59-9] (PET) is produced by esterification of terephthalic acid [100-21 -0] (1) to form bishydroxyethyl terephthalate [959-26-2] (BHET) (2). BHET polymerizes in a transesterification reaction catalyzed by antimony oxide to form PET (3). 

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. 

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. 

Dimethyl terephthalate is manufactured from terephthalic acid or directly from p-xylene. Esterification of terephthalic acid with methanol occurs with sulfuric acid as the acid catalyst. Direct oxidation of p-xylcnc with methanol present also produced dimethyl terephthalate copper salts and manganese salt are catalysts for this reaction. The dimethyl terephthalate (boiling point 288°C, melting point 141°C) must be carefully purified via a five-column distillation system. 

Dimethyl terephthalate (DMT) is produced either by the esterification of terephthalic acid or the esterification of monomethyl terephthalate produced by oxidation of methyl p-toluate. DMT is consumed in the production of polyethylene terephthalate, the polymer used in the manufacture of polyester fibers, films and bottle resins. Terephthalic acid (TPA) is also used in the production of polyethylene terephthalate but does not consume methanol. Since TPA is continuing to increase its share of the market, DMT is expected to exhibit slower growth than the overall market for polyethylene terephthalate. 

Polyesterification. High molecular weight linear polyester resins, such as poly(ethylene terephthalate) (PET), poly(propylene terephthalate) (PPT), and poly(butylene terephthalate) (PBT), can be produced by either transesterification of dimethyl terephthalate (DMT) with an excess of the corresponding diol or by direct esterification of terephthalic acid (TPA). Tetraalkyl titanates, such as TYZOR TPT or —TYZOR TBT, have been found to be excellent catalysts for either of these reactions. However, in the case of PET, the residual titanate catalyst reacts with trace quantities of aldehydic impurities produced in the polymerization process to generate a yellow discoloration of the polymer (468,469). In the case of PPT and PBT, where the color of polymer is not as critical, organic titanates are the catalyst of choice because of their greater reactivity than antimony or tin (470). Numerous processing variations have been described in the literature to minimize formation of tetrahydrofuran in the PBT process (471—472). 

Figure 6. Esterification of terephthalic acid with ethylene glycol reaction temperature 473 K, reaction time 90 min.

For the esterification of terephthalic acid with ethylene glycol at 473 K, SO /TiCh calcined at 773 K is much more active than SiC -A Ch as shown in Fig. 6 [60]. The SO /TiCh showed a maximum activity when calcined at 573 K for the esterification of oleic acid with glycerol and of propionic acid with butanol at 403 K [61], where the active sites were attributed to Bronsted acid sites from a correlation between the activity and the Bronsted acidity. The esterification of phthalic anhydride with 2-ethylhexanol to form dioctyl phthalate is also efficiently catalyzed by solid super-acids, the selectivity being more than 90% [62]. The... 

C0-p-C6H4-C00CH2CLt20)n-, a synthetic polyester prepared by esterification of terephthalic acid with methanol and subsequent polycondensation of the ester with ethylene glycol. 

Liquid-phase esterification of terephthalic acid with methanol... 

Example Kodel polyester is formed from the esterification of terephthalic acid and l,4-bis(hydroxymethyl)-cyclohexane as shown by the reactions above. 

Esterification of terephthalic acid Polyester film Export ... 

Dimethyl terephthalate is obtained by the esterification of terephthalic acid by methanol. Terephthalic acid is a high-melting (above 3Q0°C), insoluble material and requires special conditions for esterification. Two parts of methyl alcohol, 1 part of terephtiialic add, and 0.01 part of sulfuric acid are placed in a closed, a tated pr sure vessel and heated to 150°C for 2-3 hr. During the last hour, 5-6 parts of additional methyl alcohol is added slowly to the liquid reactants and distOled to remove the water of reaction. By cooling, the dimethyl terephthalate is completely separated from the solution. Yields run high, as 95 per cent. The dimethyl terephthalate can be purified by crystallization from high-boiling solvents, such as xylene, or it may be distilled. 

There has been continued interest in developing a process for direct esterification of terephthalic acid with ethylene glycol. It does not appear, however, that this is currently practiced on a commercial scale in the U.S. In Japan, a process was commercialized where terephthalic acid is reacted with two moles of ethylene oxide to form the dihydroxy ester in situ, as the starting material. One mole of ethylene glycol is then removed under vacuum in the subsequent condensation process. Also, it was reported that the polymer can be prepared by direct esterification at room temperature in the presence of picryl chloride. The reaction can also be performed at about 120 C in the presence of diphenyl chloro-phosphate or toluenesulfonyl chloride. This is done in solution, where pyridine is either the solvent or the cosolvent. Pyridine acts as a scavenger for HCl, that is a byproduct of the reaction, and perhaps also as an activator (by converting the acid into a reactive ester intermediate). 

Esterification - Ster-o-to- ka-shon (ca. 1905) n. The chemical process of combining an acid and an alcohol to form an ester. Cellulose acetate is an ester formed by the reaction of acetic acid and the hydroxyl groups of cellulose. Polyethylene tereph-thalate, the most common fiber-forming polyester, is a product of esterification of terephthalic acid with ethylene glycol. Morrison RT, Boyd RN (1992) Organic chemistry, 6th edn. Prentice-Hall, Englewood Cliffs, NJ. 

Other commercial manufacturing methods have evolved to a direct esterification of acid and glycol in place of the ester-exchange process. In direct esterification, terephthalic acid and ethylene glycol are reacted, rather than esterifying terephthalic acid with methanol to produce the dimethyl terephthalate intermediate. The ester is easier to purify than the acid, which sublimes at 300°C and is insoluble, however, better catalysts and purer terephthalic acid offer the elimination of the intermediate use of methanol. Generally, PET resins made by direct esterification of terephthalic acid contain more diethylene glycol. 

Poly(butylene terephthalate) is also subject to analogous side reactions [128], the formation of 1-butenyl end groups (Scheme 3.4) followed by splitting-off of 1,3-butadiene or tetrahydrofuran (Scheme 3.5). This latter reaction is not affected by the metallic catalyst, but is catalyzed by the carboxyl end groups, making production of PBT by direct esterification of terephthalic acid and 1,4-butanediol disadvantageous. 

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