Phosphoric acid hydrates

There are several types of protonic conductors. One of the representative protonic conductors is uranyl phosphoric acid hydrate (HUO2PO4-41120 1111 ). The electrolyte is based on the hydrate. Protonic conductivity occurs through the interexchange of hydrogen by the rotation of H2O or H30 molecules in the hydrates. Therefore, the protonic conductivity of these solid electrolytes decreases with reducing humidity. These electrolytes are restricted to use around room temperature, since they cease to be protonic conductors if they are deltydrated. 

Pinacol upon dehydration with acid catalysts e.g., by distillation from 6A sulphuric acid or upon refluxing for 3—4 hours with 50 per cent, phosphoric acid or hydrated oxalic acid) is transformed into methyl ter<.-butyr ketone or plnacolone ... 

Thermal Process. In the manufacture of phosphoric acid from elemental phosphoms, white (yellow) phosphoms is burned in excess air, the resulting phosphoms pentoxide is hydrated, heats of combustion and hydration are removed, and the phosphoric acid mist collected. Within limits, the concentration of the product acid is controlled by the quantity of water added and the cooling capabiUties. Various process schemes deal with the problems of high combustion-zone temperatures, the reactivity of hot phosphoms pentoxide, the corrosive nature of hot phosphoric acid, and the difficulty of collecting fine phosphoric acid mist. The principal process types (Fig. 3) include the wetted-waH, water-cooled, or air-cooled combustion chamber, depending on the method used to protect the combustion chamber wall. 

Both mono- and disodium phosphates are prepared commercially by neutralization of phosphoric acid using sodium carbonate or hydroxide. Crystals of a specific hydrate can then be obtained by evaporation of the resultant solution within the temperature range over which the hydrate is stable. For the preparation of trisodium phosphate, sodium hydroxide must be used to reach the high end pH because CO2 cannot be stripped readily from the solution above a pH of near 8. 

Potassium Phosphates. The K2O—P20 —H2O system parallels the sodium system in many respects. In addition to the three simple phosphate salts obtained by successive replacement of the protons of phosphoric acid by potassium ions, the system contains a number of crystalline hydrates and double salts (Table 7). Monopotassium phosphate (MKP), known only as the anhydrous salt, is the least soluble of the potassium orthophosphates. Monopotassium phosphate has been studied extensively owing to its piezoelectric and ferroelectric properties (see Ferroelectrics). At ordinary temperatures, KH2PO4 is so far above its Curie point as to give piezoelectric effects in which the emf is proportional to the distorting force. There is virtually no hysteresis. 

Tricalcium phosphate, Ca2(P0 2> is formed under high temperatures and is unstable toward reaction with moisture below 100°C. The high temperature mineral whidockite [64418-26-4] although often described as P-tricalcium phosphate, is not pure. Whidockite contains small amounts of iron and magnesium. Commercial tricalcium phosphate prepared by the reaction of phosphoric acid and a hydrated lime slurry consists of amorphous or poody crystalline basic calcium phosphates close to the hydroxyapatite composition and has a Ca/P ratio of approximately 3 2. Because this mole ratio can vary widely (1.3—2.0), free lime, calcium hydroxide, and dicalcium phosphate may be present in variable proportion. The highly insoluble basic calcium phosphates precipitate as fine particles, mosdy less than a few micrometers in diameter. The surface area of precipitated hydroxyapatite is approximately... 

For off-site transportation, the phosphoms is loaded into railcars for transfer to the sites where it is used directly as a raw material or burned and hydrated to phosphoric acid. During shipping, the phosphoms is allowed to soHdify in the cars. The railcars are commonly double walled with a jacket that can be heated with steam or hot water so that the phosphoms can be remelted on-site for transloading to local storage tanks. For overseas shipping, tanktainers with reinforced superstmcture for safe handling are used. Formerly, full tanker ships were in use. 

About 264,000 metric tons of elemental capacity is available in North America, plus another 79,000 t (P equivalent) of purified wet phosphoric acid (14). About 85% of the elemental P is burned to P2 5 hydrated to phosphoric acid. Part of the acid (ca 21%) is used direcdy, but the biggest part is converted to phosphate compounds. Sodium phosphates account for 47% calcium, potassium, and ammonium phosphates account for 17%. Pinal apphcations include home laundry and automatic dishwasher detergents, industrial and institutional cleaners, food and beverages, metal cleaning and treatment, potable water and wastewater treatment, antifree2e, and electronics. The purified wet acid serves the same markets. 

Iron Browns. Iron browns are often prepared by blending red, yellow, and black synthetic iron oxides to the desired shade. The most effective mixing can be achieved by blending iron oxide pastes, rather than dry powders. After mixing, the paste has to be dried at temperatures around 100°C, as higher temperatures might result in the decomposition of the temperature-sensitive iron yellows and blacks. Iron browns can also be prepared directiy by heating hydrated ferric oxides in the presence of phosphoric acid, or alkaU phosphates, under atmospheric or increased pressure. The products of precipitation processes, ie, the yellows, blacks, and browns, can also be calcined to reds and browns. 

Synthetic pine oil is produced by the acid-catalyzed hydration of a-pinene (Fig. 1). Mineral acids, usually phosphoric acid, are used in concentrations of 20—40 wt % and at temperatures varying from 30—100°C. Depending on the conditions used, alcohols, chiefly a-terpineol (9), are produced along with /)-menthadienes and cineoles, mainly limonene, terpinolene, and 1,4- and 1,8-cineole (46—48). Various grades of pine oil can be produced by fractionation of the cmde products. Formation of terpin hydrate (10) from a-terpineol gives P-terpineol (11) and y-terpineol (12) as a consequence of the reversible... 

Tin does not react directly with nitrogen, hydrogen, carbon dioxide, or gaseous ammonia. Sulfur dioxide, when moist, attacks tin. Chlorine, bromine, and iodine readily react with tin with fluorine, the action is slow at room temperature. The halogen acids attack tin, particularly when hot and concentrated. Hot sulfuric acid dissolves tin, especially in the presence of oxidizers. Although cold nitric acid attacks tin only slowly, hot concentrated nitric acid converts it to an insoluble hydrated stannic oxide. Sulfurous, chlorosulfuric, and pyrosulfiiric acids react rapidly with tin. Phosphoric acid dissolves tin less readily than the other mineral acids. Organic acids such as lactic, citric, tartaric, and oxaUc attack tin slowly in the presence of air or oxidizing substances. 

Phospha.tes, Pentasodium triphosphate [7758-29-4] sodium tripolyphosphate, STPP, Na P O Q, is the most widely used and most effective builder in heavy-duty fabric washing compositions (see also Phosphoric acid and phosphates). It is a strong sequestrant for calcium and magnesium, with a p c of ca 6, and provides exceUent suspending action for soils. Because of its high sequestration power, it also finds extensive appHcation in automatic-dishwashing detergents. Sodium tripolyphosphate forms stable hydrates and thus aids in the manufacture of crisp spray-dried laundry powders. 

Chemistry. The stoichiometric equations pertinent to the vapor-phase hydration of ethylene over a catalyst support impregnated with phosphoric acid have been summari2ed (84). 

With phosphoric acid-based catalysts, in which the active component is Hquid acid absorbed in the pores of the support, the reaction probably follows the path (119) for the hydration of olefins in aqueous solution ... 

The kinetics of the ethylene hydration reaction have been investigated for a tungstic oxide—siHca gel catalyst, and the energy of activation for the reaction deterrnined to be 125 kJ/mol (- 30 kcal/mol) (106,120). The kinetics over a phosphoric acid-siHca gel catalyst have been examined (121). By making some simplifying assumptions to Taft s mechanism, a rate equation was derived ... 

Hydration of Ethyl Ether. Using the same type of acid catalysts as in the hydration of ethylene to ethanol, ethyl ether can be hydrated to the alcohol. Catalysts that have been used for the hydration of ether include phosphoric acid (144), sulfuric acid (145,146), hydrochloric acid (147), metallic oxides (141,148,149) and sihcates (150). Sulfuric acid concentrations ranging from 5—25% at 200°C (144) to 63—70% at 110—135°C and 1.01—1.42 MPa (10—14 atm) (148) have been claimed. 

Manufacture. Much of the diethyl ether manufactured is obtained as a by-product when ethanol (qv) is produced by the vapor-phase hydration of ethylene (qv) over a supported phosphoric acid catalyst. Such a process has the flexibiHty to adjust to some extent the relative amounts of ethanol and diethyl ether produced in order to meet existing market demands. Diethyl ether can be prepared directly to greater than 95% yield by the vapor-phase dehydration of ethanol in a fixed-bed reactor using an alumina catalyst (21). 

Hydration and dehydration employ catalysts that have a strong affinity for water. Alumina is the principal catalyst, but also used are aluminosihcates, metal salts and phosphoric acid or its metal salts on carriers, and cation exchange resins. 

From pinacol hydrate, using phosphoric acid as a catalyst. Dehn and Jackson, J. Am. Chem. Soc. 55, 4286 (1933). 

The hydration reaction is carried out in a reactor at approximately 300°C and 70 atmospheres. The reaction is favored at relatively lower temperatures and higher pressures. Phosphoric acid on diatomaceous earth is the catalyst. To avoid catalyst losses, a water/ethylene mole ratio less than one is used. Conversion of ethylene is limited to 4-5% under these conditions, and unreacted ethylene is recycled. A high selectivity to ethanol is obtained (95-97%). 

B. 2-Methylcyclopenlane-l,3,5-trione hydrate. A mixture of 200 g. (0.89 mole) of the keto ester prepared above, 910 ml. of water, and 100 ml. of 85% phosphoric acid is healed under reflux for 4 hours and then cooled in an ice-salt bath to —5°. The trione mixed with oxalic acid separates and is collected by filtration and dried under reduced pressure. The dried material is extracted with boiling ether (250-300 ml.) under reflux, and the ethereal extract is separated from the undissolved oxalic acid. The original aqueous filtrate is also extracted with ether in a continuous extractor. The two extracts are combined, and ether is removed by distillation. The crude trione separates as a dark brown solid and is crystallized from ca. 250 ml. of hot water. The once-crystallized, faintly yellow product weighs 95-105 g. (74-82%), m.p. 70-74°. This product is used in the next step without further purification. A better specimen, m.p. 77-78°, which is almost colorless, can be obtained by recrystallization from hot water after treatment with Norit activated carbon. 

This reaction shows that the hydrated oxide SiCV-xHjO is acidic, since it reacts with a base-As we mentioned earlier, phosphorus can be found in four different oxidation states. The hydroxides of the +1, +3, and +5 states of phosphorus are hypophosphorous acid, H3P02, phosphorous acid, H3P03, and phosphoric acid, H3P04. Their structures are shown in Figure 20-4. As suggested by their names, these compounds are distinctly acidic, and are of moderate strength. The equilibrium constant for the first ionization of each acid is approximately 10-2 hypophosphorous acid ... 

This concept covers most situations in the theory of AB cements. Cements based on aqueous solutions of phosphoric acid and poly(acrylic acid), and non-aqueous cements based on eugenol, alike fall within this definition. However, the theory does not, unfortunately, recognize salt formation as a criterion of an acid-base reaction, and the matrices of AB cements are conveniently described as salts. It is also uncertain whether it covers the metal oxide/metal halide or sulphate cements. Bare cations are not recognized as acids in the Bronsted-Lowry theory, but hydrated... 

Increase in concentration of aluminium and phosphoric acid in the liquid serves to slow the reaction. This observation is in line with the above reaction scheme. Increase in the aluminium content will serve to increase the thickness of the coating formed around zinc oxide particles. Increase in phosphoric acid content implies a decrease in water content and an impairment of the hydration reaction. 

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