Isophthahc acids

Also in 1972 (6), Carbomdum researchers described a family of aromatic copolyesters which were recognized later to form Hquid crystalline melts. The polymers are based on a bisphenol monomer. In 1976, in a patent assigned to Carbomndum, a hydroxybenzoic acid—terephthaHc acid—bisphenol system, modified and softened with isophthaHc acid, was reported to be melt spinnable to produce fiber. 

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. 

The second largest use at 21% is for unsaturated polyester resins, which are the products of polycondensation reactions between molar equivalents of certain dicarboxyhc acids or thek anhydrides and glycols. One component, usually the diacid or anhydride, must be unsaturated. A vinyl monomer, usually styrene, is a diluent which later serves to fully cross-link the unsaturated portion of the polycondensate when a catalyst, usually a peroxide, is added. The diacids or anhydrides are usually phthahc anhydride, isophthahc acid, and maleic anhydride. Maleic anhydride provides the unsaturated bonds. The exact composition is adjusted to obtain the requked performance. Resins based on phthahc anhydride are used in boat hulls, tubs and spas, constmction, and synthetic marble surfaces. In most cases, the resins contain mineral or glass fibers that provide the requked stmctural strength. The market for the resins tends to be cychcal because products made from them sell far better in good economic times (see Polyesters,unsaturated). 

The manufacture of alkyd resins (qv), which are obtained by the reactions of polybasic acids or anhydrides, polyhydric alcohols, and fatty oils and acids, consumes about 17% of the phthahc anhydride demand. While materials such as maleic anhydride, isophthahc acid, and fumaric acid can also be used, phthahc anhydride is the most important. The resin provides a binder for coatings that are apphed for either protection or decoration. Ak quahty concerns have put alkyd resins under pressure from water-based coatings which do not emit organic vapors upon drying. 

Manufacture and Processing. Isophthahc acid is synthesized commercially by the Hquid-phase oxidation of / -xylene [108-38-3]. The chemistry of the oxidation is almost identical to that of -xylene oxidation to terephthahc acid, and production facihties can be used interchangeably for these two dicarboxyhc acids. However, because isophthahc acid is more soluble than terephthahc acid in reaction solvents as can be seen by comparing data in Tables 16 and 25, crystallization equipment is more important in isophthahc acid facihties. 

Chevron Chemical Co. began commercial production of isophthahc acid in 1956. The sulfur-based oxidation of / -xylene in aqueous ammonia at about 320°C and 7,000—14,000 kPa produced the amide. This amide was then hydrolyzed with sulfuric acid to produce isophthahc acid at about 98% purity. Arco Chemical Co. began production in 1970 using air oxidation in acetic acid catalyzed by a cobalt salt and promoted by acetaldehyde at 100—150°C and 1400—2800 kPa (14—28 atm). The cmde isophthahc acid was dissolved and recrystallized to yield a product exceeding 99% purity. The Arco technology was not competitive and the plant was shut down in 1974. 

Impurities in isophthahc acid from the oxidation process are analogous to those in terephthahc acid, eg, 3-formylbenzoic acid and y -toluic acid. 

Also present are other impurities such as benzoic acid and residual catalyst metals. All isophthahc acid made by this hquid-phase oxidation is now purified in a process similar to that used for terephthahc acid, as shown in Figure 4. Lower temperatures are used owing to the greater solubihty of isophthahc acid vs terephthahc acid. 

Societa Itahana Serie Acetica Sintetica (SISAS) produces isophthahc acid commercially by a proprietary process (94,95). They have installed purification facihties for hydrogenation and crystallization similar to those used for terephthahc acid. 

Production, Storage, and Shipment. A plant of 50,000-t annual capacity could be considered viable for production of isophthahc acid, although no new plants have been constmcted since the early 1980s. Storage of isophthahc acid is in silos. Shipment is in 22.7- and 25-kg bags, 0.5-t and 1-t bags, or hopper tmcks. The far lower production quantity of isophthahc acid and its more varied apphcations vs terephthahc acid mean that high volume... 

Economic Aspects. Isophthahc acid in North America sold for 1.19— 1.32/kg in 1994, depending on the shipment method. The price of xylene plays a role, although not to the same extent as -xylene in terephthaUc acid. The far lower production volumes and smaller plant sizes for isophthahc acid do not give the same economies of scale. 

Worldwide capacity available for production of isophthahc acid was about 270 x 10 t in 1994. About 200 x 10 t was actually produced. Amoco Chemical with plants in the United States and Europe is the principal producer, with over 60% of the production, and AGIC, an Amoco—Mitsubishi Gas Chemical joint venture in Japan, and SISAS produce the remainder. 

Analytical and Test Methods. Ash in isophthahc acid refers to the residue left after combustion of the sample. Ash consists of oxides of trace metals that are deterrnined individually by atomic absorption or inductively coupled plasma. A Kad Fischer titration is specific for the water content. 

Isophthahc acid is pure white, but some impurities can be yellow. A measure of these impurities is obtained by the yellowness, or b-value, of the sample. 

Health and Safety Factors. Isophthahc acid has a low order of toxicity. Inhalation by rats for 4 h at 11.4 g/m showed no toxicity. The LD -level for rats is high at 10.4 g/kg (96). As with terephthahc acid, isophthahc acid was found to form urinary tract calcuh in rats in 90 d when it constituted 3% of their diet. This led to some cancer owing to the presence of the calcuh. Some mild eye irritation is possible, so eye protection should be worn. Otherwise, normal precautions used in handling industrial chemicals should be observed with isophthahc acid. 

Isophthahc acid dust forms explosive mixtures with air at certain concentrations. These concentrations and other information on burning and explosiveness of isophthahc acid dust clouds are given in Table 27 (40,41). Fires can be extinguished with dry chemical, carbon dioxide, water or water fog, or foam. 

Uses. About 35% of the isophthahc acid is used to prepare unsaturated polyester resins. These are condensation products of isophthahc acid, an unsaturated dibasic acid, most likely maleic anhydride, and a glycol such as propylene glycol. The polymer is dissolved in an inhibited vinyl monomer, usually styrene with a quinone inhibitor. When this viscous hquid is treated with a catalyst, heat or free-radical initiation causes cross-linking and sohdification. A range of properties is possible depending on the reactants used and their ratios (97). 

The third, and fastest growing, area of isophthahc acid use is in other types of polymers, primarily as a minor comonomer with terephthahc acid in saturated polyesters. Over 20% of the isophthahc acid is sold in this apphcation. One rapidly expanding use is in polyester beverage bottles where addition of up to 3% isophthahc acid to the terephthahc acid allows faster production of more complex shapes. In this way, single piece bottles can be made, vs a round-bottomed bottle that needs a separate base cup. Fibers are also modified with isophthahc acid. 

Isophthahc acid is also used in formulations for adhesives, inks (qv), wire enamels, and dental materials (qv). Copper isophthalate [10027-31-3] is an ingredient in algicides and fungicides (98). 

Health and Safety Factors. Ttimesic acid is an irritant to the skin, eyes, and respiratory system (140). It is mildly toxic when iagested. The oral LD q ia tats has been reported as 8.4 g/kg (141). Ttimesic acid is flammable, and precautions similar to those noted for tetephthaUc acid and isophthahc acid as regards dust clouds and fire extinguishing agents should be followed. 

A number of high melting poiat semiaromatic nylons, iatroduced ia the 1990s, have lower moisture absorption and iacreased stiffness and strength. Apart from nylon-6 /6,T (copolymer of 6 and 6,T), the exact stmcture of these is usually proprietary and they are identified by trade names. Examples iaclude Zytel HTN (Du Pont) Amodel, referred to as polyphthalamide or PPA (Amoco) and Aden (Mitsui Petrochemical). Properties for polyphthalamide are given ia Table 2. A polyphthalamide has been defined by ASTM as "a polyamide ia which the residues of terephthaUc acid or isophthahc acid or a combination of the two comprise at least 60 molar percent of the dicarboxyhc acid portion of the repeating stmctural units ia the polymer chain" (18). 

Isophthahc (y -phthahc) acid [121 -91 -5] (IPA) is selected to enhance thermal endurance as well as to produce stronger, more resiUent cross-linked plastics that demonstrate improved resistance to chemical attack. TerephthaUc (p-phthaUc) acid [100-21-0] (TA) provides somewhat similar properties as isophthahc acid but is only used in selective formulations due to the limited solubiUty of these polyester polymers in styrene [100-42-5] (see Phthalic acid AND OTHERBENZENEPOLYCARBOXYLIC ACIDS). 

Resins based on phthaHc anhydride are termed orthophthalic polyesters, and resins based on isophthaHc acid are isophthaHc polyesters. The most commonly encountered resins are the orthophthaHc polyesters, because the isophthaHc polyesters, although offering improved mechanical and thermal properties, are higher in cost. Resins based on terephthaHc acid [100-21-0] improve upon the property set of isophthaHc polyesters, but are very uncommon owing to higher cost. 

Mixed xylenes are used as an octane improver in gasoline and for commercial solvents, particularly in industrial cleaning operations. By far, most of the commercial activity is with the individual isomers. Para-xylene, the most important, is principally used in the manufacture of terephthalic acid and dimethyl terephthalate en route to polyester plastics and fibers (Dacron, films such as Mylar, and fabricated products such as PET plastic bottles). Ortho-xylene is used to make phthalic anhydride, which in turn is used to make polyester, alkyd resins, and PVC plasticizers. Meta-xylene is used to a limited extent to make isophthahc acid, a monomer used in making thermally stable polyimide, polyester, and alkyd resins. 

N.A. Iris versicolor L. I. pseudacorus L. Triterpenoids, salicylic acid, isophthahc acid, alpha-phytosterol, myricyl alcohol.100 Relieve menstrual cramps, calm nervous stomach. 

Anhydrides/Acids Phthalic anhydride Malice anhydride Adipic acid Isophthahc acid Terephthalic acid Glycols... 

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