Terephthalic acid sublimation

The combined filtrates are heated nearly to boiling and acidified with a solution of 108 ml. of concentrated sulfuric acid (sp. gr. 1.84) in 400 ml. of water. After the mixture has been cooled to room temperature, the tcrephthalic acid is filtered and washed by stirring on the filter with three successive 100-ml. portions of cold water. The product is dried in an evaporating dish on a steam bath. The yield of terephthalic acid which sublimes at 800 or higher without melting is 105-109 g. (84-88%) (Notes 2 and 3). 

In many cases simple esters are more easily purified than their intractable parent acids. For example, /7-xylene is difficult to obtain in pure form because of the closeness of its boiling point to the other isomeric xylenes (o-144°C m- 138.8°C p- 138.5°C). It is thus difficult to produce terephthalic acid, which sublimes at 300°C, in a pure form. 

The terephthalate moiety, either as the acid or ester, does not undergo similarly significant side-reactions with loss of commercially useful material. Terephthalic acid can sublime and dimethyl terephthalate can vaporize, and so maintenance of the vapor stream is a must. 

Terephthalic acid [100-21-0] M 166.1, sublimes >300 without melting. Purified via the sodium salt which, after crystn from water, was reconverted to the acid by acidification with mineral acid. Terephthaloyl chloride [100-20-9] M 203.0, m 80-82 . Crystd from dry hexane. o-Terphenyl [84-15-1] M 230.3, m 57-58 ,... 

Terephthalic acid [100-21-0] M 166.1, sublimes >300° without melting. Purified via the sodium salt which, after crystn from water, was reconverted to the acid by acidification with mineral acid. 

TEREPHTHALIC ACID. CAS 100-21-01. Cf,H4(COOH)2, formula weight 166.13, crystalline solid sublimes upon heating, sp gr 1.510. The compound is almost insoluble in H2O, only slightly soluble in warm alcohol, and insoluble in ether. Terephtlialic acid (TPA) is a high-tonnage chemical, widely used in the production of synthetic materials, notably polyester fibers (poly-(ethylene terephthalate)). 

Cognate preparation. Terephthalic acid. Use 18 g (0.169 mol) of p-xylene in place of the p-nitrotoluene and proceed as above to the stage of isolation of the crude product. Wash this with 40 ml of water followed by 20 ml of ether and purify, isolate and dry the acid as detailed above for p-nitrobenzoic acid the yield of colourless terephthalic acid is 12 g (44%) it sublimes without melting at 300 °C and is almost insoluble in water and ethanol. 

Figure 6.5 shows the yields ([wt%]) of the reaction of PET using several transition metal oxide catalysts under the following conditions a temperature of 500°C, a time factor (the ratio of the mass of the catalyst W, to the PET feed rate F) of 0.317 h, and a particle size of 0.21-0.25 mm. Fc203 did not show activity, hence these results have been omitted. With respect to the reduction of terephthalic acid, FeOOH, nickel hydroxide and nickel oxide showed the decomposition activity of terephthahc acid. However, a large amount of benzoic acid, which is also a sublimate material (sublimation point 100°C), was produced over nickel hydroxide and nickel oxide. Because these nickel compounds are more expensive than FeOOH, FeOOH was considered to be a suitable catalyst for the decomposition of terephthalic acid. 

Figure 6.6 shows the change in product yield with increase in the time factor W/F. The amount of sublimate materials (terephthalic acid and benzoic acid) decreased remarkably with increase in the time factor, and no sublimate materials were observed after approximately 0.5 h. Moreover, carbon dioxide was produced, and the yield of the carbon dioxide... 

Pyrolysis of PET under mild conditions predominantly forms terephthalic acid (TPA). Since TPA easily sublimes it is often found in the condensing units of pyrolysis plants. Under high-severity conditions however, little TPA is observed. This is because at higher temperatures TPA is decomposed into benzene, carbon dioxide and benzoic acid (Figure 15.3) [2]. 

The pyrolysis of PET by Sakata [3] has been found surprisingly to yield no liquid products. It is widely known that compounds that undergo sublimation, such as tereph-thalic acid and benzoic acid, are produced by the thermal decomposition of PET and this causes problems in plastic pyrolysis plants. Interestingly Yoshioka et al. [4] found that the addition of calcium hydroxide (slaked lime) gives high selectivity for benzene formation without producing sublimation compounds such as terephthalic acid. The yield of benzene is around 35 wt% at 700°C and a 10.0 calcium hydroxide/PET molar ratio. 

Terephthalic acid is almost insoluble in hot and cold water. It sublimes without melting. It can be identified most readily by converting it into its dimethyl ester as described below. 

Terephthalic acid is obtained as a powder, which is almost insoluble in water and in alcohol. It sublimes unchanged without melting. The property of certain dibasic acids of forming anhydrides when heated, is limited to those acids which contain two carboxyl groups in the positions ortho to each other. 

Terephthalic acid (TPA), CjH4(COOH)2, is an organic acid. It is a white crystalline or powdered material that is insoluble in water. It undergoes sublimation above 572°F. In addition to being corrosive, it is also combustible. The primary uses are in the prodnction of polyester resins, fibers, and films it is also an additive to poultry feeds. The structure and molecular formula for terephthalic acid are shown in Fignre 10.9. 

Needles from H 0. Sublimes on heating without melting and with partial conversion to terephthalic acid. Spar. sol. HgO. Heat of comb. 836-1 CaL K3Fe(CN)g—>. terephthalic acid. 

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