4- trimellitic

There is a wide variety of possible structures based on the use of glycerol (v = 3), trimethylolpropane (n = 3), pentaerythritol (n = 4), and sorbitol (n = 6) or their mixture as polyol, reacting not only with phthalic anhydride (w = 2) but also with pyromellitic dianhydride (w = 4), citric acid (v = 4), trimellitic acid (v = 3), or their mixture as polyacid. The most important resins are those obtained from the polycondensation of 0-phthalic anhydride with glycerol, and the resulting network is represented hereafter. 

CeH3Me3. Liquid produced by catalytic cracking of methyl benzenes. Used to prepare trimellitic anhydride. 

See also Trimellitic acid.) [PHTTiALIC ACID AND OTTiERBENZENEPOLYCARBOXYLIC ACIDS] (Vol 18)... 

A polyester-type fluorescent resin matrix (22) is made by heating trimellitic anhydride, propylene glycol, and phthaUc anhydride with catalytic amounts of sulfuric acid. Addition of Rhodamine BDC gives a bright bluish red fluorescent pigment soluble in DME and methanol. It has a softening point of 118°C. Exceptional heat resistance and color brilliance are claimed for products of this type, which are useful for coloring plastics. 

Of the three benzenetricarboxyhc acids, only trimellitic acid as the anhydride is commercially produced in large volume, by Hquid-phase air oxidation of either pseudocumene or dimethyl benzaldehyde. The pseudocumene oxidation is another variant of the cobalt—manganese—bromine catalyst in acetic acid solvent as described in the terephthaUc acid section. The acid is available as a laboratory chemical (99). The lUPAC name of trimellitic anhydride is 5-isobenzofurancarboxyhc acid (l,3-dihydro-l,3-dioxo). 

Physical and Chemical Properties. Trimellitic acid and trimellitic anhydride are odorless white crystalline soHds in their pure form. The acid is reasonably stable up to the melting point, where dehydration to the anhydride occurs. The anhydride reacts with atmopsheric moisture, even at room temperature, to revert to the acid. Physical properties of the acid and its anhydride are Hsted in Tables 29—31. 

Table 29. Physical Constants of Trimellitic Acid and Trimellitic Anhydride...

In 1991, Alusuisse Italia announced the constmction of a 20 x 10 t/yi" trimellitic anhydride unit at Bergamo, Italy (109) and commenced production in late 1994. A European patent appHcation (110) assigned to Alusuisse suggests that the process used is very similar to that of Amoco, that is, pseudocumene is air oxidized in the Hquid phase using heavy-metal catalysts and bromine. A number of other companies have shown interest in the production of trimellitic anhydride (111—113). 

Economic Aspects. When trimellitic anhydride was introduced in semicommercial quantities in 1962, it was priced at 1.19/kg. The price was reduced to 0.55/kg as it became available in commercial quantities in 1968. The mid-1994 price was quoted as 2.31/kg from Amoco, fob, the JoHet, Illinois plant. A price history is given in Table 32. Although trimellitic anhydride production and sales figures are not available, the pubUshed U.S. Tariff Commission s production data for trimeUitate esters provides data for the trimellitic anhydride demand trend in the United States, since the largest single use of trimellitic anhydride is for the trimeUitate esters (115). These data are given in Table 32. 

Table 32. U.S. Trimellitic Anhydride Prices and TrimeUitate Ester Production...

Year Trimellitic anhydride price, /kg TrimeUitate ester production, 10 t/vr... 

The freezing point of trimellitic anhydride, the maximum temperature reached during crystallization of a molten sample, is a measure of the product purity. Impurities and trimellitic acid formed by hydrolysis depress the freezing point. 

A measure of the color developed by impurities when trimeUitate esters are produced can be correlated with the anhydride color measurement. The method measures the color difference in light transmittance between a trimellitic solution and a 3.0 N sodium hydroxide solution as a reference. The difference in light transmittance or AH (total color difference) is obtained using a colorimeter. 

Polymers based on trimellitic anhydride are widely used in premium electromagnetic wire enamels requiring high temperature performance. Several types of trimellitic anhydride-derived polymers are used as wire enamels poly(amide—imide)s (133), poly(ester—imide)s (134), and poly(amide—imide— ester)s (135). Excellent performance characteristics are imparted by trimellitic anhydride-based polymers for wire enamel requirements of flexibiUty, snap, burnout, scrap resistance, heat shock, and dielectric strength. 

Derivatives. The dual functionaUty of trimellitic anhydride makes it possible to react either the anhydride group, the acid group, or both. Derivatives of trimellitic anhydride include ester, acid esters, acid chloride, amides, and amide—imides (136). Trimellitate esters are the most important derivatives, and physical properties of more significant esters are Hsted in Table 34. 

Table 34. Properties of Trimellitic Acid Esters and the Chlorocarbonyl Anhydride...

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