Hydration reactivity

Figure 4.41. Comparison of the hydration reactivity of the cement minerals C3S, P-C2S and ordinary Portland cement (OPC) determined as a function of hydration time by integrating their Si spectra. From Barnes et al. (1985), by permission of copyright owner.

Other catalytically active species for C02 hydration include [(CR)Zn-OH] + (CR = Me2pyo[14]trieneN4, / at = 225 +23 M-1 s 1, Fig. 6a), which exhibits a pK value of 8.69 at 25 °C.40 Zinc complexes supported by tris(imidazole)phosphine-type (Fig. 6b-d) or tris(imidazole)phosphineoxide-type ligands also exhibit catalytic C02 hydration reactivity.41-44 All of these complexes exhibit maximum rate constants for C02 hydration below 2500 M-1 s 1 in the pH = 6-7 range. Above or below this pH... 

Fig. 6 Supporting chelate ligands for which catalytic C02 hydration reactivity has been reported for zinc derivatives.

Wu Y, Sun P, Anthony EJ, Jia L, Grace J (2006) Reinvestigation of hydration/reactivation characteristics of two long-term sulphated limestones which previously showed uniformly sulphating behaviour. Fuel 85 2213-2219... 

Photochemical Wolff rearrangement of diazoacetylpyrazoline forms ketene 76 in acetonitrile solution, identified by the ketenyl IR absorption, together with the ylide 77 (Eqn (4.40)). Similar intermediates are formed from diazoacetylpyrinfrdine, and the reactions of these ketenes with amines and kinetic studies of their hydration reactivity have been... 

The very low bond dissociation enthalpy of fluorine is an important factor contributing to the greater reactivity of fluorine. (This low energy may be due to repulsion between non-bonding electrons on the two adjacent fluorine atoms.) The higher hydration and lattice enthalpies of the fluoride ion are due to the smaller size of this ion. 

Historically carbohydrates were once considered to be hydrates of carbon because their molecular formulas m many (but not all) cases correspond to C (H20) j It IS more realistic to define a carbohydrate as a polyhydroxy aldehyde or polyhydroxy ketone a point of view closer to structural reality and more suggestive of chemical reactivity... 

Properties. Lithium fluoride [7789-24-4] LiF, is a white nonhygroscopic crystaUine material that does not form a hydrate. The properties of lithium fluoride are similar to the aLkaline-earth fluorides. The solubility in water is quite low and chemical reactivity is low, similar to that of calcium fluoride and magnesium fluoride. Several chemical and physical properties of lithium fluoride are listed in Table 1. At high temperatures, lithium fluoride hydroly2es to hydrogen fluoride when heated in the presence of moisture. A bifluoride [12159-92-17, LiF HF, which forms on reaction of LiF with hydrofluoric acid, is unstable to loss of HF in the solid form. 

Magnesium hydroxide can also be produced by slaking or pressure hydrating various reactive grades of magnesium oxide. The reaction is highly exothermic (AH gg = —40.86 kJ/mol (—9.77 kcal/mol)) to produce crystalline form at stoichiometric water addition ... 

AH gg = —43.03 kJ/mol ( — 10.28 kcal/mol) including heat of solution, at standard state m = V) and may require a heat sink to prevent boiling of the reaction mixture. A 30% by weight suspension of MgO in 20°C water boils in the absence of any heat sink. The time to reach boiling is dependent on the reactivity of the MgO raw material, and this time can be only several hours for the more reactive grades of MgO. Investigations of the kinetics of formation of magnesium hydroxide by hydration of MgO have been reported (79). 

Dead-burned magnesia, characterized by large crystaUite size and very low chemical reactivity, is resistant to the basic slags employed in the metals refining industry. It reacts very slowly with strong acids, and does not readily hydrate or react with carbon dioxide unless finely pulverized. 

Niobic Acid. Niobic acid, Nb20 XH2O, includes all hydrated forms of niobium pentoxide, where the degree of hydration depends on the method of preparation, age, etc. It is a white insoluble precipitate formed by acid hydrolysis of niobates that are prepared by alkaH pyrosulfate, carbonate, or hydroxide fusion base hydrolysis of niobium fluoride solutions or aqueous hydrolysis of chlorides or bromides. When it is formed in the presence of tannin, a volurninous red complex forms. Freshly precipitated niobic acid usually is coUoidal and is peptized by water washing, thus it is difficult to free from traces of electrolyte. Its properties vary with age and reactivity is noticeably diminished on standing for even a few days. It is soluble in concentrated hydrochloric and sulfuric acids but is reprecipitated on dilution and boiling and can be complexed when it is freshly made with oxaHc or tartaric acid. It is soluble in hydrofluoric acid of any concentration. 

Although numerous mud additives aid in obtaining the desired drilling fluid properties, water-based muds have three basic components water, reactive soHds, and inert soHds. The water forming the continuous phase may be fresh water, seawater, or salt water. The reactive soHds are composed of commercial clays, incorporated hydratable clays and shales from drilled formations, and polymeric materials, which may be suspended or dissolved in the water phase. SoHds, such as barite and hematite, are chemically inactive in most mud systems. Oil and synthetic muds contain, in addition, an organic Hquid as the continuous phase plus water as the discontinuous phase. 

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. 

Uses ndReactions. Dihydromyrcene is used primarily for manufacture of dihydromyrcenol (25), but there are no known uses for the pseudocitroneUene. Dihydromyrcene can be catalyticaUy hydrated to dihydromyrcenol by a variety of methods (103). Reaction takes place at the more reactive tri-substituted double bond. Reaction of dihydromyrcene with formic acid gives a mixture of the alcohol and the formate ester and hydrolysis of the mixture with base yields dihydromyrcenol (104). The mixture of the alcohol and its formate ester is also a commercially avaUable product known as Dimyrcetol. Sulfuric acid is reported to have advantages over formic acid and hydrogen chloride in that it is less compUcated and gives a higher yield of dihydromyrcenol (105). 

Thorium compounds of anionic nitrogen-donating species such as [Th(NR2)4], where R = alkyl or sdyl, are weU-known. The nuclearity is highly dependent on the steric requirements of R. Amides are extremely reactive, readily undergoing protonation to form amines or insertion reactions with CO2, COS, CS2, and CSe2 to form carbamates. Tetravalent thorium thiocyanates have been isolated as hydrated species, eg, Th(NCS)4(H20)4 [17837-16-0] or as complex salts, eg, M4 Th(NCS)g] vvH20, where M = NH, Rb, or Cs. 

Flame retardants (qv) are incorporated into the formulations in amounts necessary to satisfy existing requirements. Reactive-type diols, such as A/ A/-bis(2-hydroxyethyl)aminomethylphosphonate (Fyrol 6), are preferred, but nonreactive phosphates (Fyrol CEF, Fyrol PCF) are also used. Often, the necessary results are achieved using mineral fillers, such as alumina trihydrate or melamine. Melamine melts away from the flame and forms both a nonflammable gaseous environment and a molten barrier that helps to isolate the combustible polyurethane foam from the flame. Alumina trihydrate releases water of hydration to cool the flame, forming a noncombustible inorganic protective char at the flame front. Flame-resistant upholstery fabric or liners are also used (27). 

Sulfuric acid is about one thousand times more reactive with isobutylene than with the 1- and 2-butenes, and is thereby very useful in separating isobutylene as tert-huty alcohol from the other butenes. The reaction is simply carried out by bubbling or stirring the butylenes into 45—60% H2SO4. This results in the formation of tert-huty hydrogen sulfate. Dilution with water followed by heat hydrolyzes the sulfate to form tert-huty alcohol and sulfuric acid. The Markovnikov addition implies that isobutyl alcohol is not formed. The hydration of butylenes is most important for isobutylene, either directiy or via the butyl hydrogen sulfate. 

Carbon dioxide, the final oxidation product of carbon, is not very reactive at ordinary temperatures. However, in water solution it forms carbonic acid [463-79-6] H2CO2, which forms salts and esters through the typical reactions of a weak acid. The first ionization constant is 3.5 x 10 at 291 K the second is 4.4 x 10 at 298 K. The pH of saturated carbon dioxide solutions varies from 3.7 at 101 kPa (1 atm) to 3.2 at 2,370 kPa (23.4 atm). A soHd hydrate [27592-78-5] 8H20, separates from aqueous solutions of carbon dioxide that are chilled at elevated pressures. 

Po22olans contain reactive siUca which reacts with cement and water by combining with the calcium hydroxide released by the hydration of the calcium siUcates to produce additional calcium sihcate hydrate. If sufficient siUca is added, about 30% of the weight of cement, the calcium hydroxide can... 

Oil well cements are manufactured similarly to ordinary Portland cements except that the goal is usually sluggish reactivity. Eor this reason, levels of C A, C S, and alkafl sulfates are kept low. Hydration-retarding additives are also employed. 

The simple cerous salts can be prepared by dissolving the oxide, or preferably a more reactive precursor, in the appropriate acid or, when possible, produced by precipitation from solution. Upon crystallization a wide variety of hydrated species can result. These hydrates tend to be hygroscopic. Basic salts, eg, Ce(OH)C02, maybe formed and these can be contaminants in the sohd salts. 

Hydroxide. Freshly precipitated cerous hydroxide [15785-09-8] Ce(OH)2, is readily oxidized by air or oxygenated water, through poorly defined violet-tinged mixed valence intermediates, to the tetravalent buff colored ceric hydroxide [12014-56-17, Ce(OH)4. The precipitate, which can prove difficult to filter, is amorphous and on drying converts to hydrated ceric oxide, Ce02 2H20. This commercial material, cerium hydrate [23322-64-7] behaves essentially as a reactive cerium oxide. 

Manufacture. A high purity, completely hydrated lime of high reactivity is employed in the manufacture of calcium hypochlorite. It should contain low levels of impurities such as siUca, MgO, CaC03, CaSO, AI2O3, Fe203, and trace metals such as Co, Ni, Cu, and Mn, since some of these can cause process difficulties and can also affect the quaUty and stabiUty of the final product. 

---