Pyromellitic acid

Directions are provided for the determination of chloride in samples using CZE. The buffer solution includes pyromellitic acid which allows the indirect determination of chloride by monitoring absorbance at 250 nm. 

See also Pyromellitic acid.) [PHTTiALIC ACID AND OTTiERBENZENEPOLYCARBOXYLIC ACIDS] (Vol 18) Benzene-1,2,4,5-tetracarboxylic dianhydride-3-carboxylic acid [59025-58-0]... 

Table 36. Physical Contants of Pyromellitic Acid and Pyromellitic Dianhydride...

The use of the Hquid-phase process in acetic acid with the cobalt— manganese—bromine system as explained in the tetephthaUc acid section is also possible (149). This process has been used by Amoco Chemical to produce pyromellitic acid, and facUities remain in place to do so again in the future. As with all hquid-phase oxidations of this type, yields ate high. A separate dehydration step would be needed to yield the dianhydtide. 

Mitsubishi Gas Chemical Co. in Japan produces pyromellitic dianhydtide in the same unit used for trimellitic anhydtide production (105). This process starts with pseudocumene, which is first carbonylated with carbon monoxide in the presence of boron trifluotide and hydrogen fluotide to form 2,4,5-trimethylbenzaldehyde. The Hquid-phase oxidation of the trimethylbenzaldehyde to pyromellitic acid and subsequent processing steps ate much the same as described for the Mitsubishi Gas Chemical process in the trimellitic acid section. The production of pyromellitic anhydtide is in conjunction with a joint venture agreement with Du Pont. 

Production, Storage, and Shipment. As noted above, AUco Chemical, Amoco Chemical, Mitsubishi Gas Chemical, and Hbls all produce either the acid or the anhydride using different production techniques. The relatively small production volumes of pyromellitic acid and dianhydride results in both storage and shipment in polyethylene-lined fiber dmms of 22—136-kg capacity. 

Health and Safety Factors. Both pyromellitic acid and its dianhydride irritate skin, eyes, and mucous membranes, and they cause skin sensitization (156). When it comes in contact with moist tissue the dianhydride converts to the acid. Direct contact with should be avoided and protective clothing should be worn in areas where it is used. The LD q for intergastric administration in rats is 2.2—2.6 g/kg (157). In 6-mo experiments, the maximum nontoxic dose was 0.07 mg/kg/d, and it affected the fiver, kidney, and reproductive tract. Precautions against fire and dust explosions as explained in the terephthafic acid section should be foUowed. 

In order to prevent premature gelation the reaction mixture should be anhydrous, free from pyromellitic acid and reacted at temperatures not exceeding 50°C. 

Pyromellitic Acid (10, 90) By the oxidation of 5,6-tetrahydrobenzindane-i-one with nitric acid. Darzens and Ldvy, Compt. rend. 201, 902 (1935). 

The first patent of Edwards and Robinson147 claims the condensations of pyromel-litic acid and aliphatic diamine salt to prepare polyimide. Recently, that approach has been revisited, and biphenyl tetracarboxylic and pyromellitic acids give a salt monomer by reaction with 1 mol of an aliphatic diamine (octamethylene diamine and dodecamethylene diamine). The salts were polymerized under 250 MPa at 250°C for 5 h in closed reaction vessels (Fig. 5.32) giving crystalline polymers.148 By reaction of pyromellitic tetraacid with oxydianiline, it has been possible to isolate a monomeric salt. It was polymerized under 30 MPa giving a PMDA-ODA polyimide with water elimination. 

In most of the studies discussed above, except for the meta-linked diamines, when the aromatic content (dianhydride and diamine chain extender), of the copolymers were increased above a certain level, the materials became insoluble and infusible 153, i79, lsi) solution to this problem with minimum sacrifice in the thermal properties of the products has been the synthesis of siloxane-amide-imides183). In this approach pyromellitic acid chloride has been utilized instead of PMDA or BTDA and the copolymers were synthesized in two steps. The first step, which involved the formation of (siloxane-amide-amic acid) intermediate was conducted at low temperatures (0-25 °C) in THF/DMAC solution. After purification of this intermediate thin films were cast on stainless steel or glass plates and imidization was obtained in high temperature ovens between 100 and 300 °C following a similar procedure that was discussed for siloxane-imide copolymers. Copolymers obtained showed good solubility in various polar solvents. DSC studies indicated the formation of two-phase morphologies. Thermogravimetric analysis showed that the thermal stability of these siloxane-amide-imide systems were comparable to those of siloxane-imide copolymers 183>. 

This occurred when attempting to prepare pyromellitic acid by the action of nitric acid on hexamethylbenzene. This accident was worsened by the fact that there was no stirring. 

For the dehydration of pyromellitic acid diamide, N, -sulfinyldiimidazole was used as the dehydrating agent to give a moderate yield of dicyanoisophthalic diimidazolide, which was further transformed with hydrochloric acid into the corresponding dichloride 1131... 

In recovering pyromellitic acid from the mother liquor it is advisable first to remove the sulfuric acid by adding a slight excess of barium hydroxide and acidifying to Congo red with hydrochloric acid. 

The anhydride of pyromellitic acid may be obtained from the dry anhydrous acid by boiling with acetic anhydride. 

Mellitic acid can be decarboxylated to yield pyromellitic acid, either by the action of heat alone 4 or in the presence of sulfuric acid.5... 

The oxidation of wood charcoal by means of sulfuric acid leads to mellitic acid and its decarboxylation products 6 nitric add may also be employed.7 Pyromellitic acid has also been obtained by the electrolytic oxidation of graphite in an alkaline medium.8... 

The yield of pyromellitic acid depends considerably on the kind of charcoal used. An experiment with ordinary willow charcoal gave none of the desired product. 

Pyrocatechol, d428 Pyrogallol, t317 Pyromellitic acid, b27 Pyromellitic dianhydride, b28 Pyromucic aldehyde, f44 Pyrrolidinedithiocarbamate, p282... 

A review by Galli et al. describes several buffer-absorbing chromophores as co-ions. These include phthalate, PDG (2,6-pyridinedicarboxylic acid), PMA (1,2,4,5-benzenetetra-carboxylic acid or pyromellitic acid), TMA (trimellitic acid), MES, 2,4-dihydrobenzoic acid with s-aminocaproic acid, p-hydroxybenzoate, p-anisate, 3,5-dinitrobenzoic acid, salicylic acid with TRIS, benzoic acid with tris (hydroxymethyl)aminomethane (TRIS), and many others. On the other hand, some inorganic chromophores such as chromate (Figure 9) or molybdate may be added to a buffer. A BGE-containing chromate should have a pH above 8, because it precipitates below this value. The advantage of a TRIS buffer or buffers at around pH 6 is that carbonate will not interfere with the separation because it is not soluble in TRIS or at lower pHs. 

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