Terephthalic acid, production reactions

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 resistance of poly(ethylene terephthalate) to photochemical degradation is very good. Some thermal degradation occurs when the polymer is heated above the melting point, the principal products being carbon dioxide, acetaldehyde and terephthalic acid. The reaction may proceed by either the molecular or free radical mechanism shown below ... 

The phthalic acid and benzoic acid are reacted to form a reaction intermediate. The reaction intermediate is dissolved in sulfuric acid, which precipitates terephthalic acid (TPA). Fifty percent of the TPA is sold as a product and 50 percent is further processed at your facility into polyester fiber. The TPA Is treated with ethylene glycol to form an intermediate product, which is condensed to polyester. 

An alternative route to PET is by the direct reaction of terephthalic acid and ethylene oxide. The product bis(2-hydroxyethyl)terephthalate reacts in a second step with TPA to form a dimer and ethylene glycol, which is released under reduced pressure at approximately 300°C. 

PET is the polyester of terephthalic acid and ethylene glycol. Polyesters are prepared by either direct esterification or transesterification reactions. In the direct esterification process, terephthalic acid is reacted with ethylene glycol to produce PET and water as a by-product. Transesterification involves the reaction of dimethyl terephthalate (DMT) with ethylene glycol in the presence of a catalyst (usually a metal carboxylate) to form bis(hydroxyethyl)terephthalate (BHET) and methyl alcohol as a by-product. In the second step of transesterification, BHET... 

The principal solvolysis reactions for PET are methanolysis with dimethyl terephthalate and ethylene glycol as products, glycolysis with a mixture of polyols and BHET as products, and hydrolysis to form terephthalic acid and ethylene glycol. The preferred route is methanolysis because the DMT is easily purified by distillation for subsequent repolymerization. However, because PET bottles are copolyesters, the products of the methanolysis of postconsumer PET are often a mixture of glycols, alcohols, and phthalate derivatives. The separation and purification of the various products make methanolysis a cosdy process. In addition to the major product DMT, methanol, ethylene glycol, diethylene glycol, and 1,4-cyclohexane dimethanol have to be recovered to make the process economical.1... 

This new monomer is separated from the excess glycol and polymerized. The monomer has two hydroxy endgroups but with catalysis and temperature, it will self-condense to give ethylene glycol as the by-product. The overall result is a one-to-one reaction of terephthalic acid with ethylene glycol, but a substantial amount of glycol is internally recycled. 

Polymerisation of a diol with a dicarboxylic acid is exemplified by the production of a polyester from ethylene glycol and terephthalic acid either by direct esterification or by a catalysed ester-interchange reaction. The resulting polyester Terylene) is used for the manufacture of fibres and fabrics, and has high tensile strength and resiliency its structure is probably ... 

Although the synthesis is completed in very few steps, oxidation of 1,4-xylene to the corresponding terephthalic acid does not afford a uniform product. Partial dihalogenation gives rise to side products. The condensation reaction requires two equivalents of arylamine per halogen atom. One equivalent is needed to neutralize the generated hydrohalogen acid, which is subsequently separated as aryl-amine-hydrohalide and recycled as hydrohalide and arylamine. 

Oxidation is the first step for producing molecules with a very wide range of functional groups because oxygenated compounds are precursors to many other products. For example, alcohols may be converted to ethers, esters, alkenes, and, via nucleophilic substitution, to halogenated or amine products. Ketones and aldehydes may be used in condensation reactions to form new C-C double bonds, epoxides may be ring opened to form diols and polymers, and, finally, carboxylic acids are routinely converted to esters, amides, acid chlorides and acid anhydrides. Oxidation reactions are some of the largest scale industrial processes in synthetic chemistry, and the production of alcohols, ketones, aldehydes, epoxides and carboxylic acids is performed on a mammoth scale. For example, world production of ethylene oxide is estimated at 58 million tonnes, 2 million tonnes of adipic acid are made, mainly as a precursor in the synthesis of nylons, and 8 million tonnes of terephthalic acid are produced each year, mainly for the production of polyethylene terephthalate) [1]. 

Prepolymer produced via the terephthalic acid (TPA) monomer route shows an increased reactivity in comparison with that produced by the dimethanol tereph-thalate (DMT) monomer process [49], This behavior is possibly caused by the enhanced CEG content, which is usually higher in products from the TPA process as a result of insufficient conversion of the acid monomer in the esterification reaction (Figure 5.23). The increased reactivity may be caused by an autocatalytic influence of the carboxylic groups which seems to be disturbed by an unbalanced content of OH groups in the case of degradation. 

Acetic acid also finds use as a chemical intermediate in the production of acetate esters for paint solvents and as a reaction solvent for the manufacture of terephthalic acid. Also, acetic add is the source of the acetyl group in the manufacture of acetyl salacylic acid. 

Condensation polymers generally result from simple reactions involving two different monomers, each containing different functional groups. The usual example is terephthalic acid and ethylene glycol to make polyester. The two monomers will react in such a way that a small molecule like water or methanol is given off a co-product... 

Investigation of template poly condensation kinetics has only been studied within a very narrow scope. Polymerization of dimethyl tartrate with hexamethylene diamine was found to be enhanced by using as a template poly(vinyl pyrrolidone), poly(2-vinyl pyridine), or polysaccharides and poly(vinyl alcohol), poly(4-vinyl pyridine). In this case, the template can be treated as a catalyst. No information exists on the influence of the template on the order of reaction. The increase in molecular weight of the polymerization product by the template can be induced by a shift of equilibrium or by an increase in the reaction rate. A similar increase in the reaction rate was observed when poly(4-vi-nyl pyridine) was used in the synthesis of poly(terephtalamides) activated by triphenyl phosphite.The authors suggested that a high molecular weight template was involved in the increase of the local concentration of the substrate (terephthalic acid) by adsorption and activation via N-phosphonium salt of poly(4- vinyl pyridine). 

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