Terephthalate ring substitutions

NEW POLYETHYLENE TEREPHTHALATE) COPOLYMERS 6.4 TEREPHTHALATE RING SUBSTITUTIONS... 

The Sandoz company used the dibromoterephthalic acid method. This acid was made from p-xylcnc by brominating it to form 2,5-dibromo-p-xylene and then oxidising this to 2,5-dibromoterephthalic acid. Reaction of one mole of this acid with two moles of an arylamine in the presence of copper(II) acetate gives 2,5-bis(arylamino)terephthalic acid, which can be ring-closed to a linear quinacridone. Unsymmetrical substitution using two different arylamines is possible. 

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]. 

Poro-xylene is an industrially important petrochemical. It is the precursor chemical for polyester and polyethylene terephthalate. It usually is found in mixtures containing all three isomers of xylene (ortho-, meta-, para-) as well as ethylbenzene. The isomers are very difficult to separate from each other by conventional distillation because the boiling points are very close. Certain zeoHtes or mol sieves can be used to preferentially adsorb one isomer from a mixture. Suitable desorbents exist which have boiling points much higher or lower than the xylene and displace the adsorbed species. The boihng point difference then allows easy recovery of the xylene isomer from the desorbent by distillation. Because of the basic electronic structure of the benzene ring, adsorptive separations can be used to separate the isomers of famihes of substituted aromatics as weU as substituted naphthalenes. 

Polystyrene itself is not used for endoprosthetic purposes and its application is accounted for only because of easy substitutions in benzene rings. The method was subsequently modified for heparinization of silicone and natural rubber, polyethylene, polypropylene, polyethylene terephthalate), and other polymers. Styrene was first grafted onto the polymers by y-radiation and then the above-described reaction was performed in the second step. All the polymers synthesized in this way contained sufficiently large amounts of immobilized heparin (2.8—15.7 ng/cm2) and displayed good thromboresistance when tested in vitro — recalcified blood was not clotted for several hours. 

Quinacridone pigments are manufactured by either the condensation of 2,5-diarylamino-terephthalic acid or the oxidation of dihydroquinacridones followed by subsequent conditioning to produce the product in a pigmentary form of colloidal dimensions. For example, in the first process, the use of 2,5-dianilinoterephthalic acid results in the formation of trans linear quinacridone, PV 19, by a simple ring closure condensation where water is evolved as a by-product. Substitution of the aniline used to produce the diarylaminoterephthalic acid will result in pigments such as PR 122 where ditoluidinoterephthalic acid is used at the condensation stage. 

So far we have only discus those substituted polyamides derived from substituted phenylenediamines and isophthalic or terephthalic acids, i.e. from benzene derivatised monomers. Numerous monomers containing several aromatic rings have also been u d in the synthesis of polyamides as shown in Table 6. 

Tropones unsubstituted at C(2,7) but having electron-withdrawing groups substituted elsewhere in the ring may also undergo ready rearrangement, for example tropone-4-carboxylic acid reacts with aqueous alkali at room temperature to give terephthalic acid [195]. 

The terephthalate plasticizer DEHTP, first commercialized around 1975 as Eastman DOTP, is very similar in structure to DEHP except that the substitution of the aromatic ring is at the 1,4 position versus the 1,2 position of the aromatic ring. The structure of DEHTP is also shown in Pig. 24.1. Terephthalates are prepared by the esterification of terephthaUc acid or by the transesterification of dimethyl terephthalate with aliphatic alcohols such as butanol or 2-ethyl hexanol. Although DEHTP can be produced from terephthalic acid in a traditional DEHP esterification plant with minor modifications to the process, this process is not as efficient as the esterification of phthalic anhydride and manufacturing capacity reductions of >50% are realized. Transesterification of dimethyl terephthalate is a much faster reaction. However, this process will require significant process modifications to a traditional DEHP manufacturing unit. One benefit with this chemistry is that it does not lead to a significant drop in production capacity. The main problem with this route is the limited availability of dimethyl terephthalate in many locations. 

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