Phosphoric acids features

Uses Detergent, solubilizer for heavy-duty alkaline cleaners, acid cleaners, metal cleaners, corrosion inhibitors, leather cleaners, aq. lubricants and drilling com-pds. improves performance of acid cleaners contng. phosphoric acid Features Substantive to many substrates stable over wide pH range compat. with inotg. electrolytes... 

A widely used type of pump—mixer—settler, developed by IsraeH Mining Industries (IMI) (115), is shown in Figure 13a. A unit having capacity 8.3 m /min (2000 gal /min) has been used in phosphoric acid plants (116). The unique feature of this design is that the pumping device is not required to act as the mixer, and the two phases are dispersed by a separate impeller mounted on a shaft miming coaxially with the drive to the pump. 

Rider and Amott were able to produce notable improvements in bond durability in comparison with simple abrasion pre-treatments. In some cases, the pretreatment improved joint durability to the level observed with the phosphoric acid anodizing process. The development of aluminum platelet structure in the outer film region combined with the hydrolytic stability of adhesive bonds made to the epoxy silane appear to be critical in developing the bond durability observed. XPS was particularly useful in determining the composition of fracture surfaces after failure as a function of boiling-water treatment time. A key feature of the treatment is that the adherend surface prepared in the boiling water be treated by the silane solution directly afterwards. Given the adherend is still wet before immersion in silane solution, the potential for atmospheric contamination is avoided. Rider and Amott have previously shown that such exposure is detrimental to bond durability. 

Attack by alkali solution, hydrofluoric acid and phosphoric acid A common feature of these corrosive agents is their ability to disrupt the network. Equation 18.1 shows the nature of the attack in alkaline solution where unlimited numbers of OH ions are available. This process is not encumbered by the formation of porous layers and the amount of leached matter is linearly dependent on time. Consequently the extent of attack by strong alkali is usually far greater than either acid or water attack. 

The kinetics are the same in sulphuric and phosphoric acid media as in perchloric acid. The main kinetic features are reproduced in a nitric acid medium although a term, k[Ag(II)]V[Ag(I)], is also involved. Both terms include a strong inverse acidity dependence however, the role of the nitrate ions obscures this. 

In the presence of an oxidant (Y), hypophosphorous acid (A) is transformed into phosphorous acid (B). The kinetics of the reaction has these features ... 

Chemical entities discussed in this chapter as glycosyl donors share the principal structural feature C(anomeric)—sulfur atom bond with thioglycosides, discussed earlier. However, the electron density on the sulfur atom is diminished, and consequently its chemical reactivity differs considerably, because of substitution with electron-withdrawing groups such as carboxylic or phosphoric acid residues. This... 

Phosphoric Acid. Although the proton conduction mechanism in phosphoric acid has not been investigated to the same extent, it is evident that the principal features exhibit similarities, along with important differences. 

Various processes have been used for uranium extraction from phosphoric acid solution their main features are listed in Table 12.4. The HDEHP-TOPO process is increasingly preferred over others because of the stability of the extractant and the well-understood chemistry of the process. 

The nucleic acids DNA and RNA feature diesters of phosphoric acid... 

A feature of phosphoric acid is that it forms a series of poiymeric anhydrides that resembie carboxyiic acid anhydrides in structure and reactivity. Diphosphoric acid (formeriy caiied pyrophosphoric... 

Enols and enolization feature prominently in some of the basic biochemical pathways (see Chapter 15). Biochemists will be familiar with the terminology enol as part of the name phosphoenolpyruvate, a metabolite of the glycolytic pathway. We shall here consider it in non-ionized form, i.e. phosphoenolpyruvic acid. As we have already noted (see Section 10.1), in the enolization between pyruvic acid and enolpyruvic acid, the equilibrium is likely to favour the keto form pyruvic acid very much. However, in phosphoenolpyruvic acid the enol hydroxyl is esterified with phosphoric acid (see Section 7.13.2), effectively freezing the enol form and preventing tautomerism back to the keto form. 

Axially chiral phosphoric acid 3 was chosen as a potential catalyst due to its unique characteristics (Fig. 2). (1) The phosphorus atom and its optically active ligand form a seven-membered ring which prevents free rotation around the P-0 bond and therefore fixes the conformation of Brpnsted acid 3. This structural feature cannot be found in analogous carboxylic or sulfonic acids. (2) Phosphate 3 with the appropriate acid ity should activate potential substrates via protonation and hence increase their electrophilicity. Subsequent attack of a nucleophile and related processes could result in the formation of enantioenriched products via steren-chemical communication between the cationic protonated substrate and the chiral phosphate anion. (3) Since the phosphoryl oxygen atom of Brpnsted acid 3 provides an additional Lewis basic site, chiral BINOL phosphate 3 might act as bifunctional catalyst. 

The authors suggested the catalyst-imine interaction depicted in Fig. 10 for the present Diels-Alder reaction. Imine 94 features a free hydroxyl group appropriate for binding to the phosphoryl oxygen of the phosphoric acid moiety by hydrogen bonding. 

In 2008, Toste and coworkers reported the desymmetrization of me o-episulfonium ions 131 generated in situ from ring closure of sulfides 132 featuring a P-trichloro-acetimidate leaving group [76], Chiral BINOL-derived phosphoric acid (5)-3o (15 mol%, R = triggered the formation of the intermediate mera-epi-... 

The key feature of Br0nsted acid catalysis is often the choice of a catalyst with the appropriate acidity for particular substrate classes. Whereas less reactive substrates require stronger Brpnsted acids than the widely used phosphoric acids for activation, acid-sensitive substrates tend to decompose under strongly acidic conditions. Thus, weaker Brpnsted acid catalysts may prove beneficial. 

A well-defined chiral pocket produced by the binaphthyl skeleton and the appended bulky 3,3 substituents, (iii) A ring structure attached to the phosphoric acid moiety to prevent free rotation at the a-position of the phosphorus center. This feature is not found in other Bronsted acids such as carboxylic and sulfonic acids (Figure 5.2). 

Phosphoric acid fuel cells (PAFC) use liquid phosphoric acid as an electrolyte - the acid is contained in a Teflon-bonded silicon carbide matrix - and porous carbon electrodes containing a platinum catalyst. The PAFC is considered the "first generation" of modern fuel cells. It is one of the most mature cell types, the first to be used commercially, and features the most proven track record in terms of commercial applications with over 200 units currently in use. This type of fuel cell is typically used for stationary power generation, but some PAFCs have been used to power large vehicles such as city buses. 

The Kuhni contactor (Fig. 13e) has gained considerable commercial application in Europe. Its principal features are the use of a shrouded turbine impeller to promote radial discharge within the compartments and a variable hole arrangement to allow flexibility of design for different process applications. Kuhni extractors are used for extraction of petrochemicals and chemicals, phosphoric acid purification, as well as hydrometallurgical applications and wastewater treatment. Columns up to 16.5 ft in diameter have been constructed. 

In the case of cumene, UOP introduced a liquid-phase process in the 1940s to compete with aluminum chloride technology. The catalyst is SPA, a solid phosphoric acid catalyst in which the phosphoric acid is supported on silica. Many improvements were made to the SPA catalyst and process over the years, leading to 70% of the world s cumene being produced with SPA by the 1990s. In 1996, UOP introduced the Q-Max process, featuring a zeolitic catalyst and operating in the liquid phase (21). A new Q-Max catalyst, QZ-2001 , was introduced in 2001. 

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