Polyphosphoric acid process

Keywords Acid-doped membranes High-temperature PEMFC Polybenzimidazole Polyphosphoric Acid Process... 

Development efforts at Celanese Research Co. estabHshed soHd-state polymerization as the most practical process for engineering scale-up. Homogeneous solution polymerization of PBI in polyphosphoric acid was eliminated because of the need to work with low soHd compositions (in the range of 3—5%) during the precipitation, neutralization, and washing steps required for isolation of the product. 

Commercial condensed phosphoric acids are mixtures of linear polyphosphoric acids made by the thermal process either direcdy or as a by-product of heat recovery. Wet-process acid may also be concentrated to - 70% P2O5 by evaporation. Liaear phosphoric acids are strongly hygroscopic and undergo viscosity changes and hydrolysis to less complex forms when exposed to moist air. Upon dissolution ia excess water, hydrolytic degradation to phosphoric acid occurs the hydrolysis rate is highly temperature-dependent. At 25°C, the half-life for the formation of phosphoric acid from the condensed forms is several days, whereas at 100°C the half-life is a matter of minutes. 

Additionally, the sequestering ability of polyphosphoric acid and phosphonic acid derivatives as well is a valuable property for their use as dispersants. The main task of dispersants is to suspend solid particles in water or organic solvents and avoid their coalescence and precipitation. This complex plays an important role in many processes and as a result dispersants are used in many technical fields. 

The polyphosphoric acids can be considered as arising from the reaction of H4P207 with additional molecules of H3P04 by the loss of water. In the following process, the product is H5P3O10, which is... 

Acidic ring closure resembles the Du Pont process in that the central benzene ring of the quinacridone structure is synthesized totally. The process bears resemblance to the Liebermann method [2, see also 1.3]. Condensation of succinylosuc-cinic ester with two equivalents of arylamine affords 2,5-diarylamino-3,6-dihy-droterephthalic diester. Subsequent oxidation with suitable agents yields 2,5-di-arylaminoterephthalic diester 57. Hydrolysis and cyclization in polyphosphoric acid or other acidic condensation agents produces crude quinacridone [10]. This product already consists of very small particles. 

D-Glucose 6-phosphate is converted enzymically into L-wyo-inositol 1-phosphate (20) in a process which requires NAD+. The base-catalysed cyclization of d-xylo-hexos-5-ulose 6-phosphate (21), followed by reduction with borohydride, leads to (20) and epi-inositol 3-phosphate (22) (Scheme 3).59 This has been put forward as a chemical model for the enzymic synthesis. The phosphorylation of inositols with polyphosphoric acid has been described80 and the p-KVs of inositol hexaphosphate have been determined by 31P n.m.r.61... 

Barker and Copeland have reported a slightly modified process for the preparation of 3 (Scheme 10). 29 was reacted with phenylchloroformate to give carbamate 33. The ring closure was affected by heating 33 in polyphosphoric acid at 100 °C to provide 31. The imino chloride 32, formed as in Scheme 9, was treated with piperazine in refluxing toluene to give 34. The piperazine 34 was then alkylated with 2-chloroethoxyethanol in the presence of Nal and Na2CO3 to afford quetiapine, which was isolated as the fumarate... 

Polyhydric phenols, particularly when the two hydroxyl groups are meta oriented, react with great ease. If sulphuric acid is used as the condensing agent, careful temperature control is needed to ensure a good yield (e.g. 4-methyl-7-hydroxycoumarin, cognate preparation in Expt 8.45). In these cases the use of polyphosphoric acid is recommended and this alternative process is illustrated. Good yields are also obtained from polyhydric phenols by condensation in the presence of trifluoroacetic acid.30... 

Comment. Although a 20% solution of the nitrohydrazone in polyphosphoric acid could be cyclized by heating,71 (c) the use of polyphosphoric acid is not particularly desirable. The microwave-assisted process could be worthy of development if there was no other, more economical, way of accessing this specific indole derivative—for example, by nitration of the more readily prepared 1,2,3,4-tetrahydro-1 -oxo- (3 -carboline.71 (a)... 

Another electrophilic cyclization strategy is reported in which polyphosphoric acid cyclization of thienyl 2-hydrazones (89) affords l-(p-nitrophenyl)thieno[3,2-c]pyrazoles (90) (Equation (23)) <67CJC697>. On initial analysis, the process appears limited to p-nitrophenylhydrazones but the p-nitrophenyl unit is easily removed in a tandem reduction-oxidation sequence to afford the 1H-thieno[3,2-c]pyrazoles (3). 

The well-known herbicide spike is prepared in high yield by heating in toluene a mixture of pivalic acid, JV-methylthiosemicarbazide, sulfuric acid and polyphosphoric acid to give (228 R = H), which on further treatment with methyl isocyanate yields (228 R = CONHMe) (81USP4283543). Other patented processes are known (76GEP2541115). Details on the structure-activity relationship of compounds in this class are available (70MI42700). A thiadiazole-containing insecticide is methidathion (229). 

If even less water is used for hydration, a product known as polyphosphoric acid results. Ordinary phosphoric acid is a solution of the monomer, H3P04, in water, and is called orthophosphoric acid. If a molecule of water is removed between two orthophosphate molecules, the dimer, pyrophosphoric acid, H4P207, is formed. Similarly, the trimerand higher polymers can be made. Superphosphoric acid is a mixture of orthophosphoric acid and polyphosphoric acid and is now made from wet process acid as described later in this chapter. 

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