Phosphoric acid dimerization

Results from infrared spectroscopy indicate that the only species present in 50 % phosphoric acid are H3PO4, HjPOj and their oligomers (Wilson Mesley, 1968). There is evidence that HgPjOg, the phosphoric acid dimer, and HsPjOg, the triple ion H2PO4.. HjPOj, are also present (Elmore,... 

Two processes take place. Water is absorbed due to the hydrolysis of the pyrophosphoric acid according to the reverse of (5.1), up to the point that A = 0, showing that the dimerization of phosphoric acid is a fully reversible process. As expected, the equilibrium constant of phosphoric acid dimerization increases with temperature. Further increase in Pn o resulted in solubility of free water in the HsPOVpolymer system. There is a similar dependence on PE2O for samples used sharp increase at low / h 0 and thereafter linear variation of A. An increase of the acid doping level of the polymers results in enhanced ability to absorb water. 

The dimer of phosphonic acid, diphosphonic acid [36465-90-4] (pyrophosphoms acid), H4P2O3, is formed by the reaction of phosphoms trichloride and phosphonic acid in the ratio of 1 5. It is also formed by the thermal decomposition of phosphonic acid. Unlike the chemistry of phosphoric acid, thermal dehydration does not lead to polymers beyond the dimer extended dehydration leads to a disproportionation to condensed forms of phosphoric acid, such as [2466-09-3] and phosphine. 

Another aspect of process improvement is color improvement. Eor example, use of phosphoric acid and formaldehyde on the dimer product is said to improve color (68). Other treatments, both on the raw materials and on the finished product, have also been used. Most of these are variations of standard fatty material color reduction techniques. 

Studies have indicated that the association of HF in the gas phase leads predominantly to dimers or hexamers with small amounts of tetramers. Hydrogen bonding in liquids such as sulfuric and phosphoric acids is responsible for them being viscous liquids that have high boiling points. 

Acid phosphatase (acid phosphomonoesterase, EC 3.1.3.2) also catalyzes the hydrolysis of phosphoric acid monoesters but with an acidic pH optimum. It has broad specificity and catalyzes transphosphorylations. Acid phosphatases are a quite heterogeneous group with monomeric, dimeric, larger glycoprotein, and membrane-bound forms. Acid phosphatase activity is present in the heart, liver, bone, prostate, and seminal fluid. Prostate carcinomas produce large quantities of acid phosphatase, and the enzyme is, therefore, used as a biomarker [141]. 

The formation of 2-(indolin-2-yl)indole dimers from indole-3-acetic acid and its propyl ester in trifluoroacetic acid and phosphoric acid has been studied." The reaction involves electrophilic attack of the protonated species (24) on the free substituted indole to give the trans stereochemistry at the C(2)-C(3) bond. 

Polymerization of propene at 330° in the presence of 90% ortho-phosphoric acid under about 100 atmospheres initial pressure yielded a product consisting of paraffinic, olefinic, cycloparaffinic and cycloolefinic, and aromatic hydrocarbons (Ipatieff and Pines, 70). About 8% of the product boiled in the dimer (C6) range and about 25% in the trimer (C9) range. Isobutane was formed to the extent of more than 2% by weight of the total polymer. 

Propene also undergoes conjunct polymerization in the presence of dilute phosphoric acid at high temperatures and pressures (Monroe and Gilliland, 58). When propene was treated with 10-30% phosphoric acid at 260-305° and at 170-410 atmospheres pressure, the only operating variable which appreciably affected the composition of the polymer was the extent to which the feed was polymerized. At constant percentage reaction of the feed under these conditions, the temperature, pressure, and acid catalyst concentration had no effect on the product composition. At low conversions, the polymer consisted of nearly pure dimer at 50% polymerization, two-thirds of the total was dimer and even when the feed was almost completely polymerized, the dimer fraction amounted to 35-40 % of the total polymer. The dimer and trimer fractions obtained at temperatures of 305° or lower using a acid concentrations below 30% contained about 25% paraffins and little or no naphthenes or aromatic hydrocarbons. 

While the composition of the products depend solely on the extent of polymerization of the feed when phosphoric acid concentrations below 30% are used, with higher concentrations of acid, the character of the polymer begins to change, an excess of heavier compounds forming at the expense of the yield of dimer. Polymers obtained with 40 and 50% acid showed dimer content 10-20 % lower, and trimer content correspondingly higher, than were obtained at the same percentage of polymerization of the feed with lower concentrations of acid. 

Other acidic additives such as tartaric or phosphoric acids also increased the hydrogenation rate without affecting the selectivity. However, in the presence of these acidic additives, large amounts of dimer 28 were formed. 

As described in Figure 3.7, TRU separation is performed by implementing the DIDPA process on pretreated PUREX raffinates. A front-end denitration step by formic acid is thus required to reduce the nitric acid concentration of the feed down to 0.5 M to allow the TRU elements to be extracted by the cation exchanger di-fvo-dccyl-phosphoric acid (DIDPA). This preliminary step, however, induces the precipitation of Mo and Zr (and thus the potential carrying of Pu), which requires filtration steps. The TRU and Ln(III) elements are coextracted by a solvent composed of the dimerized DIDPA and TBP, dissolved at 0.5 and 0.1 M, respectively, in n-dodecane. The An(III) + Ln(III) fraction is back-extracted into a concentrated 4 M nitric acid solution, whereas Np and Pu are selectively stripped by oxalic acid. 

Martens et a/. 3S showed that HZSM-22 synthesized in a pure form with controlled crystal size is a promising catalyst for the oligomerization of propene to Q-C12 olefins. It was found that the reaction occurs at or near the outer surface and the products formed are mainly dimers. In addition, an increase of the linearity of the oligomers as compared with HZSM-5 or solid phosphoric acid was found. It was tentatively proposed that active sites located at the pore mouths are responsible for this shape selective effect. 

Oligomerization of butene over HMordenite has been carried out at 5 MPa and 523 K. The reaction gave mainly dimers and trimers with a minor fraction of tetramers and pentamers.[13] In contrast, oligomerization of butene over solid phosphoric acid catalyst gave mainly dimers. 

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. 

Dibutyl phosphoric acid (HDBP) also dimerizes in nonpolar solvents and solutions of HDBP in kerosene contacting aqueous nitric acid equilibrate to produce (HDBP)2, HDBP-H2 0 and HDBP-HNOs in both phases. In addition, the organic phase contains (HDBP)2-H20 and the aqueous phase (Bu"0)2P02 (DBP ) in equilibrium with HOBR " Such equilibria complicate the stoichiometry of extraction from aqueous sulfuric acid solutions. Thus the extraction of... 

Phosphorylation of alcohols and amines forming mixed esters of phosphoric acid and phosphorami-dates, respectively, is effected by triphenylphosphine and 2,2 -dipyridyl disulfide. The reaction passes through a triphenylphosphonium phosphate of type (68 equation 44) as an active intermediate. Formation of an intemucleotide linkage can be achieved by this method. °° Dimerization of monoesters of phosphoric acid producing dialkyl pyrophosphates is achieved using tributylphosphine and dibenzoyl-ethylene or p-quinonedibenzimide (equation 45). A phosphonium phosphate is the active intermediate of this reaction. ... 

The most general route to anionic or hydridic dimeric complexes utilizes a metal carbonyl dimer as a starting complex. Reaction of Mn2(CO)io with NaBH4 and subsequent treatment with phosphoric acid led to H2Mn2(CO)9F... 

Disubstituted phosphoric acids, HP0j(0R)2, provide examples of both dimers and chains exactly comparable with the two types of HSO4 ions, and infinite chains also occur in crystalline benzene seleninic acid. The dimer in dibenzylphosphoric... 

Replacement of H in H3PO4 by a radical R gives substituted phosphoric acids 0P(0H)20R and OP(OH)(OR)2 and finally the phosphoric ester, OP(OR)3. The structure of dibenzylphosphoric acid, HP02(0CH2C6Hs)2, was described in Chapter 8 the molecules are linked in pairs by O-H-0 bonds as in dimers of carboxylic acids. Examples of mono- and di-substituted ions are the phenyl-phosphate ion, (h), studied in the K salt, and the diethylphosphate ion, (i), in the Ba salt, and of an ester, triphenylphosphate,... 

According to ref. 5, monomeric (-)-2,4-0-ethylidene-D-erythrose may be obtained by heating a solution of the dimer in ethyl acetate with a catalytic amount of glacial acetic acid or 100% phosphoric acid for 20 min at 90°C. 

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